摘要:

The notion that the ecological health of the environment can be assessed is a ridiculous notion in a scientific context because there can be no objective definition of ‘health’ or method for defining degrees of health. Ecological health is a value judgement. A potentially useful concept embedded within the notion of ecological health is that environmental monitoring programs need to adopt a more holistic, ecosystems approach than has been used hitherto. In this paper, I outline a framework for ecosystem monitoring and discuss some of the variables that might be incorporated to assess ecosystem structure and processes. The interpretation of the data produced by ecosystem monitoring programs is problematic. Defining control or reference sites is virtually impossible; data can only be assessed with reference to extant ecosystems or to past situations.

ISSN:1080-7039    

DOI:10.1080/10807030009380056

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:1080-7039    

DOI:10.1080/10807030009380057

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Hormesis is a widespread phenomenon across occurring many taxa and chemicals, and, at the single species level, issues regarding the application of hormesis to human health and ecological risk assessment are similar. However, interpreting the significance of hormesis for even a single species in an ecological risk assessment can be complicated by competition with other species, predation effects, etc. In addition, ecological risk assessments may involve communities of hundreds or thousands of species as well as a range of ecological processes. Applying hormetic adjustments to threshold effect levels for chemicals derived from sensitivity distributions for a large number of species is impractical. For ecological risks, chemical stressors are frequently of lessor concern than physical stressors(e.g.,habitat alteration) or biological stressors(e.g.,introduced species), but the relevance of hormesis to non‐chemical stressors is unclear. Although ecological theories such as the intermediate disturbance hypothesis offer some intriguing similarities between chemical hormesis and hormetic‐like responses resulting from physical disturbances, mechanistic explanations are lacking. While further exploration of the relevance of hormesis to ecological risk assessment is desirable, it is unlikely that hormesis is a critical factor in most ecological risk assessments, given the magnitude of other uncertainties inherent in the process.

ISSN:1080-7039    

DOI:10.1080/10807030009380058

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The phenomenon of hormesis has been observed mainly for the response of individual organisms to stress. A reasonable line of inquiry might explore the possibility of observing hormesis at other levels of ecological organization. This initial examination focuses on ecosystem hormesis. Explorations of hormetic responses of ecosystems to stress cannot be made independently of a fundamental concept of ecosystem. The scale‐dependence of ecosystem dynamics also influences whether an ecological disturbance is in reality a stressor. Ecosystem hormesis might be claimed if one or more components of an ecosystem exhibit hormesis. By this definition, ecosystem hormesis would be a trivial extension of hormesis observed for individual organisms. A non‐trivial extension of ecosystem hormesis would include the observation that integrated (i.e.,holistic) measures of ecosystem structure or function displayed an hormetic response to an ecological stressor. Several such examples of ecosystem structural and functional hormesis are presented.

ISSN:1080-7039    

DOI:10.1080/10807030009380059

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:1080-7039    

DOI:10.1080/10807030009380060

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Although adaptive and reparative responses to radiation were recognized in the early decades of this century, mutations and chromosome aberrations were subsequently observed to increase as linear‐nondireshold functions of the dose at low‐to‐intermediate levels of exposure. For certain cancers, likewise, although the dose‐response relationships in humans and laboratory animals have been observed to vary, depending on the type of neoplasm, the dose, dose rate, and LET of the radiation, the age, sex, and genetic background of the exposed population, and other variables, the existing data have been interpreted to suggest that the risks may not depart significantly from linearity at low doses and low dose rates. Hence, although the available data do not exclude alternative dose‐response relationships, the linear‐nonthreshold model has generally come to be used as a basis for assessing the risks of low‐level irradiation for purposes of radiation protection. While the use of this model has generally been considered to be prudent on the basis of the precautionary principle, the possibility that the model may grossly overestimate the risks of low‐level irradiation remains to be excluded. Therefore, especially in the light of the growing evidence that adaptive responses may protect against the effects of small doses of radiation, further research to clarify the relevant dose‐response relationships is strongly indicated.

ISSN:1080-7039    

DOI:10.1080/10807030009380061

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Restricting the food intake of rats and mice to 60% ofad libitumintake has been shown to significantly slow their aging processes and markedly extend length of life. Evidence is presented that indicates the antiaging action of this dietary restriction is a manifestation of hormesis and acts by enabling the animal to cope with stressors, including the low‐intensity, long‐term intrinsic and extrinsic stressors conjectured to cause aging. A hypothesis is offered for the evolutionarily adaptive basis of the antiaging action of dietary restriction: It proposes that this antiaging action is a byproduct of the evolution of mechanisms that enabled animals living in the wild to survive unpredictable and relatively brief periods of food scarcity. Likely proximate mechanisms of antiaging action of dietary restriction are considered. Enhancement of the stress response genes, particularly the heat shock protein genes, appears to be importantly involved. Evidence indicates that moderate hyperadrenocorticism also plays a significant role. These proximate mechanisms may well be major players in other examples of hormesis.

ISSN:1080-7039    

DOI:10.1080/10807030009380062

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The results of numerous studies indicate that cells can become refractory to the detrimental effect of ionizing radiation when previously exposed to a low, “adapting dose”;. This phenomenon has been termed an “adaptive response”; to ionizing radiation. It has been postulated that the induced radioresistance is due to the induction of DNA repair systems which efficiently protect the adapted cells from the effects of a subsequent, high “challenging dose”;. However, a direct proof of this hypothesis is still lacking. The analyzed endpoints include chromosomal aberrations, survival, mutations, genetic instability and DNA damage repair measured by the comet assay. Frequently contradictory results were published by different authors. For example some authors observed a reduced frequency of apoptosis in adapted cells, whereas others reported the opposite. The source of variablity of the adaptive response in human lymphocytes remains unresolved. While there is no doubt that an adapting dose can trigger some protecting mechanisms within the cell it appears that there is no single, universal mechanism of the adaptive response that is valid for all cell types and irradiation conditions.

ISSN:1080-7039    

DOI:10.1080/10807030009380063

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:1080-7039    

DOI:10.1080/10807030009380064

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Three commercial brands of coffee were examined for sorption of Cu and Pb. We kept experimental conditions close to those in ordinary situations by using an automatic drip coffee maker. One‐liter increments of de‐ionized water spiked with increasing amounts of Cu and Pb were used to make pots of coffee. Influent (water) metal concentration was then compared with effluent (coffee) metal concentration. We kept influent metal concentrations in ranges that might be expected due to contamination from storage tanks and pipes in municipal water delivery systems (0.1 to 5.0 mg/L). The coffee brewing process removed 78 to 90% of both Cu and Pb from influent water. We ran experiments by varying coffee strength (function of bed depth) and varying brewed coffee volume (function of bed depth and water volume) . Most of the metal that goes through the coffee bed does so in the early stages of the brewing process before the coffee bed is wetted. The main factor influencing removal of soluble metal by coffee is contact time with the wetted coffee bed. Therefore, the strength and/or volume of coffee brewed play a critical role in metal removal. Preliminary work with steeping teabags in metal spiked water showed little to no reduction in the soluble Cu and Pb concentration. Results of this study are important for risk assessment model formulations. Daily human exposure to Cu and Pb from municipal water systems may be grossly overestimated if a large proportion of tapwater ingestion by an individual is filtered through coffee.

ISSN:1080-7039    

DOI:10.1080/10807030009380065

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor