The effect of calcium on cadmium toxicity in the freshwater amphipod, Gammarus pulex (L.).

Adult intermolt Gammarus pulex were exposed to a range of cadmium concentrations in an artificial stream water containing 20 mg calcium 1(-1). 96 hr and 48 hr LC-50 values obtained were 0.12 and 0.68 mg Cd 1(-1), respectively. The influence of external calcium level on cadmium toxicity was investigated at a cadmium concentration of 0.5 mg 1(-1). Calcium had an antagonistic effect on cadmium toxicity, and at a calcium concentration of 200 mg 1(-1) experimental animals failed to reach 50% mortality after a period of 120 hr. Over a 48 hr period of Cd uptake a solution containing 5 mg Cd 1(-1), animals in 200 mg calcium 1(-1) accumulated only half as much cadmium as animals in 20 mg calcium 1(-1). Post-molt animals were very much more sensitive to cadmium than intermolt specimens. Exposure to 0.1 mg Cd 1(-1) resulted in death in approximately 24 hr and the mean mortality time for animals in 0.01 mg Cd 1(-1) was 45 hr. These data are likely to be explained in terms of competition between cadmium and calcium for binding sites associated with key physiological processes. The results place these animals among the most sensitive organisms yet studied with regard to cadmium toxicity, and emphasize the importance of the molt in assessing toxic effects on crustaceans.