Accumulation of Organotin Compounds in the Deep-Sea Environment of Nankai Trough, Japan

Abstract

The concentration of butyltin (BT) and phenyltin (PT) compounds was measured in sediment, gastropods (Colliloconcha nankaiensis), sea cucumbers (Psychropotes verrucosa), galatheid crabs (Munidopsis albatrossae and Munidopsis subsquamosa), and bivalves (Clyptogena tsubasa and Clyptogena nautilei) collected from the Nankai Trough (water depth about 3000 m). Sediment at depths of up to 1 cm was taken by a core sampler and at depths of up to 15 cm was taken by rake. The concentration of BTs in sediment core from a depth of 0-1 cm (0.041 mg kg(-1) dry) was higher than in sediment core from 0-15 cm (0.021 mg kg(-1) dry). The relative proportion of different BTs in the 0-1-cm sediment core was similar to that in the 0-15-cm sediment core, but the concentration of PTs in the former (0.028 mg kg(-1) dry) was lower than in the latter 0-15 cm (0.052 mg kg(-1) dry). Organotin (OT) compounds were also detected in deep-sea organisms. The means of BT concentrations in C. nankaiensis, P. verrucosa, M. albatrossae, M. subsquamosa, Cl. tsubasa, and Cl. nautilei were, respectively, 0.089, 0.057, 0.018, 0.016, 0.019, and 0.026 mg kg(-1). The corresponding concentrations of PTs were 0.212, 0.363, 0.166, 0.186, 0.030, and 0.025 mg kg(-1). High concentrations of BTs and PTs were observed in gastropods and sea cucumbers. The species of deep-sea organism can be classified by delta(13)C value into two groups (A and B). The organisms in group A use organic matter chemosynthesized by symbiotic bacteria while those in group B depend on photosynthesis carried out near the surface by phytoplankton. No difference in BT or TBT concentration is observed between the two groups, but PT and TPT concentrations are higher in group B. Trophic levels in the food chain are often estimated using delta(15)N values. Group B showed a higher trophic level than group A. Although no change in BT and TBT concentration was observed to accompany increases of delta(15)N values, PT and TPT concentrations generally increased with increasing delta(15)N values. The compositions of BTs in deep-sea organisms were calculated. An increasing proportion of MBT and a declining proportion of DBT were observed at higher trophic levels. No correlation between the shell length of Cl. nautilei and BT or PT concentration was observed. The average partition coefficients of TBT for C. nankaiensis, P. verrucosa, M. albatrossae, M. subsquamosa, Cl. Tsubasa, and Cl. nautilei were 2.6, 0.72, 0.63, 0.19, 0.43, 0.30, and 0.46.