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concentrations that were toxicologically hazardous to benthic fauna (Waldock and Thain 1983; Chau et al. 1984; Maguire et al. 1986). Tributyltin species can be accumulated from the sediments by oligochaetes (Tubifex tubifex, Limnodrilus hoffineisterii), thus making it potentially available to bottom-feeding fish; oligochae es can also degrade tributyltins by a sequential debutylation, with Tb- estimates of 5 months in water and 4 months in water-sediment mixtures (Maguire and Tkacz 1985). BIOLOGICAL Information on background concentrations of total tin in tissues of field populations of animals and plants was abundant, but few data were available on organotin species (Table 7). Tin concentrations in marine algae and macrophytes varied between 0.5 and 101 mg total Sn/kg dry weight and clearly demonstrated that most species of aquatic flora bioconcentrate tin from seawater (Table 7). Marine plants are also important in the cycling of tin. Living algae are effective in immobilizing tin from seawater and regulating the formation and degradation of toxic methyltin compounds (Donard et al. 1987). Dead and decaying algae accumulate inorganic and organotin compounds, release them, and ultimately remove tin from the estuary to the atmosphere by formation of tetramethyltins (Donard et al. 1987). Organotin content in fish tissues is quite variable,.ranging from a low of 3% to 6% of the total tin body burden (Tugrul et al. 1983) to 18% for goatfish (Upeneus moluccensis) to 52% for Mullus barbatus, another species of goatfish (Salihoglu et al. 1987). By contrast, the limpet (Patella caerulea) contains 35% to 75% of its total tin body burden as organotin (Tugrul et al. 1983). In January 1982, France banned organotin compounds for use in antifouling paints. By 1985, tin and organotin concentrations in seawater and. Pacific oysters (Crassostrea gigas) were 5 to IOX lower than those found in 1982 (Alzieu et al. 1986). In Arcachon Bay, France, a decrease in the incidence and extent of anomalies in oyster calcification mechanisms was noted that seemed to be correlated with decreases in tin contamination (Alzieu et al. 1986). Crassostreid oysters can accumulate radiotin (Sn-113) to a higher degree than other species of bivalve molluscs, a characteristic that may be useful as a bioindicator in the event of contamination due to this isotope (Patel and Ganguly 1973). Antifouling paints containing tributyltin compounds are used widely on netting panels of sea cages at fish and shellfish aquaculture units to minimize the obstruction of water exchange through the-cages (Davies et al. 1987). Under these conditions, tributyltin paints were detrimental to the growth and survival of juvenile scallops and to calcium metabolism and growth 27