摘要:

C o n t e n t s Vol. 3, No. 2. October 1970 Pollution of the environment Pollution of soils I. J . Graham-Bryce and G. G. Briggs Water pollution H. Fish Air pollution C. F. Barrett Fermentation-the last ten years and the next ten years L. M. Miall The teaching of chemistry in Victorian and Edwardian times (Fourth Grove lecture) D. Betteridge Cumulative index 0 The Royal Institute of Chemistry 30 Russell Square, London WCIB 5DT 85 87 105 119 135 161 177

ISSN:0035-8940    

DOI:10.1039/RR97003FP003

出版商:RSC    

年代:1970

数据来源: RSC

摘要:

R. I .C. Reviews R.I.C. Reviews, published twice yearly, reviews areas of chemistry of interest to the chemist who has no specialist knowledge of the field under review, but who wishes to keep abreast of the growth of chemistry as a discipline. These reviews should prove useful to students in familiarizing themselves with a particular field. R.I.C. Reviews interprets the significance of chemistry in a wide context and publishes articles on the economic, social and historical aspects of chemistry, as well as on the reseaSch and applied sectors. Suggestions for future titles are welcomed. Prospective contributors should write to the Editor, enclosing a synopsis (of about 250 words) indicating the scope of their subject. The preferred length for reviews is 8000 words. Subscriptions from R.I.C. members are handled by the Royal Institute of Chemistry, 30 Russell Square, London WCl B 5DT. All other subscriptions are handled by The Chemical Society Publications Sales Office, Blackhorse Road, Letchworth, Herts. Annual Subsci-iption: f2 (R.I.C. members, f l 10s)

ISSN:0035-8940    

DOI:10.1039/RR97003FX005

出版商:RSC    

年代:1970

数据来源: RSC

摘要:

POLLUTION OF THE ENVl RONMENT 19’70 has been designated European Conservation Year. This has focused an unprecedented amount of attention on the problems of pollution in modern society. In the debate that is emerging in a torrent of newspaper articles, books and television programmes it is essential that chemists take a responsible, positive stand. It is not sufficient to decry opposition to chemical activities that is based on misinformation or a failure to understand salient facts. Nor can one strike high-minded attitudes to the effect that what scientists do is outside the public domain and should remain a mystery to the uninitiated. It can be forcefully argued that the chemist is responsible for ensuring that the public has a clear understanding of the intricacies behind such simplicitudes as ‘pollution is bad, no pollution is good’. As a groundwork for his own efforts as a member of a community of citizens, it is necessary that the scientist should have access to balanced background information on environmental pollution. It is hoped that the first three articles in this issue of RIC Reviews will contribute some of the essential information to chemists, who will then be able to pass it on, in unhysterical vein, to the community at large.

ISSN:0035-8940    

DOI:10.1039/RR9700300085

出版商:RSC    

年代:1970

数据来源: RSC

摘要:

87 . . .. . . .. .. .. .. * . 92 .. .. .. . . * . * . .. . . 95 Current situation . . . . Significance of residues in soil . . .. .. .. .. .. 101 Future possibilities 102 Conclusions Bibliography Pollution of Soils I. J. Graham-Bryce, M.A., B.Sc., D.Phil., and G. G. Briggs, B.Sc., Ph.D. * . Rothamsted Experimental Station, Harpenden, Herts * . Introduction Routes of arrival in soil . . .. .. .. .. Interaction with soil Breakdown .. .. . . * . .. .. .. . . .. .. 0 . .. .. 103 . . .. 104 .. Persistence . . .. .. . . .. . . .. .. 88 . . .. .. .. .. .. .. 89 .. . * . . .. .. .. 97 .. 0 . . . . . .. .. .. .. INTRODUCTION Materials intended to improve crops, and waste products from other activities, have always become incorporated in soils.Some of these materials are persistent, for example even in Roman times the use of a persistent pesticide- arsenic-was recommended. Until recently, however, deleterious effects were localized and sporadic. Awareness of radiochemical fallout and the occur- rence of persistent synthetic pesticides in soils has led to much public concern, and pollution of soils is now widely regarded as an important problem. The concept of pollution is imprecise and judgement as to what constitutes a pollutant is very much a matter of opinion. The materials involved are not all unequivocally injurious: some may be harmless or beneficial when present at small concentrations or in other situations. Others are ambivalent; for example organochlorine insecticides may control undesirable soil insects while also killing beneficial insects and causing other unwanted effects.Harmful concentrations of biologically active chemicals may arise naturally. For example, soils may contain concentrations of elements such as copper, zinc and molybdenum large enough to be toxic to plants or stock, although smaller concentrations are essential for proper growth. In this article, we define a polluted soil loosely as one which contains enough of a given material to cause undesirable effects in the soil, the atmo- sphere above it or water draining from it. The community must decide what it regards as an undesirable effect. Acceptable residue levels in crops have usually been set by dividing the concentration likely to harm human beings by a substantial safety factor.From this point of view a polluted soil is one that gives crops containing more than this arbitrary level. However, using the crop alone as an indicator gives no information on the amount of material either in water running off the soil, or in the air above the soil, or the effect Graham-Bryce and Briggs 87 on organisms in the soil other than the plant. Detection of the specified amounts requires adequate methods of analysis, and the prominence of per- sistent pesticides and radioactive fallout, which evoke rather special popular alarm, is to some extent an accident resulting from the existence of extremely sensitive and rapid analytical techniques. Fractions of a picogram of organo- chlorine insecticides can be detected by gas chromatography with electron- capture detection, and if analytical methods in general were equally sensitive, contamination by other pollutants might cause increased concern.Analysis of natural materials by gas chromatography at the greatest sensitivities is difficult and some reports of very small amounts can be regarded sceptically. There are reports of DDT residues being identified in soil samples which were sealed and stored before it was used as an insecticide. Nevertheless, pollution of soils is a real problem and its implications are particularly serious for materials such as 90Sr and organochlorine insecticides, which have a long life and can become transferred through stages in food chains.The same basic principles govern the behaviour and ultimate fate of any material reaching the soil. The climate, and the physical and chemical properties of the soil and the applied material, are the principal factors influencing the distribution between the soil, the atmosphere above it and water draining through or running off it. Given a suitable combination of these factors, usual agricultural methods could give rise to polluted soil, atmosphere or water. In practice there are remarkably few materials giving serious problems. With the benefit of hindsight, it seems probable that these could have been predicted, and we shall attempt to discuss the principles involved, using examples mainly from the behaviour of pesticides. We have confined our attention strictly to soil.However, in considering processes that lessen concentrations in soil and therefore decrease pollution, it must be emphasized that removal by volatilization and leaching merely pass on the contaminant to another part of the environment where it may cause even greater problems. Failure to recognize that dangers to the community do not cease when persistent materials are removed from the immediate area being considered has contributed to the present difficulties. Biologically active chemicals only cease to be potential dangers when they are degraded into harmless decomposition products. ROUTES OF ARRIVAL IN SOIL Application of agricultural chemicals adds extraneous materials ranging from solid fertilizers to gaseous fumigants directly to soil. Fertilizers, sys- temic insecticides and many herbicides, such as the substituted ureas and triazines, are applied to be taken up by plant roots.Soil insecticides and fumi- gants are applied to control soil-borne pests such as wheat bulb fly, wire- worms and nematodes. R.I.C. Reviews For optimum performance, agricultural chemicals are formulated in many different ways including liquids, granules and dusts. They may be applied to the soil surface or incorporated either uniformly or placed in various ways, or may be in the form of seed dressings. As a result, there is a wide range of initial distributions of concentration in the soil, from a uniform value several centimetres deep to bands of large concentration on the surface.88 In addition, much of the pesticide applied to shoots and leaves reaches the soil by being washed off by rain, by leaf fall, or simply because application inevitably cannot be restricted to the desired target. Similarly, other polfu- tants reach the soil unintentionally. Much of the material discharged into the atmosphere eventually settles on the soil or is brought down in rain. Radio- active fallout is a well publicized example on a worldwide scale. Dust, smoke and SO2 from fuel are also widespread and their effects on soil acidity around cities are well established. The quantities of material involved are often large compared with amounts of 1-2 kg ha-1 (0.1-0.2 g m-2) commonly applied for pesticides, and in heavily industrialized areas as much as 1 kg of dust and grit may be deposited per square metre each year, although this material may have small biological activity.On a more local scale specific materials may be potentially dangerous. For example, smoke from brickworks contains considerable quantities of fluorine and gives rise to concern, because large amounts of fluorine can be retained by growing plants which are eaten by stock. A notorious example of localized pollution is the Lower Swansea Valley, where severe contamination of the soil by Cu and Zn, from metal smelting during the 18th and 19th centuries, devastated the traditional plant life. INTERACTION WITH SOIL Materials in soil become distributed between the soil solution, soil air and soil solids, and the nature of this distribution greatly influences subsequent behaviour.Partition between the solution and air at equilibrium can be predicted from a knowledge of the solubility and vapour pressure. Although some chemicals have such small volatility that the air phase may be neglected, many pesticides have significant vapour pressures and vapour movement often makes a considerable contribution to their transport to sites of action. This applies particularly to fumigants such as methyl bromide and D-D mixture (dichloropropene plus dichloropropane) applied to control nematode pests inhabiting the soil. Partition onto the soil solids occurs by sorption on the highly reactive surfaces, and also insoluble compounds may be formed with soil constituents.Soils contain very small particles, especially in the clay fraction, where particles are of colloidal size and have an enormous specific surface. Typical values for the readily accessible surfaces of whole soils measured by nitrogen adsorption range from 25-100 m2 g-l, so there is a very large interfacial area at which non-specific surface adsorption can occur. The nature of these surfaces ranges widely-the soil colloids include layer lattice silicates, various oxides and hydroxides and organic materials. Many of the surfaces carry permanent or pH-dependent charges ; for example, the surfaces of the principal clay minerals consist of planes of oxygen atoms or hydroxyl groups associated with localized permanent negative charges caused by isomorphous replace- ment of cations within the lattice. The edges of clay minerals, and carboxyl and phenolic groups associated with the organic matter give rise to pH- dependent charges.From the nature of these surfaces, therefore, it will be clear that there are also many ways in which more specific adsorption can take place and that a large proportion of many pollutants will become Graham-Bryce and Briggs 89 associated with the surfaces. Even in an ‘air-dry’ soil the relative humidity is enough for most clay surfaces to attract at least a monolayer of water so that, except in the very top soil during hot dry conditions, this sorption takes place in the presence of water which competes for the surfaces. The extent of adsorption can be described by adsorption isotherms deter- mined from slurry experiments with large solution/soil ratios.For pesticides, such isotherms have usually been found to fit the empirical Freundlich equation, x/m = KCn (where x/m is the amount adsorbed per unit weight of soil, K and n are constants and C is the equilibrium concentration in solution) with values of n in the range 0.7 to 0.95, although usually only a small fraction of the avail- able surface is occupied by the adsorbed molecules. Values of I(, reflecting the affinity of the pesticides for the surfaces, range widely. In the slurry experiments most of the sorption occurs within minutes and equilibrium is usually reached within a few hours. In relation to subsequent behaviour, the extent to which adsorption is reversible when solution concentrations decrease is very significant.The possibility of irreversible sorption has some- times been suggested, although with no clear theoretical reasons, but where tested by properly designed experiments the process has always been shown to be largely reversible. However, desorption may be considerably slower than adsorption, particularly on soils with much organic matter. The bipyridylium herbicides, paraquat and diquat, provide examples of extreme sorption which is responsible for their outstanding property of being inactivated in contact with soil. The strong sorption brings the solution concentration to immeasurably small amounts at normal rates of use so that the herbicide becomes unavailable to plant roots.These herbicides exist as cations with a flat configuration and the strong binding results from both electrostatic forces and forces resulting from the close approach of a highly polarizable flat ion to the flat charged clay surfaces. Most other pesticides are less strongly sorbed, although they may still be present predominantly in the adsorbed state. Many studies have shown that, for un-ionized materials not involved in ion-exchange reactions with the charged sites, the extent of sorption in different soils is related to the content of organic matter rather than to the mineral fraction, as it is with the bipyridylium herbicides. Many of these pesticides are hydrophobic and presumably they have affinity for the hydrophobic surfaces in the organic matter.Correlations between partition coefficients in oil/water systems and sorption by soil have been obtained for such compounds. Some pesticides, such as sodium chlorate, TCA (trichlor- acetic acid) and some of the organophosphorus insecticides such as dimeth- Paraquat cation I,l’-Dimethyl-4,4’-bipyridylium ion CH,- / -7 D iq uat cation 9,IO- Di h yd roSa, I Oa- d iazon iap hen an t h rene ion 90 R . I. C. Re views Ci&. COOH TCA Trichloroacetic acid Dimethoate S /I (CH30)2PSCH2CON HCH3 Di methyl S-(N-met hyl- carbamoyl methyl)- phosphorothiolothionate oate, are only very slightly sorbed and may be regarded as the opposite end of the scale from the bipyridylium herbicides.Adsorption, by decreasing the concentration available in the soil solution or soil air, has a pronounced effect on almost all aspects of later behaviour. In this review we are interested in its influence on processes leading to loss of the contaminant from the soil. There may be considerable losses during application of a calculated dose of pesticide to soil; for example, spray may be lost by drift, or dust may be blown away, and some pesticide may also be retained by the machinery used for application. Apart from these losses during application, disappearance may be considered under two broad headings: transfer and decomposition, both of which may be affected by adsorption. Over a long period, significant mixing may occur through the activities of soil fauna such as earthworms and mites, but there has been no systematic study of these processes. Except for this rather uncertain biological transport, mobility within the soil depends solely on the physical processes of molecular diffusion in soil solution and, for volatile materials, in the soil air space; and mass flow, that is, transport by flowing water.Diffusion in soils is retarded by the tortuous and restricted pathways through the pores and by adsorption, which immobilizes the portion of the diffusing material associated with the solid. Diffusion in soil water is slow and because the average displacements are proportional to the square root of time, it decreases in effectiveness with time. (Average displacements over a period of one month are likely to be of the order of 1 cm.) It is therefore negligible over long distances.Vapour diffusion is approximately 10000 times faster than diffusion in solution at the same volume concentration, so that even for materials with large waterlair partition coefficients it may be a more significant mechanism. Near the soil surface, air movement and changes in barometric pressure may assist vapour diffusion and increase evaporation. Evaporation may be very important in removing pesticides from soil. It has been calculated that a pesticide with a molecular weight of 200 and vapour pressure of 10-4 mmHg (0.013 Pa) could lose as much as 20 kg ha-1 month-1 from an inert surface during a temperate summer, whereas usual amounts applied are in the region of 1-2 kg ha-l.Although this loss would be diminished by sorption and solution in soil water, these factors would be partially offset by the upward capillary movement of water to replace that evaporating from the soil, which would cause the pesticide to concentrate at the surface. Also, many pesticides have vapour pressures considerably greater than 1 0-4 mmHg. At first sight an equally obvious route for removal from soil would be leaching in drainage water, but its importance is probably frequently over- estimated. Water is lost from soil by evaporation and transpiration by plants, Craham-Bryce and Briggs 91 2-Chloro-4,6-bisethylamino- I ,3,5- C,H,NH Si mazine triazine BREAKDOWN NHC,H, as well as by drainage.In summer, particularly in the drier parts of Britain, evapotranspiration usually exceeds precipitation and the soil is drying out rather than transmitting water to drainage. Over the year as a whole, for an average rainfall of 75 cm in south-east England, drainage to water tables is likely to amount to only about 25 cm although this depends considerably on local topography. The effectiveness of this percolating water in leaching a pollutant depends on the extent of sorption; the soil may be regarded as acting like a crude chromatographic column. Thus, moderately sorbed materials such as simazine may be used selectively to control shallow rooting weeds in deeper rooting crops, such as field beans, because very little leaching takes place provided the soil contains enough organic matter.In contrast, weakly adsorbed materials like sodium chlorate are readily distributed throughout the root zone. Sometimes there may be channelling (for example during thunderstorms) down the large cracks caused by shrinkage in clay soils during summer, but the importance of this has not been assessed. Except for materials of slight solubility, such as DDT, leaching is unlikely to be limited by solubility. Two cm of rain provides 200 000 kg of water per hectare, enough to dissolve 1 kg ha-l of a pesticide with a solubility of 5 ppm. Adsorp- tion allows the soil to accommodate far more molecularly dispersed pesticide than could be dissolved in the soil water alone. It has sometimes been sug- gested that solubility and ease of leaching are related.From what has been said it will be clear that adsorption rather than solubility governs leaching, and these two properties depend on quite different factors. Apart from application losses and volatilization from the soil surface, materials are lost from soil principally by microbial or chemical decomposi- tion, or a combination of both. Usually plant remains initially decompose rapidly in soil, but a small fraction remains as very stable polymeric materials. Radiocarbon dating of soil organic carbon gives an average age of about 1000 years for the carbon in surface soils, clear evidence of the great stability of some natural materials in soil. For pesticides, many well known microbial conversion steps have been observed in soil, such as oxidation and reduction, N- and 0-dealkylation, nitrile, amide and ester hydrolysis, dehalogenation, aromatic ring hydroxyla- tion and epoxide formation from alkenes.For materials that are readily metabolized there is usually a lag phase followed by a rapid decay. Organisms have been isolated that degrade various pesticides in pure culture and the breakdown pathways determined. But the situation in soil is much more complex because there is a mixed population of organisms and sorption or 92 R.I.C. Reviews chemical reaction can remove materials, that are easily metabolized, from solution. For example, there are at least three pathways known for the metabolism of 2,4-dichlorophenoxyacetic acid (2,4-D) in solution but the pathway in soil is not known.Where decay is slow, chemical and microbial breakdown are difficult to distinguish but many stable materials are probably decomposed incidentally during the decomposition of soil organic matter by the action of extracellular enzymes. For example, this has been suggested for picloram (4-amino-3,5,6-trichlorpicolinic acid), which decomposes at a rate proportional to the amount of organic matter in the soil, and so proportional to the microbial activity. Agricultural soils are usually moist and well aerated, although they can be anaerobic at times, especially in less accessible and finer pores. Conditions are therefore suitable for hydrolysis, and oxidation-reduction reactions and chemical transformations of added chemicals by these reactions can be expected.In vitro, many of the potential hydrolysis reactions proceed much faster at the extremes of pH so that in agricultural soils which are mostly near neutral, slow rates might be expected. However, because of electrical double-layer effects in solutions near charged surfaces, the pH in the environ- ment of adsorbed pesticides may differ considerably from that measured in dilute salt suspension, leading to faster reactions. Chemical hydrolysis of nitriles, esters and activated aryl and alkyl halides has been demonstrated. For compounds such as the chlorotriazines, reaction to form the inactive hydroxytriazines takes place on the surface of the soil colloids. Dichlobenil (2,6-dichlorobenzonitrile) is apparently hydrolysed in solution and sorption onto organic matter slows this hydrolysis.Malathion and some other organophosphorus insecticides are hydrolysed in radiation- sterilized soils by a heat-labile factor extractable with sodium hydroxide. Many fungicides rely for their activity on reaction with thiol, amino and other nucleophilic groups in organisms and so can react with suitable groups on soil F' 2,4-D 2,4-Di c h I o ro p h en ox yaceti c aci d Picloram CI 4-Amino-3,5,6-trichloropicolinic acid Dichlobenii 2,6-Dichlorobenzonitrile Graham-Bryce and Briggs 93 Malathion !I I Trifluralin S COOCzHj 5-[ I ,2-Di(ethoxycarbonyl)- ethyl]dimethylphosphorothiolothionate (CH30)zPSCHCHzCOOCzH5 NO, q- c1 Cl 2,6-Di n itro-N,N-di propy l-4- trifluoromethylaniline Dieldrin endo-5,8-dimethanonaphthalene I ,2,3,4,10, I O-Hexachloro-6,7-epoxy- I ,4,4a,5,6,7,8,8a-octahydro-exo- I ,4- organic matter.Another example of reaction with soil organic matter is pro- vided by the herbicide trifluralin which is converted in soil to a substituted o-phenylenediamine that condenses with organic matter. Reductive cleavage of the alkali-extracted organic matter regenerates the diamine. Many agricultural chemicals have been observed to undergo photo- chemical reactions in solution, but these do not seem to be very important in practice, although small amounts of photoproducts of dieldrin and aldrin have been detected in soils treated with large amounts and there is some evidence for photochemical breakdown of paraquat.Overall kinetics of disappearance from soils are usually close to first order with amounts customarily applied to