Monitoring of platinum in the environment Since the introduction of catalytic converters for the control of vehicle emission a controversial discussion has begun on platinum emission and its eventual consequences for the environment. This brief overview covers the main aspects of anthropogenic emission of platinum and its bioavailability. Modern analytical methods for Pt determination in different environmental samples are also presented. Introduction Discussion concerning the exposure of the environment to toxic metals such as lead cadmium or mercury from several sources have been carried out for a long time. Platinum because of its inertness was considered harmless for a long time. It belongs to the group of elements that are the least abundant in the Earth's crust with a mean concentration1 of 5 mg kg21.Due to its speciÆc physical and chemical properties platinum Ænds application in various technological processes (chemical electrical petrochemical) and in jewellery. Between 1986 and 1995 the industrial demand for Pt increased by 66%. In 1994 42% of platinum production was used in catalytic converters 39% in the jewellery industry 4% in chemistry 4% in the glass industry 5% in electronics and 6% in the oil industry and others.2 So far more than 50% of the platinum produced has been used in environmentally relevant spheres. Platinum determined3 in snow samples from Greenland Antarctic and the Alps (in order to assess the past natural background) was in the concentration range 0.008±2.7 pg g21.The lowest value was measured in ancient ice from Greenland dating back 7000 years. Platinum has been included in the investigations into potential toxic substrates to human health since the widespread introduction of catalytic converters for automobile exhaust gases. These catalysts which contain platinum This Chemistry of Society Royal The journal This journal is is # The Royal Society of Chemistry 2000 2000 along with palladium and rhodium remove 90% of the carbon monoxide unburned hydrocarbons and nitrogen oxide present three major gaseous environmental pollutants. Catalytic converters used in cars or in industrial processes are the most important source of the environmental impact of platinum.While the beneÆts from their use are obvious recent studies have shown increasing Pt content in different environmental samples. Although emission in the form of airborne particulate material or dust from the abrasion and deterioration of the catalyst is considerable lower than for example Pb emission from leaded fuels it is nevertheless relevant with respect to the low natural background. Platinum concentrations in road sediments collected in Sweden4 increased from 3.0 ng g21 in 1984 to 8.9 ng g21 in 1991. Measurements along roads in the USA5 and Germany6 also showed elevated platinum concentrations in dust samples. In contrast to the large body of information concerning the toxicity of mercury or lead and their environmental effects the corresponding information on platinum has not yet been fully obtained.Recently hospital efØuents have been considered as a source for Pt emission into waste water and sewage sludge.7,8 These efØuents contain platinum from excreted antineoplastic drugs which have been widely used in cancer chemotherapy for some years. Other possible Pt sources in the environment such as metallurgical plants fertilisers or pesticides are also being determined.9 Pt emission from trafÆc A converter designed for an average family car contains about 1.8 g of platinum group metals.10 The amount of platinum emitted from catalytic converters has up to now been the subject of controversial discussion. In engine test stand experiments11 it was Viewpoint found that under conditions simulating city trafÆc Pt emission is in the range 2± 78 ng km21.The particles emitted (metal in a highly dispersed form together with aluminium oxide) were mainly greater than 10 mm. The highest platinum concentrations were measured in this fraction. However recent calculations,9 under more realistic street conditions showed that platinum emission attributed to the trafÆc reaches 0.8 mg km21. The most likely reason for the difference between this and the test stand experiments is the relation between the emission rate and the speed of an individual car. Moreover laboratory experiments are normally performed under excellent technical conditions with respect to the engine employed.Taking into consideration the results from the test stand experiments and also the amount of platinum determined in the soil and grass samples a Pt