Chemical stressors

Havens, K.E. 1994. An experimental comparison of the effects of two chemical stressors on a freshwater zooplankton assemblage. Environ. Pollut. 84 245-251. 

Ecological risk assessment in EIA is to evaluate the probability that adverse ecological effects will occur as a result of exposure to stressors2 related to a proposed development and the magnitude of these adverse effects (Smrchek and Zeeman, 1998 US EPA, 1998 Demidova, 2002). A lion s share of site-specific EcoRAs were concerned with chemical stressors—industrial chemicals and pesticides. 

Histological studies and investigations of disposition processes are being coupled in order to assess the condition of populations of California mussels Mytilus californianus. Whether results of future studies of this sort can be used diagnostically to reveal the presence of chemical stressors in the environment and contribute to evaluation of their impact is a concern which motivates much of our experimental work. 

Jonker, D., A.P. Freidig, J.P. Groten, A.E. de Hollander, R.H. Stiemm, R.A. Woutersen, and V.J. Feron. 2004. Safety evaluation of chemical mixtures and combinations of chemical and non-chemical stressors. Rev. Environ. Health 19 83-139. 

Urhahn T, Ballschmiter K (1998) Chemistry of the Biosynthesis of Halogenated Methanes Cl-Organohalogens as Pre-Industrial Chemical Stressors in the Environment Chemosphere 37 1017... 

Because exposure occurs where receptors co-occur with or contact stressors in the environment, characterizing the spatial and temporal distribution of a stressor is a necessary precursor to estimating exposure. The stressor s spatial and temporal distribution in the environment is described by evaluating the pathways that stressors take from the source as well as the formation and subsequent distribution of secondary stressors. For chemical stressors, the evaluation of pathways usually follows the type of transport and fate modeling described in Chapter 27. Some physical stressors such as sedimentation also can be modeled, but other physical stressors require no modeling because they eliminate entire ecosystems or portions of them, such as when a wetland is filled, a resource is harvested, or an area is flooded. 

Finally, many extrapolation methods are limited by the availability of suitable databases. Although these databases are generally largest for chemical stressors and aquatic species, even in these cases data do not exist for all taxa or effects. Chemical effects databases for mammals, amphibians, or reptiles are extremely limited, and there is even less information on most biological and physical stressors. Extrapolations and models are only as useful as the data on which they are based and should recognize the great uncertainties associated with extrapolations that lack an adequate empirical or process-based rationale. 

Each of the classes of models discussed above can be used for different kinds of extrapolations, including extrapolation of biochemical or mortality effects observed in individuals to effects at the population level, extrapolation of results obtained from semifield experiments to the real field, and integration of population and landscape characteristics to landscape-level population consequences of chemical stressors. For additional information on population models and their use in ecological risk assessment, the reader is directed to the reviews found in Sauer (1995), Caswell (1996), ECOFRAM (1999), Newman (2001), Pastorok et al. (2002), Regan (2002), Bartell et al. (2003), and Sauer and Pendleton (1995 2003). 

Food-web modeling holds great promise in analyzing and predicting effects of chemical stressors (Baird et al. 2001) and has been developed for both terrestrial... 

Several field gradient studies revealed predictive relationships between chemical stressors and biotic responses. For example, exposure to mixtures of heavy metals has shown concentration-response relationships with macroinvertebrate community indices (Hickey and Clements 1998 (dements et al. 2000). This indicates that response thresholds for ecological indicators (e.g., species diversity and EPT taxa) may be available for use in toxic impacts, providing the nature of the toxicant is known (e.g., metals, organics, and ammonia). The field studies have shown strong concentration-response relationships with stressors, with metal response related to the cumulative criterion unit (CCU) value for the sum of the metals present (Hickey and Clements 1998 Clements et al. 2000). The CCU concept was discussed in greater detail in Chapter 5. 

Diagnostic indicators such as indicator species and community metric approaches are useful in extrapolation between smaller test units to landscapes and between landscapes themselves. The use of these indicators in extrapolation can be improved by constructing databases with information on the life-cycle characteristics of species, their occurrence and mobility in the landscape, and their sensitivity to the chemicals of concern. In the extrapolation of site-specific ecological impacts of chemical stressors, it is important to use more than one indicator to increase the discriminatory power of identifying impaired sites and to reduce the possibility of false negatives (type 2 errors, in which responses are present but not observed). 

Kaufer, D., Soreq, H. (1999). Tracking cholinergic pathways from psychological and chemical stressors to variable neurodeterioration paradigms. Curr. Opin. Neurol. 12 739 3. 

Sources of data that might be used in the construction of stressor-response functions include the results of toxicity tests (lethal, chronic) performed under controlled laboratory conditions, direct measures of exposure and response in controlled field experiments, and the application of statistical relationships that estimate the biological effects of chemicals based on physical or chemical properties of specific toxicants. The order of preference among these sources of data lists field observations as the most valuable, followed by laboratory toxicity tests, and finally by the use of empirical relationships. In the absence of directly relevant data, the development of stressor-response functions may require the use of extrapolations among similar stressors or ecological effects for which data are available. For example, effects might have to be extrapolated from the available test species to an untested species of concern in an ERA. Similarly, toxicity data might be available only for a chemical similar to the specific chemical stressor of concern in an ERA, and thereby require an extrapolation from one chemical to another to perform the assessment. 

This chapter deals with perhaps the most difficult topic in environmental toxicology how to measure and then evaluate the impact of toxicants at ecological levels of organization. The chapter starts with an evaluation of methods and ends with a discussion of the responses of ecosystems to chemical stressors. 

Several researchers have attempted to employ multivariate methods to the description of ecosystems and the impacts of chemical stressors. Perhaps the best developed approaches have been those of K. Kersting, A.R. Johnson, and a new approach developed by Matthews et al. 

---