KINETICS OF EXCESS (ABOVE BACKGROUND) COPPER AND ZINC IN HYALELLA-AZTECA AND THEIR RELATIONSHIP TO CHRONIC TOXICITY

One-week-long metal uptake experiments with Hyalella azteca are potent ially a powerful tool for rapidly assessing the impact of copper or zi nc in contaminated water samples. Copper and zinc concentrations in wh ole body Hyalella are independent of body size for both control and me tal-exposed amphipods. Uptake rates are rapid for both metals, but cop per concentrations in Hyalella during continuous exposure peak at abou t 1 week, then gradually decline back towards control levels at an app arent rate of 0.039 d(-1). Hyalella can, therefore, control body coppe r concentrations during exposure to elevated copper, but only graduall y and after long exposure periods. Depuration rates for copper and zin c (0.16 and 0.68 d(-1) respectively) are approximately five times slow er than the apparent depuration rates during uptake, assuming a simple diffusion model. Uptake at increasing water concentrations results in saturation for both metals with maximum accumulations of 3.6 mu mol/g dry weight above background. A mathematical model including saturatio n kinetics satisfactorily explains the more rapid approach to equilibr ium observed during uptake than during depuration. Significant chronic mortality occurred at metal exposures that resulted in predicted accu mulations of 1.8 mu mol Cu/g or 1.3 mu mol Zn/g above background after 1 week of uptake.