soil. Where there is chemical break- down by reaction with active sites in soil the distribution of the material becomes important. When active sites are few, the concentration of the chemical may be large in relation to the number of sites. Breakdown will then tend to be independent of concentration when the chemical is not distributed through a large volume of soil, either initially or by subsequent leaching. This may explain the increased persistence of the triazine herbicides during dry summers. Similarly, the rate at which picloram decomposes is proportional to concentration at small concentrations but independent at large ones.First-order kinetics have been successfully used to calculate long term residues from dieldrin treatments, using a half-life of about four years. Two examples illustrate the interaction of some of these factors in decom- position. Anhydrous ammonia applied below the soil surface will be lost partly as vapour unless the surface is sealed by compaction behind the injector. There will be a zone of large concentration around the injection point where pH is high and condensation reactions with soil organic matter can occur. Ammonium ion is held by ion exchange and some can be fixed in the interlayer spaces of expandable-lattice clay minerals. As the ammonia diffuses outwards, pH falls and microbial oxidation to nitrate occurs. Micro- bial activity is temperature-dependent and conversion to nitrate is much 94 R.I. C. Re views CI \ Diuron 3-(3,4-DichlorophenyI)- I , I -dimethyl- urea faster during summer than spring. Nitrate is not sorbed by soils and is readily leached. Diuron (N’-3,4-dichlorophenyl-N,N-dimethylurea), a pre-emergence herbi- cide, is fairly strongly sorbed by organic matter. Micro-organisms convert it slowly to the N-methyl derivative, which is more water-soluble but more strongly sorbed than diuron and is therefore much less herbicidally active in soil although about equally active in nutrient solution. A further microbial N-demethylation produces the still more strongly sorbed and herbicidally inactive 3,4-dichlorophenylurea, which then breaks down to 3,4-dichloro- aniline.The amine is considerably less strongly sorbed and has a moderate vapour pressure. When concentrated, two molecules can couple to give a mixture of products including 3,3’,4,4’-tetrachloroazobenzene, a strongly sorbed and very stable compound which probably has some biological activity. However the decomposition of diuron in the field is so slow (about a year for complete disappearance) that the amine is decomposed almost as fast as it is produced and concentrations do not build up sufficiently for bimolecular steps to be observed and only unimolecular decomposition steps are important. Finally, contaminants may be removed from soil by growing crops. Al- though this decreases contamination in soil, it is undesirable because it brings residues directly to stock or people.Extensive precautions are taken to limit residues of pesticides in crops and such uptake is a very minor mecha- nism for removing unwanted materials from soils. It may be calculated that even if a crop contained the largest concentrations of residues permitted, only a small fraction of the applied material would be removed from the soil. PERSISTENCE On the basis of this discussion of the factors affecting the behaviour of chemicals in soil, the properties of a potentially dangerous pollutant can be described. To prevent losses by leaching or evaporation, it would be fairly strongly sorbed and have small volatility, but not to such an extent that it would become deactivated and unavailable to exert any biological activity in the soil.It would be stable chemically even under the extreme conditions of the adsorbed state and it would not form a suitable substrate for micro- organisms. As would be expected, materials reaching the soil fit these proper- ties to different degrees and have a wide range of persistence. Of course, persistence is a variable property and is affected by factors such as climate and soil type, but approximate times for at least 75 per cent of the applied dose to disappear are given in Table 1 for some representative compounds. These times relate only to persistence in soil; it must be emphasized again that volatilization and leaching may contribute to removal of the more stable materials so that their life in the environment as a whole may be considerably 95 Graham-Bryce and Briggs Table 1. Persistence of materials in soils: approximate times for at least 75 per cent of added dose to disappear longer.In most cases it is very difficult to assess the relative importance of the different processes contributing to disappearance. In spite of the complexity of the processes involved and the large variations with climate and soil type, the kinetics of disappearance often approximate to those of a first-order reaction with the rate of disappearance proportional to the amount present. This is a very broad generalization and the last residues often disappear more slowly than would be predicted, but it does allow potential accumulation of repeatedly applied chemicals to be calculated approximately.There is an initial build-up until the rate of loss between applications has increased to equal the amounts applied. For half-lives of up to one year, residues will not be more than twice the annual application, whereas a half-life of four years leads to a maximum accumulation of approximately six times the annual dose. Not all pesticides show these kinetics. Potentially more dangerous situations arise when the original pesticide decomposes to a further toxic residue which is not lost, but accumu- lates in proportion to the amount of pesticide originally applied. Such be- haviour has been suggested for heavy metal and arsenic compounds; for 1-5 Disulfoton Diethyl S-[2-(ethylthio)ethyI] phosphorothiolothionate Chiorfenvinphos 2-C h loro- I -(2,4-d ichloropheny1)-vinyl diethyl phosphate p,p’-DDT I , I, 1 -Trichloro-2,2-di-(4- chloropheny1)ethane Compound Methyl bromide Ammonia 2,4-D Disulfoton C hlorfenvinphos Diuron S i mazi n e Dieldrin DDT 96 Normal rates of use per application (kg ha-1) 1000 up t o 100 I 1-2 1-4 0.5-2 0.5-1 -5 1-5 Use Fumigant for soil sterilization Fertilizer Foliar herbicide Systemic organophosphorus insecticide 0 rgano p hos p hor us soi I insecticide Soil-applied substituted-urea herbicide Soil-applied triazine herbicide Soil and crop organochlorine insecticide Soil and crop organochlorine insecticide CCI, Persistence <I week 3 weeks 1 month 6 weeks 6 months 8 months I year > 3 years > 5 years 0 CHCI CI I e C I CI !H - - R.I.C. Review example the herbicide methane-arsonic acid (MSMA) is metabolized by soil micro-organisms to arsenate, which is not dissipated and can accumulate steadily in soils. For a pesticide to cause major pollution problems it must be used widely at large doses, as well as have the appropriate properties. This implies that it will not be very specific in its action and must be cheap. The present situation with regard to pollution of soil may be related to these requirements, together with the properties of different materials reflected by their persistence times such as those shown in Table 1.CURRENT SITUATION In relation to the criteria for a potential pollutant, most herbicides are too short lived to cause problems. Persistence is obviously an undesirable property because of the danger of harming subsequent crops, and excessively persistent compounds would therefore never be developed commercially. Herbicides that are stable are either not toxic enough to organisms other than weeds or not sufficiently available in soil to produce changes in flora and fauna significant in comparison with those brought about by growing a crop. As herbicides are often required to act selectively between weed and crop, blanket treatments of large areas with a single compound are unlikely and the appropriate chemical is usually chosen for each specific purpose.The different sensitivity of crops in a rotation usually requires a different material each season. Dosages are small and repeated treatment during a season unlikely. The possibility of crop failure is a powerful constraint to over- dosing and insidious unknown accumulation is unlikely because presence of the herbicide would be revealed by plant damage. For all these reasons, herbicides do not fit the requirements of an ‘ideal’ pollutant well and it is not surprising to find that pollution by herbicides is not widespread. However several herbicides can persist for more than a year and individual ‘carry-over’ problems have been reported, particularly with triazine and substituted urea herbicides which are widely used.Such problems are most likely in a rotation where a sensitive crop succeeds a resistant one. The increasing trend towards growing the same crop, especially cereals, for several successive years may lead to more cases where a single compound is used repeatedly, but fortu- nately the materials most commonly used in this way are not very persistent. 2,3,6-Trichlorobenzoic acid (2,3,6-TBA) and 3,5,6-trichlorpicolinic acid (picloram) can persist for long periods and may leave residues in straw that are toxic to plants grown on straw bales in greenhouses, but fortunately, as with most herbicides, these compounds are relatively harmless to mammals. Fumigants are usually even more transitory than herbicides, but insecticides show a very wide range of persistence and the longer-lasting ones are potential causes of trouble, especially as some are toxic to organisms other than pests.Some of the organochlorine insecticides such as DDT and the cyclodienes seem almost tailor-made to fit the requirements for a pollutant discussed earlier. They are sparingly soluble and not very volatile. They are strongly sorbed, are inert chemically and are not readily decomposed by micro- organisms. It should perhaps be emphasized that the persistence of organo- chlorine insecticides was originally regarded as a very desirable feature Graham-Bryce and Briggs 97 because it offered prolonged protection against soil-inhabiting insect pests from a single application. However, this property, combined with toxicity to many different insect pests and small cost, led to very widespread use, so that their prominence as pollutants can be readily understood.Most reports of pollution of soils by pesticides relate to these organochlorine insecticides. The problems are increased because these materials are lipophilic and can be stored in fatty tissues and concentrated from soil or water through food chains. Widespread concern has led to extensive if somewhat inconsistent monitoring for persistent pesticides in many countries and to a voluminous literature on the subject. Most of the investigations with soils are for agricul- tural land, although the presence of organochlorine insecticides in air and rain indicates that residues probably occur very widely in untreated land also.Table 2 shows some typical residue figures from various sources ; a much more extensive summary is given in the review by Edwards, cited at the end of this article, from which these are taken. The most common contaminants in agricultural soils are DDT and its relatives, which were detected in almost all samples analysed. Average values for all the surveys are of the order of a few parts per million. Orchard soils contain the largest amounts, reflecting the intensive treatment given to fruit trees. Repeated spraying during the season of 1-2 kg ha-1 per application to control insect pests on the foliage has given rates of up to 40 kg ha-1 a-1 for many years in some orchards. Much of this eventually reaches the soil and residues exceeding 100 ppm are not uncommon, especially in the US.98 Persistence of residual herbicides when applied at excessive rates. This barren patch in a potato crop marks the spot where a tractor stood with the herbicide spray left on five years before. (Effects are still visible after nine years.) R.I.C. Reviews No. of related compounds y-BHC sites Heptachlor and epoxide Chlordane Dieldrin Crop ref. Country Aldrin - - A B C 0.20 7. I 0.3 9.7 21 5 10 2 0.09 0.15 - - 0.4 0.5 0.02 - 0.15 - 0.04 0.02 0.06 4 5 6 9 4 0.2 0.3 0. I 0. I 0.3 - 0.8 I .2 1.4 1.5. 3.2 9.5 61.8 5 I1 8 Table 2. Mean residues of organochlorine insecticides in soils (ppm) DDT and Great Britain potatoes orchards arable orchards Canada sugar beet pasture corn cereals glasshouse tobacco vegetables orchards us turf and cu It ivated cotton desert and prairie arable 0.04 - 0.33 - - t D Davis, Ann.appl. Biol., 1968, 61, 29 Pest. Mon. J., 1968, 2, 93. 2.9 0.03 - - 2.4 I .6 227 3 5 41 Butcher and R. T. Murphy, J. econ. Ent., 1965, 58, 1026 0.06 B C. A. Edwards, N.A.A.S.q. Rev., 1969, no. 86, 47 C B. N. K. E J. E. Fahey, J. W. G W. L. Trautmann, 0.7 t = trace refs: A G. A. Wheatley, J. A. Hardman and A. H. Strickland, PI. path., 1962,81, I I D C. R. Harris, W. W. Sans and J. R. W. Miles, J. ogric. Fd Chem., 1966, 14, 398 F C. Lahser and H. G. Applegate, Texas J.Sci. 1966, 18, 12 CI+ CI Aldrin 1,2,3,4,10, I O-Hexachloro- I ,4,4a,5,8,8a- hexahydro-exo- I ,4-endo-5,8- dimethanonaphthalene CI CI Chlordane I ,2,4,5,6,7,8,8-0ctachloro-3a,4,7,7a- tetrahyd ro-4.7-methanoindane CI CI CI CI Heptachlor I ,4,5,6,7,8,8-Heptac h loro-3a,4,7,7a- tetrahydro-4,7-methanoindane CI CI Many soils used extensively for growing vegetables also contain large amounts of DDT. DDT is only slightly more persistent than dieldrin and the quantities of aldrin/dieldrin and DDT used in agriculture are comparable, so that it is not surprising to find that this is the next most important residue, although amounts are usually considerably less than of DDT. Compared with DDT and aIdrin/dieldrin, quantities of other chlorinated insecticides used in Great Britain are extremely small and very few residues have been found.However, in the United States, relatively large amounts of chlordane and heptachlor are common. The large residues of organochlorine insecticides are often the result of prac- tices unlikely to be repeated with present knowledge. Addition of persistent pesticides to fertilizers, and ‘insurance’ treatments given without knowledge of whether pests were present or not, have often contributed unnecessarily to residue problems, and the practice of frequent blanket spraying, for ex- ample in orchards, with a single broad-spectrum pesticide is now regarded as highly undesirable because of its effects on predators and beneficial insects, and the danger of selecting resistant populations of pests, Although residue problems with synthetic organic pesticides probably receive most publicity now, earlier inorganic materials were potentially at least as dangerous.Lead and arsenic residues from lead and calcium arsenate insecticides often reached alarming levels, again mainly in orchard soils where figures of several hundred ppm were not unusual. The use of these insecticides has declined since the war, but some old orchard soils remain unproductive because the residues are phytotoxic to subsequent crops. Al- though the danger with the organic arsenicals now used as herbicides and defoliants is less, their prolonged use should be carefully watched. 100 R. I. C. Re views Other agricultural chemicals cause less concern.Some of the older copper fungicides and mercury seed dressings leave residues of heavy metals which are persistent, and although occasional examples of copper killing soil fauna in orchards have been reported, these are not widespread in this country. Quantities used in seed dressings are small so that mercury residues are not large compared with natural amounts in soil. More recent synthetic organic fungicides have tended to be reactive compounds that are soon decomposed. The major plant nutrients added in fertilizers are nitrogen, phosphorus and potassium. Phosphorus is immobilized by forming various sparingly soluble phosphates and potassium is firmly held in the soil by ion exchange. Am- monium ions are also held by ion exchange but are converted by micro- organisms to nitrate and in this form nitrogen is very mobile and easily leached.In grassland, the crop intercepts most of the nitrate but with arable crops large losses can occur in spring during wet seasons. Clearly a large supply of nutrients is desirable to grow large yields but nitrate leached from the soil may be one of the nutrients stimulating the growth of micro-organisms in streams, lakes and reservoirs. The possibilities of nitrogen and phosphorus being moved from agricultural soils to water supplies have been discussed by Cooke and Williams. On a smaller scale, sewage cake from town sewage works is used as manure in some areas. This often contains large amounts of heavy metals from industrial eWuents, and can therefore cause pollution by heavy metals in soil.These are very persistent and can be taken up by plants so they may be a considerable danger in localized areas. SIGNIFICANCE OF RESIDUES IN SOIL The significance of the pesticidgresidues found in soils is difficult to assess. Except in ‘carry-over’ problems of herbicides or phytotoxic effects of arsenic residues in old orchard soils, there is no evidence that pesticide residues generally affect soil fertility. Even in the badly contaminated orchard soils, established deep-rooted trees continue to grow well although soil structure may have deteriorated and a surface mat of organic matter accumulated because the soil fauna have been killed. There seems to be little direct hazard to the consumer because few residues are transmitted to the fruit, although use of such soils for root crops, which absorb residues more readily, might contaminate food supplies. However, organochlorine residues are common in soil fauna, particularly earthworms inhabiting treated soils, and there is evidence that soil invertebrates may accumulate the insecticides to larger concentrations than in the soil.Birds that feed on these animals are at risk. The long-term biological and ecological significance of these residues is even less clear. There is no doubt that the composition of the soil fauna and soil micro-organism population is disturbed by pesticides, but whether this is permanent and what effects it has are largely unknown.Without good experi- mental information, it is wisest to proceed with caution, as is now generally recognized. The existence of large residues in soil is also undesirable as it acts as a reservoir for contamination of water supplies and other parts of the environment. Graham-Bryce and Briggs 101 We suggested earlier that with present knowledge current soil pollution problems might have been predicted. The dangers from long-lived materials soluble in lipids are now apparent and, with the present emphasis on less persistent chemicals, if DDT and some other organochlorine insecticides were newly introduced, they would probably not now pass the approval schemes operated by many countries. For many established uses, DDT and other chlorinated hydrocarbons are the best materials available and their use will continue until there are effective alternatives.The kinds of danger caused by these compounds are appreciated and perhaps more attention should be given to predicting other types of potential danger which have not so far been considered. Some processes which could be important will be discussed, but it must be emphasized that these examples are used only to illustrate possible types of mechanism and there is no evidence that these dangers exist in practice, Two old established materials that have been little investigated are penta- chloronitrobenzene (PCNB) and the fumigant mixtures containing dichloro- propene and dichloropropane (D-D mixture). PCNB has been used on a small scale in the US at about 110 kg ha-l to control potato scab. It is reported to persist in soil and its breakdown products are not known. Reduction of nitro groups to amines does occur in soils and, with such large doses, con- densation of the amines to highly chlorinated azo compounds is a possibility.These azo compounds are stable and soluble in fat and further work seems Deterioration in the structure of an orchard soil caused by repeated application of copper fungicides t o the foliage. (Left) Orchard soil showing weakly developed structure and accumulated surface mat of organic matter resulting from absence of earthworms. (Right) Neighbouring soil, uncontaminated by copper fungicides. (Courtesy Dr J. M. Hirst) FUTURE POSSIBILITIES R.I.C.Reviews 102 desirable if PCNB is likely to be used widely. It should be pointed out that the necessity for applying PCNB is dictated by the consumer. There is nothing wrong with potatoes whose skin is affected by scab, but they sell badly in the prepacked market. The consumers’ choice gives the farmer no alternative but to try control measures. Soil fumigation has long been a practice for some crops that repay cost of treatment. Recent work with dichloropropene/dichloropropane mixtures makes fumigant treatment in arable crops likely. There is little published work on the fate of these materials in soil and even at the smallest rates used, about 70 1 ha-l, a small percentage conversion to polymeric products could leave a significant residue of a chlorinated, fat-soluble material of unknown biological activity.Paraquat and diquat are relatively stable and can be detected chemically for considerable periods after application. But they are bound so strongly to mineral particles that they are not available to exert biological activity once they reach the soil. Their continued use in large quantities is certain and repeated applications could lead to much potentially active material being held in the deactivated adsorbed form. As highly-polar doubly-charged cations, they lack the lipid solubility that allows concentration of chlorinated hydrocarbons in food chains or by aquatic organisms but some questions about their eventual fate remain to be answered. CONCLUSIONS Residues of organochlorine insecticides and some other pesticides already present in soils will take several years to disappear, even without further additions.Although applying materials such as activated carbon to contami- nated soils lessens their effects, such treatments are unlikely to be practicable on a large scale and there is little that can be done to accelerate the removal of persistent pesticides. Where possible, changing to non-persistent pesticides such as the organophosphorus and carbamate insecticides, together with more careful use of persistent materials, seem to be the only ways to lessen residues. However organophosphorus and carbamate insecticides are generally much more toxic to mammals than organochlorine compounds and are therefore more dangerous to handle and cause greater short-term risks. Also persistence is a desirable feature for controlling some pests such as soil insects and the degree to which replacements for the organochlorine insecticides are success- ful is often largely a measure of the degree to which they persist. There seems little possibility that pesticides can be abandoned with the increasing world demand for high quality food, so that it is essential that the potential dangers are fully appreciated and taken into account in their use. Because residue chemists exist to find residues, it is no surprise that ana- lytical methods are becoming more and more sensitive. A needle weighing one gram in a haystack weighing 20 tons is at a concentration of 0.05 ppm and detection at these levels would be an easy analytical feat using modern methods. One cannot be complacent about pollution arising from agricultural sources, but certainly in Britain it is relatively minor in comparison with that from people and industry. It is simple to ban the use of a pesticide; cutting sewage output requires more drastic action. Graham-Bryce and Briggs 103 BIBLIOGRAPHY G. W. Cooke and R. J. Williams, ‘Losses of nitrogen and phosphorus’ rom agricultural land.’ Symposium on eutrophication, Society of Water Treatment and Examination, 1970. C. A. Edwards, ‘Insecticide residues in soil,’ Residue Rev., 1966, 13, 83. C. A. Edwards, ‘Persistent pesticides in the environment.’ Chemical Rubber Co. Critical Reviews in Environmental Control, February 1970. C. G. L. Furtnidge and J. M. Osgerby, ‘Persistence of herbicides in soil,’ J. Sci. Fd Agric., 1967, 18, 269. C. A. I. Goring, ‘Physical aspects of soil in relation to the action of soil fungicides,’ Ann. Rev. Phytopath., 1967, 5, 285. H. Martin (ed.), Insecticides and.fungicides handbook, 3rd edn. Oxford : Blackwell Scientific, 1969. L. J. Andus (ed.), The physiology and biochemistry of’ herbicides. London and New York: Academic, 1964. J. D. Fryer and S. A. Evans (eds), Weed control handbook, 5th edn, vol. 1. Oxford: Blackwell Scientific, 1968. R.I.C. Reviews 1 04

