Relationships between contaminant levels in marine sediments and their biological effects on embryos of oysters, Crassostrea gigas

Surface sediment samples from 10 coastal locations were analyzed with respect to their physical and chemical characteristics as well as their biological quality. The toxicity of the decanted fresh and freeze-dried sediments and of their elutriates was assessed by bioassays with embryos of the oysters Crassostrea gigas. The concentration inhibiting normal embryogenesis in 20% of the larvae (EC20) was used as a measure of toxicity and compared with the physical and chemical properties of the sediments and elutriates by principal components analysis. Decanted whole sediments were one to four orders of magnitude more toxic than their elutriates because the latter have lower contaminant concentrations. The biological effects of decanted whole sediment depended mostly on the levels of heavy metals and polycyclic aromatic hydrocarbons (PAHs), while in the case of the elutriates, the toxicity was mainly correlated with the concentrations of total ammonia and of dissolved organic carbon (DOC). Freeze-dried sediments and their elutriates were up to one order of magnitude more toxic than fresh sediments and elutriates, respectively, presumably because the freeze-drying procedure increases pollutant bioavailability or causes a release of unidentified organic compounds having toxic effects.