Detoxication of zinc and cadmium by the freshwater protozoan Tetrahymena pyriformis: I. The effect of water hardness

Abstract

Estimated 8-hr LC 50 values of zinc and cadmium were less than 1 ppm in the absence of soluble calcium and magnesium, but were raised, for example, to 24 ppm of zinc and 19 ppm of cadmium by the addition of calcium plus magnesium at a concentration (500 ppm) equivalent to that of very hard water. Experiments with 65Zn showed that uptake of this element from sublethal concentrations over 8 hr was reduced from approximately 50 × 10 −2 μg liter −1 to 10 × 10 −2 μg liter −1 per 10 6 cells by the addition of 500 ppm of calcium and magnesium. Diminished uptake may partly explain the antagonism observed in the toxicity tests.