Influence of salinity and temperature on acute toxicity of cadmium to Mysidopsis bahia molenock.

Acute toxicity tests were conducted to compare estimates of toxicity, as modified by salinity and temperature, based on response surface techniques with those derived using conventional test methods, and to compare effect of a single episodic exposure to cadmium as a function of salinity with that of continuous exposure. Regression analysis indicated that mortality following continuous 96-hr exposure is related to linear and quadratic effects of salinity and cadmium at 20 degrees C, and to the linear and quadratic effects of cadmium only at 25 degrees C. LC50s decreased with increases in temperature and decreases in salinity. Based on the regression model developed, 96-hr LC50s ranged from 15.5 to 28.0 micrograms Cd/L at 10 and 30% salinities, respectively, at 25 degrees C; and from 47 to 85 micrograms Cd/L at these salinities at 20 degrees C. Trimmed Spearman-Karber method used in analysis of a second data set yielded estimates at 20 degrees C and 25 degrees C comparable to those of multiple regression analysis. At 30 degrees C, the 96-hr LC50 was less than 11 micrograms/L. The relationship of median tolerance to cadmium concentration and exposure time was related to the interaction of both factors and independent of salinity between 10 and 30% at 25 degrees C. The quadratic model predicts mortality of 50% following exposures of less than 12 hr to the highest concentration examined (92 micrograms/L). For exposure durations of 16 and 24 hr, 50% mortality is predicted to occur at 78 and 56 micrograms/Cd/L, respectively.