Toxicity of mechanically and chemically dispersed oils in marine organisms

Oil spills can seriously affect marine environment causing toxicity through physical smothering and carcinogenic effects of their constituents, particularly polycyclic aromatic hydrocarbons (PAHs). The use of dispersants is often presented as a rapid technique to reduce the oil slick, by promoting its dispersion in the water column, but a similar approach is highly controversial and debated for potential synergistic effects of dispersants, and the possible increase in PAHs bioavailability and toxicity. Italian legislation considers chemical dispersion as the last option, and candidate products need to be previously characterized The required analyses, however, consider the ecotoxicological potential of the dispersant alone. The aim of this study was to provide an integrated approach, considering interactive effects of chemical dispersants and oil on bioaccumulation, early biochemical and cellular effects in different tissues of Mytilus galloprovincialis, and acute toxicity in different target species. Therefore, mussels were exposed for two days to dispersant alone, mechanically and chemically dispersed oils, followed by a recovery in clean seawater. At different times, results on bioaccumulation of PAHs and biomarker responses were combined with those of a battery of ecotoxicological bioassays, and elaborated within a multidisciplinary Weight Of Evidence (WOE) model to obtain an index of risk for the different treatments and times. The results show that the dispersant favours the bioaccumulation of PAH in M. galloprovincialis in the presence of the two oils followed by a slow return to the initial conditions; transient effects was found in some biomarkers; the ecotoxicological bioassays confirm the highest toxicity of the oils+dispersant compared to oils dosed alone. The WOE model confirm a greater risk associated with chemically dispersed oils. This research gave a more realistic point of view, suggesting a more articulated and integrated evaluation of eligibility of dispersant products, differently from that currently considered by Italian legislation.