Urgent caution to trace organometal pollution: Occurrence, distribution and sources of methyltins, butyltins and phenyltins in sediments from South Hangzhou Bay, China.

The concentrations of seven organotin compounds (OTCs) were determined seasonally in 22 sediment samples (brackish, freshwater and shrimp pond sediments) in South Hangzhou Bay, China. For the brackish and freshwater sediments, methyltins of up to 43.0 ng Sn g-1 dw showed no significant variation with seasons or locations (p > 0.05). However, butyltin levels in summer (44.0 ± 30.2 ng Sn g-1 dw) were about two folds higher than those in spring (20.4 ± 18.7 ng Sn g-1 dw) and four folds higher than in autumn or winter (both≈10 ng Sn g-1 dw), which is mainly attributed to the heavy contamination near the shipyard, mariculture and textile plants in summer. Phenyltins in spring reached the peak level of 28.4 ng Sn g-1 dw, about three times of other seasons. Meanwhile, there was a significant variation of phenyltins in summer with high-value sites also in the vicinity of mariculture. Thus, excepting the contribution of agricultural activities to phenyltins, mariculture is likely to be a potential source of butyltins and phenyltins into the marine environment (particularly in summer). This hypothesis has been partly validated by determining adjacent shrimp pond sediments, which showed ubiquitous contamination of butyltins and phenyltins in summer and spring (14.2-44.2 ng Sn g-1 dw and 2.2-16.9 ng Sn g-1 dw), but only one sample had the detectable methyltin levels with 8.8 ng Sn g-1 dw of momomethyl-tin. On the other hand, seven OTCs showed a stronger affinity to brackish sediments than the adjacent freshwater sediments, probably owing to the differences of physicochemical parameters and microbial activities in sediments. Overall, OTC contaminants have become more diversified and complicated in coastal zones, suggesting that future studies should pay attention to other OTC species like phenyltins and methyltins, not only the butyltins.