emission rate of 0.5±0.8 mg Pt km21 should serve as a realistic basis for Øux calculations.9 The Pt species emitted from the catalytic converters are attached to particles of alumina mainly in the form of nanocrystal platinum. However Xray photoelectron spectroscopy studies12 showed small amounts of ionic forms on the surface resembling that of a pure metal exposed to a stream of oxygen. Such oxidic species of platinum could easily be mobilised by complexation.13,14 Experiments using platinum chloride complexes have already demonstrated the availability of water-soluble Pt compounds to plants.15 Several percent of the total platinum content in airborne dust was determined as being species that are soluble in 0.07 mol dm23 HCl.16 Wei and Morrison4 concluded from sequential extraction of road sediments that transformation of Pt from inorganic to organic bound species occurs especially on organic-rich materials.SigniÆcant concentrations of trafÆcemitted platinum have been detected in a variety of environmental samples (Table 1). Several studies have shown a 99N 99N J. Environ. Monit. 2000 J. Environ. Monit. 2000 2 Viewpoint Table 1 Platinum content in different environmental samples Place of sampling (data) Sample Dortmund Germany (1992) Munich Germany (1993±1994) Munich Germany (1994) Frankfurt Germany (1995) Gent Belgium (1995) Hanau Germany (1995) Richmond UK (1996) Ken UK (1996) Siegen Germany (1996) Karlsruhe Germany (1997) Airborne dust Airborne dust in local buses Tunnel dust Road dust Grass near motorway Soil near motorway Road dust Soil from botanic garden Grass near motorway Road dust apg mg21 of air.decrease of platinum concentration with greater distances from the motorway.4,23 Almost all the platinum was deposited within a distance of 2±5 m from the road and at w20 m no platinum pollution could be detected. Only the uppermost soil layer down to 20 cm contained traceable concentrations. Helmers and Klu»mmerer calculated24 that 2100 kg of platinum will be emitted in Germany by cars with Pt/Rh catalytic converters up to the year 2018.In these calculations it was taken into consideration that since the early 1990's new cars have been equipped with advanced types of converters mainly based on palladium. Platinum deposited on the roads can be washed out during rain and transported to urban rivers by means of stormwater outfalls. This metal has been found to be toxic to aquatic life.25,26 In Bavarian rivers Pt concentrations of between 0.05 and 8.5 ng dm23 were measured and this metal is generally enriched in sediments and aquatic plants.20 Platinum concentrations in the range 0.04±12.4 mg g±1 were determined27 in the freshwater isopod Asellus aquaticus which lives on sediments. The uptake mechanism depends on the form of platinum present in the environment; Pt(II) was accumulated at a lower rate than Pt(IV).Pt emission from industrial processes Very little is known about the industrial impact of platinum on the environment. The metallurgical industries especially copper±nickel processing plants seem to be the most important contributor to its emission. Moreover the loss of Pt from the catalyst gauze used in the chemical industry should be considered. For example the loss of platinum from Pt/ Rh alloy gauze used for oxidation of 100N 100N J. Environ. J. Environ. Monit. Monit. 2000 2000 2 Concentration range/ng g21 0.6±130 3.0±33a 170 51 1.4±1.7 23±112 0.42±29.8 0.8±1.6 17.0±95.6 112±169 ammonia in the manufacture of nitric acid is 0.061 g of Pt per tonne of HNO3 produced.28 In sediment samples collected from Kelly Lake in Canada (situated about 4 km from the high stack of a nickel smelter) abnormally high Pt concentrations (1000±2800 mg g21) were detected.29 These concentrations were elevated by a factor of 100±1000 when compared to the geogenic background values.The dust taken directly from the stack's interior (as the presumed source) contained 11 000 mg g21 of platinum. High concentrations of platinum (max. 466 mg g21) have also been detected in the upper layer of soil in the vicinity of major metallurgical plants in the Monchegorsk area on the Kola Peninsula Russia.30 Even at a distance of 2.5 km from the plants a mean value of 50 mg g21 was found.The study of anthropogenic platinum emission (also Pd Rh and Au) into snow during one winter season (1995/96) was reported by Gregurek et al.31 The samples were collected from the surroundings of the industrial plants Zapoljarnyj Nikel and Monchegorsk on the Kola Peninsula. Values of up to 650 ng dm23 were found and the concentrations increased