Toxicity of copper, lead, and zinc mixtures to Ceriodaphnia dubia and Daphnia carinata

Acute and chronic bioassays were conducted to determine the effects of copper, lead, and zinc mixtures on Ceriodaphnia dubia and Daphnia carinata. Copper, lead, and zinc combined at up to 5.2, 4.5, and 51.8 μg/L, respectively, did not cause significant mortality during acute exposures, although mixtures of 10.6, 9, and 101.1 μg/L and higher resulted in 65–100% mortality. Binary combinations of Cu+Zn (1.3+13.0 μg/L) and Cu+Pb (1.3+1.1 μg/L) and ternary combinations of Cu+Pb+Zn (1.3+1.1+13.0 μg/L) had a significant effect on reproduction of C. dubia. Toxic units and associated confidence intervals were calculated to characterize the nature of metal interactions. In most cases, and based on confidence intervals encompassing a value of 1, most of the metal interactions would be classified as additive. However, a more than additive effect was indicated by the acute tests for both species exposed to Cu+Pb, for D. carinata exposed to Cu+Zn, and for C. dubia exposed to all three metals.