Mussels as Bioindicators: Effects of TBT on Survival, Bioaccumulation, and Growth Under Natural Conditions

During nine field-transplant experiments (1987–1990), juvenile mussels were exposed to mean tributyltin (TBT) concentrations from 2 to 530 ng l-1 for 12 weeks under natural conditions in San Diego Bay. Mussels were used as biological indicators and monitored for survival, bioaccumulation, and growth. Mussel growth was the primary biological response used to quantify TBT effects. Chemical analyses were used to estimate TBT contamination in water and mussel tissues. Integrating intensive measurements of chemical fate and biological effects increased the environmental significance of the data. Multiple growth measurements on individuals increased the statistical power. Size effects were minimized by restricting test animals to 10–12 mm in length, and methods were developed to minimize handling efffects. This monitoring approach also permitted documenting temporal and spatial variability in TBT and its effects that have not been previously reported. Survival, bioaccumulation, and growth were generally higher than predicted from laboratory studies. Survival was not directly affected by seawater or tissue TBT concentrations. Growth was significantly related to both seawater and tissue TBT, with the bioconcentration factor inversely proportional to seawater TBT concentration. Threshold concentrations always causing significant reductions in juvenile mussel growth are estimated at 100 ng l-1 TBT for seawater and 1.5 µg g-1 TBT for tissue, but growth could be affected by much lower concentrations of TBT under the most adverse conditions. Temperatures above 20°C were also found to reduce juvenile mussel growth rates.