The partition behavior of tributyltin and prediction of environmental fate, persistence and toxicity in aquatic environments

Tributyltin (TBT) is one of the most toxic anthropogenic compounds introduced into the aquatic environment. It has a relatively high affinity for particulate matter, providing a direct and potentially persistence route of entry into benthic sediments. To understand TBT behavior, computational programs are an exceptionally helpful tool for modeling and prediction. EPISuite program was used for evaluation of the prediction data including fate, persistence and toxicity from the partition coefficient values. Without experimental data, the model is useful for prediction but is essentially a default model. A site specific assessment is possible by measuring the partition coefficients and entering the experimental values obtained into the model. This paper describes the results of a study undertaken to determine the partition coefficients and the effect of various parameters on such partition coefficients. The octanol-water partition coefficient (Kow) was determined by the OECD shake-flask method, with the logarithm values obtained ranging from 3.9 to 4.9 depending on salinity. The sediment-water partition coefficient (Kd) was determined by ASTM method of generating Freundlich adsorption isotherms, the obtained values ranged from 88 to 4909 L kg1 depending on sediment properties, salinity, pH, and temperature. The experimental partition coefficient Kow and Koc (calculated from Kd) were used as input data into the prediction program to provide accurate values for the natural samples in situ. The experimental prediction showed lower toxicity than the default model, but represent actual toxicity and accumulation at the natural site. Moreover, the environmental fate was significantly different when the experimental values and the default values were compared.