Immunotoxicity of new antifouling compounds, alternative to TBT, on tunicate haemocytes.

Xenobiotics, which cause severe alterations of the immune responses, can provoke the death of individuals and the local disappearance of the involved species. Organotin compounds were massively introduced since the second half of 1960s in the formulation of antifouling paints for the preservation of submerged structures from the settlement of various aquatic sessile organisms. They resulted highly immunotoxic to benthic marine invertebrates, in particular filter-feeding ones, and most of them persist for a long time in the environment. After their ban, industries turned their attention to new biocidal combinations. About twenty new substances are at present in commerce in Italy in various paint formulations, in which the biocidal compounds play various roles, i.e. as alternative substances to TBT or as boosters to increase the toxic performance of the main biocides towards a wider spectrum of fouling organisms. We carried out assays of acute toxicity on shortterm cultures of haemocytes of the colonial ascidian Botryllus schlosseri to evaluate the alterations of the immune responses, as described by a series of biomarkers, by sublethal concentrations of seven active ingredients employed in the formulation of new antifouling paints. Results indicate severe and irreversible effects on immunocyte morphology and functionality with mechanism of action sometimes similar to that of TBT, i.e. induction of apoptosis, cytoskeletal protein disassembly, inhibition of both phagocytic and cytotoxic ability, negative interactions with mitochondrial oxidative phosphorylation, cytosolic Ca2+ homeostasis and GSH content. The comparison of our results suggests the following order of immunotoxicity: TBT ~ Cu(I) ~ ZnP > Sea-Nine 211 ~ Chlorothalonil > TCMS pyridine > Diuron > Irgarol 1051. Owing to the immunosuppressive effects of these compounds on tunicates, which make organisms more vulnerable to both pathogenic agents and other xenobiotics, we remark that more assays of acute and chronic toxicity should be necessary before leading new potentially pollutants into the market, in order to prevent the repetition of the irreversible errors on coastal biocoenoses already occurred with TBT. [This work was supported by grants of Co.Ri.La.]