ISSN:0035-8940    

DOI:10.1039/RR9700300087

出版商:RSC    

年代:1970

数据来源: RSC

摘要:

Water Pollution H. Fish, B.Sc., F.R.I.C., F.lnst.W.P.C., F.I.P.H.E. Chief Purification Officer, Thames Conservancy, London WC2 Historical aspects . . . . .. * . The present administrative position . . The present technical position . . . * The river authority role, 110 Wastewater purification and disposal, 1 13 Research and results, 114 Future requirements Bibliography 1 . . . .. .. .. .. . . .. In its simplest sense, water pollution can be taken to mean the fouling of water. There can be no doubt that when water is fouled it certainly is polluted, but if water is not fouled it does not follow that it is unpolluted. Another common mode of expression is to say that if water is polluted, it is no longer pure. But, to the chemist, absolute purity is unattainable, and purity is a matter of degree.In this context, pollution is also a matter of degree, and exactly what constitutes water pollution in some circumstances may not be considered as pollution in other circumstances. For example, a few bacteria of faecal origin present in 100 ml of a drinking water supply would constitute dangerous pollution, but the same state of affairs in a river or lake would not constitute significant pollution. In contrast, the presence of a fraction of a milligramme per litre of chlorine in a river or lake water would constitute harmful pollution, whereas the same situation in a cooling-water system would not constitute significant pollution. In this review, the pollution of water resources only will be considered.Water resources include the inland waters in streams, rivers, lakes and ponds, the groundwaters in permeable strata underground and the tidal waters of estuaries and creeks. In their natural state these waters, which have varying degrees of chemical purity, could be considered unpolluted because their quality has not been altered by man’s actions. Quality can be described in a variety of ways, but these can be expressed in terms of physical characteristics, in terms of chemistry, and in terms of macro- and microbiology. It is neces- sary to establish what degree of alteration of these quality terms transforms a water from the unpolluted to the polluted state. In short we must define generally when an alteration of quality matters to us.From the practical point of view, a change of water quality matters when the uses that we wish to make of water-for water supply, fishing or other sporting amenity, or our aesthetic enjoyment of it as part of the environment-are inhibited; or when environmental aspects of the public health are jeopardized by that change of water quality. .. 116 .. .. . . . . 117 Fish * . .. .. .. . . 106 .. . . 108 .. . . .. . . 110 . . . . 0 . 105 Qn this basis, a practical definition of water resources pollution can be given. Water resources are said to be polluted when, because of man’s actions in adding or causing the addition of matter to the water or in altering its temperature, the physical, chemical or biological characteristics of the water are changed to such an extent that its utility for any reasonable purpose, or its environmental value, is demonstrably depreciated.The practical aspects of water pollution and its control in the UK will be considered by reference to the position in England and Wales. Although somewhat different administrative arrangements exist for water pollution control in Scotland and Northern Ireland, the basic approach is the same as in England and Wales. HISTORICAL ASPECTS The British people have the distinction of being the first to have caused gross pollution of water. This occurred during the Industrial Revolution when mechanization permitted greatly increased manufacturing output and created a new intensive demand for labour, which led to the formation of the first industrial conurbations in the North, Midlands and South Wales.Discharges of sewage and trade effluent from these towns rendered the receiving rivers fishless and foul, and the water abstracted from them for public supply was contaminated with disease organisms. Following the massive cholera out- breaks in these towns in the early and middle nineteenth century, wholesome water supplies were sought and developed in the hill country and the disease outbreaks ended-but the river pollution continued. Yet for London no economic alternative to the River Thames as a source of water could be found, and the waterworks intakes were moved upstream of the Metropolis. This accident of geography explains why it has been essential to control effectively pollution of the River Thames (and the River Lee) over the last 100 years and why these rivers are still clean, even though the density of urban and industrial development on them is now nearly as great as anywhere else in the country. River pollution in the North continued and eventually became so bad that the first general pollution prevention legislation was enacted as the Rivers (Prevention of Pollution) Act 1876.This Act is the one on which the current law is modelled, and, in itself, it was a very sound measure. Its great fault was that it was to be applied by the Local Government Boards, who were also responsible for sewage discharges from towns. But in the catchment areas of the Rivers Thames and Lee, the conservancy boards operated their own private Acts of Parliament to control pollution.R.I.C. Reviews Over the next three-quarters of a century, government commissions and committees examined the problems of sewage purification and river pollution control, and apart from certain ineffective pollution control provisions made in the Salmon and Freshwater Fisheries Act 1923, no new general statutory provision was made until 1948, when the River Boards Act was passed. This Act set up 29 river boards, who were to be responsible for river flood control, pollution prevention and freshwater fisheries protection, over virtually all of England and Wales. New pollution prevention legislation was 106 10 5 0 10 30 II - - 0 7a 30 Mile Fig. I. The river authority areas of England and Wales.The Conservators of the River Thames are only responsible for underground water resources in the excluded area. given to the river boards in the Rivers (Prevention of Pollution) Act 1951, and stemming of the flood of river pollution began in earnest. In 1960 and 1961, supplementary legislation, in the form of the Clean Rivers (Estuaries and Tidal Waters) Act 1960 and the Rivers (Prevention of Pollution) Act 1961, was enacted. Finally in 1963, following water shortages in the severe drought of 1959, and the growing scarcity of and competition for new water supplies, Fish 107 the Water Resources Act was passed. This legislation provided for the 29 river boards to be transformed into 27 river authorities.These, and the two conservancy boards (hereafter referred to collectively as the river authorities) were given additional powers to include the quantitative aspects of conserva- tion of all water resources in their river management functions. The river authority areas are shown in Fig. I . At present, a committee of the Ministry of Housing and Local Govern- ment-the Central Advisory Water Committee-is in session considering what further changes will be necessary in water management to deal with future problems. THE PRESENT ADMINISTRATIVE POSITION The responsibility of central government for water pollution control rests with the Minister of Housing and Local Government. The Ministry supervises the work of the local sewerage authorities in sewerage, sewage purification and disposal, and controls their capital investment; but it has no power to take over any of their duties in default.It also supervises the pollution control work of the river authorities and has the power to take over their duties in default. The Water Resources Board, formed under the provisions of the Water Resources Act 1963 as a planning and advisory body to assist the Minister and river authorities on the quantitative aspects of water resources management, has no significant responsibilities for water pollution control. Figure 2 shows the responsibilities for water management in England and Wales. The Rivers (Prevention of Pollution) Acts 1951 and 1961, make two basic provisions. First it is an offence to cause or knowingly permit poisonous, noxious or polluting matter to enter a stream.Secondly, no discharge of sewage or trade efRuent to a watercourse (including a ditch which may dry out in summer) is legally made unless the consent of the appropriate river authority to that discharge has been obtained, or sought and not yet refused. In granting consent, which may not be unreasonably'withheld, a river authority lays down conditions as to the quantity and quality of the discharge. Provided a discharge conforms with the conditions of consent it is not to be considered as being poisonous, noxious or polluting, or as contravening Section 8 of the Salmon and Freshwater Fisheries Act 1923 which relates to the destruction of fish by pollution. The Clean Rivers (Estuaries and Tidal Waters) Act 1960 similarly provides that no new discharge of sewage or trade effluent to estuaries, and other defined arms of the sea, can be legally made without the consent of a river authority. The Water Resources Act 1963 makes two other provisions for water pollution control.First, no discharge of sewage or trade effluent or other polluting matter, made by means of a well, borehole or pipe into the ground, is legal unless the river authority has given its consent to such discharge. Again such consent may specify conditions as to the quantity and quality of the discharge. Secondly, a river authority may take emergency action to remove, or to mitigate the consequences of, pollution of a watercourse which has already occurred.These provisions are reasonably effective in the control of pollution arising R.I. C. Reviews 108 i .B Fish 109 from continuous discharges of used waters. But the decisions of river authori- ties as regards consents and conditions of consent may be questioned by any discharger of effluent by appeal to the Minister of Housing and Local Govern- ment, who will decide the matter and, if necessary, direct the river authority. In addition to dealing with domestic sewage produced in their areas, the local sewerage authorities are required, by the Public Health (Drainage of Trade Premises) Act 1937, to make provision for accepting trade effluents (including farm effluents) into public sewers for treatment and disposal at sewage purification works.These arrangements can be made by a consent procedure, or by agreement, and the sewage authority may levy charges on the industrialist or farmer concerned to cover the cost of conveyance, purifica- tion and disposal of the trade effluent. Sewerage authorities are not obliged to accept trade effluents if to do so would seriously interfere with the fabric of sewers or with sewage treatment processes or would overload sewers. The dischargers of trade effluent to sewers are expected to provide such pre-treat- ment plant as may be necessary to render the quality of the trade effluent with- in the conditions of consent or agreement laid down by the sewerage authority. Again, disputes may be settled by appeal to the Ministry of Housing and Local Government.The legal requirements of the river authorities may be enforced in Magistrates Courts or County Courts, and conviction will result in the offender receiving a maximum fine of 2200, or, in the case of repeated offences, a maximum period of imprisonment of six months. Conviction for un- authorized discharge of trade effluent to a sewer carries a maximum fine of 250. Nevertheless it is a practical fact that the control of water pollution arising from discharges of sewage and trade effluent must be essentially a co- operative exercise between river authorities, sewerage authorities, industria- lists and farmers. The subject is so technically complicated that widespread and rigid application of the law would be useless and self-defeating.The existence of the law is necessary to ensure that the required co-operation is forthcoming, and application of the law is generally reserved for those cases where lack of co-operation or negligence results, or is likely to result, in serious river pollution. THE PRESENT TECHNICAL POSITION The river authority role A river authority aims to maintain or restore the wholesomeness of inland waters-although there is no authoritative guidance on when inland waters are to be considered as ‘wholesome’. In general, a river authority, advised by its scientists and inspectorate staffs, seeks to prevent visual, smell or fly- swarm nuisance arising in rivers and streams, and to maintain satisfactory fish life in, or restore long-lost fish life to, rivers and streams. In so far as the maintenance or restoration of fish life in a river or stream does not produce water of adequate quality for public supply, an authority will also try to improve further the quality of discharges of effluent so that the water will be suitable for use as a source of public supply. In doing this, the following main effects1Y2 of pollution have to be controlled. 110 R .I.C. Reviews 1. The physical effects, such as deposits of solids in sludge banks, oil films, detergent foaming, gross turbidity or discoloration, and artificial rises in temperature derived from cooling water discharges. 2. The oxygen-demanding effects of biodegradable organic pollution. Sewage and. trade effluents, such as those from the food industries and farming, contain residual organic matter in suspension and solution which serves as food for the micro-organisms of decay.This biodegradation of organic matter is oxygen demanding and may take up all the oxygen dissolved in the stream water and redissolving from the air. If the stream water becomes devoid of dissolved oxygen, it will become putrid and offensive to sight and smell as a result of bioreduction of sulphate and devoid of fish and other oxygen-dependent fauna, and the rate of biodegradation of organic matter in the resulting anaerobic phase will be greatly reduced. The bio-oxidation of ammonia to nitrate is also oxygen consuming but is reversible to the bio- reduction of nitrate to nitrogen gas when the concentration of dissolved oxygen drops to less than 1 mg 1-l.At dissolved oxygen saturations of about 30 per cent ( 3 mg 1-1 dissolved oxygen at about 10 "C) most fish life will become asphyxiated within a short time. 3. The acutely toxic effects of cyanides, phenols, heavy metals, ammonia, pesticides etc. to fish and other aquatic fauna. These vary with water tempera- ture, dissolved oxygen saturation and the presence of mixtures of poisons. 4. The bioconcentration of non-degradable synthetic materials, such as organochlorine and other pesticides, through aquatic food-chains which debilitates fish and harms fish-eating animals. 5. The mineralizing effects of chloride and sulphate additions to the water, and the eutrophication characteristics of nitrate and phosphate derived from excreta and household synthetic detergents, and passed on to rivers and streams in sewage effluents.6. The taste and odour producing effects of very low concentrations of phenols, essential oils and certain mineral oils, in waters abstracted for treatment for public supply. 7. Residuals of potentially dangerous chemicals in waters abstracted for public supply, which may not be removed in conventional waterworks purification processes. 8. Rapid and large fluctuations of numbers of faecal bacteria, derived from sewer overflows in wet weather, in waters abstracted for public supply. Fish The required control is achieved by applying effluent quality conditions in the consent procedures. Where the clean water dilution in a stream receiving, or scheduled to receive, effluent is considerable, say not less than about 8 to 1, it is usual for a river authority to require the effluent to contain not more than 30 mg 1-1 suspended solids nor have a Biochemical Oxygen Demand in five days at 20 "C (BODS) exceeding 20 mg 1-1-the so-called Royal Commission standard. A similar standard would also be applied to an effluent afforded much less dilution than 8 to 1 if the receiving stream, by virtue of its turbu- lence of flow, had a high reaeration capacity.Where the dilution available and the reaeration characteristics of the receiving stream are unfavourable, it is usual for the river authority to require lower concentrations of suspended 111 solids and BOD in effluents-limits as low as 5 mg 1-1 for each characteristic have been applied.The objects of these prescriptions of quality are to prevent deposits of solids forming in watercourses below effluent outfalls, and to prevent marked loss of oxygen concentration in the stream water in consequence of the BOD of the effluent. Deposits of organic suspended solids on the bed of a stream cause local concentration of BOD which can exert a deoxygenating effect on the overlying water far in excess of the dissolved and colloidal BOD present in the stream flow. This benthal effect is largely brought about by the respiring and stirring-up effect of fauna specifically developing and proliferating in sludge deposits. In addition to these general prescriptions of quality, river authorities also limit the concentrations of specific toxic and other undesirable materials in effluents.Limitations on the concentration of ammonia in effluents, to control both the deoxygenating and toxic effects of this material on stream waters, are being increasingly applied. Sampling and laboratory examination of effluents and waters, and inspection of effluent purification plant to check the quality of effluents and the receiving waters, represents a large part of the work of the pollution control departments of river authorities. Because of increasing abstraction of stream flows for public supply, in- dustry and agriculture, and the resulting increasing discharge of these waters after use, the clean water dilution available in rivers and streams is steadily decreasing, requiring a compensating rise in the quality standards applied to effluents.On the freshwater lengths of the River Thames and its tributaries upstream of Teddington Weir, 250 million gallons per day (mgd) of sewage and trade effluent (excluding cooling waters) is discharged into a natural flow which can drop in dry weather to about 250 mgd. Of this total river flow of 500 mgd in a drought period, about 300 mgd are taken to supply two-thirds of London’s water supply. This very high level of river water utilization is maintained by requiring almost half of the total volume of effluent discharged to conform with standards of quality better or very much better than the 30 mg 1-1 suspended solids and 20 mg 1-1 BOD5 limits.In dealing with pollution control in the tidal waters of estuaries and other confined coastal waters, the river authority approach is similar to that applied to freshwaters, although the effects of tidal flow, in increasing the clean water dilution available to effluents or in increasing the time of retention of effluent- polluted water within the estuary, need to be taken into account. At the seaward end of estuaries the prescriptions of effluent quality can be con- siderably relaxed because of the immense reaeration capacity and dilution available in the nearby open sea. At the head of estuaries it may be necessary to prescribe standards as high as those specified for freshwaters. Control of the pollution of groundwaters by effluent discharges raises quite different considerations on effluent quality.The oxidative capacity of the surface soil is very considerable, and while this capacity diminishes with depth below the surface, the filtration and adsorptive capacity of the subsoil and lower strata is also very considerable. It is impossible to explain the technological approach of the river authority on this subject in a few words. The two basic factors involved are whether, having regard to the nature of R.I.C. Reviews 112 the subsoil and the depth of injection of an effluent, the effluent will physically reach any underground water of value or potential value as a water resource, and secondly, what will be the condition of the effluent at that point and its effect on the groundwater.Considerations of these factors do, of course, take account of the natural facts that waters after passing into the ground receive no further reaeration from the atmosphere, and that groundwaters, other than deep primordial ones, do in effect flow as rainfall percolates into aquifers and emanates in springs, in pumped abstractions, or as discharges from the sea-bed. Groundwaters generally are clean, but in a few localities these have been grossly and almost irreversibly fouled. Although effluent discharges are the main sources of water pollution, some or all of the main causes and effects of pollution can and often do arise from sources other than continuous discharges of effluents. Most of the surface water drainage from yards, streets and roads in urban areas is dis- posed of to rivers and streams.This can be quite polluting in terms of sus- pended solids and organic matter content, and may contain de-icing chemicals applied to roads in severe weather. Spillages of oils or chemicals often reach watercourses via surface water drains and sewers, and the frequency of such events increases as usage, storage and transport of these materials increases. Accidents or negligence at premises discharging trade eilluent to sewers from time to time results in gross contamination of sewage flows arriving at sewage works, where they not only cause discharge of the contaminating pollution in the sewage effluent, but also sometimes render the sewage purifi- cation wholly ineffective. It is important to note that ignorance or negligence on the part of employees, and not on the part of management, is the main cause of these accidental pollutions.Usually in these cases, the only practic- able course of action is to control the pollution after it has reached the river, and to take steps to prevent repetition of the mishap. Drainage from agricultural land, particularly that discharged through under-drains, contains nitrate and phosphate (and calcium sulphate from clay soils)-much of this is derived from artificial fertilizers. This adds to the general eutrophication of rivers and other surface waters caused by dis- charges of sewage effluents. Pollution arising from the agricultural use of pesticides, apart from that caused by accident or negligence, is not as serious as may be feared.While the use of persistent pesticides obviously needs very careful control, problems arising from agricultural use of other pesticides should not become more serious than any other pollution problem unless aerial spraying, particularly by fixed-wing aircraft, becomes widespread. Wastewater purijication and disposal Though the prime movers in pollution control are the river authorities, their efforts and directions would be useless without the massive effort which is exerted by sewerage authorities, industrialists and farmers to control wastes and to purify them to river authority prescriptions. The farmer generally seeks to dispose of wastes from animal husbandry back onto the land, either by simple spreading of liquid manure or by ‘organic-irrigation’ systems of slurry disposal.These methods are very effective but are not without their difficulties from the agricultural point of view. The trend towards more Fish 113 intensive factory farming, and correspondingly more complex effluent dis- posal problems, is being regarded with some concern by river authorities and agriculturists alike. Only a very small proportion of the farm effluents pro- duced are discharged to public sewers in the same way as industrial effluents, but perhaps in the future this position will change. The purification of sewage involves three basic processes. The primary process is the sedimentation of solids in settlement tanks.The settled liquors are then bio-oxidized in percolating filters or activated-sludge plants. The latter processes incorporate sedimentation in secondary tanks to remove most of the solids produced in bio-oxidation from flocculation of colloidal matter and from saprophytic generation of the cellular material of oxidizing bacteria and higher organisms. The tertiary processes include treatment in sand- filters or microstrainers or by land irrigation for final removal of solids. The use of the tertiary processes (which should not be confused with the ‘tertiary’ processes now being applied abroad for removal of phosphate and other materials from effluents) is not usually necessary unless the final effluent is required to conform with a standard of quality better than the 30 mg 1-1 suspended solids, 20 mg 1-1 BOD5 standard.In all three processes, solids separated from the sewage are run as wet sludges (96 to 99 per cent water) which are either passed straight to under-drained beds for atmospheric drying, or are digested anaerobically to reduce the bulk of solids by methane production. Digested sludges are either dewatered by pressure or vacuum filtration, dried on under-drained beds or redistributed on farmland in the wet state. Most of the sludge produced at sewage works is disposed of on farmland as a soil-conditioner and mild manure, some is dumped at sea, and an increasing proportion is incinerated. Organic industrial effluents from the food manufacturing industries, leather industries and certain textile industries can be purified by similar techniques, with or without chemical precipitation, before discharge to watercourses.Some 90 per cent of all the industrial effluents reaching freshwater streams, including nearly all the effluents from the engineering and chemical industries which are generally intractable to bio-treatment without dilution with sewage, are disposed of via public sewers to sewage purification works. Substances in these effluents which would inhibit sewage purification or render the sewage effluent toxic or otherwise of unacceptable quality are pretreated before dis- charge to sewer by a variety of means, including rather special applications of bio-oxidation, and chemical treatment and precipitation.Research and results The third force in the control of pollution is the Water Pollution Research Laboratory at Stevenage, currently under the direction of the Minister of Technology. Over the last 40 years, this Laboratory has made an indispens- able contribution to water pollution control both at home and abroad. Its Annual report^,^ Notes on Wuter Pollutioi~,~ and the research papers it has produced for publication in water pollution control Journals5p6 give a unique record of progress in water pollution control in its broadest aspects. The results have been scantily referred to in the spate of television, radio and newspaper reporting on water pollution over the last 12 months. Since R.I.C. Reviews 114 1951, when the first part of the current pollution control legislation became operative, a vast amount of new pollution has been prevented, and a great deal of pollution of long-standing has been eliminated.For example, virtually the whole freshwater length of the River Thames and its tributaries supports fish life, and the main river provides more angling and boating amenity than any other river in the country despite the load of effluent it receives (Fig. 3). In Essex in 1958, a survey showed that about 200 miles of river and stream were clean and about 100 miles were polluted. In 1965, a second survey showed a great reduction of pollution-only 17 miles of river remained polluted. The Ministry of Housing and Local Government can take credit for reaching, through its Standing Committee on Synthetic Detergents and the co- operation of detergent manufacturers, a classical solution of the detergent problem which in the 1950s threatened to submerge our riversides in foam.Similarly, through its application of the Radioactive Substances Act 1960, it can take credit for containing effectively the problem of radioactive effluents. At the request of the Ministry of Housing and Local Government, river authorities have recently completed a comprehensive survey of the quality of rivers and streams in their areas. This survey will undoubtedly show that by far the greater part of the total length of rivers and streams in England and Wales support fish life and are providing or can provide immense quantities of 115 Fig. 3.Leisure activities on the Thames below Shepperton Lock. Fish 9 water for general supply purposes. But there are still far too many miles of river in the North and the Midlands which are fishless and unusable as sources of water supply, except for heavy industrial cooling and quenching purposes, and still too many estuaries which are fishless. Yet none of these causes significant nuisance and improvements are being planned and will be made as quickly as our capacity and preparedness for investment in effluent purification plant permits. More important than cleaning-up the remaining dirty rivers is the necessity to keep our cleaner rivers clean. This means that we must control potential pollution more effectively, particularly that likely to arise directly from the development and use of new non-degradable chemicals, and indirectly from increasing eutrophication of waters.FUTURE REQUIREMENTS Although a very great deal can be said on the subject of how best to meet the sometimes daunting challenges of water pollution control in the future, particularly in the broad aspect of protection of our environment, a number of factors of fundamental importance can be identified. First and foremost we must keep our feet firmly on the ground, or at least our heads out of the clouds, on the subject. All our environmental problems spring from the fundamental fact that, apart from in the high energy zones of nuclear reactions, matter cannot be created or destroyed and consequently we are obliged to live with the waste matter we produce or its degradation products.The pollution of water is inevitably bound-up with other forms of environmental pollution, and unfortunately the amount of freshwater, the raw material essential for our life and industry, is subject to seasonal and longer-period maxima and minima. Undoubtedly we have the capacity to produce all the clean water we want in the future by further conservation of rainfall and run-off and desalination of sea water. But the production of ever increasing quantities of clean water implies the production of ever increasing quantities of effluent which must be properly purified and disposed of, if we are not to increase our depredations of the aquatic part of the environment and the very sources of water we wish to render clean.The natural processes of waste assimilation and recovery are all recyclings, and our water use and wastewater disposal must follow these cycles. In some areas, we are still overloading the river part of the hydrological cycle with too much degradable organic pollution, and we are approaching overload on most lowland reaches of rivers with mineral salinizing or eutrophicating pollution and non-degradable organic matter generated by modern chemical manufacture. This overloading of our river systems, now and in the future, can only be controlled by treatment of used waters to remove the unaccept- able pollutants from the 99 per cent or more of water contained in the total waste.The fundamental question arising is should we carry this process to the stage where the water is recovered in a very clean state so that it may be reused, after return to rivers and aquifers, for all purposes, leaving us with only the separated pollutants or their breakdown products to be dis- posed of if not reusable, thereby limiting drastically our new demands on natural water resources ? Or should we continue our present arrangements of making increasing new calls on natural water resources and of only R.Z.C. Reviews 116 partially oxidizing and/or separating the grosser contaminants from used water, leaving the remainder to change the quality of our rivers and coastal waters gradually until they all take on a uniform ‘greyness’-neither clean nor obviously dirty, but very unnatural? Whatever basic approach is adopted, the existing identifiable deficiencies of our water pollution control arrangements will need to be made good in the very near future.The amount of investment in wastewater purification, disposal and reuse should be greatly increased in accordance with regional and nationally-approved plans. The present amount of ME90, plus about a 10 per cent increase per annum, probably needs to be doubled in annual total and annual increment within the next decade. Existing legislation must be brought into a more realistic relationship with the rate of change of development and technology. The broad principles of the law need to be laid down, with innovations as to its scope, particularly to deal with better control of waste disposal into the ground; control of pollutive development and the manufacture of dangerous new chemicals; changes in agricultural practice; and the causes and remedy of unintentional or negligent pollution.The detailed provisions could then be applied and modified as necessary by the Ministerial Order procedure, which enables necessary changes to be rapidly brought into effect. The number of sewage disposal authorities needs to be drastically reduced from the present 1400 to ensure that each authority is financially and tech- nically capable of carrying out its duties effectively. Additionally, and for the same reasons, the number of river authorities should be approximately halved, and amalgamations of small water supply authorities into viable, forward looking and scientifically directed authorities should be accelerated. Research effort into all aspects of water pollution and its control needs to be greatly increased, and more effectively co-ordinated. Finally, but probably most important, the social implications of pollution, its consequences and control need to be explained to people of all ages, with emphasis on the everyday problems and individual responsibilities as well as on the sensational occurrences and possibilities. Above all, broad teaching on this subject in the schools should be commenced on an appropriate basis. Unless determined action is taken on these lines, the considerable progress in controlling water pollution made over the last 20 years could be lost within a decade. Although we were the first gross polluters, we now have the best record in the world in water pollution control. There is no good reason why we should not maintain this lead and example for the rest of the world to follow, and there is good reason to believe that we shall. BIBLIOGRAPHY 1 L. Klein, Aspects of river pollution. London: Butterworths, 1957. 2 B. A. Southgate, Water poZlution and conservation. Harrow : Thunderbird Enterprises, 1970. 3 Water pollution research. Annual Reports. London : HMSO. 4 Notes on water pollution, 1-44. Stevenage: Water Pollution Research Laboratory. 5 Journal of the Institute of Water Pollution Control. 6 Efluent and Water Treatment Journal. 117 Fish

ISSN:0035-8940    

DOI:10.1039/RR9700300105

出版商:RSC    

年代:1970

数据来源: RSC

摘要:

.. .. .. .. .. .. .. 121 .. . . .. . . 122 'Grit and dust fall . . .. .. .. . . . . . . . . 120 Air Pollution C. F. Barrett, M.Sc. Ministry of Technology, Warren Spring Laboratory, Stevenage, Herts * . Aerosols . . . * Gases The dispersion and removal of pollution f . 122 . . .. .. * . . * . . . . Possible effects on climate Bibliography . . . . I . Natural removal of pollution from the atmosphere, 123 Smoke and sulphur dioxide in Great Britain . . Effects on health, 127 Secondary pollutants Sulphur compounds Carbon monoxide.. . . .. . . . . .. . . 128 . . . . . . .. . . 129 .. .. . . . . .. .. . . 130 Carbon dioxide . . . . . . .. . . . . .. .. 131 . . .. .. . . .. .. 132 .. . . .. 124 .. 134 . . .. .. . . .. . . * .This account is concerned mainly with pollution arising from the activities of man-sometimes called anthropogenic pollution. Radioactive pollution is not considered; nor are viable particles-spores, bacteria etc. As is usual, if not entirely logical, attention is confined to pollution of the external atmo- sphere, ignoring the air inside buildings. A useful classification of pollutants is into gases, particles in more or less permanent suspension (aerosols) and partides which fall out of the air more or less rapidly. The distinction between the latter two (which is not clear cut) lies in the terminal velocity for gravitational settling, which depends on the size, shape and density of the materials. Table 1 gives the terminal velocities of spheres of unit density in air at 20°C.Table I . Gravitational settling velocity for spheres of unit density in air at 20°C Diameter (pm) Terminal velocity (mm s-1) I x 10-2 8.5 x 10-4 3.5 x 10-2 0.78 0. I 0.5 5 I 10 3.0 72 250 50 I 00 119 An increase in density of the particles increases the terminal velocity in proportion. Non-spherical particles usually have a smaller terminal velocity than spherical ones of the same mass. The table shows that the smaller particles will remain in suspension for long periods. The dividing line between suspended material and that which will deposit fairly rapidly can be taken to be a diameter of about 10 pm. The larger particles form a fairly distinct part of the air pollution problem and will be discussed first.(103 t) 295 33 I Table 2. Emissions of grit and dust (1964) Grit and dust emitted Fuel Industrial coal Power station coal Oil I I4 Total 740 GRIT AND DUST FALL The deposit of relatively large particles, called grit and dust fall, is a common nuisance of urban life, especially in areas where there is much industrial development. These particles cannot enter the respiratory system and do not form a health hazard. Most of the material is a product of combustion arising mainly from the ash in the fuel. A fairly crude estimate of the emissions in Great Britain in 1964 is given in Table 2. In certain areas the grit and dust arising from fuel combustion is out- weighed by the dust created by industrial processes and this can give rise to specific local complaints.The cement and iron and steel industries have been prominent in this respect. Ash heaps, coal dumps and the handling of various materials can also produce local nuisances; dust of natural origin is hardly ever a problem in this country. Dust fall is commonly measured by exposing a jar or can to the air for one month and then weighing the material which has settled in it. Unfortu- nately different countries use collectors of different sizes and shapes and comparison of results may be difficult. Table 3 gives an analysis of the results of about 950 gauges in the UK in 1962-3 in terms of type of area. Median deposits are given rather than means because there are a few very high results from each type of area which make the mean less representative.Results from gauges sited to monitor a particu- lar factory have been excluded. There is a tendency for the observed deposits to decrease with time. Table 3 can be used as a rough standard in the absence of a better one. An interesting idea for a fundamental standard was put forward some years ago by Carey. He suggested that the main nuisance is the dingy appearance of a surface when covered by a light film of dust, and found by experiment that the effect was distinct when the fraction of the area covered was between 0.2 and 0.4 per cent, depending on the contrast. By assuming that outdoor 120 R.I.C. Reviews dust 1s removed by heavy rain at intervals of about 10 days in this country he concluded that if the rate of dust coverage was less than 0.04 per cent per day it would be seldom noticed.This figure might therefore be regarded as an upper limit to the tolerable rate of deposit. AEROSOLS The non-viable particles in the atmosphere cover an enormous range of radius from about 0.6 nm to 20 pm. The largest particles which fall out rapidly have already been dealt with. Particles smaller than 0.1 pm exist in enormous numbers and are electrically charged. Despite their numbers they contain little of the mass and are only of importance in the electrical proper- ties of the atmosphere with which this article is not concerned. The particles in the approximate range of 0.1-10 pm are of importance in producing haze (up to about 1 pm), in cloud physics and in air chemistry; they include smoke.The numbers of particles increase very rapidly with decrease in radius and the size distribution can be approximated by: dN/dr = Cr-4 with radii between r and r + dr. This distribution corresponds to a constant over the range r = 80 nm to 10 pm, where dN/dr is the number of particles log radius-volume or log radius-mass distribution-assuming the average density is constant over the size range. On individual occasions departures from the distribution are observed-it is essentially a statistical relationship. The form of the distribution is determined partly by the modes of production and partly by the changes which aerosol distributions undergo with time as a result of coagulation of small particles, sedimentation of large particles and a condensation-evaporation cycle in cloud, fog and rain.‘This is a ‘self- preserving distribution’ whose form, once established, will remain unchanged with time. As might be expected, a wide variety of substances is to be found in different parts of the spectrum and there is a large variability with place and time. The complexity of the subject precludes a proper discussion and only a few remarks will be made here; smoke is discussed in a later section. An obvious effect of these particles is a reduction in the clarity of the atmosphere. At low relative humidities, this is called haze and normally has a somewhat yellowish colour by transmitted light because the shorter wave- I I6 82 I12 90 70 Table 3.Median values of grit and dust fall (1962-3) Median grit and dust fall (mg m-2 d-1) I59 Type of site Purely industrial area An area of dense old-fashioned housing An area of low density housing The commercial centre of a town Open ground in the centre of a town The outskirts of a town Open country 30 121 lengths are more attenuated. As the relative humidity rises the particles swell and become droplets of aqueous solution with diameters of a few micro- metres or more. At this stage we have mist or fog rather than haze. These droplets are large compared with the wavelength of light and scatter light non-selectively ; mists therefore appear white. They also produce a much greater reduction in visibility than does haze; visibilities of less than 1 km are produced by mist and fog; haze is present when visibility exceeds 1 km.In the haze regime it has been found that the visibility is equal to the dis- tance that contains about 1 g m-2 of suspended material. This phenomenon could be used to supply a criterion for maximum allowable concentration- namely, that it should not cause a noticeable reduction in clarity of the air. (NO2 can cause a noticeable coloration of the sky and this has been used to set an upper limit of 0.25 ppm in Los Angeles.) The nuclei of interest in cloud physics can arise from man’s activities but this source is of little importance, except perhaps locally, compared with natural production. GASES Table 4 gives a summary of the observed concentrations in both polluted and unpolluted atmospheres of the major primary pollutants, i.e.those not formed only by reactions in the atmosphere. The values are given in terms of the volume or mole mixing ratio, i.e. ratio of number of molecules of gas to air in parts per million. Factors are listed to convert these concentrations to pg 111-3. The figures in the last column give an idea of the orders involved; where a range is given, it applies to ‘normal’ conditions and does not cover the greatest extremes. Some pollutants are discussed in more detail in later sections following a discussion of the dispersion of pollutants and their modes of removal from the atmosphere. THE DISPERSION AND REMOVAL OF POLLUTION The processes by which pollutants are dispersed in and removed from the atmosphere are briefly discussed here.Large particles are not considered and therefore the influence of gravitational settling can be entirely ignored. Concentrations in polluted atmospheres S O 2 HzS co NO + NO2 I 0-3 (6-20) x 10-3 Table 4. Concentrations of gaseous pollutants. Pollutant Background concentration (ppm) (ppm) 0.2 x 10-3 0.2 x 10-3 0. I S 320 0.02-1 (0.5-1) x 10-3 1-30 500 25 2 Conversion factor (PI3 m-3/PPm) 2860 I520 I260 I960 1340, 2050 760 712 I .5 N H3 CH4 Other hydrocarbons - 10-50 x 10-2 I . 5 < 10-3 co2 122 R. 1. C. Re views Dispersion is the result of air movement. When air blows over a building, or other obstruction, the flow on the lee side is very disturbed and tends to bring to the ground rapidly and in high concentration any pollution emitted from the building itself or from a short chimney on it. For example, the smoke from domestic chimneys may be seen at almost any time to descend rapidly to ground level and it is partly for this reason that pollution from domestic fires is so serious in our cities.For large sources it is important to make the chimney high enough so that the effluent can escape from the aerodynamic effects of the building and wind tunnel tests are sometimes used to determine a suitable height. Other things being equal, ground level concentrations are proportional to 1/UH2 where U is the wind speed and H the effective height of emission.The advantage of high chimneys is obvious, but the effective height includes the rise produced by the buoyancy of the effluent. This can be a major factor for large sources; rises of several hundred metres are achieved, for example, by large power stations. Pollution from tall sources is only observed at ground level when mixing extends up to their level; but this mixing reduces the pollution from low (e.g. domestic) sources. There is no simple relation between rates of emission and ground level concentration. Another factor of great importance is the (hydrostatic) stability of the atmosphere which depends on the vertical temperature gradient. When warm air overlies cold (a condition often referred to as an inversion) buoyancy forces inhibit vertical air movement and the condition is ‘stable’.An exact analysis shows that the borderline between stable and unstable conditions occurs with a fall in temperature (or ‘lapse rate’) of nearly 1 “C km-1. Stable layers occur frequently and are important because they limit vertical mixing. They may occur at any level in the atmosphere. Cities at night often have a stable layer (at a height of perhaps 300 m) with a well-stirred layer below. All low-level pollution will be retained in the lower layer, but if pollu- tion can be emitted above the stable layer it will not affect ground level at all- another advantage of high chimneys. In summary, dispersion is favoured by tall chimneys in windy areas free from inversions. On a larger scale, mixing within a hemisphere is normally complete within a few weeks whereas the exchange between hemispheres is slower, requiring about a year.These times refer to the lower atmosphere or troposphere. This is bounded at the top by a permanent inversion called the tropopause; above this is the stably stratified stratosphere with poor vertical mixing. The tropo- pause occurs at a height of 7-10 km in middle latitudes and 15-17 km in low latitudes. Exchange between troposphere and stratosphere is not easy. Most of the movement out of the troposphere into the stratosphere occurs at the high tropical tropopause while the return flow is mostly at irregularities of the middle latitude tropopause. The lifetime of material in the stratosphere is months, depending on height.Natural removal of pollution from the atmosphere Large particles are removed by gravitational settling at their terminal velocity. By analogy we can define a ‘velocity of deposition’ Vd for gases and 123 Barrett Table 5. Contributions to the sulphate ion concen- tration in rainfall aerosols where vd = rate of removal/unit area concentration in the air above the surface Values of order 1 cm s-1 are common for many materials including ‘smoke’ and SOZ. Rain is an important cleansing agent in the atmosphere for both particles and soluble gases. Rain drops are inefficient for removing particles with diameters smaller than 1 or 2 pm. Particles in the higher troposphere may act as nuclei on which water droplets form which later fall as rain.This process is sometimes called ‘rainout’; the process of scavenging by raindrops is called ‘washout’. Table 5 (taken from a study by Beilke and Georgii) gives the relative importance of these processes in determining the sulphate ion concentration in rainfall in Germany with a moderately polluted continental atmosphere. The smallness of the rainout of SO2 is due to a low concentration at cloud level. In most cases rainout is the principal means of removal. SMOKE AND SULPHUR DIOXIDE IN GREAT BRITAIN These pollutants occur in far higher concentrations than any others except CO and COz and have attracted the largest share of attention, especially in this country. Smoke (sometimes suspended particulate matter) is not a definite chemical species but is defined by a standardized method of measurement. Air is drawn through a clean filter paper to produce a dark stain. The reduction in reflectivity is then used as a measure of the smoke concentration. In the US a similar measurement is called a soiling index and expressed in conventional units.In this country the results are expressed in terms of a mass concentra- tion of an arbitrary standard smoke. This unit corresponds to true mass concentration for average urban smoke but can diverge widely for smokes of different composition. The method should be regarded as a simple means of obtaining an index of pollution and one which is particularly relevant to such effects as transmission of sunlight, visibility and soiling of materials.Usually the smoke filter is combined with a measurement of sulphur dioxide based on the sulphuric acid formed after absorption in hydrogen peroxide. In the majority of cases this simple method gives reliable results. The combined equipment has the great advantages of cheapness and simplicity and it can be used successfully by relatively unskilled staff. In this country at present, there about 1200 sets operated mainly by Public Health Depart- ments of Local Authorities producing daily mean concentrations ; this scheme of measurements makes up the ‘National Survey of Air Pollution’. The 124 R. I. C. Reviews Sulphur dioxide (M m-3) Table 6. Regional distribution of smoke and sulphur dioxide Smoke Domestic coal consumption per head of population Region North Western Northern Yorkshire and Humberside Scotland Northern Ireland East Midlands West Mid lands East Anglia Greater London South Eastern, excl.London Wales South Western average concentrations 1968-9 I47 97 I40 87 96 102 I09 I08 97 88 79 77 63 51 46 39 39 33 I19 87 151 78 62 68 125 tt) 0.61 0.69 0.57 0.45 0.63 0.53 0.45 0.33 0.06 0.17 0.62 0.23 Survey is co-ordinated by Warren Spring Laboratory at Stevenage and produces a vast quantity of reliable data. A few of the results will now be outlined. The distribution of the annual average smoke and sulphur dioxide concen- trations in the United Kingdom in 1969 is summarized in Table 6.The Registrar General’s statistical regions are used and the names are sufficiently self-explanatory for the present purpose. The entries are arranged in decreasing order of smoke concentration and the figures in column 3 show that in the towns in the South the smoke concentration is only one-third to one-half of the concentration in towns in the North. Column 2 suggests that the emission of smoke per person from domestic heating is greater in the North in about the same proportion. Domestic smoke emission is of major importance for two reasons : the poorer dispersion characteristics compared with industrial chimneys has already been mentioned; in addition, the emission is much greater for a given rate of coal burning because of the extremely inefficient combustion in the domestic grate.Figure 1 gives estimates of smoke emissions in the UK, with a forecast trend for the next few years. The great dominance of the domestic contribu- tion is evident. The sharp fall in the industrial component is partly due to the Clean Air Act of 1956, which probably had some influence as early as 1955 when it was under discussion. The reduction in domestic smoke is partly due to the same act which gave Local Authorities power to set up Smoke Con- trol Areas in which the burning of fuels other than ‘smokeless’ fuels is pro- hibited. The concentrations experienced follow a broadly similar trend to the emissions, though there are some deviations attributable to variations in dispersion in different years. The fall has gone further in the South than the North and it is significant that the famous smogs (smoke fogs) of London appear to be extinct.The increasing cleanliness of the air is a matter of observation and confirmed by a number of measurable quantities such as fog frequency, visibility and loss of sunshine. All smoke is undesirable but Barrett l l l l i l l - Esti Aatefd $om actual fuel consumption - --Estimated from forecast fuel consumption 7 l i l l I l 1 1 l 1 1 1 1 1 1 \ \ -Total -Domestic \- Industrial 58 1950 52 54 56 60 62 64 66 68 70 Year Fig. I . Smoke emissions in the United Kingdom. there appear to be grounds for moderate optimism that the smoke problem is being resolved.The pattern of sulphur dioxide emissions is shown in Fig. 2. Although the domestic contribution is a relatively small one, its contribution to the ground level concentrations is a high one partly because of the poor dispersion al- ready alluded to, and also because the emission occurs where people live. On the other hand the power station contribution is much smaller than the rate of emission would indicate because it is emitted from tall chimneys with large buoyancy and usually far from large towns. Figure 2 shows that the emission of sulphur dioxide reached a maximum in 1963 and has declined by about 6 per cent since then. The fuel policy outlined in a White Paper of 1967 indicates that this decline should continue to 13 per cent by 1975.The reason is the increasing use of gas and nuclear energy. The concentration of SO2 shows a decline of about 30-35 per cent in the decade 1958-1 968, though individual years show very considerable depar- tures from this trend. The decline is greater than that of the total emissions probably because of the increasing height of emission, but there may also be a secular trend of increasing dispersion. Evidently even without any specific 126 72 74 R. I. C. Reviews I l l I l l 1 l l l l 1 l I l l l l l l i 1 1 1 1 - - Estimated from actual fuel consumption --- Estimated from forecast fuel consumption i 1 I I I I I I Domestic I I I 1 I t 1 1 I I I t I I I I i I I 0 . 0 - 1 I action some improvement in pollution by SO2 is to be expected in the next few years.Eflects on health The effort against air pollution is motivated largely by concern for the effect on health and in particular the 4000 deaths attributed to the London smog of December 1952 led to a Royal Commission and the Clean Air Act of 1956. In this country chronic bronchitis is of greatest concern, because of its great prevalence. Although many other factors are involved in bronchitis (cigarette smoking in particular) there seems no doubt that pollution is involved. Despite a great deal of research, the effective constituents have not been identified, but smoke and SO2 acting alone and together are thought to be implicated. One study found that levels of 750 pg m-3 of smoke and 700 pg 111-3 of SO2 in Greater London were associated with increases in the total number of deaths; another found that patients suffering from chronic bronchitis felt worse when smoke concentration in London rose above 300 pm m-3 and SO2 above 600 pg m-3. Since the concentrations of both smoke and SO2 are influenced by the same meteorological factors they will tend to rise and fall together and it is difficult to separate their effects (they will in any case interact).The epidemiological evidence points to smoke as being the major culprit. Professor Lawther, head of the air pollution unit of the Medical Research Council, has expressed the view that, provided the concentration of smoke was low, peak concentrations Brrrett 127 of SO2 less than 1000 pg m-3 were unlikely to be harmful.To keep below this limit would mean aiming at a maximum mean annual concentration of SO2 of 100-150 pg m-3. This figure can be compared with those in Table 6. SECONDARY POLLUTANTS This term is used for pollutants which are the products of reactions in the atmosphere. The most important occur in the photochemical smog which is most prominent in Southern California. This is quite distinct from the original smoke fog of London. A photochemical smog exhibits some reduc- tion in visibility, eye-irritation and characteristic patterns of plant damage. Typically it reaches a maximum at midday with clear skies, low relative humidity and temperatures of 25-35°C. It is the result of a high density of automobile emissions in a region of poor dispersion and an abundance of solar radiation for photochemical reactions.The meteorology of the smog is dictated by very large scale features of the circulation of the atmosphere which produce light winds and a very strong inversion aloft. This inversion limits the vertical movement of pollu- tion and also ensures clear skies. (Some modifications are produced by sea breezes and the presence of a mountain range, but these are of secondary importance.) Broadly speaking, such conditions are to be expected in sub- tropical latitudes especially on the western sides of continents. Figure 3 shows the average diurnal variation of concentration of some of the pollutants during days of eye irritation. These patterns would be difficult to account for by diurnal variations in traffic flow and in dispersion.The extra factor is photochemically initiated reactions in the atmosphere, the raw materials being nitrous oxide (NO) and alkenes (and some other organic compounds). A large variety of both long and short reaction chains occurs, producing a wide variety of products including alkyl nitrates, peroxyacyl nitrates, alcohols, ethers, acids and peroxy-acids. Many free radicals act as intermediates ; and, because of the great dilution, these radicals have lifetimes of minutes or hours. Table 7 gives some typical reactions. + RCO* R2CO + hv -+ R* R-R + OR* + 0 --+ R* R* + 0 2 --+ RO; Table 7. Formation of photochemical smog: typical reactions NO2 + hv 3 NO + 0 Primary reactions 0 2 + 0 4 0 3 Secondary reactions Chain reactions RCO* + 0 2 -+ RCO* RO," + 0 2 4 RO* + 0 3 RO; + RH --+ ROOH + R* RO* + RH --+ ROH + R* RCO* + NO2 4 RCO, $- NO2 RCO: + NO -+ RCO + NO2 RCO + NO 4 RCO* + NO2 R.I.C.Reviews 128 6 8 6 4 2 12 4 10 am bm Noon Fig. 3. Average concentrations during days of eye irritation in downtown Los Angeles. Hydrocarbons, aldehydes and ozone 1953-4. Nitric oxide and nitrogen dioxide for 1958. From data of the Los Angeles Air Pollution Control District (after Leighton). The eye irritation is attributed mainly to formaldehyde and acrolein as well as peroxyacyl nitrates, of which peroxyacetyl nitrate (PAN) seems to be the most important. Ozone and PAN are also the principal causes of the characteristic smog type of plant damage.Ozone is responsible for intense rubber cracking in the Los Angeles area. SULPHUR COMPOUNDS In this and the next two sections, the atmospheric circulation of three impor- tant classes of pollutants-sulphur, carbon monoxide and carbon dioxide- is discussed. The common sulphur compounds in the atmosphere are S02, H2S and sulphates (including HzS04). Sulphur dioxide is emitted almost entirely from pollution sources, totalling 126 x 106 t a-1 (63 x 106 t of S). Comparison of this rate and of the quantities observed shows that after forma- tion the SO2 molecule has an average lifetime in the atmosphere of only a few days. A number of mechanisms for removal exist. It may oxidize to form H2S04 or sulphates in a number of ways which are not yet fully understood. An important mode of removal is washout by rain as mentioned earlier.Another is absorption by vegetation. (Sulphur is necessary for growth and will be removed from the soil if it is available.) The rate of removal from the atmosphere has been found to correspond to a deposition velocity of order 1 cm s-1. In contrast to S02, the major sources of HzS are natural-decaying organic matter (for example in swamps) and also volcanic areas. The emission rate Barrett 129 is rather uncertain but a recent global figure is 97 x 106 t a-1. Industrial emissions are nearly negligible by comparison, perhaps 3 x 106 t a-1. H2S is rapidly oxidized to SO2 by ozone in a heterogeneous reaction on surfaces, for example those of aerosols; its lifetime is estimated to be a maximum of 28 h in ‘clean’ conditions and very much less in polluted air.Sulphate particles are produced by the oxidation of SO2 and from sea- spray. About half the mass is in particles smaller than 0.15 pm and sulphates make up about one-quarter of the total aerosol mass. Loss from the atmo- sphere occurs by gravitational settling and removal by precipitation. The lifetime in the atmosphere is estimated as 20-30 days. The average quantities of sulphur in the atmosphere in the three forms are estimated to be: so2 H2S so4 63 10 13 problem. CARBON MONOXIDE 0.25 pg m-3 0. I4 pg rn-3 0.7 pgrn-3 The environmental sulphur cycle is still somewhat uncertain. A recent study by Robinson and Robbins finds no accumulation in the atmosphere but an accumulation of 86 x 106 t (as S) each year in the oceans.The inputs to this are (in millions of t a-1 of sulphur) : pollution sources (of S 0 2 ) soil application (as fertilizer) rock weathering It would seem that air pollution by sulphur is not a global problem but confined to certain areas. In most cases, provision of adequate dispersion by using tall chimneys, for example, is a satisfactory way of dealing with the The toxic properties of carbon monoxide and its prevalence in the exhaust of petrol engines make it a subject of interest. The acute symptoms have been studied for many years but recently attention has been paid to the effects of lower concentrations both on the performance of fine tasks and on possible long-term effects. Individuals with, for example, severe anaemia or impair- ment of circulation to vital organs are more susceptible than the fully fit.For such people it has been estimated that exposures for 8 h to 30 ppm when added to other sources could increase mortality and morbidity, and this figure was adopted as a community standard by the California Department of Health; subsequently the standard has been reduced to 20ppm. Broadly similar decisions have been made by a number of other authorities. A recent survey of busy streets in British cities found that 30ppm was exceeded for only about 2 per cent of the time, the maximum continuous period of excess being only a few minutes. On streets, therefore, this country seems to have little cause for concern. A recent estimate of the global emission in 1966 was 2.1 x 108 t, of which petrol engines were responsible for 83 per cent.The only natural source considered was forest fires estimated to produce 0.1 x 108 t or about 5 per R. I. C. Reviews 130 cent of the total. More recent measurements of oceanic water suggest that some process in the oceans emits an additional 0.09 x los t annually. The dominance of man’s activity is evident, and since 1945 the increasing use of the motor car has produced a nearly linear increase in CO emission of ’7.4 per cent annually. Measurements of background CO in the past have been insufficient to show with certainty whether there has been a correspond- ing increase in concentration.The ambient level at present appears to be about 0.1 ppm; the total mass of the atmosphere is 5.3 x 1015 t ; hence the total mass of CO in the atmo- sphere is about 5.6 x lo8 t, or about 23 years’ emissions. On the whole the atmospheric content is thought likely to be lower rather than higher than the figure given and, at present, it is difficult to account for this relatively short lifetime of such an unreactive gas. One important sink for CO is in the stratosphere where reaction with OH radicals occurs readily: CARBON DIOXIDE OH + CO + C02 + H The OH radicals are produced by the reaction of photochemically-generated excited oxygen atoms with water vapour. However, it seems likely that the rate of transport into the stratosphere is too low to remove all the annual production and that some other sink must exist.Bacteria or plant respiration have been suggested but data are lacking. With the present lack of knowledge of the fate of CO in the atmosphere it is impossible to say with certainty what will happen to the ambient concentrations if automobile emissions continue to rise at their present rate. This is by far the most common pollutant in the atmosphere; it is of interest mainly because it has been increasing in concentration and the increase may cause climatic changes, a possibility first suggested at the beginning of the century by both Chamberlain and Arrhenius. Despite the shortage of good measurements in the past, it has been possible to conclude that there has been an increase of about 11 per cent from the beginning of the century (when the concentration was about 290 ppm) to the 1950s.Since then very careful measurements have been made in areas unaffected by local sources. These data indicate an increase of about 0.7 ppm per year since 1958. Although differing views have been expressed it seems probable that the increase is due to the burning of fossil fuel. About half the C02 so produced remains in the atmosphere, probably about 14 per cent enters the ocean and the remainder goes into the biosphere, mainly in trees and other terrestrial plants and humus. Only long-lived plants and humus are of importance; most of the plant material formed is reoxidized within a few years.The oceans are estimated to contain 60 times as much carbon dioxide as the atmosphere, but only the top few hundred metres exchange with the atmosphere over short periods; and only the dissolved and hydrated C02 content is available. Most of the C02 is present as carbonate and bicarbonate which do not have much effect over a time scale of decades. Barrett 131 10 The basis for the above conclusions may be found in the Report of the US President’s Science Advisory Committee cited in the bibliography. To a considerable extent it is based on the variations of radiocarbon (14C) content of the atmospheric C02. This is generated at a nearly constant rate by cosmic rays and decays with a half-life of 5600 years. Fossil fuel is old enough to contain no l4C and burning it reduces the proportion of 14C in the air; tree rings allow the determination of past concentrations.After 1954 the concentration rose as a result of hydrogen bomb tests, vitiating future measurements. Immediately before these tests, the proportion of 14C was lower by between 1 and 2 per cent than it was in the middle of the nineteenth century . With increasing fuel usage the COz concentration in the atmosphere must be expected to increase. In the Report mentioned it is suggested that the most likely concentration in the year 2000 will be 25 per cent above that of 1950. Clearly such an estimate is very uncertain, but it does raise the question whether such a large increase, which may well be itself greatly exceeded in later years, is likely to cause changes in the environment.Two such changes have been suggested-in the rate of photosynthesis and in the earth’s climate. The first, though likely, seems of smaller importance and will not be dis- cussed. POSSIBLE EFFECTS ON CLIMATE This section will be concerned only with large-scale effects, all of which depend on changes in the radiation balance of the atmosphere. Solar radiation is similar to that of a black body at 6000 K, and it has a maximum at a wave- length of 0.5 pm. The earth’s surface radiates as a black body of about 288 K with maximum radiation at 10 pm. The two streams of radiation scarcely overlap in wavelength and are affected quite differently by the atmosphere.Some of the incoming radiation is returned to space (about 35 per cent) by clouds, by scattering from dust particles (some scattered light however finds its way to the earth’s surface) and by reflection from the earth’s surface. Only a minor part is absorbed in the atmosphere; most is absorbed by the surface of the earth. The terrestrial radiation is strongly absorbed in the atmosphere by three trace constituents-HzO, COZ and 0 3 . The last is important only in the stratosphere. The water vapour absorption extends over a wide region of wavelength. The main CO:! absorption is around 15 pm where H2O absorp- tion is small. The result of all this absorption is to keep the earth a good deal warmer than it would be otherwise. The observed temperatures are also influenced by air movement : convection distributes heat vertically and the general circulation of the atmosphere redistributes it globally.In the past 20 years or so high speed computers have been applied to the prediction of atmospheric motions; the stage has not yet been reached when the effects of small changes in radiation can be quantitatively determined (though it is expected within a few years) and such effects can at present be treated only semi-quantitatively. Usually when climatic changes are discussed changes of temperature are the major, often the only, parameter mentioned, but they are inevitably bound up with changes in the circulation which may be equally R.I.C. Reviews 132 important-for example in altering rainfall. The temperature changes mentioned are apparently small but almost any detectable change will have noticeable effects.To indicate the order of magnitude, the much discussed recent changes are estimated to be a rise averaged over the earth's surface of 0.4 "C from the 1880s to the 1940s followed by a fall of about 0.2 "C in the next quarter century-a fall which may be continuing. Any changes produced by man will be superimposed on naturally produced changes which may well be dominant. The natural causes are not known but changes in radiation have always been popular with theorists and in some cases at least the ideas seem well founded. These changes can arise from changes in the output of the sun, variations of the earth's orbit (this is irrelevant in the present time scale), dust from volcanic eruptions and from changes in COX concentration which are known to have occurred in the past, independent of man's activity.Only three effects of man's activity will be discussed here-the increase in COX concentration, the increase in aerosol content and the exhausts of jet aircraft. There is no need to consider the rate of heat release which at present amounts to only 1/2500 of the radiation received at the earth's surface, increasing at 4 per cent per annum. In calculating the effects of increasing COZ it has been possible to take into account convection but not, as yet, atmospheric circulation. Another diffi- culty is the treatment of the water vapour which will increase with tempera- ture. The most recent and best treatment indicates that doubling the COZ concentration would produce an increase in temperature of 2°C.By the year 2000 the COX concentration is estimated to increase by 25 per cent and a significant warming effect may be expected. Recently attention has been drawn to the increasing turbidity (a measure of the optical effects of aerosols) of the atmosphere over the past 60 years. Part of this is due to the dust from volcanic eruptions [e.g. Krakatoa (1883), Katmai (1912), Kamchata (1956) and Mt Agung (1963)] and part to human activity. Over 60 years the increase is thought to be about 20 per cent; more recent measurements appear to indicate an increase of 30 per cent per decade. Calculations suggest that a turbidity change of 3-4 per cent, averaged over the whole world, would produce a reduction in temperature of 0.4 "C. Thus, this is also a significant effect. If, in the future, there are 400 supersonic aircraft operating regularly they will introduce water vapour into the stratosphere at a rate of about 1.5 t s-l. This may be compared with an estimated natural flux into and out of the stratosphere of about 5 t s-1. Therefore it is possible that these aircraft may bring about a significant increase in the water vapour content of this very dry region. The main effect of the additional water vapour will probably be to increase cloudiness wherever there is rising motion. The type of cloud produced would diminish solar radiation reaching the earth, but have little effect in the radiation leaving it: the net effect would be cooling. To sum up, if present trends in pollution continue it seems likely that sig- nificant changes will be made to the radiation affecting the earth. The effect on climate is impossible to assess with certainty but may be important. Beside this possibility, local effects seem of minor significance. 133 Barrett BIBLIOGRAPHY A. C. Stern (ed.) Air pollution (3 vols). New York and London: Academic Press, 1968. C. E. Junge, Air chemistry and radioactivity. New York and London: Academic Press, 1963. P. A. Leighton, Photochemistry of air pollution. New York and London: Academic Press, 1961. E. Robinson and R. C. Robbins, Sources, abundance and fate of gaseous atmospheric pollutants (Final Report SRI Project PR-6755) for American Petroleum Institute, New York, Feb. 1968. Restoring the quality of our environment. Report of the Environmental Pollution Panel, President’s Science Advisory Committee, The White House, November 1965. 134 R.I.C. Review3

