High Percentage of Butyltin Residues in Total Tin in the Livers of Cetaceans from Japanese Coastal Waters

There have been few reports on quantitative discussion of organic tin compounds based on total tin in environmental media and biota. The present study determined concentra tions of total tin (∑Sn = organic + inorganic) and butyltin compounds (∑BTs = MBT + DBT + TBT) in the livers of cetaceans collected from Japanese coastal waters in order to estimate the ratio of ∑BTs:∑Sn and to elucidate the role of anthropogenic butyltins in the view of total tin accumulation in these higher trophic organisms. Additionally, some cetacean species from open seas and oceans were also subjected to analyses for comparison purposes. Higher concentrations of ∑Sn and ∑BTs were found in coastal species than in offshore species, indicating greater input of tin compounds in coastal waters surrounding Japan. ∑Sn concentrations increased with an increase in ∑BTs residues in all species analyzed ( r = 0.95, p < 0.001). Furthermore, ∑BTs made up considerably higher percentages of the hepatic ∑Sn in coastal species, with up to 74% in finless porpoise ( Neophocaena phocaenoides ) and 90% in bottlenose dolphin ( Tursiops truncatus ). These findings suggest that hepatic tin in coastal cetaceans predominantly exists in organic form such as butyltin compounds, implying that tin residues in marine mammals reflect mostly the input from anthropogenic sources. Despite some similar features expected between the residues of tin and mercury, anthropogenic exposure to tin compounds seems to be more apparent than exposure to mercury, which generally originates from natural exposure.