Sublethal Effects of Tributyltin on the Hard Shell Clam (Mercenaria mercenaria)

Chronic bioassays, lasting at least seven days, show that veliger stages of clams, Mercenaria mercenaria, are the most sensitive to exposure to tributyltin compounds (TBT). Post-set clams survived exposures up to g/l for 25 days. No veligers, the planktonic larval stage, however, survived seven days in 750 ng/l. Valve length of veligers, an index of growth, was statistically less than controls in concentratons of 50 ng/L and above on day 14 of development. When clam embryos are exposed to TBT, effects on subsequent stages are the most severe, suggesting that TBT exerts its most damaging effects very early in larval development. Data from these studies suggest that acute toxicity to clams would not occur in most habitats due to exposure to TBT from antifouling coatings. Sublethal effects, however, could result from lower exposures typical of some sites. Field observations to assess ecological consequences would be most useful to confirm risk estimates.