with the proximity to the industrial sources. The prevailing wind direction plays an important role in the metal distribution. Platinum group element contents in particulate matter deposited in snow reØect their distribution in primary ores. This fact can be used as a simple method for Ængerprinting and tracing of different industrial sources.Generally elevated platinum values due to automotive catalysts are restricted to a narrow range along roadside soil whereas those due to emission from processing plants display a large-area dispersion and are preferentially transported by the wind.21 Both sources Reference 16 17 18 19 20 21 22 22 20 6 have different interelement ratios especially the Pt :Rh ratio. The emission of platinum during the production processes either into the atmosphere or into waste water was calculated as being up to 98 kg year21 for Germany alone.24 Pollution from medical application Platinum complexes based on cisdichlorodiamineplatinum( II) (cisplatin) have been widely used in the therapy of some cancer forms.A new generation of Ptbased drugs carboplatin and lobaplatin show increased activity together with reduced toxicity.32 However only a small part of these anti-cancer drugs are absorbed by the body. After administration only 10±20% of the carboplatin becomes bound to protein 50±75% is excreted in the urine in the Ærst 24 h and for cisplatin 31±85% of the dose is excreted during the Ærst 51 days.7 A study by Schierl et al.33 showed that the platinum concentration in the urine can be higher than a factor of 40 as compared with the normal level 8 years after a patient's last cisplatin therapy. As neither hospital sewage nor urine and excretions from patients treated with Ptbased drugs are specially treated platinum is emitted in hospital sewage.Usually the efØuents from hospitals are simply treated together with household sewage in municipal sewage treatment plants. From the efØuent of Freiburg University Hospital one of the largest hospitals in Germany a platinum concentration of 1±2 ng dm23 in the communal sewage is the result.3 The Pt levels detected in the sewage of various hospitals and hospital departments in Germany were approximately 110± 176 ng dm23 during the day and 38 ng dm23 at night. A total Pt emission for all German hospitals of Fig. 1 Platinum and palladium content in sewage sludge ashes from the municipal puriÆcation plant of Stuttgart. 28.6 kg year21 was calculated on the basis of the annual amounts of Pt drugs used in the treatment of patients.7 Comparable values were observed on a European scale.8 Compared with platinum emissions from other sources the efØuents of hospitals are not the most signiÆcant ones but they should not be disregarded.In archived samples of sewage sludge ashed from the puriÆcation plant of Stuttgart a signiÆcant increase of Pt has been observed (Fig. 1).18 This is consistent with the data of Scha» fer et al.6 who observed that from 1993 to 1997 the platinum concentration in sewage sludge incineration ashes from the municipal sewage plant at Karlsruhe doubled from 64 to 138 mg kg21. The Pt :Rh ratio of about 20 in the sludge differed markedly from the ratio of 6 typically found in environmental samples that are mainly inØuenced by trafÆc emission.This indicates that urban sludges not only receive and concentrate emissions from trafÆc but also from hospital and medical efØuents or industrial sources.6,34 For example extraordinarily high concentrations of Pt (1.1 mg kg21) were found in the sludges of the city of Pforzheim; these levels were caused by the concentration of jewellery producers in the city.18 Bioavailability of Pt species With regard to the increase of platinum emissions and allergic and cytotoxic potential of its compounds,35,36 several research groups mainly located in Europe are dealing with the mobility and bioavailability of this metal in the environment. The highest mobility of platinum in soil is observed at a pH of close to 1; in neutral solutions (pH 6±7) mobility is much lower while the presence of NaCl increases the mobility.19 Animal tests with rats (using as a model substance Pt(0) with a solubility of 10% in NaCl solution) were carried out to prove platinum bioavailability.37 After intratracheal instillations the highest concentrations of Pt were found in the lungs and the lung macrophages.Smaller amounts were detected in the blood kidneys spleen stomach and liver showing the bioavailability of platinum particles. After oral administration 97% of the platinum dose was excreted via the faeces and 0.09% via