Parameters controlling the partitioning of tributyltin (TBT) in aquatic systems

Abstract

In the present study the distribution of TBT between solid and water phase as a function of several parameters was determined. Two types of clay minerals (Na-montmorillonite SWy and kaolinite KGa) and quartz sand were used as sorbents in conventional batch experiments. Sorption coefficients (Kd) followed the order montmorillonite (89 l/kg) > kaolinite (51 l/kg) > quartz (25 l/kg), while for sorption coefficients normalized to the surface area (Kd′) an opposite trend was observed, with the lowest value determined for montmorillonite (2.79 × 10−3 l/m2) and the highest for quartz sand (8.04 × 10−2 l/m2). The results demonstrate that numerous environmental parameters influence the adsorption process of TBT, such as solid/solution ratio, clay content and salinity. Another important factor governing TBT adsorption is pH, because it affects both the TBT species in the water phase as well as the surface properties of the mineral phase. The maximum of TBT adsorption onto clays was always around pH 6–7. According to the data, it is evident that the content of organic matter in the solid phase plays an important role on TBT adsorption, either as particulate organic matter (POM) or organic matter adsorbed to mineral particles (AOM). Experiments were carried out with well characterized organic matter and the results showed a linear increase of Kd from 51 up to 2700 l/kg upon the addition of 5% of particulate organic matter to pure phased kaolinite. TBT adsorption onto mineral surfaces, which were previously enriched with adsorbed organic matter, was investigated at different pH. The present study points to the importance of identifying and characterizing sorbents and envrionmental conditions, in order to predict and model TBT distribution in natural systems.