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

The effect of the strong metal-complexing agent EDTA on survival, grow th, and copper and zinc concentrations in Hyalella azteca was studied to determine if metal concentrations id control amphipods represent mi nimum physiological levels. Exposure to EDTA concentrations of up to 5 60 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 backgroun d metals are firmly bound to Hyalella. Chronic (4 week) exposure to ED TA resulted in increased mortality and reduced growth rates, both of w hich could be partially ameliorated by adding zinc to culture media. T his implies that EDTA toxicity results, in part, from zinc deficiency. In spite of this, however, zinc concentrations in Hyalella were not r educed in amphipods raised in the presence of high EDTA, implying that the observed background zinc levels represent minimum physiological l evels. Copper additions to media were ineffective at reducing EDTA tox icity. Nevertheless, control concentrations are probably close to mini mum physiological levels for copper as well, because high EDTA did not appreciably reduce copper in Hyalella in chronic tests, in spite of i ts ability to impair copper uptake from water at moderate water concen trations.