Pollution is a matter of life or death. In 2019, 9 million premature deaths were caused by pollution, an impact similar to tobacco products. Much of this was caused by air pollution, particularly by wood smoke in low and middle income countries. More than a million deaths were caused by water pollution. Ecotoxicology has a particular focus on fish and other freshwater animals. This discipline applies what is known about toxicity tests and extrapolates it to the larger aquatic environment. The intent is to set standards that protect aquatic life and, as a byproduct, provide early warning for direct environmental poisoning of humans. The challenge for ecologists is to predict the effect of a wide range of substances on a wide range of plants and anmals and to offer concrete advice to limit the effects of industral pollution.
The tools available for extrapolating from laboratory toxicity tests include:
- predictive equations to account for the effects of temperature, acidity, water hardness and other environmental characteristics on toxicity
- quantitative structure activity relationships that predict the biological effects of new chemical structures and inform which substances to test for toxicity
- demographc models , which predict the impact on a population for chemicals that are particularly toxic for reproduction or juvenile development
- Species sensitivity distributions that highlight which species in the ecosystem are most sensitive to the chemical
- Passive samplers that collect chemicals over weeks or months rather than at a single point in time. These devices allow a better description of what fish and molluscs are exposed to.
One of the early applications of ecotoxicology was to determine the impact of persistent chemicals, which result in higher concentrations in animals with long-term exposures (bioconcentration) and in those that are exposed through their diet (biomagnification). This latter effect is especially a problem for top predators in a food web, as each level of the web has a greater concentration of the chemical than their prey. There is currently some doubt about whether biomagnification commonly occurs, but the prospect of high concentrations of pollutants in larger organisms has led to the banning of 21 persistent chemicals through the Stockholm Convention. Often, the pesticides and industrial chemicals that have replaced persistent chemicals are highly toxic in short-term exposures but have less impact on the environment because they do not persist.
Another challenge for ecotoxicology is the possibility of cumulative effects by different toxins. When two toxins are in the environment, do they work indepedently of each other or is their combined effect more or less than one would expect? The number of possible combinations of pollutants is too great to test systematically. Surely, some combinations are worse than others. Studies in the North American Great Lakes have shown that muliple pollutants tend not to combine to have a stronger impact on the environment. There is much more to learn in this area.
The work of scientists in organizations like the Environmental Protection Agency helps prevent premature deaths due to pollution. They provide objective guidelines for sustainable development and a voice for the natural world which must live with what we put into the air and water.