EDTA TOXICITY AND BACKGROUND CONCENTRATIONS OF COPPER AND ZINC IN HYALELLA-AZTECA

The effect of the strong metal-complexing agent EDTA on survival, growth, and copper and zinc concentrations in Hyalella azteca was studied to determine if metal concentrations id control amphipods represent minimum physiological levels. Exposure to EDTA concentrations of up to 560 mu M for 1 week did not reduce metal levels (mean background = 1.2 mu mol Cu/g and 1.0 mu mol Zn/g dry weight), indicating that background metals are firmly bound to Hyalella. Chronic (4 week) exposure to EDTA resulted in increased mortality and reduced growth rates, both of which could be partially ameliorated by adding zinc to culture media. This implies that EDTA toxicity results, in part, from zinc deficiency. In spite of this, however, zinc concentrations in Hyalella were not reduced in amphipods raised in the presence of high EDTA, implying that the observed background zinc levels represent minimum physiological levels. Copper additions to media were ineffective at reducing EDTA toxicity. Nevertheless, control concentrations are probably close to minimum physiological levels for copper as well, because high EDTA did not appreciably reduce copper in Hyalella in chronic tests, in spite of its ability to impair copper uptake from water at moderate water concentrations.