The toxic effect of trialkyltin compounds is used in antifouling paints to protect vessels against biofouling organisrns. Tributyltin oxide (TBTO) or fluoride (TBTS) leaches by diffusion from the paint layer into the seawater. Trialkyltin compounds in aqueous solutions are resistant to hydrolysis and biodegradation, but are rapidly converted into diakyl, monoalkyl and inorganic tin by UV irradiation. As inhibiting agents of the oxidative phosphorylation, organotin compounds are extremely dangerous for aquatic organisms such as molluscs. The following estimated toxicity levels for Crassostrea gigas oyster larvae have been put forward : at 100 µg.l(1) the fecondation is inhibited, at 10 µg.l1 the already of 20 % of the eggs is affected larval development is inhibited at 1 µg.1(1) and already affected at 0.1 µg.l(1)