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 chronic (8d) copper toxicity tests with the estuarine zooplankter, Eurytemora affinis and develop an acute-to-chronic ratio (ACR) for this species. Dissolved copper, copper speciation and organic complexation were measured on selected samples during these toxicity tests. Organic complexation 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 occurring during the first 48 hours. Due to the loss of dissolved copper during exposures, a decay model was developed to calculate the adjusted dissolved copper concentrations that were used to determine the final toxicity values. The 48h LC50, 96h LC50 and 8d chronic values were 83.0, 69.4 and 64 μg/L dissolved copper, respectively, using the adjusted 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-complexnd inorganic copper concentration was therefore a very small fraction of the total copper added during these experiments. Non-complexnd inorganic copper (II) speciation predicted by a model identified seven significant species of copper. 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-complexnd inorganic fraction, or less than 0.2% of the total copper in solution.