Effects of Contaminants on Behavior: Biochemical Mechanisms and Ecological Consequences: Killifish from a contaminated site are slow to capture prey and escape predators; altered neurotransmitters and thyroid may be responsible for this behavior, which may produce population changes in the fish and their major prey, the grass shrimp

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Effects of environmental contaminants can be studied at various levels of organization, including biochemical and cell levels, the level of individual organisms, and the population and community level. It is assumed that effects at the molecular and cellular levels precede detectable effects at the individual organism level, which precede effects at the population and community level. Biochemical and cellular effects can therefore be used as early warning signals, or “biomarkers,” of exposure or response to toxic chemicals. In most cases, however, little is known about links from the cellular or biochemical level to the organism level or links from the organism level to the population and community level.

Much of the research on toxicology of metals has been done at the biochemical and cell levels and at the individual organism level. We have considerable knowledge about how metals are taken up into organisms, distributed among tissues, and bound to specific molecules. We have learned much about how they can affect biochemical pathways and enzyme functioning. For higher levels of organization, there are studies of alterations in physiology, reproduction, development, and behavior. Effects on ecological parameters such as population size and size structure have been noted, and effects on diversity and community structure (“ecotoxicology”) have been frequently demonstrated.