ABSTRACT
In the second part of the text, attention was focused on particular pollutants or groups of pollutants. Their chemical and biochemical properties were related to their known ecotoxicological effects. Sometimes, with the aid of biomarker assays, it has been possible to relate the responses of individuals to consequent effects at the level of population and above. Biomarker assays provided the essential evidence that adverse effects on populations, communities, and ecosystems were being caused by environmental levels of particular chemicals. The examples given included population declines of raptors due to eggshell thinning caused by p,p′-DDE, and decline or extinction of dog whelk populations due to imposex caused by tributyl tin (TBTs). These were relatively straightforward situations where much of the adverse change was attributable to a single chemical. In other cases, as with the decline of raptors in the U.K., effects were related to one group of chemicals, in this case the cyclodienes. Since these events, there have been extensive bans on certain chemicals, and there is less evidence of harmful effects due to just one chemical or group of related chemicals. Interest has moved toward the possible adverse effects of complex mixtures of chemicals, sometimes of contrasting modes of action, often at low levels.
