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the total world production, although use of R SnX types as selective biocides <br />has increased disproportionately in recent yeas (Davies and Smith 1982). Tin <br />now has more of its organometallic derivatives in commercial use than any <br />other element (Blunden et al. 1985). <br />Biocidal applications of organotins to control marine fouling <br />communities, agricultural pests, and as selective molluscicides merit brief <br />additional comment. The use of antifoulants on ships is necessitated by the <br />damage some organisms can cause to wooden structures and by the reduced fuel <br />efficiency and speed due to drag when vessels become heavily fouled (Laughlin <br />et al. 1984). Until recently, the most widely used antifouling paint <br />contained a copper base that is biocidally active when copper leaches as an <br />ion from the paint (Hall et al. 1987). However, short effective lifetimes and <br />high costs have limited the usefulness of copper-based paints. <br />Organocompounds of arsenic, mercury, or lead have also been used in <br />antifouling paints, but these paints have been removed from the commercial <br />market due to the toxicological risks during preparation and application and <br />to their hazards to the environment (Blunden et al. 1985; Hall et al. 1987). <br />Organotin coatings are currently promoted because of their excellent <br />antifouling action, long lifetime (up to 4 years), and lack of corrosion <br />(Messiha and Ikladious 1986). Organotin coatings, especially tributyltins, <br />present potential environmental problems to nontarget aquatic biota due to <br />their extreme toxicity. <br />Use of organotin antifouling paints on recreational and commercial water <br />craft has increased markedly in recent years. In Maryland, for example, 50% <br />to 75% of the recreational boats used in Chesapeake Bay are covered with <br />organotin paints (Hall et al. 1987). The organotin biocide released by <br />hydrolysis from the surface of the paint film into seawater provides the <br />antifoulant action. In consequence, the depleted outer layer of paint film, <br />containing hydrophilic carboxylate groups, is easily eroded by moving seawater <br />exposing a fresh surface layer of organotin acrylate polymer. In continuing <br />tests by the U.S. Navy, ablative organotin fouling coatings have demonstrated <br />more than 48 months of protection (Blunden et al. 1985). As discussed later, <br />the use of organotin compounds in antifouling paints has been severely <br />curtailed. Several organotins have been used extensively as agricultural <br />pesticides, especially tricyclohexyltin and triphenyltin compounds (Hunter <br />1976; Kumpulainen and Koivistoinen 1977; Blunden et al. 1985). In general, <br />these compounds showed low phytotoxicity, low toxicity to nontarget organisms, <br />no evidence of development of resistant insect strains, and degradation to <br />form harmless tin residues. It is probable that agricultural uses of <br />organotins will increase. The toxicity of triorganotin compounds to aquatic <br />invertebrates, especially slow release formulations of tributyltins, is <br />usually high, and this property has been used advantageously to eradicate <br />certain species of freshwater snails that are intermediate vectors of <br />schistosomiasis, i.e., Biomphalaria spp., Bulinus spp. (Chliamovitch and Kuhn <br />1977; CEC 1978; Duncan 1980; Seinen et al. 1981). Unfortunately, nontarget <br />biota, including some sensitive species of fishes, are killed at recommended <br />16