Single-species Laboratory Tests Research Articles

Putting the eco in ecotoxicology

Testing of pesticides and often other persistent chemicals increasingly involves aquatic mesocosms. Since our intention is to protect natural systems, predictions of their response based on surrogate systems are desirable. Toxicity tests at a variety of levels of biological organization are now available, ranging from single-species laboratory tests to those carried out in field enclosures of portions of natural systems. Validation is essential to determine accuracy of the predictions that will almost certainly not be identical for the wide variety of testing systems now available. Some important scientific considerations in the development of protocols are discussed.

Ecotoxicological Effect Indices: A Rapidly Evolving System

Ecotoxicology has evolved from a modest number of single species, acute toxicity tests to an integrated system of hazard evaluation for predicting adverse effects of chemicals and complex mixtures on environmental health. The process of screening and regulating chemicals and industrial discharges has improved water quality but has generally not been validated in receiving ecosystems. This deficiency results from the regulation of individual chemicals that rarely occur alone in the environment and from the size of the problem. Many receiving ecosystems have literally hundreds of discharges of complex effluents. Typical single species laboratory tests fail to account for the complexity of ecosystems and the strong interactions that may occur among the component species. Evidence is accumulating that complex test systems such as microcosms and mesocosms can fill this void. Microcosms and mesocosms can be constructed and experiments conducted in a cost-effective manner, and several end points can be measured in complex systems using the standard dose-response paradigm. For example, the current regulation of chlorine discharges is based on three chronic exposures to chlorinated sewage effluent. In a microcosm test, we determined adverse biological effects at nearly an order of magnitude less chlorine (1 μg/1) for the loss of microbial species. To be effective hazard evaluation tools, microcosms and mesocosms must include ecologically meaningful processes and must be useful in making decisions regarding environmental safety and harm. This can only be done with adequate statistical design and intensive sampling. Nevertheless, laboratory ecosystems can be useful in making direct measurements of effects on a large number of interacting species and can be tied to a site-specific problem in a particular ecosystem or can be standardized by using regional type ecosystems as references. By using complex natural communities, the ability to validate test system predictions increases since the test system complexity mimics that found in the real world. Despite hopes that a few sensitive species might be used to make decisions quickly on environmental effects, ecological health will only be maintained when scientists and regulators come to grips with the problem of protecting ecologically important processes as well as sensitive species. This will mean developing tests with increasing environmental realism in which environmentally realistic concentrations of chemicals can be tested without resorting to the use of safety factors or extrapolation from limited data bases. Developing such tests does not mean skyrocketing costs for screening chemicals and effluents, but suggests that regulators and toxicologists will need to deal with new information and learn new skills rather than relying on historically pleasing but ecologically deficient testing programs.