Immunotoxic effects of the antifouling compound Sea-Nine 211TM on haemocytes of an edible bivalve mollusc.

The present work is inserted in a wider research context focused to the study of the effects of antifouling biocides, recently introduced in paint formulations, on various filter-feeding benthic invertebrates largely spread in the lagoon of Venice, i.e. tunicates, sipunculids and bivalves. In particular, we considered the new compound Sea-Nine 211TM (4,5-dichloro-2-n-octyl-4-isothiazolin-3-one), recently introduced as a primary biocide in the formulations of the antifouling paints for the boat hulls in place of the organotin compounds, which were banned by IMO after 2003 due to their high toxicity towards many not-target aquatic organisms. In the lagoon of Venice, the edible Manila clam Tapes philippinarum was imported in 1980s for a commercial use and now is diffused with increasing populations which compete with those of the autochthonous congener species. Research was carried out with a series of acute toxicity assays using short-term haemocyte cultures (60 min at 25 °C) exposed to various sublethal Sea-Nine 211TM concentrations ranging between 0.1 and 25 µM. Results regard the influence of this xenobiotic on both cytoenzymatic and cell functionality indexes that allowed to know immunosuppressant mechanisms at the cellular level and possible molecular interactions. Although no effect on cell adhesion was observed, severe and irreversible morpho-functional effects like those reported for organotin compounds occurred. In particular, at 1 µM Sea-Nine 211TM exerted significant (p < 0.001) inhibitory effects on cell spreading, yeast phagocytosis, hydrolytic enzyme (β-glucuronidase) activity, induced apoptosis and caused an oxidative stress, the latter evaluated through a decrease in cytoplasmic glutathione content. Our data suggest that this biocide, specifically introduced as an alternative to organotin compounds, is immunotoxic. Since immunosuppression makes organisms more sensitive to both microbial infections and other environmental xenobiotics increasing risk for animal survival and the mechanisms of action of Sea-Nine 211TM are still unknown, this xenobiotic does represent a potential risk for benthic filter-feeding invertebrates living in the water-sediment interface. T. philippinarum does rapidly bioaccumulate great amounts of xenobiotics, thus increasing attention to human health. Nevertheless, due to its high sensitivity, this species can be also employed as useful biosensor in marine pollution monitoring for a wide range of contaminants in lagoon environments. This work was supported by grants of Co.Ri.La.