CERC Publication: Laboratory and field techniques in ecotoxicological research: strengths and limitations

Abstract

Proponents of single-species laboratory tests have indicated that such procedures offer cost-effective, replicable, reproducible, and interpretable means of assessing chemical safety. Acute toxicity tests in the laboratory provide practical means for: (1) estimating effect concentrations of chemicals; (2) ranking chemicals for their relative toxicity; (3) evaluating the relative sensitivities of different organisms to a given chemical; and (4) evaluating the effects of water quality on chemical toxicity. Critics, have stated that single-species tests are inadequate for predicting the potential hazards of chemicals to aquatic life in complex ecosystems. Immigration, emigration, food resources, predator-prey relations , and competition are important factors on the ultimate environmental effects of contaminants; none of these factors are routinely simulated in standard single-species tests. Similarly, many physical, chemical, and biological factors can alter the amount, form, or availability of contaminants in the environment. Simple laboratory tests were not predictive where: (1) the chemical or environment was altered under actual exposure conditions, such as when acid deposition mobilized metals from sediments or when mercury is microbially methylated to the more toxic form; (2) the organisms could avoid a toxicant; or (3) secondary effects occurred due to alterations in grazing, competition, or predation resulting from the loss of a keystone species. Tests involving more complex environmental simulations were often successful in identifying these unpredictable results. The information gained in ecotoxicological testing adds to the basic knowledge of ecosystem structure and function. This addition is important, for the costs of such testing may be small when compared with the resultant expense of mitigating damage of toxicants in the environment for which the hazard has not been fully assessed.