the urinary tract (where 100% is denoted as the total Pt content excreted in the faeces and urine over 8 days) during the Ærst 2 days.Platinum can enter the food chain either through deposition of Ptcontaining particles or by uptake from water and from waste water sludges used as fertilisers for plants. Some work has been undertaken on plants exposed to dissolved platinum salts.15,38±41 The uptake into different parts of the plants decreases in the order rootwstemwleaf. The evaluation of Pt content in different plants grown on contaminated soils (collected from areas adjacent to a German highway) shows a measurable transfer of metal from soil to plants. The transfer coefÆcients (deÆned as the concentration ratio between the levels in the plant and the soil) for Pt were similar to copper.42 It is noteworthy that analysis of common grass collected in the vicinity of a motorway near Stuttgart (Germany)43 also showed increasing amounts of Al Ce La Nd and Zr in parallel with platinum between 1992 and 1994.Two cultivation experiments were carried out in order to check to what extent platinum can enter the food chain by accumulation in plants.38 The grass Viewpoint grown on a sandy loam soil spiked with a water-soluble Pt compound [Pt(NH3)4](NO3)2 hardly accumulated the metal (accumulation factors were in the range 0.004±0.016). Cucumber plants which were grown hydroponically in nutrient solutions containing the same Pt compound strongly enriched platinum; accumulation factors were 11±42 in the green plant fraction and 1700±2100 in the roots. This indicates the important role of soil in the immobilisation of Pt compounds.From the grass cultures not treated with tetraammineplatinum(II) nitrate only one Pt species (molecular weight 160±200 kDa) was isolated while in the treated grass samples (uptake exclusively by the roots) up to seven different species were detected (molecular weight 19±1000 kDa).40 The platinum binding ligands in this fraction were characterised as Æxed to phytochelatins or to polygalacturonic acid behaving as an ion exchanger.40,43,44 However 90% of the absorbed platinum was bound to the low molecular species such as methionine or peptide glutathione. Wine samples served as an example for following the path growth continuing with the fermentation process of grape juice and resulting in the Ænal product.Fermentation experiments with grape must with a ``natural'' Pt content of 0.4 ng dm23 proved that added and co-fermented platinum was 70±90% adsorbed and thereby was almost completely enriched in the yeast.39 Only a small amount of the Pt passed into the wine. Vineyard locations near roads with high trafÆc showed noticeably higher mean values for platinum content (Table 2). Although platinum is emitted mainly in the form of Pt metal or metal oxide particulates there is evidence that at least part of this is soluble and can undergo transformations in the environment. Platinum allergy is conÆrmed as being due to a group of charged compounds that contain reactive ligand systems; the most effective of which are chloride ligands and the allergic response increases with an increasing number of chlorine atoms.45 The exposure±effect relationship for a platinum salt allergy in workers in catalyst production plants was conÆrmed.46 The platinum levels in the urine and blood of these employees could be up to 100 times higher than non-exposed control individuals.47 Chronic exposure to soluble platinum 101N 101N J.Environ. J. Environ. Monit. Monit. 2000 2000 2 Viewpoint Table 2 Content of platinum in different parts of grapes and soil (year of vegetation 1991)39 Content of Pt/ng g21 Near high trafÆc roads Sample 0.84 0.33 0.13 0.009 0.0004 Soil Leaf Stalk Berry Wine compounds may lead to toxic effects which are collectively known as a syndrome called platinosis.Increased platinum blood levels (3.8±4.0 ng ml21) were also found48 in medical staff occupied in the administration of Ptbased drugs in comparison with unexposed subjects (0.69±1.2 ng ml21). Analytical methods Analytical methods for the determination of platinum in environmental samples have been signiÆcantly improved during recent years.10,49,50 Adsorptive cathodic stripping voltammetry graphite furnace atomic absorption spectrometry (GFAAS) and inductively coupled plasma-mass spectrometry (ICP-MS) are the most sensitive methods of detection. Voltammetric methods use the adsorption of the platinum formazone complex formed in situ on a hanging mercury drop electrode.This complex catalyses the production of hydrogen and the reduction current