Combined toxicity of cadmium and lead on early life stages of the Pacific oyster, Crassostrea gigas

Trace metals cause toxic effect on the early development period of marine animals, however only few studies address the toxic interactions of trace metals on bivalves. In the present study, the individual and combined toxicities of dissolved cadmium (Cd) and lead (Pb) on early life stages of the Pacific oyster Crassostrea gigas have been investigated. Embryotoxicity, larvae mortality and genotoxicity were measured under single and combined exposure of the two tested metals. For embryotoxicity, the median effective concentration (EC50) values for individual Cd, Pb and their mixture were of 272.2 mu g/L, 660.3 mu g/L and 373.1 mu g/L, respectively. The median lethal concentrations (LC50) for 96 h larval mortality were determined to be 353.3 mu g/L, 699.5 mu g/L and 205.5 mu g/L for individual Cd, Pb and their mixture, respectively. Moreover, the Marking-Dawson additive toxicity indices were 0.10 for embryogenesis and 1.40 for larval mortality indicating, respectively, an additive effect and a trend to synergism for the Cd and Pb combination. Furthermore, DNA strand breaks were observed in oyster embryos after individual Cd, Pb and their mixture exposure, and a significant positive correlation was demonstrated between embryotoxicity and genotoxicty. The current study suggests the toxicity of Cd is higher than that of Pb, and the Cd-Pb mixture is slightly more toxic than individual Cd or Pb to the Pacific oyster. These data will be helpful to predict the toxicity of metal mixtures, and provide biological criteria for the implementation of marine water quality standards to protect these marine organisms.