ISSN:0035-8940    

DOI:10.1039/RR9700300119

出版商:RSC    

年代:1970

数据来源: RSC

摘要:

.. Brewing .. .. .. * . . . . . . . .. .. .. . . . . .. . . .. .. 137 FERMENTATION-THE LAST TEN YEARS AND THE NEXT TEN YEARS L. M. Miall, M.A., F.R.I.C. Fermentation Development Dept, Pfizer Ltd, Sandwich, Kent Yeast Hydrocarbon fermentations, 138 Acids Lactic acid, 140 Acetic acid, 141 Citric acid, 142 Amino acids, 144 135 .. 140 . . .. . . . , * . * . 147 148 150 153 158 159 . . . . .. . . . . . . . . . . .. .. . * . . . . Ribonucleotides . . . I ) Vitamins and provitamins Transformations . , Antibiotics Conclusion. . .. * . References . . . . * . .. . , .. . . . . . . . . .. . . . . .. .. . . .. . . . . . . Enzymes . . .. .. .. . . . . . . .. . . 157 . . . . . . . . .. . . In this review the word ‘fermentation’ is used in its modern sense; it cannot be strictly defined, but is roughly equivalent to the production of compounds by micro-organisms.Usually the word is extended to cover production of the micro-organisms themselves. In attempting to forecast likely developments in the next decade it is obviously wise to consider what has happened in the last 10 years or so and to try to make an intelligent extrapolation. In such an article it is possible to give only a very brief account of this vast and specialized technology; for those who want to go deeper, the references given are mostly either to more detailed reviews of specific aspects of the subject or to very recent papers not covered by reviews. BREWING The production of beer and other alcoholic beverages is by far the biggest branch of the fermentation industry; the subject is so vast that it would need a review to itself, and this discussion will be confined to one of the most likely future developments.Until recently, brewing has been a batch process, but much work on continuous brewing has been carried out in the last decade following the original work at the Brewing Industry Research Foundation.1,2 Only the fermentation step will be considered here. The conventional batch fermentation begins with the cultivation, on a laboratory scale, of a small quantity of the appropriate micro-organism. 135 Miall . . . * . . .. This is added to a larger vessel containing the appropriate medium in which the micro-organism reproduces itself and, after a suitable time, this is itself added to a still larger vessel, which may or may not be the final fermenter. At the end of the production run the process begins again.In continuous culture, having once established a process on the largest required scale, fresh medium is added continuously, the final brew is drawn off continuously, and the process is kept as near to equilibrium as possible-the micro- organisms reproduce at a rate determined by the addition of nutrients. Brewing seems an obvious process to be operated continuously, but it has required many years of development in many breweries before large-scale introduction. It was first operated on a production scale in New Zealand, and recently Watney Mann Ltd, one of the biggest of the British brewing combines, has announced a continuous fermentation capacity of 20 000 barrels a week.A barrel is 36 gallons or 163.3 litres, so that one way of bringing this figure home is to realize that roughly five and three-quarter million pints of continuously fermented beer are being consumed per week in this country. It is a fairly safe assumption that this figure will increase considerably in the next 10 years. When fermentation technologists meet at symposia and similar occasions, the talk is apt to turn to problems of continuous culture, with the academic microbiologists often accusing their industrial counterparts of dragging their feet in the introduction of such an obvious (from the engineering point of view) technique.The majority of fermentations follow the type of curve shown in Fig. I where production of product is plotted against time. The total fermenter residence time (t), plus the down-time (d) when the fermenter is being emptied, cleaned, filled and sterilized, should be compared with the time (x) during which production is at maximum rate. But continuous culture a high proportion of ( t + d ) so that there is a relatively small potential saving does not always give such an obvious saving. In a slow fermentation, x may be in continuous culture. With a rapid fermentation and a concentrated medium, the total occupation time of the fermenter may be small, and if the fixed costs of the process are small compared with material costs, the potential saving will again be small.Against the potential time-saving, other factors have to be taken into account. In many fermentations the cost of the substrate necessitates as complete a conversion to product as possible, so the fermentation is con- tinued to the end. This is also necessary when complete removal of the sub- strate facilitates subsequent recovery of the product. In continuous culture, this would be equivalent to operating at point B instead of point A (Fig. I ) and would immediately remove the advantage. The problem could be over- come by having a second vessel in line, with a longer retention time, but two vessels cost more than one! Similarly, the rate of reproduction of the micro- organisms may not be in phase with their desired activity, or a different medium may be required for growth.This would necessitate another fer- menter, this time before the main production one. The problems of contamination and of mutation in continuous culture are real, but have probably been exaggerated; the contaminant or mutant would have to have a rate of reproduction greater than the parent strain, or R.I.C. Reviews 136 Product YEAST Ti me Fig. I. Typical fermentation curve. it would be washed out. The problems with micro-organisms with mycelial growth are much greater than with bacteria and yeasts which reproduce by simple division or budding, though penicillin fermentations have been run continuously on a laboratory scale.3 Each fermentation has to be run in continuous culture long enough for the costs of continuous versus batch culture to be determined, and in most cases these favour batch culture.But beer, yeast from petroleum, baker’s yeast and vinegar have been made or are made on a large scale by continuous culture and undoubtedly the same will apply in the future to other substances. Some fermentations that might be particularly suitable to continuous culture, such as industrial alcohol production, have failed to compete with purely synthetic production. From brewing, it is natural to pass on to consider yeast production-not only the long established manufacture of baker’s yeast, but also the more recent and potentially more interesting production of food or fodder yeast from petroleum products, with all that this implies for helping to solve the problem of protein for the underfed millions.It is difficult to see any major Miall 137 developments in the production of baker’s yeast, other than the introduction, or more strictly re-introduction, of continuous culture. The Distillers Com- pany plant at Dovercourt used to operate a type of continuous culture procedure, using six fermenters in series,* but the plant only operated a 53-day week, reputedly because of weekend labour problems (a statement most firms in the fermentation industry find difficult to accept), and it was subsequently shut down and sold. It is easy for those outside the details of a process to be critical, but baker’s yeast production seems to be a process ideally suited for continuous culture and one day it should be so operated again.HjJdrocarbon fermentations The most exciting development in the last 10 years, the one with the greatest future potential, and the one that has revived interest in an industry that was to some extent becalmed after the great expansion in antibiotics production in the late 40s and ~ O S , has been the proof that many micro- organisms can grow and reproduce efficiently on hydrocarbons. Although papers on hydrocarbon fermentations had appeared spasmodically for many years,5 hydrocarbons were not seriously considered as substrates for micro- biological conversions until the work of Champagnat and colleagues of the Societk Franqaise des Pktroles, Bp.6~7 Essentially the BP workers developed two processes.One involves growth of specially selected strains of yeast on heavy gas oil. The yeast grows preferentially on normal unbranched straight- chain alkanes which have to be removed in refinery operations anyway, at the same time converting the carbon to its own biomass. This necessarily involves very large fermenters, since only about 7 per cent of the heavy alkanic crude oil substrate is unbranched and so metabolized by the yeast. But it has been stated that the upgrading of the gas oil alone makes the operation worth while. This process has been operated for over five years in a pilot plant making a dried product with 65-68 per cent protein (fish meal has 65 per cent) and rich in essential amino acids and vitamins.The other process involves the separation of the paraffins by a molecular- sieve technique and the growth of yeast on the Clo to C18 straight-chain fraction. Both processes are operated continuously in single fermenters and published information indicates that they can be run under non-aseptic conditions. That neither of these processes is economically much better than the other is shown by the fact that large plants are being erected to work both processes: at Lavera in France, a 16 700 tons a year plant to operate on gas oil, and at Grangemouth in Scotland, a 4000 tons a year plant to use normal alkanes. The former is expected to be in operation early in 1971, the latter, late in 1970. For once fermentation know-how is being passed to Japan.The Kyowa Hakko Co. has bought the rights of the process from BP and is to produce protein from normal alkanes at the rate of 1000-1500 tons a year. Since World War 11, the Japanese have put so much effort into fermentation technology that now one is almost surprised at new develop- ments coming from anywhere but Japan. Because of the difficulty of completely separating the yeast from petroleum residues and doubts about the long term toxicity of such residues, it has been 138 R.I. C. Reviews necessary to conduct very lengthy toxicological testing in rats and various other animals.8 The products of the plants being built are to be used as animal foodstuffs and only after considerably more experience with animals are they likely to be included in human foods.Yeasts will not grow on alkanes with fewer than six carbon atoms, but many bacteria will grow on lower alkanes, including methane. 9 The metabolic pathway by which methane is utilized by micro-organisms is an unusual one which has been worked out by Quayle and his colleagues.1° Briefly, methane is oxidized to formaldehyde which reacts with ribose-5-phosphate to form the ketohexose allulose-6-phosphate-this then isomerizes to fructose-6-phos- phate. Five out of every six molecules of fructose-6-phosphate rearrange through a rather complicated sequence to give six molecules of ribose-5- phosphate and the cycle is complete. The overall result is to get one molecule of fructose-6-phosphate from six molecules of methane. Shell Research Ltd is working actively in this field.11 They have done a lot of work on the conversion of gaseous hydrocarbons to bacterial cells, but little has been published.The Agricultural Division of Imperial Chemical Industries Ltd has been studying a process for making fodder from North Sea gas. It has been stated that, during 1970, the company will be in a position to decide on the manufacture of protein on a semi-technical scale either in the form of bacteria from natural gas or of yeast from higher molecular weight petroleum products. An expenditure of several million pounds is contemplated for a development effort running through the 1970s and maybe beyond. What is surprising, and potentially disturbing, is to find that while certain micro-organisms have been found to be well tolerated in animal foods, they cause digestive disturbances when fed at the same level to man.Only straight-chain aliphatic hydrocarbons can be used for making micro- bial protein. Aromatic hydrocarbons have more obvious specific uses as substrates for the preparation of compounds on their metabolic pathway. Thus cumk acid can be made microbiologically from p-cymenelz and salicylic acid from naphthalene. The latter process was developed some years ago and was said to be nearly competitive with production from sodium phenate. CH CH OH COOH CH3 cumic acid p-cymcne a - aCooH A recent paper13 describes how a three- to four-fold increase in salicylic acid yield was obtained using mutant strains of a Corynebacter.A strain of Pseudomonas aeruginosal4 has given a 94 per cent weight by weight conversion of naphthalene to salicyclic acid. This is obviously a process that might well 139 Miall be developed further if the economics are right. Many other transformations of aromatic hydrocarbons have been shown to occur.15 These conversions are on obvious pathways of the breakdown of the respec- tive hydrocarbons. What at one time would have been regarded as more surprising is the finding that a-ketoglutaric acid, a tricarboxylic cycle acid on the standard carbohydrate breakdown pathway, can be made in good yield from a mixture of normal alkanes by the yeast Candida lipolytica.16 Similarly, L-glutamic acid17 can be made from normal alkanes by strains of Corynebacter.In both these conversions the level of thiamine in the medium is critical. With the yeast it has been shown that there is an a-ketoglutarate decomposing system that is actuated by thiamine; presumably the same will apply to the Corynebacter. While complete proof of the pathway remains to be found, it is generally accepted that the alkane is broken down to acetic acid which enters the normal tricarboxylic acid cycle as acetyl coenzyme A. This effect of thiamine illustrates an important technique that the fermenta- tion technologist employs to get accumulation of an intermediate breakdown product-to inhibit the action of an enzyme by starving it of coenzyme. Biotin has a similar effect in the production of glutamic acid from carbohydrate sources, and in many other fermentations the levels of trace metals are highly important.Other methods of controlling enzymes are by direct poisoning and by the use of mutant strains of micro-organisms. Enzymes are often controlled by repressor mechanisms, and to influence such enzymes an alteration to the repressor mechanism may be necessary. The last decade has seen the gradual fading out of some of the traditional fermentation processes, at least in the more industrialized countries. Ethanol, except in relatively crude form for drinking purposes, is no longer made by fermentation in the UK or the US, though in countries like India, with no petroleum industry and with the virtual necessity to use indigenous raw materials, its microbiological manufacture survives.Much the same applies to the acetone-butanol fermentation, which from many aspects-political, technical, biological, chemical, engineering and economic-has the most interesting history of all.lB This still survives on a manufacturing scale in Japan, but in the UK and the US both acetone and butanol are now made only from petrochemical sources. ACIDS Lactic acid Lactic acid is now made both microbiologically and chemically and it remains to be seen whether the long established fermentation process can compete with a purely chemical process. The only lactic acid producer in this country, Messrs Bowman (now part of Croda International), uses a fermentation process involving the action of a LactobaciZlus on a starch hydrolysate.19 The process is run at about 50°C and does not involve aeration, so it has con- siderable advantages over many other microbiological processes, both in relative freedom from contamination and in simplicity of plant.Lactic acid, a liquid at room temperature, cannot be purified by conventional crystalliza- R. I.C. Reviews 140 tion processes. A number of purification procedures have been studied, but solvent extraction is favoured for large-scale operation. In the US, Monsanto Chemical Co. makes lactic acid by hydrolysis of lactonitrile, which is a by-product of the manufacture of acrylonitrile from acetylene, but not of the more favoured route from propylene. Lactonitrile can also be made from acetaldehyde and hydrogen cyanide and this process for making lactic acid is operated in Japan.At one time it looked as if the salvation of the fermentation process might lie in possible regulations requir- ing the use of the naturally occurring L(+)-lactic acid in foodstuffs. The microbiological process makes both isomers, but could be adapted without too much difficulty to make the L-isomer, whereas resolution of a racemate produced in the chemical process would be expensive. The introduction of such a regulation now seems unlikely. This anaerobic bacterial process which is relatively free from contamination might be thought to be particularly suitable for continuous operation and, indeed, the process has been run on a laboratory scale for as long as 64 days.If the process could be made to work satisfactorily on a large scale the mean fermenter residence time for converting a 9 per cent maize or barley meal hydrolysate would be reduced from the present five days of a batch process to two days. But no news has been divulged that this has been done. Acetic acid Vinegar is a fermentation product that is now made by a continuous process.20 Its production is a two-step process-first the production of a suitable alcohol solution and then its oxidation to acetic acid by strains of Acetobacter. In Britain, the vinegar made is malt vinegar, using a fairly conventional yeast fermentation of malted barley. Wine producing countries normally convert poor quality wines to vinegar; in general, any suitably available crude sugar solution can be used.In the past, the acetification step was carried out by pumping the alcoholic liquor through tubs packed with materials such as birch twigs or beechwood shavings, which acted as a support for the bacteria. It is now effected by a continuous submerged culture technique in which the feed is pumped into the vessel at a rate adjusted to balance the rate of aeration and to keep the Acetobacter population in a steady state. This step now goes at nearly theoretical efficiency, compared with about 65-70 per cent in the older process. Vinegar production in England exceeds 10 Mgallons a year of material containing about 5 per cent w/v of acetic acid. Acetic acid is manufactured commercially by the liquid phase oxidation of acetaldehyde or butane.In certain circumstances, and on a relatively small scale, a submerged fermentation process such as that described for vinegar can be operated on a dilute aqueous solution of ethanol with the required salts added. The acetic acid is recovered by extraction with ethyl acetate and separated by distillation. It is claimed that 905 kg of alcohol give 1000 kg of acetic acid, and that there are factories operating at twice this daily capacity in Turkey and in Spain. But there does not seem to be any future in the produc- tion of acetic acid by fermentation, except in these rather restricted circum- stances. MiaN 141 Citric acid The pure chemical made in the largest tonnage by a fermentation process is citric acid; total western European capacity is about 60000 tons a year.Much of it is still made by growing Aspergillus niger or related moulds on the surface of a molasses medium in shallow pans or trays. That this is still done by companies which make other products by more modern submerged culture processes shows that the surface culture process is not as obsolete as it sounds. Indeed, the Japanese use their ‘koji’ process, growing moulds on bran in surface culture, to make a number of products. Production of citric acid in submerged culture, first shown to be possible by Perquin21 in 1938, is gradually coming into greater use. John & E. Sturge Ltd is the latest company to announce the use of submerged culture, which it has been operating on a small scale for three years.It is probably also significant that the French company, Usines de Melle, and the Dutch com- pany, Noury van der Lande, have announced that they are integrating their activities and building a new plant. In the past, Usines de Melle has operated a submerged process, and Noury van der Lande, which is much the bigger producer, a surface culture process. Pfizer Inc., by far the largest manufac- turer of citric acid in the world, is building a new plant in Eire for its produc- tion. Most of the citric acid manufacturers keep their processes a close secret and relatively little has been published that throws light on the details of one of the most interesting and the most difficult of all the fermentation processes.Meyrath has published a short, but useful and critical review22 which in turn refers to other reviews and papers. He very rightly criticizes much of the earlier published work on the grounds that insufficient attention was paid to trace metal contamination. For example, what use is a comparison of sucrose and glucose as carbon sources, if their purities are not specified, when it was realized as far back as 1910 that the ‘addition of a trace of iron salt . . . resulted in re-utilization of the citric acid with accumulation of oxalic acid’ P 3 A more recent paper points out that the addition of only two parts per thousand million of manganese to beet molasses treated with ferrocyanide cuts the citric acid yield by 10 per ~ e n t .2 ~ The pathway from sugar to citric acid was largely worked out in the 1950s by Johnson and his co-workers at Wisconsin.25 The Embden-Meyerhof- l coo- CHg coo- J H z I HO-C-COO- co. j3-h I coo- CH3 l /to coo- \ (!OO\iH;3/ GO I S-COA H.I.C. Reviews 1 42 Parnas pathway is followed to give ~-glyceraldehyde-3-phosphate and dihydroxyacetone phosphate, which are interconvertible, and which, by a further series of reactions, give pyruvate. Pyruvate is either decarboxylated to acetate (in the form of acetyl coenzyme A) or adds on carbon dioxide to give oxalacetate; these two products react together to form citrate. The enzyme aconitase, responsible for the conversion of citrate to aconitate and isocitrate, is inhibited, largely by depriving it of the necessary metal coenzymes, so that the tricarboxylic cycle does not operate and citric acid accumulates.Most other acids on or related to the tricarboxylic cycle (Fig. 2) can be CoA I coo coo-. I HOC-COO-- I citrate coo- I co I CH2 I coo- oxalacetate malate co I -0oc epoxysuccinate -~ ~- Fig. 2. The tricarboxylic acid (Krebs') cycle. Miall coo- 5 coo - l 5H.3 itaconate /+-coo- CH. coo- CH? l I ' c-coo- cis-aconitate coo- H-C-COO- isocitrate coo- coo- l CH? coo- I I HC-COO- co I coo- oxalosuccinate glutamate 143 made by fermentation processes, but are mostly either not in demand or can be made more cheaply by chemical synthesis. Fumaric acid can be made in very high yield by strains of Rhizopus26 and, until quite recently, it was assumed that fumarate is made not by the full tricarboxylic cycle, but via the glyoxalate by-pass.The latter involves the splitting of isocitrate with isocitrate lyase to succinate and glyoxalate, and the condensation of gly- oxalate with acetyl coenzyme A to L-malate; fumarate could be formed from either succinate or malate. However, it has recently been shown that isocitrate lyase is strongly repressed under typical fermentation conditions, and alterna- tive evidence is presented for formation of fumarate from carbon dioxide and a three-carbon compound.27 On an industrial scale, fumaric acid is made from maleic anhydride by a purely chemical method.