associated with this reaction is related to the platinum concentration. However this method is negatively affected by even very low residual levels of organic matrix in the solution. The accuracy of GFAAS for low platinum levels strongly depends on the background absorption correction.49 For environmental samples it also requires a preconcentration step.49±51 Platinum in dust samples was enriched by electrodeposition into a graphite tube packed with reticulated vitreous carbon and determined by atomic absorption directly from the packed tube used for preconcentration.52 Some efforts have been made using solid sampling techniques after preconcentration on an ion exchange resin.49 ICP-MS offers the best sensitivity and convenience for simultaneous determination of other platinum group metals.A variety of sample introduction modes into the ICP such as ultrasonic or 102N 102N J. Environ. J. Environ. Monit. Monit. 2000 2000 2 TrafÆc free Æeld-paths 0.30 0.10 0.05 0.002 0.0001 thermospray nebulisation electrothermal vaporisation slurry techniques or direct injection have been used.53±56 Flow injection and isotope dilution are included in some procedures. Problems with ICP-MS occurred due to strong interferences by spectral overlap of HfOz ions with isotopes of Pt.53 The values obtained by several laboratories for platinum concentrations in environmental samples as measured by GFAAS and ICP-MS were tested with respect to the rules of quality assurance and quality control including sampling and sample decomposition.Considerable differences have been observed among the results.57 The reactivity bioavailability and toxicity of platinum are not necessary correlated with the total content but also depend on its chemical form oxidation state the chemical bonds in which it is involved and possible associations with other components of a given matrix. The different platinum species have to be separated before analysis this can be performed by chromatographic40,43,44 or electrophoretic58,59 techniques. Methods such as HPLC-ICP-MS and CE-ICPMS are able to generate information concerning the transformation behaviour of platinum in soils and plants.Conclusions The importance of platinum has increased enormously as a result of technological developments in catalytic converters for automobiles and chemical industries. For a long time Pt compounds have been considered harmless and they have had little impact on the environment. In the last twenty years however increasing platinum concentrations in soil dust contaminated grass and sewage sludge have been detected. The main pathways by which platinum can enter the food chain have to be taken into account aerosol deposition caused by Pt emission from motor vehicles and industrial sources transport by hospital efØuents via contaminated waste water and direct entry into soils via artiÆcial fertilisers.The primary sources from which platinum can be incorporated into the human body are therefore plants or agricultural products. However many problems are not solved yet and many questions are currently under discussion; the most important among them is the bioavailability and toxicity of platinum species. According to its chemical relationship with nickel and palladium Pt possesses a relatively high allergic potential. Therefore long-term monitoring studies are necessary to control the impact of platinum emission into the environment. Similarly more information concerning the exposure of the human population to Pt in water air and foodstuffs and the health effects of such exposure is needed.The author thanks Prof. A. Hulanicki for comments on the manuscript. Preparation of this paper was supported by grant No. 3TO9A 083 17 from the Polish State Committee for Research. References 1 R. Hartley Chemistry of the platinum group metals Elsevier Amsterdam 1991. 2 H. Renner in Metals and their compounds in the environment ed. E. Merian VCH Weinheim 1991. 3 C. Barbante G. Cozzi G. Capodaglio K. Van de Veide C. Ferrari A. Veysseyra C. F. Boutron G. Scarponi and P. Cescon Anal. Chem. 1999 71 4125. 4 C.Wei and G. M. Morrison Anal. Chim. Acta 1994 284 587. 5 V. Hodge and M. O. Stallard Environ. Sci. Technol. 1986 20 1058. 6 J. Scha» fer J. D. Eckhardt Z. A. Berner and D. Stu» ben Environ.Sci. Technol. 1999 33 3166. 7 K.Ku»mmerer and E. Helmers Sci. Total Environ. 1997 193 179. 8 K.Ku»mmerer E. Helmers P. Hubner G. Mascart M. Milandri F. Reinthaler and M. Zwakenberg Sci. Total Environ. 1999 225 155. 9 E. Helmers Environ. Sci. Pollut. Res. 1997 4 100. 10 R. R. Barefoot Environ. Sci. Technol. 