ACUTE AND CHRONIC TOXICITY OF COPPER TO THE ESTUARINE COPEPOD EURYTEMORA-AFFINIS - INFLUENCE OF ORGANIC COMPLEXATION AND SPECIATION

The objectives of this study were to conduct acute (48 and 96h) and ch ronic (8d) copper toxicity tests with the estuarine zooplankter, Euryt emora affinis and develop an acute-to-chronic ratio (ACR) for this spe cies. Dissolved copper, copper speciation and organic complexation wer e measured on selected samples during these toxicity tests. Organic co mplexation measurements were critical to determine the bioavailability of copper to the test species. Concentrations of dissolved copper at selected test conditions displayed a loss of 20 to 35% over the course of the acute and chronic experiments with the most significant loss o ccurring during the first 48 hours. Due to the loss of dissolved coppe r during exposures, a decay model was developed to calculate the adjus ted dissolved copper concentrations that were used to determine the fi nal toxicity values. The 48h LC50, 96h LC50 and 8d chronic values were 83.0, 69.4 and 64 mu g/L dissolved copper, respectively, using the ad justed dissolved copper concentrations. An acute-to-chronic ratio of 1 .3 was calculated using the 48 h and 8 d toxicity values. Voltammetric analysis of selected samples indicated greater than 99% complexation of copper in all samples with complexing capacity increasing with both time and copper concentration. The non-complexed inorganic copper con centration was therefore a very small fraction ofthe total copper adde d during these experiments. Non-complexed inorganic copper (II) specia tion predicted by a model identified seven significant species of copp er. Of these seven species, CuCO3 was the dominant species accounting for approximately 78% of the total copper. The free cupric ion (Cu2+) accounted for only 8% of the dissolved non-complexed inorganic fractio n, or less than 0.2% ofthe total copper in solution. (C) 1997 Elsevier Science Ltd.