~-Malic acid is made by many micro-organisms, but the only demand is for the much cheaper racemic acid which can be made chemically. Itaconic acid is of interest because it is a compound of relatively simple structure, not optically active, which is made most efficiently by fermentation using Aspergillus terreus or Aspergillus itaconicus. Problems in its manufacture are very similar to those in the manufacture of citric acid.28 Itaconic acid and its derivatives have various special uses in the plastics and artificial fibres industries. Aspergilhs fumigatus and some other moulds make trans L- epoxysuccinic acid in good yield;29 and a-ketoglutarate can be made by many micro-organisms-its production from hydrocarbons has already been mentioned.Amino acids The route to glutamate involves the amination of a-ketoglutarate and therefore largely follows the tricarboxylic cycle pathway. Glutamic acid, used on a vast scale as a flavouring agent in the form of monosodium glutamate, is another of the major fermentation products. In Europe, there are now three plants in Italy with a total yearly capacity of about 11 000 tons and one in France, with a capacity of 5000 tons. Total world production and consumption of mono- sodium glutamate is believed to be over 100 000 tons a year-about two-thirds of this is produced and half consumed in Japan. It should be pointed out that figures quoted for total capacity are largely meaningless. The recovery process for monosodium glutamate can utilize fairly standard equipment and the fermentation process needs completely standard fermentation equip- ment, so many companies with fermentation plant could utilize as much or as little of their capacity as they like for the manufacture of a compound such as monosodium glutamate.Glutamic acid is made using Micrococcus glutamicus or other gram- positive, non-motile, non-spore forming bacteria. The processes using carbohydrate as the substrate fall into three types-those using glucose and a restricting level of biotin to control glutamic acid production, and those using molasses with the addition either of polyoxyethylene fatty acid or of penicillin to control glutamic acid production. These latter compounds are assumed to eliminate a permeability barrier in the cell membrane and so stop intracellular accumulation of glutamic acid ;30 thus they obviate the need for feedback control.Biotin is also assumed to act on the cell membrane. R.I.C. Reviews 144 One Japanese company, Sanraku-Ocean Co., has recently switched from molasses to acetic acid as its starting material. Acetic acid is an interesting starting material for microbiological processes. It is taken into the standard metabolic pathways via the glyoxalate and the tricarboxylic acid cycles as acetyl coenzyme A. In the IJK its price does not make it appear likely that it could compete with cheap carbohydrate sources such as molasses, but special circumstances such as isolation problems may affect a straight price compari- son, and relative costs may be very different in Japan.The manufacture of glutamic acid by fermentation of hydrocarbons has already been mentioned ; here the level of thiamine is one critical factor, and, again, the addition of penicillin enhances glutamate prod~ction.~~ 932 Monosodium glutamate can be made by a number of purely chemical processes. The most favoured is that used by the Ajinomoto Co. It starts with acrylonitrile which is subjected to an 0x0 reaction to give p-cyanopropion- aldehyde. This is treated with hydrocyanic acid and ammonia to give an aminonitrile, which is then hydrolysed to glutamic acid.33 1 I CH2:CH.CN -+ OHC.CH2.CH2.CN + NC.CH.CH2.CH2.CN -+ HOOC.CH.CHz.CH2.COOH N H2 N H2 Naturally, this gives the racemic acid, and patent~3~735 have been taken out for obtaining the required L-isomer by seeding with its crystals, a procedure that sounds most uncertain for large-scale operation to one who has not experienced it.An enzymic process for obtaining the required isomer sounds much more attractive. Enzymes from a strain of Pseudomonas can convert the L-glutamic acid present in a racemic mixture to L-Zpyrrolidone-5-carboxylic acid.36 CH2 CHz- CH2 CH2- I I CH .COOH CO CH.COOH HOOC NH:! / I ‘NH’ i At the same time, enzymes from certain Lactobacilli racemize the D-giutamic acid to the equilibrium mixture.37 Ultimately the DL-glUtamiC acid is all con- verted to L-pyrrolidone carboxylic acid, which can be converted readily back to L-glutamic acid. An alternative process involves the production of DL- pyrrolidone carboxylic acid chemically and its conversion, in 90 per cent yield, to L-glutamic acid by a strain of Pseudomonus alcaligenes.38 The synthetic process is apparently only competitive with the fermentation process when worked on a large scale and to full plant capacity. Recently there has been overcapacity and this has hit synthetic production more than production by fermentation.However, the pattern for the future production of many optically active compounds is likely to involve largely chemical syntheses with final microbiological involvement in obtaining the required isomer. Another example of such a microbiological step is the conversion of D-phenylalanine to the L-isomer with Pseudomonas Jluorescens, a conversion that is thought to go via phenylpyruvic a ~ i d .~ g Miall 145 The other amino acid that has been made on a large scale by fermentation processes is lysine-its biosynthetic pathway is shown below. COOH CHzNHz [CHZ]:~ CH. NHe I I I CH. NHz COOH CH.NH2 CHO COOPOzH COOH I I CHc CH2 - I CH. NHz CHI NHn CH. NH2 / I !OOH Aspartyl semialdehyde I --.) YHZ I COOH Aspartyl phosphate Diaminopimelic acid \ CHn I I COOH Aspartic acid - 1 [iHnl:, I COOH CH2OH - I CH. NH;, I I I COOH I I CH. NHs COOH Threonine Lysine CH:$ CHOH hionine Homoserine \Met Lysine was first produced by fermentation in a two-step process-the produc- tion of diaminopimelic acid by Escherichia coli, and its decarboxylation by Aerobacter aerogenes or another strain of Escherichia coli.Subsequently a homoserine auxotroph of Micrococcus glutamicus was developed which made lysine directly.*O (An auxotroph is a mutated strain of micro-organism which will not grow in the absence of a specific factor.) This is a typical example of feedback inhibition and has been explained by the theory that there are three distinct aspartyl semialdehyde dehydrogenases inhibited respectively by lysine, threonine and homoserine. This has been shown to be true for Escherichia coli, and if it also operates in Micrococcus glutamicus, if the production of homoserine and threonine is blocked, two out of three enzymes would operate without control and lysine made by these pathways would accumulate.A purely synthetic process to make lysine was developed by the Dutch State Mines Company, but their plant has recently been shut down. A com- bined chemical and microbiological process has been developed by workers at E. I. du Pont de Nemours & C O . ~ ~ This involves the manufacture of DL- diaminopimelic acid from 2-ethoxy-3,4-dihydropyran by a highly efficient four-step process which goes in 80-90 per cent yield. The racemic diamino- pimelic acid is selectively decarboxylated to L-lysine using an enzyme from Bacillus sphaericus (see next page). This looks like being the process for the future. If other amino acids are required on a large scale, microbiological or combined chemical and microbiological methods can no doubt be developed for their manufacture.Cereal proteins are generally deficient in lysine and, to a lesser extent, may also be deficient in threonine or tryptophan. Proteins R. I. C. Reviews 146 CHO CN I I --+ CHOH [CH2]:3 --.) [CHiJs CHO CHOH I 1 I CN I NH:! I I CH. COOH I + [CH& CH . COOH I N Hz 00. C2Hj NH-CO, NH I t CH-CO’ I [CHe]:i NH I CH-CO, I NH-CO’ made by microbiological processes tend to be deficient in sulphur-containing amino acids, but racemic methionine is as active, biologically, as the L- isomer and hence purely chemical methods of synthesis suffice. Processes for the preparation of both L-threonine and L-tryptophan by the action of various micro-organisms on the corresponding- bhydroxycarboxylic acid have been worked 0 ~ t 4 ~ and L-threonine can also be made by a direct fermen- tation using an Escherichia coli mutant.43 RIBONUCLEOTIDES From amino acids, we turn to nucleic acid derivatives.The chief reason for the current interest in producing ribonucleotides on a large scale is that guanosine-5-monophosphate (GMP), inosine-5-monophosphate (IMP) and xanthosine-5-monophosphate (XMP) have, in that order, a strong flavour- enhancing effect. This operates, particularly, as a monosodium glutamate sparing effect. Thus the addition of 5 per cent of a GMP/IMP mixture to monosodium glutamate reduces the total amount of glutamate to a fifth of that required to give the same flavour in the absence of nucleotide.Most of the work on purine nucleotide production has been done by Japanese workers but the subject has recently been reviewed by Demain.44 To date IMP has been made by direct extraction from fish and by the enzymic hydro- lysis of ribonucleic acid from yeast. Many micro-organisms break down ribonucleic acid, which may constitute up to a fifth of their dry weight, under a number of conditions of stress, such as heating, cooling and treating with detergents; but undoubtedly the processes for the future will involve direct synthesis of the nucleotides. The biosynthetic pathway to the nucleotides has been worked out and essentially involves step-by-step synthesis of the purine ring system with ribose present throughout.The first step is the synthesis of phosphoribosyl pyrophosphate from ribose-5-phosphate and adenosine triphosphate : the subsequent pathway is shown on the next page (several steps have been omitted). Miall 11 147 phosphoribosyi pyrophorphate H,N-CO H,N-(' ,N - CH + aminoimidazole ribotide \ t - N 11 + aminoirnidazole carboxamide ribotide (AICAR) From IMP paths lead to AMP and via XMP to GMP. Each nucleotide loses phosphate to give the corresponding nucleoside and loses ribose to give the purine. Production of nucleotides by micro-organisms involves the use of auxo- trophs with requirements for adenine, guanine or purines in general, so that feedback inhibition can be avoided. AICAR, which is said to have flavour en- hancing properties, can be made either by inhibiting the next step in the syn- thetic sequence, the transfer of a formyl group, by sulphonamides or by using an Escherichia coli mutant lacking the transformylase. More recently mutants have been obtained from Bacillus megaterium that accumulate AICAR in concentrations up to 11 gl-l.459*6 This can be converted to disodium 5- guanylate in five chemical steps.To date, the best process for nucleotide production uses an adenine requiring strain or auxotroph of Brevibacterium ammoniugenes which, in shaken flasks, gives up to 12.8 g 1-1 of lMP.47 / inorinic acid (IMP) 148 phorphoribosylamine OH OH glycinarnidc ribotide t\l -CH R.I.C. Reviews VITAMINS AND PROVITAMINS Nothing worthy of note has been published recently on the fairly long established procedures for makiw , riboflavine and vitamin Bl2 micro- biologically.The former was reviewed in 195948 and the latter in 1964.49 However, considerable work has been carried out on the preparation of /?-carotene using the mould Blakeslea t r i ~ p o r a . ~ ~ There are two particularly interesting aspects of this fermentation; one is the constitution of the medium; and the other the use of a mixture of two mating types of mould. Originally, it was found that addition of 0.1 per cent of /?-ionone was necessary for maximum yield. Later it was shown that this could be replaced by cheap citrus by-products (citrus oil, citrus pulp or citrus molasses) giving yields of carotene of the order of 1 g 1-l.Indications are that it is the presence of limonene that is responsible. Spent mycelium of Blakeslea trispora from a previous fermentation was found to be an even better source of carotenoid precursers. A number of other mould, yeast and bacterial cells have the same effect, as have solvent extracts of these. Other compounds, which have been shown to act as activators of /?-carotene production, include isonicotinyl hydrazine and various amides, imides and lactams. The process involving the use of citrus molasses was scaled up to a 10 1 operating volume, and in 1963 production costs for the crude dried solids made at a rate of 5000 tons per year were estimated to be $31.35 kg-1 of contained /?-carotene. It was soon realized that 10-15 times as much carotene was obtained by using mixed mating types of Blakeslea trispora, rather than unmated cultures.Mated cultures produce a number of compounds (the so-called ,&factor) which can stimulate carotene production in unmated cultures.51 The + strain is believed to produce the /?-factor and the - strain the extra /?-caro- tene. At one time it was believed that this hormonal action of soluble com- pounds would not give the same stimulation as mixed cultures, but this is not the case;52 stimulation with equivalent amounts of the hormones induces as much carotene production in the - strain as was obtained with mixed strains. The hormones have been shown to be trisporic acids.53 (-)Trisporic acid B, the most active component, has the formula: 0 CH3 H3C COOH CH, (-)Trisporic acid B What, if any, significance can be attached to the various terpenoid com- pounds that stimulate carotene production remains to be seen.The accepted biosynthetic pathway to the carotenoids involves the condensation of two molecules of geranylgeranyl pyrophosphate to give an open chain c40 compound, which then ring closes at each end, so none of these ring com- pounds are likely to be carotene precursors. The UK market for carotene is not large (in 1965 it was in the region of Miall 149 Limonene @Carotene E75 000, primarily for use in margarine), and much work would be needed to work out a process for vitamin A production that is competitive with synthetic production.Unfortunately, conversion of carotene to vitamin A is an inefficient process in many animal species;54 cows can suffer from vitamin A deficiency on a diet with plenty of carotene. Micro-organisms do not have any use for vitamin A either and hence they lack the enzyme required to make it from carotene. Enzymic conversion would have to be done with an enzyme from a mammalian source such as hog intestinal mucosa, an enzyme which has not as yet been extracted and shown to work in vitro. B-lonone TRANSFORMATIONS I CHOH + CO CH20H Transformations are usually understood to be relatively simple one or two step alterations in molecules, which are themselves fairly complicated, carried out by micro-organisms. Probably the simplest transformation that has been done on a commercial scale is the production of dihydroxyacetone from glycerol by Acetobacter suboxydans.CHzOH I I I CH~OH CHzOH The production of gluconic acid from glucose is another example. This can be effected by Aspergillus niger, Penicillium notatum, Acetobacter sub- oxydans, Pseudomonas strains and indeed any organism that makes glucose oxidase. Gluconic acid is made on a large scale for conversion to glucono-6- lactone, which is used as a raising agent and has various other uses in the food industry; and for making sodium gluconate, used as a sequesterant, and iron and calcium gluconates, used as sources of these elements in veteri- nary and human medicine. However, when thinking of microbiological transformations one naturally thinks of ster0ids.