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Because natural populations are linked by a variety of ecological interactions (for example, predation and competition), the response of any particular population to chemical exposure depends on how the rest of the ecosystem is affected. Mathematical models and field experiments demonstrate that such interactions can amplify or diminish the impacts of contaminants on populations. When direct toxic effects result in persistent, significant changes in some parts of an ecosystem, other populations in the ecosystem become vulnerable to indirect effects. Protection of aquatic populations, then, requires protection of aquatic ecosystems.
The threshold of persistent, significant damage to an ecosystem is a distinct discontinuity in the gradient of ecosystem response to increasing chemical exposure. The safe level of exposure for an aquatic ecosystem can be determined experimentally using microcosms or field enclosures. It is hypothesized that safe exposure levels for ecosystems are usually near the lower end of the chronic toxicity range for single species. Data on chemical effects in ecosystems are needed in order to calibrate standard bioassays and to verify the accuracy of methods for extrapolating from bioassay results to nature.
aquatic toxicology, hazard assessment, aquatic ecosystems, bioassays, microcosms, field experiments, modeling
Research staff member, Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN