Kinetics of excess (above background) copper and zinc in Hyalella azteca and their relationship to chronic toxicity

Abstract

One-week-long metal uptake experiments with Hyalella azteca are potentially a powerful tool for rapidly assessing the impact of copper or zinc in contaminated water samples. Copper and zinc concentrations in whole body Hyalella are independent of body size for both control and metal-exposed amphipods. Uptake rates are rapid for both metals, but copper concentrations in Hyalella during continuous exposure peak at about 1 week, then gradually decline back towards control levels at an apparent rate of 0.039 d−1. Hyalella can, therefore, control body copper concentrations during exposure to elevated copper, but only gradually and after long exposure periods. Depuration rates for copper and zinc (0.16 and 0.68 d−1 respectively) are approximately five times slower 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 μmol/g dry weight above background. A mathematical model including saturation kinetics satisfactorily explains the more rapid approach to equilibrium observed during uptake than during depuration. Significant chronic mortality occurred at metal exposures that resulted in predicted accumulations of 1.8 μmol Cu/g or 1.3 μmol Zn/g above background after 1 week of uptake.