~5 Micro-organisms have been found that can hydroxylate either in the a- or p- configuration almost every position in the steroid molecule.The most important are hydroxylation in the lla position by R. I. C. Reviews 150 CH,OH CH,OH i Prednisolone Triamcinolone I co Rhizopus nigricans and in the 1 l p position by Curvularia Iunata, and intro- duction of a double bond in the 1 : 2 position by Corynebacterium simplex to give prednisolone and related compounds. Other steroid transformations of industrial importance involve hydroxyla- tion in the 16a position by Streptomyces roseochrornogenes (this is involved in the manufacture of triamcinolone), oxidation of a 3-hydroxyl group to a keto group, and splitting off the side chain from position 17. A fairly recent development is the demonstration that the spores of many moulds have the ability to effect such transformations.For example, the spores of Aspergillus ochraceus will effect 1 1 a-hydroxylations and those of Septomyxa afinis can be used for 1-dehydrogenations.56 The spores can be grown on bran or barley and stored at -20°C for a year or more without losing their activity. Reactions have been run on a 200 gallon scale under non-sterile conditions and in a simple medium, so that recovery of the highly expensive products is easier and more efficient. If spores could be physically fixed in, say, polyacrylic beads in the same way as enzymes are now being fixed, they could be packed in a column and so make the whole process very easy; but this remains to be demonstrated.Until now, microbiological transformations have been used in the manu- facture of the anti-inflammatory steroids, but not of those in much greater use as oral contraceptives. These have used oestrone as the starting product, and oestrone, made from diosgenin by a sequence of reactions ending with a pyrolysis step at over 5OO0C, is a highly expensive raw material. Oestr 3r.e 19-Hyd roxycholesterol-3-acetate Miall 151 /I-Sitosterol Sih and his co-workers have shown that 3-/I-acetoxy- 19-hydroxycholest-5- ene, which is conveniently prepared chemically from cholesterol acetate, can be converted to oestrone in good yield by a species of Nocardia.57 The same conversion can be done on 19-hydroxy-4-stigmasten-3-0ne,5~ which is easily obtained from p-sitosterol, a compound that occurs widely in plants. The Upjohn Co.has a stockpile of over 100 tons of P-sitosterol which has been separated as a waste product from soya bean sterols used in progesterone production. It is now appreciated that such microbiological transformations are not restricted to steroids. There are a number of simple conversions, particularly hydroxylations, that micro-organisms can do much more efficiently than chemists. Recent examples are the conversion of acetanilide to the 2-hydroxy derivative by the higher fungus Amanita muscaria and to the 4-hydroxy derivative by Streptomyces species,59 and the hydroxylations of N-(3-chloro- sclerotiorurn.The latter gives hycanthone, which is used as a schistosomacide. NH-CH2-CH2-N(C2H,J2 (C, H 4 2 N H-C H2-C H 2-N I CI I CI Q 4-methylpheny1)-N,N’-diethylenediamine6 O and of lucanthone61 by Aspergillus -9 CH,OH CH3 CH3 CH20H The conversion of phenylalanine to tyrosine comes under this heading,62 as does the conversion of tyrosine to ~-3,4-dihydroxyphenylalanine (L-dopa), which shows promise in the treatment of Parkinson’s disease.63 Both these conversions can be carried out by a number of micro-organisms. This last conversion is of interest in that the normal first step in the micro- biological decomposition of tyrosine is deamination, so the amino group must be chemically protected. This can be done by preparing an N-formyl or similar derivative.It is also necessary to add ascorbic acid to stop melanin 152 R.I.C. Reviews COOH COOH I I CHNH, CHNHl CHNH, I ~ I I OH Tyrosine 6APA I Phenylalanine ANTIBIOTICS H COOH HO 4 OH Dopa formation. This ability of micro-organisms to effect a specific step or steps in a sequence of reactions looks likely to be of very considerable use in the next decade, in the manufacture of pharmaceutically-active compounds. It was the discovery of penicillin and the proof of its remarkable antibacterial properties that triggered off the post-war expansion in the fermentation industry. After beer, it is possibly antibiotics that will immediately come to most chemists’ minds when thinking about fermentation products. But, in fact, compared to some of the fermentations already discussed, there is less intrinsic interest in the production of antibiotics-the interest lies more in their use and method of operation.Production is often improved more by hit and miss procedures such as alterations in medium and mutations without consideration of any specific auxotroph requirements. Metabolic pathways are seldom completely worked out. Antibiotics are a miscellaneous collection of molecules, mostly fairly complex, which are classed together only because they are made by micro-organisms and adversely effect other micro-organisms. The reason for their production is not even clear; it is unlikely that many of them are naturally produced at concentrations at which other micro-organisms are inhibited.Bu’Lock’s classification of secondary r n e t a b ~ l i t e s ~ ~ treats them essentially as storage products, made primarily to keep the micro-organisms’ enzyme systems in good working order. Recent work has been partly to find new antibiotics-there are still gaps in the armoury-and partly to improve existing ones by either chemical or biological modifications. The supreme examples are the semi-synthetic penicillins, all arising out of the discovery of the enzyme penicillin acylase, which is made by a variety of micro-organisms and which splits micro- biologically-produced penicillins to 6-aminopenicillanic acid (6APA). This is the essential step in the production of the newer penicillins, all of which are made chemically from 6APA.Of these, ampicillin, the first broad spec- trum penicillin, still has the greatest use. Benzyl penicillin R = C,H,CH,CONH- R = NHZ- R == D( - )C6HS. CH. CO. NH- Ampicillin I -COOH Miall 153 Closely related, structurally, to the penicillins are the cephalosporins. Again manufacture involves both microbiological and chemical steps. The mould Cephalosporium acremonium makes cephalosporin C. ( R = -NHCO(CH2)3CH 6-Methylpretetramid COOH NH; X = -CH20COCH3 )(=-cH,-N+ The metabolic pathway to the penicillins and cephalosporins has been elucidated by a number of workers.65 That to the tetracyclines has been partly worked out thanks to the very elegant work of McCormick and his col- leagues,66 and it is now known in detail how the substituted naphthacene, 6-methylpretetramid, is converted to tetracycline or to the 5-hydroxy or 7-chloro derivatives.Cephaloridine NH - x == - cH,oco--cH, 0 OH 0 and Cephalothin This is split chemically to 7-aminocephalosporanic acid (R = NH2, X = CH2QCOCH3) from which the cephalosporins used in medicine are made. These have the structures R=C)-CH,-c--NH-- OH OH OH OX 0 'coo- 0 R = Q- CH,-c-- *; C-NH, 6-Methylpretetramid is believed to be built up of acetate or malonate units, but evidence for the details of the synthetic route is lacking. As with the penicillins, new tetracyclines have been made by chemical modification of the molecule and not by new microbiological processes. Other than the penicillins, cephalosporins and tetracyclines there are about 154 H / ll II W:HNH2 OH ti 0 3 CH,, ,CH3 CH, OH OH N OH 0 Oxytetracycline R.1. C. Reviews 20 antibiotics in such regular use in Britain as to be included in the British Pharmacopeia or the British Pharmaceutical Codex. These fall into a number of groups : polypeptides or substituted polypeptides containing D-amino acids, mostly made by bacteria, such as bacitracin;67 the macrolides, com- pounds made by species of Streptomyces and characterized by having one or more unusual sugars such as desosamine in the molecule-an example is erythromycin ;6S the polyene antibiotics with a number of conjugated bonds in the molecule, such as n y ~ t a t i n ; ~ ~ and unusual glycosides, such as strepto- mycin.70 's' / NH, H,N-L-lieu-L-Cys-L-Leu-D-Glu-L-lleu-L-Lys-D-Orn-L-lleu-D-Phe-L-His-L-Asp-L-Asp HN I c=o ' 'cook4 155 OH OH H Streptomycin Useful antibiotics that do not fit happily under any of these headings are cycloserine,71 chlorarnphenic01,~2 novobiocin,73 griseofulvin74 and fusidic acid,75 which has a steroid structure.The majority of antibiotics are active against gram-positive bacteria. The Miall 11* Bacitracin A 0 CH, Erythromycin o+ CH, 1 N H 2 - C O O v CH’ OCH, Griseofulvin 61 tetracyclines, chloramphenicol and certain of the new penicillins, such as ampicillin, are broad spectrum antibiotics acting against both gram-positive and gram-negative bacteria. A few, mostly peptides, are used only against gram-negative bacteria.Certain antibiotics are in particular use in treating tuberculosis ; these include streptomycin, cycloserine and viomycin (a cyclic peptide whose formula has only recently been completely elucidated). Griseofulvin is specifically antifungal. One gap has been recently filled by carbenicillin, a new penicillin which is active against Pseudumunas infections, but there are still others. It can be predicted that the search for new and better antibiotics will continue, though the law of diminishing returns has already been in action for some years. The state has now been reached in which, once an antibiotic has been discovered, its point of attack can usually fairly soon be worked out and at least a partial explanation given for its action.This should lead ultimately to the position where a particular molecule can be designed to attack a particu- lar synthetic step in a particular micro-organism. It is probable that in the next few years the search may be concentrated on antiviral compounds, though it is very doubtful that compounds will be found which have the spectacular effects in the antibacterial field of penicillin or even the sul- phonamides. Antiviral activity has been claimed for a number of antibiotics, but this is usually because of their action on some step in protein synthesis, an action which normally makes them too toxic for medicinal use. Rifampicin, one of the rifam~cins,~~ has recently been shown to act against pox virus, vaccinia virus and trachoma virus, but it remains to be seen how effective it is clinically.Another potential use of antibiotics is as anti-tumour com- pounds; examples are actinomycin D,77 d a u n ~ m y c i n ~ ~ and streptonigrin.79 156 ?H “0 0 Novobiocin I H Cycloserine R. I . C. Reviews The recent ban on the use of antibiotics used in human medicine as animal growth promotants means that new growth promotants are urgently needed. All those used to date have antibacterial properties, so that once again it is natural to look for suitable compounds amongst those made by micro- organisms. Bacitracin, which is only used topically in human medicine, is already used as a growth promotant in a number of countries. Flavomycin, made by a species of Streptomyces and described as belonging to a new group of compounds, is the first antibiotic specifically prepared for this purpose.Yet another example of the miscellaneous uses of antibiotics is provided by nisin,@J which is used in cheese processing. This is a mixture of cyclic peptides with antibacterial activity produced by some strains of Strepto- coccus lactis, and contains the unusual amino acids lanthionine, /?-methyl- lanthionine and dehydroalanine. Thus there are many possibilities for the use of antibacterial substances made by micro-organisms other than in human medicine. ENZYMES It is widely predicted that the next 10 years or so will see a greatly increased industrial use of enzymes. A high-powered panel was recently considering the future of the British chemical industry by the ‘Delphi’ method and more than one of the panel believed that enzyme-based chemical processes would be among the major chemical innovations in the next 10-15 years.The Science Research Council is very actively supporting enzyme research through its Enzyme Chemistry and Technology Committee and has made a &200000 grant to University College London to support such work for five years, as well as grants to other institutions. It seems highly likely that all this interest will generate new uses for enzymes and that the enzymes concerned will largely be made by microbiological methods. Already fungal amylases, made by Aspergillus niger and species of Rhizopus, are widely used in breadmaking, in the production of soluble carbohydrate solutions from starch and in other applications.81 Various types of subtilisin, the alkaline protease of B. subtilis, are used in detergentsS82 Another proteo- lytic enzyme, keratinase, believed to be made by Streptomyces jradiae, is used in the leather industry and yet another type of protease has very similar properties to animal rennet and is made commercially by the moulds Endothia parasitica and Mucor pusillus. 83 Pectinase is made by various Aspergilli,g4 and glucose oxidase by many micro-organisms, in particular Penicillium notatum and Aspergillus niger. There are also many medicinal, analytical and other academic uses of microbial enzymes. Two of the more interesting recent developments are the use of L-asparaginase from Escherichia coIi,85 Erwinia carotovora86 and other micro-organisms in the treatment of certain forms of cancer; and the experiments involving the use of dextranase from Penicilliurn funiculosum for the prevention of dental caries.8 7 9 8 8 It is probable that a greatly increased production of enzymes will be required because of recent developments in the use of immobilized enzymes. Enzymes can be immobilized either chemically, by specifically binding them to insoluble supports such as various cellulose derivatives or silica, or physi- cally, by adsorption on to inert carriers or by entrapping them in Miail 157 polymers.89990 Such treatment means that enzymes can be packed in columns and used in the same way as one might use many inorganic catalysts, or that, if used in batch reactions, they can relatively easily be recovered and used again.Immobilization has the further advantage of greatly increasing the stability of the enzyme; it opens up many new possibilities for the use of enzymes on an industrial scale. As with antibiotics the development of processes for enzyme production is largely by hit and miss methods, such as screening for suitable micro- organisms, treatment of these to get better mutants, ad hoc variation of the medium. Some background knowledge is applied, but it does not ob- viously follow, for example, that to make high concentrations of protease it is necessary to have high concentrations of protein in the medium.CONCLUSION To review the whole subject of industrial fermentations would take a book. All that has been attempted here is to highlight some recent developments and to do a little crystal gazing. Many relevant topics have been omitted and some of these are now listed together with references. Amongst simple sub- stances the production of gluconic acid and kojic acid have not been men- tioned, nor has 2,3-butylene glycol.91 The microbiological step from sorbitol to sorbose is part of the standard process to make ascorbic acid: a possible alternative route to ascorbic acid incorporates two fermentation steps-the conversion of glucose to 5-ketogluconic acid with Acetobacter suboxydans, and of L-idonic acid to 2-keto-~-gulonic acid with Pseudomonas Jluorescens. Other steps are purely chemical.A process recently proposed for making xylitol (used as a sweetening agent) from glucose involves three fermentation steps-glucose to D-arabitol with Debaryomyces hansenii, D-arabitol to D-xylulose with Acetobacter suboxydans and D-xylulose to xylitol with Candida guillierrnondii.92 Other polyols, including glycerol, mannitol, arabitol and erythritol can all be made by fermentation processes;93 much work has been done on the production of microbial polysaccharide gums, as well as d e ~ t r a n . 9 ~ Production of the ergot alkaloids should be menti0ned.9~ So should that of the gibberellin plant hormones.96 Bacillus thuringiensis is cultured for its insecticidal use.97 A future possibility, though not a proba- bility, is the cultivation of nitrogen fixing micro-organisms for addition to the soil.About six years ago, J. J. H. Hastings said ‘. . . ever since 1 can remember the fermentation industry has been dying . . . it is the pharmacist who has halted the coffin of the fermentation industry’.98 But six years have altered the picture very considerably. The future of the fermentation industry now looks very healthy and it no longer relies on the pharmaceutical industry to keep it alive. There has recently been considerable expansion in the industry and one can predict with confidence a greater expansion in the next decade. The production of protein from hydrocarbons, wider uses of antibiotics, greatly increased uses of microbiologically-made enzymes and a far wider use of microbiological processes as steps in synthetic sequences, particularly for hydroxylating and for making optically active isomers; all these should keep fermentation technologists active and happy in the future. R.I.C.Reviews 158 REFERENCES 1 J. S. Hough and A. D. Rudin, J. Inst. Brew., 1958, 64,404, 2 J. S. Hough and R. W. Ricketts, J. Inst. Brew., 1960, 66, 302. 3 J. Pirt and D. S. Callow, J. appl. Bact., 1960, 23, 87. 4 A. J. C. Olsen, SCZ Monogr., 1961, 12,81. 5 A. C. Van der Linden and G. J. E. Thijsse, Adv. Enzymol., 1965, 27, 469. 6 A. Champagnat, Br. Pat. 914 567. 7 A. Champagnat, C. Vernet, B. Lain6 and J. FiIosa, Nature, Lond., 1963, 197, 13. 8 D. A. B. Llewelyn in Microbiology (ed.P. Hepple), 63. London: Institute of Petroleum, 1968, 9 R. Whittenbury, ProceJs Biochem., 1969, 4 (l), 51. 1968. 13 I. D. Hill and A. Gordon, Biotechnol. Bioengng, 1967, 9, 91. 10 M. B. Kemp and J. R. Quayle, Biochem. J., 1967,102,94. 11 D. W. Ribbons in Microbiology (ed. P. Hepple), 47. London: Institute of Petroleum, 12 K. Yamada, S. Horiguchi and J. Takahashi, Agric. biol. Chem., 1965, 29, 943. 14 T. Ishikura, H. Nishida, K. Tanno, N. Miyachi and A. Ozaki, Agric. biol. Chem., 1968, 32, 12. 15 R. L. Raymond, Process Biochem., 1969,4 (9), 71. 16 R. Tsugawa, T. Nakase, T. Kobayashi, K. Yamashita and S . Okumura, Agric. biol. Chem., 1969,33,929. 17 Y. Imada, J. Takahashi, K. Yamada, K. Uchida and K. Aida, Biotechnol. Bioengng, 1967, 9, 45.18 D. Ross, Prog. ind. Microbiol., 1961, 3, 71. 19 G. Machell, Ind. Chem., 1959, 35, 283. 20 J. White, Process Biochem., 1966, 1, 139. 21 L. H. C. Perquin, Bljdrage tot de kennis der oxydative dissimilafie van Aspergillus niger van Tieghem. Delft: Meinema, 1938. 22 J. Meyrath, Process Biochem., 1967, 2 (lo), 25. 23 C. Wehmer, Technical mycology (ed. F. Lafar), 350. London: Charles Griffin, 1910. 24 D. S. Clark, K. Ito and €4. Horitsu, Biotechnol. Bioengng, 1966, 8,465. 25 W. W. Cleland and M. J. Johnson, J. biol. Chem., 1954, 208,679. 26 R. A. Rhodes, A. A. Lagoda, T. J. Meisenheimer, M. L. Smith, R. F. Anderson and R. W. Jackson, Appl. Microbiol,, 1962, 10,9. 27 A. H. Romano, M. H. Bright and W. E. Scott, J. Bact., 1967, 93, 600.28 R. C. Nubel and E. J. Ratajak, Br. Pat. 950 570. 29 L. J. Wilkoff and W. R. Martin, J . biol. Chem., 1963, 238, 843. 30 M. Shibukawa, M. Kurima, S. Okabe and T. Ohsawa, Agric. biol. Chem., 1968,32,641. 31 J. Takahashi, K. Kobayashi, Y. Imada and K. Yamada, Appl. Microbiol., 1965, 13, 1. 32 I. Shiio and R. Uchio, J . gen. appl. Microbiol,, Tokyo, 1969, 15, 65. 33 C. W. Huffman and W. G. Skelly, Chem. Rev., 1963, 63,625. 34 Ajinomoto & Co. Inc., Br. Pat. 844 952. 35 Ajinomoto & Co. Inc., Br. Pat. 865 31 1. 36 Kyowa Hakko Co. Ltd, Br. Pat. 884 415. 37 Kyowa Hakko Co. Ltd, Br. Pat. 933 802. 38 Y. Kawai and T. Uemura, Agric. biol. Chem., 1966, 30,438. 39 I Chibata, T. Tosa and R. Sano, Appl. Microbiol., 1965, 13, 618. 41 B.S. Gorton, J. N. Coker, H. P. Browder and C. W. Defiebre, Znd. Engng Chem. Prod. 40 H. T. Huang, Prog. ind. Microbiol., 1964, 5, 70. 42 S. Takesue, T. Yokouchi and H. Wada, US Pat. 3 133 868. Res. Dev., 1963, 2, 308. 43 I. Shiio and S. Nakamori, Agric. biol. Chem., 1969, 33, 11 52. 44 A. L. Demain Prog. ind. Microbiol., 1968, 8, 35. 45 K. Kinoshita, T. Shiro, A. Yamazaki, 1. Kumashiro, T. Takenishi and T. Tsunoda, 46 I. Kumashiro, A. Yamazaki, T. Meguro, T. Takenishi and T. Tsunoda, Biotechnol. Biotechnol. Bioengng, 1967, 9, 329. Bioengng, 1968, 10, 303. 47 A. Furaya, S. Abe and S. Kinoshita, Appl. Microbiol., 1968, 16, 981. 48 T. W. Goodwin, Prog. ind. Microbiol., 1959, 1, 137. 49 L. Mervyn and E. L. Smith, Prog. ind. Microbiol., 1964, 5, 151.50 A. Ciegler, Adv. appl. Microbiol., 1967, 7 , 1. 53 L. Caglioti, G. CaineIli, B. Camerino, R. Mondelli, A. Prieto, A. Quilico. T. Salvatori 51 R. P. Sutter and M. E. Rafelson, J. Bact., 1968, 95, 426. 52 H. van den Ende, J. Bact., 1968,96, 1298. and A. Selva, Tetrahedron, 1966, Suppl. no. 7, 175. Mia11 I 59 54 W. M. Beeson, Fedn Proc. Fedn Am. SOCS exp. Biol., 1965, 24,924. 55 W, Charney and H. L. Herzog, A handbook of microbial transformations of steroids. New York, Academic, 1967. 56 C. VCzina, S. H. Sehgal and K. Singh, Adv. appl. Microbiol., 1968, 10, 221. 57 C. J, Sih, S. S. Lee, Y. Y . Tsong and F. N. Chang, J . Am. chem. SOC., 1965, 87, 2765. 58 C. J. Sih and K. C. Wang, J . Am. chem. SOC., 1965,87, 1387. 59 R. J. Theriault and T. H. Longfield, Appl. Microbiol., 1967, 15, 1431. 60 D. Rosi, T. R. Lewis, R. Lorenz, H. Freele, D. A. Berberian and S. Archer, J. med. Chem., 1967,10, 877. 61 D. Rosi, G. Peruzzotti, E. W. Dennis, D. A. Berberian, H. Freele, B. F. Tullar, and S. Archer, J. med. Chem., 1967, 10, 867. 62 P. Chandra and L. C . Vining, Can. J. Microbiol., 1968, 14, 573. 63 C. J. Sih, P. Foss, J. Rosazza and M. Lemberger, J. Am. chem. SOC., 1969, 91,6204. 64 J. D. Bu’Lock, Adv. Appl. Microbiol., 1961, 3,293. 65 E. P. Abraham, G. G. F. Newton and S. C . Warren in Biogenesis of antibiotic substances (ed. Z . Vanek and Z. Hostalek), 179. London: Academic, 1965. 66 J. R. D. McCormick in Biogenesis of antibiotic substances (ed. Z . Vanek and Z . Hosta- lek), 73. London: Academic, 1965. 67 R. J. Hickey, Prog. ind. Microbiol. 1964, 5, 93. 68 W. M. Stark and R. L. Smith, Prog. ind. Microbiol., 1961, 3, 211. 69 D. Perlman, Prog. ind. Microbiol., 1967, 6, 1. 70 D. J. D. Hockenhull, Prog. ind. Microbiol., 1960, 2, 131. 71 F. C. Neuhaus, in Antibiotics (ed. D. Gottlieb and P. D. Shawl vol. 1, 40. Berlin, Heidelberg and New York: Springer, 1967. 72 C. G. Smith and J. W. Hinman, Prog. ind. Microbiol., 1963, 4, 137. 73 H. Hoeksema and C. G. Smith, Prog. ind. Microbiol., 1961, 3, 91. 74 A. Rhodes, Prog. ind. Microbiol., 1963, 4, 165. 75 W. 0. Godtfredsen and S. Jahnsen, Process Biochem., 1969 4 C12), 11. 76 P. Sensi and J. E. Thiemann, Prog. ind. Microbiol., 1967, 6, 21. 77 E. Katz and H. Weissbach, Prog. ind. Microbiol., 1967, 6, 61. 78 A. Di Marco, Antibiotics, 1967, 1, 190. 79 K. V. Rao, K. Biemann and R. B. Woodward, J . Am. chem. SOC., 1963, 85, 2532. 80 N. J. Berridge, G. G. F. Newton and E. P. Abraham, Biochem. J., 1952, 52, 529. 81 G. T. Banks, F. Binns and R. L. Cutcliffe, Prog. ind. Microbiol., 1967, 6, 95. 82 M. H. J. Zuidweg, A. J. Vroemen and R. Beukers, Process. Biochem., 1969, 4 (8), 19. 83 J. L. Sardinas, Process. Biochem., 1969, 4 (7), 13. 84 L. Nyiri, Process Biochem., 1968, 3 (8), 27. 85 L. T. Mashburn and J. C . Wriston, Archs Biochem. Biophys., 1964, 105,450. 86 H. E. Wade, R. Elsworth, D. Herbert, J. Keppie and K. Sargeant Lancet, 1968, ii, 776. 87 H. M. Tsuchiya, A. Jeanes, H. M. Bricker and C. A. Wilham, J. Bact., 1952, 64, 513. 88 R. J. Fitzgerald, D. M. Spinell and T. H. Stoudt, Archs oral Biol., 1968, 13, 125. 89 1. H. Silman and E. Katchalski, A. Rev. Biochern., 1966, 35, 873. 90 G. Kay, Process. Biochem., 1968, 3 (8), 36. 91 S. K. Long and R. Patrick, Adv. appl. Microhiol.. 1963, 5, 135. 92 H. Onishi and T. Suzuki, Appl. Microbiol., 1969, 18, 1031. 93 J. F. T. Spencer, Prog. ind. Microhiol., 1968, 7, 1. 94 K. L. Smiley, Fd Technol., Lond., 1966, 20, 112. 95 M. Abe and S. Yamatodani, Prog. ind. Microbioi., 1964, 5, 203. 96 J. F. Grove, Q, Rev. chem. SOC., 1961, 15, 56. 97 J. R. Norris, J. appl. Bact., 1970, 33, 192. 98 J. J. H. Hastings, Chemy Znd., 1964, 147.5. R.I.C. Reviews 160

