Aqueous speciation and 1-octanol-water partitioning of tributyl- and triphenyltin: Effect of pH and ion composition

Due to their widespread use as antifouling agents in boat paints, tributyltin (TBT), and triphenyltin (TPT) have been found to be present in marine and freshwater ecosystems at concentrations exceeding acute and chronic toxicity levels. In order to assess the environmental behavior and particularly the bioavailability and bioaccumulation of these compounds, their aqueous speciation and partitioning behavior between nonaqueous phases and water need to be known. In this work, the effect of pH and of the concentration of various anions on the l-octanol-water partitioning of TBT and TPT has been systematically investigated. A simple model is presented that enables a quantitative description of the overall I-octanol-water distribution ratio of TBT and TPT as a function of pH and salt concentration. Acidity constants of 6.25 and 5.20 were determined for TBT a nd TPT, respectively. Furthermore, the aqueous phase complex formation constants with chloride, perchlorate, bromide, and nitrate as well as the 1-octanol-water partition constants of the corresponding complexes are reported. In addition,the Setschenov constants of TBT-and TPT-hydroxide have been determined for NaCl (0.6 and 0.4, respectively) and are estimated for other salts.