Immunotoxic effects of organotin compounds in Tapes philippinarum

Since 1970 in Italy the cultivation of Tapes philippinarum has experienced a rapid expansion in the lagoons and along te coasts of the Northern Adratic Sea, with important economic and social implications. This type of bivalve culture, however, has developed without a precise plan and the necessary technical assistance. Over the past few years, in parallel with the diffusion of this and other types of mollusc cultures the need to acquire a better knowledge and control of the lagoon environment has arisen. A remarkable problem is the superposition of areas with intense maritime activity and agricultural exploitation with those of mollusc cultivation. Among the main pollutants concerning these areas organotin compounds (OTC) represent one of the most harmful group of substances both for mollusc cultivation and human health, since bivalves are filter-feeding organisms which rapidly bioaccumulate the environmental contaminants. With the aim to study the effects of OTC - already reported to be immunotoxic in mammals - in T. philippinarum, we have investigated whether they exert an immunosuppressant role also on in vitro yeast phagocytosis by haemocytes of this species. The phagocytic index is significantly reduced by OTC in an irreversible manner and depends on concentration and lipophilic affinity, but neither cell mortality nor cytolysis occur. For butyltin compounds, which are used as biocides in antifouling paints, the order of inhibition is TBT > DBT > MBT (p < 0.01 for 0.05 µM TBT and DBT, p < 0.001 for 0.1 µM MBT). For triphenyltin compounds, which are used as agriculture pesticides against cercosporiasis of sugar beet, the order of inhibition is TPTC > TPTA > TPTH (p < 0.05 for 0.01 µM TPTC and for 0.05 µM TPTA and TPTH). As this test is rapid and easily reproducible, it can effectively applied together with other ecotoxicological bioassays in evaluation studies of OTC environmental impact.