1997 31 309. 11 H. P. Ko» ning R. F. Hertel W. Koch and G. Rosner Atmos. Environ. Part A 1992 26A 741. 12 R. Schlo» gl G. Indlekofer and P. Oelhafen Angew. Chem. 1987 99 312. 13 D. Nachtigall H. Koch S. Artell, K. Lewsen G. Wu» nsch T. Ru» hle and R. Schlo» gl Fresenius' J. Anal. Chem. 1996 354 742. 14 S. Artelt H. Koch D. Nachtigall and U. Heinrich Toxicol. Lett. 1998 96±97 163. 15 H. J. Ballach and R.Witting Environ. Sci. Pollut. Res. 1996 3 1. 16 F. Alt A. Bambauer K. Hoppstoch B. Mergel and G. To» lg Fresenius' J. Anal. Chem. 1993 346 693. 17 R. Schierl and G. Fruhmann Sci. Total Environ. 1996 182 21. 18 E. Helmers H. Schwarzer and M. Schuster Environ. Sci. Pollut. Res. 1998 5 44. 19 F. Zerini B. Skerstupp F. Alt E. Helmers and H. Urban Sci. Total Environ. 1997 206 137. 20 T. Hees B. Wenclawiak S. Lustig P. Schramel M. Schwarzer M. Schuster D. Verstrache R. Dams and E. Helmers Environ. Sci. Pollut. Res. 1998 5 105. 21 F. Zerini F. Dirksen B. Skerstrupp and H. Urban Environ. Sci. Pollut. Res. 1998 5 223. 22 M. L. Farago B. Kavqanagh R. Blanks J. Kelly G. Kazanatzis I. Thornton P. R. Simon J. M. Cook S.Parry and G. M. Hall Fresenius' J. Anal. Chem. 1996 354 660. 23 E. Helmers and N. Mergel Fresenius' J. Anal. Chem. 1998 362 522. 24 E. Helmers and K. Klu»mmerer Environ. Sci. Pollut. Res. 1999 6 29. 25 C. Wei and G. M. Morrison Hydrobiology 1992 235 597. 26 I. Veltz F. Arsac S. Biaganti-Risbourg F. Habets H. Lechenault and G. Vernet Arch. Environ. Contam. Toxicol. 1996 31 63. 27 S. Rauch an G. M. Morrison Sci. Total Environ. 1999 235 261. 28 N. Yuantao and Y. Zhengfen Platinum Metals Rev. 1999 43 62. 29 J. H. Crocket and Y. Terruta Can. Mineral. 1976 14 58. 30 V. Pavlov M. Often and C. Reimann J. Geochem. Explor. 1997 58 283. 31 D. Gregurek F. Meleher H. Niskavaara V. Pavlov C. Reimann and E. F. StrumpØ Atmos. Environ.1999 33 3281. 32 H. J. Gauchelaar D. R. Uges P. Aulenbacher E. G. de Vries and N. H. Mulder Pharm. Res. 1993 9 808. 33 R. Schierl B. Rohrew and J. Hohnloser Cancer Chemother. Pharmacol. 1995 36 75. 34 D. Laschka and M. Nachtwey Chemosphere 1997 34 1803. 35 M. Niezborala and R. Garnier Occup. Environ. Med. 1996 53 252. 36 P. J. Linnett and E. G. Hughes Occup. Environ. Med. 1999 56 191. 37 S. Artelt O. Creutzenberg H. Koch K. Lewsen D. Nachtigall U. Heinrich T. Ru» hle and R. Schlo» gl Sci. Total Environ. 1999 228 219. 38 D. Verstaete J. Riondato J. Vercanteren F. Vanhaecke L. Moens R. Dams and M. Verloo Sci. Total Environ. 1998 218 153. 39 F. Alt H. R. Eschauer B. Mergel J. Messerschmidt and G. To» lg Fresenius' J.Anal. Chem. 1997 357 1013. 40 F. Alt J. Messerschmidt and G. Weber Anal. Chim. Acta 1998 359 65. 41 J. Scha» fer D. Hannker J. D. Eckhardt and D. Stu»ben Sci. Total Environ. 1998 215 59. 42 E. Helmers Chemosphere 1996 33 405. 43 G. Weber F. Alt and J. Messerschmidt Fresenius' J. Anal. Chem. 1998 362 209. 44 N. Jakubowski C. Thomas D. Klueppel and D. Stuewer Analusis 1998 26 M37. 45 M. E. Farago P. Kavanagh R. Blanks G. Kazatzis I. Thornton P. R. Simpson J. M. Cook H. T. Delves and G. E. M. Hall Analyst 1998 123 451. 46 R. Merget R. Kulzer A. Dierkes- Globisch R. Breitstadt A. Gelber A. Kniffka S. Artelt H. P. Koening Viewpoint F. Alt R. Vormberg X. Baur and G. Schultze-Werninghaus J. Allerg. Clin. Immun. 2000 105 364. 47 F. Alt A. Bambauer K. Hoppstoch B. Mergler and G. To» lg Fresenius' J. Anal. Chem. 1993 346 693. 48 O. Nygren and L. Lundgren Int. Arch. Occup. Environ. Healtth 1997 70 209. 49 I. V. Kubrakova T. F. Kudinova N. M. Kuzmin I. A. Kovalev G. I. Tsysin and Y. A. Zolotov Anal. Chim. Acta 1996 334 167. 50 K. Pyrzyn� ska Talanta 1998 47 841. 51 B. Godlewska-Z « y�kiewicz B. Les�niewska J. Micha�owski and A. Hulanicki Int. J. Environ. Anal. Chem. 1999 75 71. 52 E. Beinrohr M. L. Lee P. Tscho» pel and G. To» lg Fresenius' J. Anal. Chem. 1993 346 689. 53 M. Parent H. Vanhoe L. Moens and R. Dams Fresenius' J. Anal. Chem. 1996 354 664. 54 M. Totland I. Jarvis and R. E. Jarvis Chem. Geol. 1993 104 175. 55 R. Vlasœa�nkova V. Otruba J. Bendl M. Fisœera and V. Kanicky Talanta 1999 48 839. 56 D. Klueppel N. Jakubowski J. Messerschmidt D. Stuewer and D. Klockow J. Anal. At. Spectrom. 1998 13 255. 57 W. Wegschneider and M. Zischka Fresenius' J. Anal. Chem. 1993 174 49. 58 S. Lusting J. De Kimpe R. Cornelis P. Schramel and B. Michalke Electrophoresis 1999 20 1627. 59 B. Michalke and P. Schramel Fresenius' J. Anal.Chem. 1997 357 594. Krystyna Pyrzyn�ska Department of Chemistry University of Warsaw 02±093 Warsaw Pasteura 1 Poland 103N 103N J. Environ. J. Environ. Monit. Monit.