Relative sensitivity distribution of freshwater planktonic crustaceans to trace metals

Cladocerans and copepods are common inhabitants of ponds and lakes, but assessments of the toxic effects of chemicals on aquatic organisms are often based mainly on toxicity data for cladocerans of the genus Daphnia. The paucity of toxicity data for copepods and other species of cladocerans raised the question whether toxicity data derived primarily from daphniids can be extrapolated to protect other planktonic organisms. In this study, we address this question by systematically comparing between the sensitivities of cladocerans and copepods to the metals Cd, Cu, Pb, Ni, and Zn using the species sensitivity distributions. Our results indicate that cladocerans are consistently more sensitive than copepods to Cd and Cu. Most importantly, sensitivities of D. magna, D. pulex, and Ceriodaphnia dubia, the three most commonly tested cladocerans, to these metals are higher than those of most copepod species and fall within the range of those exhibited by other cladocerans. C. dubia, a cladoceran with relatively small body size, is more sensitive to all metals than most other cladoceran species. Our results imply that water quality criteria of trace metals derived from datasets dominated by Daphnia are likely also protective to copepods and most other cladocerans.