Experimental factors that may affect toxicity of aqueous and sediment-bound copper to freshwater organisms

Because of recent concerns regarding the ability of acute (48-96 h) sediment toxicity tests to accurately assess the potency of sediment-bound contaminants, effects of exposure duration, test organism selection, and test endpoint on the observed toxicity of aqueous phase copper and a copper-contaminated freshwater sediment were evaluated. Toxicity of sediment-bound copper was assessed by monitoring survival and reproduction of Ceriodaphnia dubia Richard, survival of Daphnia magna Straus and Hyalella azteca Saussure, and survival and growth of Chironomus tentans Fabricius and Pimephales promelas Rafinesque. Organisms were exposed in static systems for 48 h, 96 h, 7 d, 10 d, and 14 d, which enabled measurement of acute and chronic toxicity. Relative sensitivities of test organisms exposed to copper in water and copper-contaminated sediment varied with test duration and test endpoint. In general, C, dubia was the most sensitive organism tested, followed in decreasing sensitivity by D. magna, P. promelas, H. azteca, and C. tentans. A temporal mortality threshold was demonstrated by C. dubia and D. magna when exposed to copper, with little mortality occurring after 96 h of exposure. Effects of test duration on copper toxicity were most pronounced for H. azteca and C. tentans, with mortality and growth effects becoming increasingly sensitive with increasing test duration. Formulated sediment served as a suitable control and reference sediment in this study, and matched a variety of field-collected test sediment characteristics. In tests utilizing copper-contaminated sediments, observed responses (mortality, growth, reproduction) corresponded with overlying water concentration of copper rather than concentration of copper in bulk sediment or pore water.