Ecotoxicology is the study of the toxic effects of chemicals on the aquatic and terrestrial environment. Ecotoxicologists study the immediate effect of a toxic substance on individual organisms and species in food webs, with the ultimate aims of predicting effects on wildlife populations, ecosystems and on human food resources such as fish and shellfish.

Ecotoxicologists aim to understand (and ideally predict and prevent) undesirable events in the natural environment, by carrying out ecotoxicity testing and risk assessment on new chemicals that may be used, disposed, or otherwise reach the environment. They are often also involved in conducting detailed monitoring studies of invertebrates and fish in polluted rivers and estuaries, looking at species at many levels within a food chain. It may also be necessary to monitor the physiological and biochemical responses of organisms following exposure to a pollutant, which may reflect a toxic effect. In many cases, sub-lethal effects such as changes in behaviour, development or reproduction may be just as important for the survival of a species as a lethal effect.

Typically, ecotoxicologists are involved in tracing the metabolism, accumulation and movements of natural and synthetic chemicals through different food chains. They may identify population changes after exposure to pollutants, particularly genetic changes such as the development of resistance to pesticides in insects.

In seeking to predict and prevent pollution impacts, the ecotoxicologist’s main task is increasingly to develop models which can be used to predict the fate and effects of chemicals within an ecosystem. Often, to do this successfully, there must be close co-operation with both ecologists working in the field and those in the laboratory, using the latest techniques of biochemical toxicology and chemistry. Fieldwork allows some ecotoxicologists to spend time outdoors, investigating the effects of chemicals in aquatic and terrestrial ecosystems. For the aquatic environment, this often involves working on research ships or possibly scuba diving; whilst for the terrestrial environment, ecotoxicologists may conduct surveys of farmland birds and mammals.

Ecotoxicologists help to protect the environment and existing ecosystems for future generations, and they make important contributions to protecting food resources in agriculture, aquaculture and fishing around the world.