Clinical tests in aquatic toxicology: state of the art

Hazard assessment of chemicals to aquatic organisms involves the use of many toxicity tests. Acute toxicity tests, embryo-larval toxicity tests, and chronic toxicity tests that measure survival, growth, and reproductive effects now provide the most relative utility for evaluation of potential chemical hazards to aquatic life. Physiological, biochemical, and histological measurements have a low relative utility as diagnostic tests in aquatic toxicology because it is not yet possible to relate changes in these sublethal responses to adverse environmental impacts. The problem of interpreting the toxicological significance of chemical-induced changes in biochemical and physiological mechanisms is twofold: (1) the understanding of physiological and biochemical regulatory mechanisms in fish is limited; and (2) parallel changes in these mechanisms are difficult to correlate with toxicant exposure and impaired ability of fish to survive. To overcome this problem, more physiological and biochemical research must be conducted in conjunction with toxicity studies that measure important whole-animal responses. Toxicant-induced biochemical and physiological responses must be correlated unequivocally with responses related to reproduction, growth and development, survival, or fish health if pertinent diagnostic tests are to be developed for use in aquatic toxicology. The use of diagnostic tests in hazard assessment procedures can decrease the time required for safety evaluation of chemicals, define no-effect exposure concentrations more adequately, and provide a better understanding of the mode of action of chemicals. Considerations for improving the status of the "state of the art" of diagnostic or clinical tests in aquatic toxicology are discussed.