Five different rapid-chronic toxicity tests were evaluated using hexavalent chromium as a reference toxicant. Rapid-chronic values were derived with hexavalent chromium for the fertilization test with the sea urchin Arbacia punctulata, the sexual reproduction test with the red macroalga Champia parvula, the larval growth test with the sheepshead minnow Cyprinodon variegatus, the reproduction test with the mysid Mysidopsis bahia, and the reproduction test with the polychaete Dinophilus gyrociliatus.
The results from rapid-chronic tests with mysids, sheepshead minnows, and the polychaete were compared with acute LC50 values. The acute values with hexavalent chromium were similar to rapid-chronic values for these species. Therefore, to evaluate the health of the testing animals and assess the variability of their response to a reference toxicant through time, less expensive short-term acute toxicity tests should be considered.
Among five species used in rapid-chronic toxicity tests with hexavalent chromium, Champia parvula was the most sensitive and the most variable. The least sensitive species tested was Arbacia punctulata, with a mean EC50 value of 341.8 mg Cr+6/L.
The toxic effect of hexavalent chromium was consistent in repeated experiments for all species with the exception of two-day rapid-chronic tests with Champia parvula. The results of this evaluation clearly indicated that before introducing new species or a new test method, several toxicity tests should be conducted under standardized conditions using one reference toxicant in order to evaluate the suitability of the test method in aquatic toxicological studies.