Distribution of tributyltin chloride in laboratory simulated estuarine microcosms

The sorption of tributyltin (TBT) chloride from aqueous solution to sediment and partitioning between overlying water and pore water were investigated in both batch sorption experiments and laboratory simulated estuarine microcosms using the natural sediment collected from Tianjin Harbor. Sorption coefficients of 8862 l/kg at 25 degrees C and 7511 l/kg at 35 degrees C were respectively obtained from batch adsorption isotherms. Rates of adsorption and desorption in the sediment were fast with 98% of the maximum sorbed amount by the sediment and 80% of the equilibrium aqueous TBT concentration desorbed from the sediment achieved within 30 min. The sorption of TBT on the sediment was a reversible process. The rate of TBT partitioning into pore water was more rapid than the sorption process and the apparently fast rate of the sorption in the upper sediment was due to mixing between pore water and overlying water. Salinity had little effect on the sorption of TBT on the sediment while the partitioning coefficient between pore water and surface water decreased with increasing salinity. The pH had significant effects on both sorption on the sediment and partition into the pore water. A study in simulated estuarine microcosms indicated that TBT sorption on the sediment followed the process of TBT partitioning into the pore water after TBT rapidly disappeared from the overlying water. Microbial activity promoted the distribution of TBT in the pore water and sediment. Biodegradation of TBT to DBT, MBT and even inorganic tin occurred in the lower layers of sediment samples. (C) 2000 Elsevier Science Ltd. All rights reserved.