Procedures for use of freshwater fishes in the development of reproducible toxicological information.

Toxicity testing with fish began early in this century, but standardized methods have been developed only within the last three decades. Standardized test procedures promote reproducibility of results; healthy fish properly handled and acclimated to test conditions are a given prerequisite. The principles of acute toxicity testing are important in the design of chronic tests for suspected carcinogens because certain factors influence the activity of chemicals or contaminants. The pH of test water is a critical factor in governing the uptake of chemicals by fish. Buffering is required so that uniform pH in waters of different hardnesses and different pHs in water of a given hardness are maintained. The importance of water quality control is graphically demonstrated by the lampricide 3-trifluoromethyl-4-nitrophenol; the toxicant is over 50 times more toxic in water at pH 6.5 than at pH 9.5. Results of laboratory tests on toxicity or carcinogenicity of single compounds in a clean environment represent an oversimplification of the real world because organisms are actually exposed to multiple chemicals or stresses. Because the environment is a complex interaction of physical, chemical, and biological factors that are extremely variable and dynamic, simulation of these systems in the laboratory is, at best, artificial; therefore, results developed must be considered to be predictive.

Toxicity of paired mixtures of candidate forest insecticides to rainbow trout.

The toxicities of Zectran, Dylox, Volaton, Guthion, pyrethrum extract, and the synthetic pyrethroids SBP-1382, and RU-11679 were determined individually and in paired mixtures against rainbow trout. The carbamate Zectran was the least toxic, and the synthetic pyrethroids were the most toxic. Nine of the mixtures produced less than additive toxicity (antagonism), nine produced additive toxicity, and two produced greater than additive toxicity (synergism). None of the mixture toxicities deviated markedly from additive,and only two pairs of mixtures would pose a greater toxicological hazard to fish than the respective individual chemicals.