Comparative DNA damage and oxidative effects of carcinogenic and non-carcinogenic sediment-bound PAHs in the gills of a bivalve

Polycyclic aromatic hydrocarbons (PAHs) regarded as carcinogenic and non-carcinogenic to humans are ubiquitous hydrophobic pollutants that tend to be trapped in aquatic sediments. As a consequence of their acknowledged toxicity and pro-mutagenic or even carcinogenic potential, PAHs are deemed prioritary in biomonitoring programmes. Still, the differences between the toxicity of carcinogenic and non-carcinogenic PAHs are poorly known especially, when aquatic organisms are exposed to ecologically-relevant concentrations of these compounds in sediments. Laboratory bioassays with sediments spiked with phenanthrene (Phe) and benzo[b]fluoranthene (B[b]F), non-carcinogenic and carcinogenic PAH, respectively, were conducted and the effects of exposure (related to DNA damage and oxidative stress) were analyzed in the gills of a burrowing clam, Ruditapes decussatus (Bivalvia, Veneridae). To ensure ecological relevance, two contaminant concentrations (termed "low" and "high") were selected in accordance with available PAH sediment quality guidelines. The results showed that, even in "low" concentrations, both compounds caused a likely genotoxic effect in the gills, which is in accordance with the link between PAHs in water. Glutathione S-transferase activity and glutathione biosynthesis appear to be associated with limited lipid peroxidation even though they were insufficient to prevent higher and faster genotoxicity induced by exposure to the carcinogenic B[b]F, comparative to Phe. Overall the findings indicate that low concentrations of sediment-bound PAHs, carcinogenic or not, may be rendered significantly bioavailable to benthic filter-feeders as to induce genotoxicity, revealing that even PAHs considered non-carcinogenic to humans detain a latent, albeit significant, pro-mutagenic hazard to bivalve molluscs.