A continuous-flow system was developed for evaluating the effects of insoluble and volatile organics on the developmental stages of fish. A closed test system, devoid of standing air space, was used to minimize volatility as a variable. Insoluble compounds were suspended in influent water by mechanical homogenization, without the use of carrier solvents. Tests were performed with aniline, chlorobenzene, and phenol. Water hardness was maintained at 50 and 200 mg/litre calcium carbonate, and exposure was continuous from fertilization through four to eight days after hatching for largemouth bass, channel catfish, goldfish, and rainbow trout. The results indicated that there was good reproducibility of exposure concentrations down to 1 µg/litte or less. For a calculated concentration of 1 µg/litre phenol, the actual test-water concentrations (mean ± standard error) for four replicates were 0.7 ± 0.2, 1.2 ± 0.3, 1.3 ± 0.3, and 1.5 ± 0.3. When phenol was administered in hard water, the LC1 and LC50 values determined at hatching were 0.2 and 80 µg/litre for trout, and 2.0 and 710 µg/litre for goldfish. Phenol was less toxic in soft water. Chlorobenzene at 0.09 mg/litre produced complete mortality of trout eggs. When bass eggs were exposed through four days after hatching, the LC50s for chlorobenzene ranged from 50 to 60 µg/litre. The aniline LC50 values calculated for catfish, goldfish, and bass eggs treated in soft water were 5.6, 10.2, and 47.3 mg/ litre, respectively. Because of the differential rates of larval mortality for the three species, the LC50 range narrowed considerably when the exposure time was increased beyond hatching. Water hardness exerted no appreciable effects on the toxicity of either chlorobenzene or aniline. All three organic compounds produced significant frequencies of teratic larvae.
Chronicity frequently is the most important and sensitive factor in determining the impact of toxicant stress on aquatic biota. However, chronic values are often unavailable or inadequate to provide decisive judgments in hazard assessment. Time and cost constraints involved in generating traditional chronic data also pose equally important problems in basic toxicological research. In assessing rapid means for estimating chronicity, attention is given to predictive models based on structure-activity relationships, extrapolations from acute toxicity data, and use of short chronic (mini-chronic) tests. High priority is placed on further development and evaluation of mini-chronic tests, which have been used successfully to characterize single compounds and complex effluents, evaluate effluent treatability, and determine the effects of point-source discharges on natural receiving waters. Methods most commonly used have involved (1) a five to eight-day fish embryo-larval test, (2) a seven-day cladoceran test, and (3) a seven-day fathead minnow larval growth test. General research needs are summarized as follows: (1) Evaluation of short toxicity tests presently available. This should include accuracy and reproducibility of endpoint determinations and statistical correlations between minichronic data and results obtained using traditional chronic and embryo-larval tests. (2) Design of multiple species tests, in-stream flow-through tests, and other short-term test procedures for estimating chronic effects of complex effluents and single compounds. (3) Determination of the effects of laboratory and field conditions, general water quality characteristics, and selection of animal species on results of mini-chronic tests. (4) Consideration of nonorganismal tests or mathematical models that may be used to estimate chronicity. Such research may include enzyme inhibition tests, QSAR-based modeling, and extrapolations based on acute toxicity data. (5) Investigations of the physiological and biochemical mechanisms involved in acute and chronic toxicity. Analyzing the accuracy and extrapolative value of acute, mini-chronic, and chronic tests data depends in large measure on understanding the pharmacodynamics of toxicants affecting aqautic biota.
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