INFLUENCE OF ACCLIMATION AND EXPOSURE TEMPERATURE ON THE ACUTE TOXICITY OF CADMIUM TO THE FRESH-WATER SNAIL POTAMOPYRGUS-ANTIPODARUM (HYDROBIIDAE)

Forty-eight-hour acute toxicity testS were performed to determine the influence of acclimation temperature (5, 15, and 20-degrees-C) and exp osure temperature (5, 15, and 20-degrees-C) on the toxicity of cadmium to the freshwater gastropod Potamopyrgus antipodarum. Mortality varie d with cadmium concentration and treatment conditions, but did not con form to conventional sigmoid concentration-response (i.e., dose-respon se) relationships. Because the shapes of the concentration-response cu rves were treatment dependent, a nontraditional approach for data anal ysis was employed. Regardless of acclimation temperature, mortality in creased with increasing exposure temperature, and at all exposure temp eratures snails acclimated at 15-degrees-C were most susceptible to ca dmium toxicity. Estimated LC50 values were within 1 to 4 mg Cd/L. Alth ough the shapes of the concentration-response curves were different fo r each treatment, the slopes were generally quite steep, indicating a uniform response for the whole population. At a given Cd concentration , acclimation temperature and exposure temperature accounted for 57 an d 40%, respectively, of the variation in mortality, and LC50s changed by a factor of four. The results indicate that changes in environmenta l variables can alter both the degree of response and the response dis tribution of a population, and that past as well as prevailing environ mental conditions can influence organismic responses to toxicants.