Combined Toxicity of Lead and Cadmium on Embryogenesis and Early Larval Stages of the European Clam Ruditapes decussatus

Individual and combined toxicities of lead (Pb) and cadmium (Cd) were investigated using sperm motility and embryo-larval bioassay of the clam Ruditapes decussatus. Fertilization and embryogenesis success and larval mortality were recorded after incubation of sperm (during 30 min before use for insemination), fertilized eggs (24 h) and D-shaped larvae (96 h) in seawater, both with single metals and combinations of the two tested metals. In spermiotoxicity bioassays, these metals, both individually and in combination, significantly (p < 0.05) reduced the fertilization rate only at two higher concentrations that were studied. Median effective concentration (EC50) values were 1033 mu g/L (5 mu M), 2098.5 mu g/L (18.6 mu M), and 1442 mu g/L (10.8 mu M), respectively for individual Pb, Cd, and the mixture (Pb + Cd). Embryogenesis success was also noticeably affected by the single metals and their mixture. Median effective concentrations (EC50) values were 256.5 mu g/L (1.24 mu M), 570.9 mu g/L (5.08 mu M), and 355.4 mu g/L (2.68 mu M), respectively for individual Pb, Cd, and the mixture (Pb + Cd). Median lethal concentration (LC50) for 96 h larval mortality bioassay registered for individual Pb, Cd, and for the mixture were 453.6 mu g/L (2.2 mu M), 877.8 mu g/L (7.8 mu M), and 565.6 mu g/L (4.3 mu M), respectively. Marking-Dawson additive toxicity indices were 0.01, 0.08, and 0.18, respectively, for spermiotoxicity, embryotoxicity, and larval mortality tests, indicating additive effects with a slight trend toward synergism, which was statistically significant only for larval mortality. This work shows that both clam embryos and larvae bioassays are useful tools that can be used to evaluate toxicity of field samples of seawater, sediments, and effluents containing several toxicants.