Tributyltin Effects on Juvenile Mussel Growth

Juvenile mussels (Mytilus edulis <20 mm) were exposed to three concentrations of tributyltin (TBT) in two site-specific, flow-through bioassays with unfiltered seawater. Mean TBT concentrations were 70, 80 and 200 ng/l in Test I (196 days) and 40, 50 and 160 ng/l in Test II (56 days). Treatments did not significantly affect juvenile mussel growth during the first 56 days of exposure in either test. After 63 days, all treatments significantly reduced growth in Test I. No significant mortalities occurred at any TBT concentration in either test. Increases in weights and lengths of Tank Control animals in Test II were much greater than during the first 56 days of Test I. Further, weight increases in the Pier Control were almost four times greater than in the Tank Controls during Test II. These data suggest that test animals were probably under significant stress induced by the Sioassay test system. The data also suggest that the effects of TBT on juvenile mussel growth may have been overestimated in this and other studies.