Bioaccumulation and bioavailability of tributyltin chloride: Influence of pH and humic acids

The influence of pH and humic acids on bioaccumulation and bioavailability of tributyltin chloride (TBT) was studied in Daphnia and yolk sac larvae of fish Thymallus thymallus. In both organisms, bioaccumulation followed a first-order uptake process, and metabolism of TBT was slow. Bioconcentration factors in Daphnia and Thymallus were 198 and 2015, respectively. Uptake rates and bioaccumulation of TBT in Daphnia were significantly higher at pH 8.0, where TBT predominates as neutral TBTOH species than at pH 6.0, where it predominates as cation. Humic acids led to a decrease in TBT bioaccumulation at ≥ 1.8 mg·l−1 dissolved organic carbon (DOC) in Daphnia and ≥ 4.0 mg·l−1 DOC in Thymallus larvae. Bioaccumulation of TBT decreased with increasing concentrations of humic acids. Hence, chemical speciation of TBT is a determinant factor for the bioavailability, and thus bioconcentration and toxicity of this organotin compound.