ISSN:0035-8940    

DOI:10.1039/RR9700300135

出版商:RSC    

年代:1970

数据来源: RSC

摘要:

fifth Grove Lecture Methods and philosophy of teaching . . .. .. .. .. THE TEACHING OF CHEMISTRY IN VICTORIAN AND EDWARDIAN TIMES D. Betteridge, B.Sc., Ph.D. . . . . . . .. Financial considerations . . . . .. .. * - Chemistry Department, University College, Singleton Park, Swansea Background Schools, 161 Higher education, 162 Parliamentary grants, 163 Running costs, 163 Salaries and staffing, 163 School, 164 University, 167 Roscoe Conclusions References BACKGROUND Schools * . * . * . 161 . . 163 .. . . . . * . The Great Exhibition of 1851 showed how effective British science was, and its profitability enabled the South Kensington scientific establishment to be founded. The Paris exhibition of 1867 showed that a scientific lead could only be maintained by continual research.The Devonshire Commission’s Report, published in several volumes 1881-4, showed how science could be organized with the patronage of the State. These three major scientific events were of the utmost influence on the men concerned with the development of science teaching in Victorian and Edwardian times. That developments took place is baldly indicated in the facts, noted below, which concentrate on the fundamental problems of Heads of Departments and Headmasters: numbers of students, quality of students, number of competitive establishments, and the monies available for staff and equip- ment. The numbers of children at school increased from about 1 in 15 of the popula- tion in 1820 to 1 in 6 in 1905, as fol1ows:l .. . . Betteridge .. * . . . 164 . . 175 176 .. .. .. .. . . . . .. . . 169 .. .. .. .. .. . . .. .. I820 I860 I866 I870 I905 650 000 803 708 I 048493 I 450000 6 064 000 161 Table I. Number of day scholars presented in various specific subjects 1875-9513 Year yo presented of Animal Total presented scholars on register physiology Chemistry FrenchlGerman Latin 26 - I095 2007 3850 65 88 I 365 360 250 678 3 336 5 178 7 256 12829 966 24725 20869 15842 17003 3.7 4. I I .4 I .6 2.4 1875 102541 1880 160333 64 376 1885 1890 78611 1895 128012 ~ From M. E. Sadler and J. W. Edwards, Special reports on educational subjects 1896-7, pp 47,64.London: HMSO, 1897. However, the Newcastle Commission noted in 1861 that 42 per cent attended for less than 150 days per year.2 The numbers of students being taught science increased towards the end of the century3 and, for example, the Aberdare Commission* noted in 1881 that approximately 30 per cent of the pupils in Swansea were taught Natural Science. Table 1 gives some idea of the relative importance of subjects and the proportion of students who were entered for national e~aminati0ns.l~ Higher education The working classes were given the opportunity of acquiring higher education at Mechanics Institutes: the first of these was started in 1823 by Birkbeck and they were energetically championed by Br~ugham.~ By 1851 there were over 700 institutes with 110 000 members (less than 1 per cent of the popula- tion).Good cheap books were made available by the efforts of the Society for the Diffusion of Useful Knowledge, but the level aimed at was too high and the movement faded away. The middle classes became active in securing a sound education for their children, which did not necessarily involve religious instruction or tests. Various colleges were founded which subsequently developed into univer- sities,6 e.g. University College London (1 828), King’s College, London (1 83 l), Durham (1 833), Owens, Manchester (1 85 1). The upper classes went to Oxford or Cambridge for a good preparation for the Church or professions. The atmosphere is captured by Peacock:7 ‘At Oxford, they walked about to see the curiosities of architecture, painted windows and undisturbed libraries. The Reverend Dr Folliat laid a wager with Mr Crotchet “that in all their perlustrations they would not find a man reading” and won it.’ But in 1851 graduate students were allowed to take a course in Natural Science and in the 1870s the Clarendon and Cavendish laboratories were founded.The University population increased as shown in Table 2. The apparent discrepancy, by modern standards, between the number of science students and the number of science degrees arises because most were part-time students and most had little or no previous science. For example, in 1900 the University of Wales was graduating an average of two honours graduate chemists per annum, whilst the constituent college at Aberystwyth had 20 students in the Intermediate class and six in the Finals class.8 1 62 R.I.C.Reviews ~ -~ Year Numbers reading science and technology Numbers obtaining science degrees Total num be rs I S 000 I8 000 3 000 3 000 300 300 900 1 279 3 500 10 000 Table 2. University population, 1890-1922 I890 I900 1910 1922 20 000 31 000 FINANCIAL CONSIDERATIONS Parliamentary gran ts6 The government grants to schools increased steadily from E20 000 in 1833 to E636 806 in 1865. Despite, or perhaps because of, an expenditure of E78 000 000 on the Crimean War the system of grants was altered to payment by results. As the Chancellor of the Exchequer pithily put it, ‘If it is not cheap, it shall be efficient.If it is not efficient, it shall be cheap’. Payments were made, as part of the Revised Code of 1862, on the basis of attendance and examination results. The teacher received a flat-rate fee for each pupil who passed. The organization was the responsibility of the Science and Arts Department of the Board of Trade, which ultimately developed into the DES. The universities received comparatively little from the Government, 80-90 per cent of their income was derived from fees and endowments. But the government grant increased from El5 000 in 1888 between 11 universities to &66 000 in 1906 between 17. Running costs Manchester’s Department of Chemistry, which was one of the largest and richest University Departments, had an income of E1667.10.7d.in 1905. Of this 5441.18.3d. was spent on teaching, E50 on chemicals for lecture demon- strations, and E389.11.ld. on apparatus and chemicals for research.9 By contrast, it was agreed that a school chemistry course could be profitably run at an annual fee of E2.2.0d.10 In 1868,11 Owens College offered to provide the student with a table, fuel, water, gas and the cheaper reagents but the student was expected to provide the more expensive reagents and his own apparatus. Expensive apparatus such as condensers and thermometers could be hired. In 1909 at Bangor, only El50 or El0 per department was provided for the purchase of books for the library . l2 Salaries and stafing The salary level for school teachers remained remarkably constant and low as Table 3l3 shows.At universities, in addition to basic salary, bonus payments were made on the basis of the number of students attending lectures. These persisted into the 20th century. Roscoe in 1871 added a bonus of E1213.6.6d. to his basic Betteridge 163 Table 3. Average salaries of certificated school teachers in England and Wales Masters Average salary of Principal Asst teacher Year teacher All Principal All teachers reacher 94 I09 121 121 I20 I22 yo in receipt o f salaries > f300 teachers - - - 90 90 98 Mistresses 1870 - 1875 - 1880 - 132 134 138 1885 1890 1895 Average salary of Principal Asst Year teacher teacher A// Principal All teachers teacher 57 65 73 74 76 81 1875 - 1870 - 1880 - 1885 79 1890 83 1895 88 School - - - 63 66 73 salary of E150.5 More typical perhaps was Hoffman, who in his early years at the Royal College of Science, forewent part of his salary, his fees and his house.At Leeds in 1903-4, a professor might supplement his basic salary of &500 with a bonus up to E1000. The lecturer’s salary scale was E200-400 and the assistant lecturer’s E100-200.9 The average wage for the manual worker was &89 in 1840 and El44 in 1891.14 The staff of a successful university department was typically one professor, one assistant lecturer and one technical assistant. METHODS AND PHILOSOPHY OF TEACHING During the early part of the 19th century, Bell and Lancaster independently introduced a cheap and popular system of education, which was based on the proposition that ‘Any boy who can read, can teach? A monitor, after being taught a lesson by the teacher, could teach a group of boys, who in turn could teach further boys.It was claimed that one master could teach a school of 1000 boys. The lessons were learnt by rote and books of the time have numbered paragraphs so that each pupil could learn his bit. Some of these books contain a fair proportion of science, e.g. Pratt’s.15 It is not surprising that this early attempt to bring cost effectiveness into teaching failed, and a more favourable staff-student ratio than 1 : 1000 was normal. Nevertheless, the quality and the cost of education caused such concern that the Government in 1858 set up a Royal Commission under the 164 - - - 2.1 I 2.95 3.2 I - - I .05 I .56 2.0 I I .97 yo in receipt of salaries > f200 teachers - - 0.5 I I .34 I .68 I .93 - - - 2.05 2.75 3.5 I R.I. C. Reviews C .- 165 Betteridge chairmanship of the Duke of Newcastle to enquire into the state of Popular Education. The report led to the Revised Code of 1862. The immediate effect of making payments on the basis of attendance at school and the number passing examinations was to increase the number of hours spent at school and to reduce the amount which the Government paid out on education. Naturally, it was not long before it was demonstrated that students could pass examinations without being educated and books were written with the express purpose of facilitating the process.(One examination question includes ‘describe the apparatus you have actuaZfy seen’.16) It was also found that the brighter students were left to fend for themselves whilst the teachers concentrated on those who represented a marginal return. Addi- tionally, it was held to be unfair to treat students of widely differing back- grounds in the same way. The Cross Commission of 1880 criticized the system and it was slowly withdrawn. There were some permanent effects of the system. First, a National Exami- nation system had been introduced. Secondly science, by inclusion amongst the examinable subjects, was shown to be an acceptable subject for schools.Thirdly, it is probable that despite the limitations of the system, many more students had come into contact with science than would have otherwise. Whether their contact with science did more harm than good may be debat- able. Fourthly, the system led to the training and licensing of teachers, since only approved teachers were eligible for payment, The numbers examined were, in 1861, 1300; 1870, 34 000; 1887, more than 100 000. The mechanical process of training students to pass examinations was strongly criticized by Armstrong, who proposed a heuristic approach, i.e. ‘the art of making children discover things for themselves’. The following extracts from one of his papers indicate the aims and philosophy of the method :17 ‘Heuristic methods of teaching are methods which involve our placing students as far as possible in the attitude of the discoverer-methods which involve their finding out, instead of being merely told about things.It should not be necessary to justify such a policy in education. Unfortu- nately, however, our conceptions are blunted by early training, or rather by want of training. Few realize that neither is discovery limited to those who explore Dark Continents or Polar Regions, nor to those who seek to unravel the wonders of Nature; that invention is not confined to those who take out patents for new devices; but that, on the contrary, discovery and invention are divine prerogatives, in some degree granted to all, meet for daily usage, and that it is consequently of importance that we be taught the rules of the game of discovery and learn to play it skilfully.The value of mere knowledge is immensely over-rated and its possession over-praised and over-rewarded ; action, although appreciated when its effects are noted, is treated as the outcome of innate faculties, and the extent to which it can be developed by teaching scarcely considered. ‘The essential feature in the chemistry scheme was that students were to be set work to solve problems experimentally. They were not merely to be told: “This is the case-satisfy yourself that it is by repeating the following R. I. C. Reviews 166 experiment”. Moreover, quantitative exercises were introduced at the outset and were insisted on as all-important.Lastly, the instruction was not confined to non-metallic elements, but metals in common use and organic substances consumed as foods were also to be studied; oxides of nitrogen and other objets de Zuxe, which in no way concern our daily life, being relegated to the repertory of the professional chemist. ‘Largely in consequence of the discussions that have taken place as to the presumed antagonism of religion and science, the public have been led to misconceive the position of the scientific worker, and to disregard the moral value of scientific training. It is very important, therefore, to emphasize the fact that experimental work, when properly conducted, affords means of developing character unquestionably superior to any provided by the other subjects in the school curriculum, mainly because it touches upon daily practice at every point as well as on account of its disciplinary value.’ Apparatus was to be simple but a good balance must be purchased, preferably at the expense of ‘a few of the worthless textbooks with which scholars are now so overburdened’, because ‘The balance, let me again insist, is to be regarded as an instrument of moral culture, to be treated with utmost care and reverence’.Considerable effort was expended on training teachers to use the method, which was clearly a forerunner of the Nuffield scheme. But it was found that good results were only obtained with good teachers and since training was carried out in the evening, only the keen were introduced to the method.Further, if the scheme were to be followed exactly only budding Lavoisier’s would really succeed. Consequently, it fell into disuse. University Before 1858 and to a decreasing extent afterwards, teaching was carried out largely through practicals. There would be one lecture a day and the rest of the time was spent in the laboratory. It was not common for students to know much science before they went to the university, probably at the age of 16, and they might enter the course at any time of the year as Sherlock Holmes did (see A study in scarlet). It was possible to adjust the level and amount of work to suit the demands and attainments of the student.The brighter students might carry out research under the direction of the professor. It seems likely that this method of teaching was responsible for the present staff : student ratio. The lectures were illuminated by demonstrations, which allowed students to become familiar with the facts of chemistry at reasonable expense. The practical classes were largely taken up with ana1ysis.l This approach was effectively terminated by the introduction of the external degree of the University of London in 1858 and by the increasing use of school examinations, noted above. Students of the new University College sat for the London degree, so that this, rather than the recommendation of the professor, became the measure of success. Since it was a national degree it Betteridge 167 led to the standardization of standards and courses, which is still a feature of the English and Welsh universities.One hundred years later, the balance between subjects and between lectures and practicals within a subject is still recognizably that decided upon in 1858. It was a hard-fought decision since some wanted the degree to be general practical classes as a consequence of the Nuffield scheme. A number of remarkably good books were published during the period in question. Several, due to their originality and style, read as freshly and excitingly today as they must have then (e.g. Roscoe’s, Mellor’s, A. Smith’s etc.). They concentrated, in the main, on presenting facts, showing how these facts could be proven or demonstrated and on the theoretical explanation so far as it was known.In many respects, partly because of the reluctance to change syllabuses, these books have been ‘re-authored’ and used to the present day. At a time of reaction against their successors, it must be observed that the originals contained the latest news from the research laboratory and in that sense were very modern. In another sense, they were old fashioned in that they included facts per se even if they did not understand their signifi- cance. Thus, many interesting facets of chemistry were introduced that nowa- days might be dropped on the grounds that they did not serve to illustrate the theories which are deemed to be important. Fig. 2. Moissan’s electric furnace from Mellor’s Modern inorganic chemistry, 1916.and others specialized, e.g. Tyndall wanted a degree in Heat. It will be interesting to see if there is a move to return to teaching through R.I.C. Reviews 168 ROSCOE Scientists are fortunate that their cause was argued during these crucial years by very able men. It is difficult to imagine now how difficult it was for them to be effective; although several became notable public figures, the perusal of standard and non-standard works of history, memoirs, biographical dictionaries and contemporary novels suggests that although f2ted by some they were, in the main, ignored by the politicians. One who, as teacher, politician and chemist, serves to illustrate, in the Victorian sense, the principles outlined above, is Henry Enfield Roscoe.lgJ* He was born into a respectable Liverpool family in 1833, and although the family suffered a number of misfortunes he was always clearly a gentleman.He was sent to school and taught chemistry by Balmain, who had original ideas. One was to give each boy in the class a glass containing ferrous sulphide and another containing dilute sulphuric acid. When Balmain gave the word, they added the acid to the sulphide and ran off. The result, as Roscoe notes was ‘such a foul stench that each boy will carry down the recollection of that moment to his grave and will remember to his dying day the formula which Balmain wrote on the blackboard FeS A HO f SO3 = FeOS03 -+ HS When he was 15 he went to University College and studied under Graham and then Williamson, becoming the latter’s private assistant.After five years, in 1853, he was awarded his BA with Honours in Chemistry. He then went to Bunsen at Heidelberg and in 1855, at the age of 22, received his doctorate cum laude. In 1857 he was appointed to the Chair of Chemistry at Owens College, Manchester, and was acknowledged to be largely responsible for transforming that institution from a very shaky one into one of the most influential and soundly based universities. He recalled that shortly after his arrival: ‘I was standing one evening preparing myself for my lecture by smoking a cigar at the back gate of the building when a tramp accosted me and asked me if this was the Manchester Night Asylum.I replied that it was not, but that if he would call again in six months, he might find lodging there!’ His programme for the day was to give his lecture at the beginning of the day and then to deal with his correspondence whilst the laboratory classes were getting underway. He would then visit the laboratories, treat each student individually and finally he would visit the private laboratories to see how his private assistants were progressing with their research. As numbers increased, demonstrators took over the supervision of laboratory work and Schorlemmer was appointed to the first Chair of Organic Chemistry to be held in this country. The nature of the course and philosophy of Roscoe is clearly indicated in the following extracts from his memoirs: ‘The personal and individual attention of the professor is the true secret of success, it is absolutely essential that he should know and take an interest 169 Bet reridge in the work of every man in his laboratory, whether at the beginning or at the finish of his course.The professor who merely condescends to walk through his laboratory once a day, but who does not give his time to showing each man in his turn how to manipulate, how to overcome some difficulty, or where he has made a mistake, but leaves all this to be done by the demonstrator, is unfit for his office, and will assuredly not build up a school. It is in the laboratory, and there alone, that cnemistry, like every other experimental science, can be properly learnt, and it is by peripatetic teaching of the professor and his demonstrators that the student benefits most.‘As regards elementary laboratory teaching my idea is that, to be of any use, it must inculcate method and accuracy both in theory and practice. The student must be put on the right track, and made to understand what he is doing, and why he does it. Moreover, he must gradually gain the power of exact observation and of logical inference. All these faculties are exercised and developed in a properly organized and thorough course of qualitative chemical analysis. The objections which have been urged by some against this system as “mere test-tubing” indicate to my mind a want of knowledge on the part of the critic of how to teach, and what can be taught; on the contrary, I venture to assert that no elementary course of practical scientific work is more useful, either in training the hand or the head, than a properly conducted course of qualitative analysis.This, however, presupposes that the exposition of the theory accompanies the practice of qualitative analysis, and that a course of demonstrations, in which the reactions and methods of separation are systematically ex- plained and discussed, is attended as well as the general course on theoretical chemistry. ‘Having in the first year’s course of qualitative analysis and preparative chemistry obtained a knowledge of the principles of the science and a certain amount of facility of manipulation and reliance on his own powers of experimentation and observation, the student on entering upon his second year’s course commences quantitative analytical work.In this he learns by degrees what scientific accuracy means, how exact results can be obtained by careful quantitative work, and thus gains in confidence and certainty. Here, too, constant personal supervision on the part of the professor and of his demonstrators is absolutely requisite, as everything depends on the care with which the various operations are carried on. The main object of this course is not only to give the pupil reliance on his own power of exact work but to make him aware of the sources of experimental error, and to enable him to estimate their amount. This can be accom- plished as well by accurate volumetric as by gravimetric work. All the analyses thus made by the pupil must be carefully entered up in a general log-book, as well as in his private note-book, so that at any time reference can be made to the extent and accuracy of his work.R.I.C. Reviews ‘On this firm foundation of a competent theoretical knowledge of inorganic chemistry, and of a thorough practical acquaintance with qualitative and quantitative inorganic analysis, including the preparation of chemical compounds in a pure state, and on this alone, can, I have 1 70 always been convinced, the proper and higher education of the chemist, whether for purely scientific or for technical purposes, be based, and upon this view I consistently acted. Thus I always set my face against the pupil “practising” the rough and ready methods used in works before he has learnt to appreciate the exacter processes, and it was my constant endeavour to supplant the often crude and incorrect trade tests by a more precise, though perhaps somewhat more lengthy system.Having, however, once obtained a satisfactory judgement as to the capability of the several methods, the student may be allowed to occupy himself, according to his taste or necessities, with the determination and valuation of pure and impure products according to the most approved commercial processes. ‘Having thus gained a practical acquaintance with quantitative methods, and having attended a course of experimental lectures on both elementary and advanced theoretical inorganic chemistry, the pupil is now in a position to begin the study of the carbon compounds or organic chemistry.‘Although, as I have already remarked, I am convinced of the essential importance of laboratory practice as bringing the student face to face with Nature, I would by no means depreciate the value of attendance on a thorough course of experimental lectures. In this way the principles and the important facts of the science are brought before the student in a consecu- tive and systematic manner, and illustrated by experiment, preparation, and diagram in a way impossible for the pupil himself to accomplish. The delivery of my lectures to both day and evening students was a constant pleasure to me; the devising of new experimental illustration is always a matter of interest, whilst the introduction of recent discoveries gives zest to both lecturer and audience. I likewise made it a practice to obtain courses on special subjects from some of our assistant lecturers or from our Berkeley Fellows.These proved of signal value to both teachers and taught, and were fully appreciated by the senior men. ‘Having secured thorough and advanced teaching in both the inorganic and organic branches of the science, it became necessary to see how far it was possible to introduce lectures and practical instruction in some special branches of applied chemistry. I have always held that the application can only be properly and thoroughly learnt in the factory or works, just as a Fig.3. Imaginary representations of the reaction 12 + Hz -+ 2HI according to the kinetic theory, from Meiior’s Modern inorganic chemistry, 1916. Betteridge 171 trade cannot be taught in a school unless, indeed, the school becomes a shop. This is, however, no reason why the scientific principles of the various industrial processes and even of their details should not be brought in orderly fashion before the pupil who is intended afterwards to conduct such processes. I am of the opinion that, provided a secure scientific basis is laid such lectures given by a teacher who has had practical as well as theoretical experience are of great value to the technical student, and this view I endeavoured to carry out. ‘One of the chief functions of a school of chemistry is to train teachers, and its highest aim is to guide students in the methods of original scientific investigation, and thus fit them for extending the boundaries of the science.That this had to be done, if the school is to be in any degree successful, I had learnt (amongst much of other invaluable experience) from my venerated teacher Professor Bunsen.’ Roscoe was also very active in spreading the gospel of science and chemistry. In 1862 when many were put out of work during the Lancashire cotton famine, a consequence of the American Civil War, Roscoe and Gaskell organized lectures for the unemployed poor. These were so successful that they were followed in 1866 by a series of Penny Science Lectures. These were mainly given in Hulme Town Hall but sometimes in the Free Trade Hall, which was always crammed. Tyndall, for example, gave a lecture to 3700 people.As a lecturer Roscoe was much in demand, and he gave many lectures throughout the country despite the attendant difficulties : ‘The difficulties which are met with in delivering experimental lectures at a distance from his own laboratory are only fully realized by the lec- turer himself. Probably these difficulties were never more acutely felt than by myself in giving lectures on spectrum analysis. For these lectures my friend and assistant, Joseph Heywood, and I had to carry about with us a whole paraphernalia of batteries, acids, electric lamps, Rhumkorff coils and a host of minor breakable articles, for this was before electricity could be had by pressing a button.It frequently happened there was no con- venient place where I could set up the battery of some forty or fifty Grove cells which was needed. If it was placed near the lecture-room, the smell from the fumes was something unbearable; if it was put up outside, it frequently rained and all sort of difficulties would arise. Sometimes the zincs in some of the cells were not properly amalgamated and they were corroded very rapidly, or, what was worse, sometimes the porous cells had been injured in transit and the nitric acid got at the zinc, and then there was a nice mess, and the battery had to be taken to pieces and cleaned. ‘The responsibility of making all the experiments succeed is no light matter, and no one but those who have gone through the experience can understand the excitement and worry which such lectures entail.The lecturer has to assume a confident air, and yet he cannot be certain that at the last moment he will be able to perform what he has promised. Where merely drawings have to be exhibited or slides shown the thing is entirely different. To carry out a lecture on spectrum analysis at that time without R. I. C. Reviews 172 Fig. 4. Roscoe en route t o Algeria to observe an eclipse-the ship was wrecked. Bet reridge 173 help of the dynamo required all one’s presence of mind and skill. Nothing detracts more from the effect of a lecture than when a certain result is anticipated and explained beforehand, as it is necessary to do, the thing does not come off.It does not mend matters when the lecturer says “Oh, well, this is not very important; we will go on to the next.” ‘I did not, as a rule, allow my public lecturing to interfere with my college work, and I have often, after packing up all my apparatus, a matter of no slight difficulty, travelled late at night in order to meet my class at nine o’clock the next morning. I remember on one occasion 1 had to give a lecture in Birmingham. I met my class at Owens College in the morning; I packed all my apparatus after the lecture, took the train to Birmingham, arrived there about three o’clock, worked for three or four hours in preparing the lecture, delivered it from eight to nine o’clock, packed up my traps, caught the night mail at twelve, got home at three am, and lectured to my class at nine in the morning. But with all this 1 enjoyed lecturing very much.‘The packages of apparatus which I had to take about were often of portentous size and strange appearance. On one occasion after a lecture at Hull, my assistant Heywood and I, encumbered by many packages, arrived at the station as our train was on the point of departure, to be greeted by an excited porter: “Now, you Punch and Judy men, take your seats at once” .’ l t is scarcely surprising that he was called upon to write books. What is surprising is the number that were sold; by 1906, 355 000 copies of his Primer and 211 000 of Lessons in elementary chemistry. He also wrote Advanced inorganic chemistry and the great Treatise on chemistry.In all he was assisted by a co-author. Thus he was responsible for defining the appropriate levels of approach to chemistry from the junior classroom to the research labora- tory. Like all good influential books they have been rehashed but not im- proved by lesser authors and have exerted their influence on the teaching of the subject for much longer than their strict due. As befitted the husband of a skilful photographer and the uncle of Beatrix Potter, they were well illustrated. He was antipathetic to exams: ‘. . . we, hidebound by examinations, are too apt to ignore the essential aim of university life-the advancement of learn- ing . . . It is in spite of, and not by the help of our plan of cram almost from birth to maturity that the innate creative power of the Anglo-Saxon blood comes out.How much more might the race yield if originality were encouraged instead of being repressed and often destroyed by examination grinding, and if freedom to teach and to study were in vogue with us as in Germany.’ R.1: C. Re views Roscoe was also a good politician and was called upon to serve on various official commissions and enquiries into the state of technical education. This enabled him to observe the level of chemistry teaching in schools. He was not always impressed. On one occasion he learnt that only the elder boys were taught chemistry and that from his Primer, he commented: ‘Here were boys from 16-18 years of age, who were being taught chemistry out of a book, which I wrote, so to speak, for little boys out of the street’.174 He notes however that by the turn of the century this picture was no longer a true one. His political abilities and family connections were also recognized by his election to parliament as the Liberal member for South Manchester in 1885. The University Council refused to allow him to retain a position within the University and so he had to sever his connections of almost 30 years. Manchester’s loss was London’s gain for after a short spell in the House he was defeated at the election of 1895 and the next year became Vice-Chancellor of the University of London for six years. He died in 1915. It is clear that the present-day problems of the cost of education, productivity of teachers, standards and the importance of introducing research outlooks into elementary teaching are not new.This article is only a brief survey of matters which could usefully be more familiar to those concerned with present developments. Fig. 5. Roscoe’s quantitative laboratories-an influential design. He also heard of the school where boys were taught chemistry by their latin master from Roscoe’s Elementary lessons. There was no practical work and the lesson was alleged to proceed thus: ‘Magister (loquitur): “Now boys have you all got your Roscoe?”: Boys: “Yes, Sir” : M : “Well, pages 42-54.” Then he proceeds to correct the latin exercises. Bell rings. M. “Well, have you read your Roscoe?” B.: “Yes, Sir”.M: “Then you can go”.’ CONCLUSIONS Betteridge 175 Productivity drives failed in the past basically because they led to a lower quality product, The heuristic approach fails because of the immense demands made upon a teacher by the experimental approach to teaching. The quality of teaching in Victorian and Edwardian times seems to have been remarkably high, especially when taken in relation to the resources available to the teacher. To maintain these standards, the staff: student ratio was about 1 : 10; and there were lecture demonstrations and 'peripatetic professors', who regularly consulted with students. We still have an examina- tion system and a basic teaching pattern derived from this period. Roscoe argued that the educational system was analogous with the system for the Defence of the Realm, that in a sense it was our Civil Defence and as such should be subject to continuous review so that any improvement could be introduced as soon as it had been tested.It is clear that any review ought to take account of the lessons of the past. REFERENCES 1 C. Birchenough, History of elementary education (2nd edn). London : University Tutorial Press, 1925. 2 Newcastle Commission 1861, quoted in ref. 6. 3 G. W. Roderick, The emergence of a scientific society in England, 1800-1965. London: Macmillan, 1967. 4 Report of the Committee appointed to enquire into the condition of intermediate and higher education in Wules, London: HMSO, 1881. 5 J. G. Crowther, Statesmen of science. London: Cresset, 1965. 6 S. J. Curtis, History of education in Great Britain (7th edn). London: University Tutorial Press, 1967. 7 T. L. Peacock, Crotchet castle, chapter 18. First published 183 1. 8 Calendar of the University of Wales, 1900-1. 9 Reports from University Colleges, 1905. London: Board of Education, HMSO, 1905. - I 10 C. G. Williams. A manualof chemicalanalysis for the use of schools (preface by E. Davies). London: Simpkin and Marshall, 1958. 11 Chem. News, 1868,18, 139. 12 ReDort of the Committee on the University of Wales and the Welsh University Colleges. Ldndon HMSO, 1909. 13 M. E. Sadler and J. W. Edwards in Special reports on educational subjects, 1896-7. London: HMSO, 1897. 14 A. C. Bouley, Wages in the United Kingdom in the nineteenth century. Cambridge: University Press, 1900. 15 J. Platts, The literary and scientific class book (2nd edn). London: Whittaker, Treacher, 16 Reproduced in W. Jago, Inorganic chemistry (10th edn). London : Longmans, Green, 1896. 17 H. E. Armstrong in Special reports on educational subjects, vol. 2 1898. London: HMSO, 1898. 18 D. Betteridge, Talanta, 1969, 16, 995. 1830. 19 H. E. Roscoe, The life and experiences of Sir Henry Enfield Roscoe, DCL, LLD. London: Macmillan, 1906. 20 E. Thorpe, The Right Honorable Sir Henry Enfield Roscoe. London: Longmans, Green, 1916. R. I.C. Reviews 176

ISSN:0035-8940    

DOI:10.1039/RR9700300161

出版商:RSC    

年代:1970

数据来源: RSC