Tributyltin (TBT) compounds, which are a subgroup of the organotin family of compounds, were contained in antifouling paints for ship hull and fishing net from the mid-1960s to 1990s. TBT has caused severe adverse ecological effects; one of them is irreversible imposex development in the rock shell, Thais clavigera.
Environmentally discharged TBT is highly accumulated in harbor sediments because it is highly hydrophobic and persistent in sedimentary environments. The yearly trends of TBT concentrations in the sediments of major harbors in Japan have been monitored and hot-spots of TBT have been determined by the Ministry of Land,
Infrastructure and Transport and the Ministry of the Environment. In order to assess the risk of TBT in the environment, many physico-chemical characteristics and the fate of TBT in sedimentary environments have to be evaluated. Among them,the adsorption characteristics of TBT onto harbor sediments are in strong need of
analysis. Many previous studies have applied quartz sand or kaolinite for TBT adsorption experiments, however, there is still little information available for organic rich sediments. Moreover,previous studies have shown a few orders of magnitude difference in sediment-water partition coefficient Kd.
　Based on these backgrounds, this research aimed at the assessment of the adsorption characteristics of TBT, DBT (dibutyltin) and MBT(monobutyltin) compounds onto organic-rich harbor sediments.0.04-5.0g dry sediment samples from Tagonoura, Minamata and Nagoya harbors and sand samples from Banzu tidalflat and Toyoura seacoast were mixed with 40mL ultrapure water in 50mL centrifuge tubes with pH and salinity control. TBT standard solution or equimolar mixture standard solution of TBT,DBT and MBT were added in the tubes. The tubes were shaken for 20 hours under room temperature and dark condition and then centrifuged. Quantifications of TBT, DBT and MBT concentrations in the separated water and sediment samples were performed by GC-ICP-MS.
　The dominant parameter for adsorption of TBT was found to be TOC concentration, with compared to other parameters: doping concentration, temperature, salinity and pH. The adsorption capacity was observed to be varied with C/N ratio which reflects the composition of organic contents. The observed Kd values were higher than that from Meador's equation, because of richness of TOC in harbor samples and coexistence of DBT. Kd was also confirmed to be sensitive with temperature. The sensitivity of Kd with salinity and pH was little for organic-rich sediments while considerable sensitivity was observed for organic-poor sediments.