Aquatic toxicology is the study of the adverse effects of toxins and their activities on aquatic ecosystems. Aquatic toxicologists assess the condition of aquatic systems, monitor trends in conditions over time, diagnose the cause of damaged systems, guide efforts to correct damage, and predict the consequences of proposed human actions so the ecological consequences of those actions can be considered before damage occurs. Aquatic toxicologists study adverse effects at different spatial, temporal, and organizational scales. Because aquatic systems contain thousands of species , each of these species can respond to toxicants in many ways, and interactions between these species can be affected.
Consequently, a virtually unlimited number of responses could be produced by chemicals . Scientists study effects as specific as a physiological response of an important fish species or as inclusive as the biological diversity of a large river basin. Generally, attention is first focused on responses that are considered important either socially or biologically. For example, if a societal goal is to have fishable waters, responses to toxicants of game fishes and the organisms they depend on would be of interest.
The two most common tools used in aquatic toxicology are the field survey and the toxicity test. A field survey characterizes the indigenous biological community of an aquatic system or watershed . Chemistry, geology, and land use are also essential components of field surveys. Often, the characteristics of the community are compared to other similar systems that are in good condition. Field surveys provide the best evidence of the existing condition of natural systems. However, when damaged communities and chemical contamination co-occur, it is difficult to establish a cause-and-effect relationship using the field survey alone. Toxicity tests can help to make this connection. The toxicity test excises some replicable piece of the system of interest, perhaps fish or microbial communities of lakes, and exposes it to a chemical in a controlled, randomized, and replicable manner. The most common aquatic toxicity test data provide information about the short-term survival of fish exposed to one chemical. Such tests demonstrate whether a set of chemical conditions can cause a specified response. They also provide information about what concentrations of the chemical are of concern. Toxicity tests can suggest a threshold chemical concentration below which the adverse effect is not expected to occur; they can also present an index of relative toxicity used to rank the toxicity of two chemicals. By using information from the field survey and toxicity tests, along with other tools such as tests on the fate of chemicals released into aquatic systems, aquatic toxicologists can develop models predicting the effects of proposed actions.
The most important challenge to aquatic toxicology will be to develop methods that support sustainable use of the aquatic and other ecosystems. Sustainable use is intended to ensure that those now living do not deprive future generations of the essential natural resources necessary to maintain a quality lifestyle. Achieving the goal of sustainable use will require aquatic toxicologists to have a much longer temporal perspective than we now have. Additionally, in a more crowded and increasingly affluent world, cumulative effects will become extremely important.
[John Cairns Jr. ]