Long term behaviour and degradation kinetics of tributyltin in a marina sediment

One-meter sediment cores sampled in a marina have been submitted to extensive characterization and organotin speciation. Geochemical homogeneity has been demonstrated. Butyltin species are present at all depths with a predominance of TBT or MBT in the upper or lower layers, respectively. Seasonal variations of butyltin compounds have been identified and together with a knowledge of local conditions we estimate the sediment layers represent 14 years of deposition. A first order multi-step kinetic model of the sequential degradation of TBT in, successively, DBT, MBT and Sn (IV) is proposed. The half-life of TBT was estimated (on a 14-year period) to be 2.1 years and those of DBT and MBT (on a 5-year period) 1.9 and 1.1 years, respectively.