Uptake, tissue distribution and metabolism of 14C-labelled tributyltin (TBT) in the dog-whelk, Nucella lapillus

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Abstract
A study of tributyltin (TBT) uptake, tissue distribution and breakdown in dog-whelks, Nucella lapillus, was carried out using 14C-labelled tributyltin chloride. The compound was introduced into animals by exposure to sea-water, from a diet of labelled mussels and by injection. Measurements of 14C were made on tissue extracts containing total 14C, TBT+DBT and TBT. Organs examined included digestive gland, kidney, mantle, foot, viscera, gonads and blood. Absorption of dissolved TBT occurred primarily via tissues associated with the mantle: autoradiographic evidence showed that of these the ctenidium (gill) and osphradium were probably most important. Of non-reproductive tissues, mantle displayed least evidence of TBT degradation whereas kidney and digestive gland contained lower proportions of 14C as TBT (~60%) than other tissues. By virtue of its more rapid response, initially at least, the kidney had a primary role in degrading dissolved TBT that reached the blood. Dog-whelks feeding on labelled Mytilus edulis absorbed organotins very efficiently via the digestive gland, which then played a major role in TBT breakdown. However, the capacity for degradation is not sufficient to prevent, TBT concentration factors of the order of 100,000 (dry tissue/water) being attained in N. lapillus. Autoradiography revealed surprisingly high grain-counts in nerves, which may be significant in view of evidence in the literature that neurohormones are intermediaries in the chain linking TBT with imposex.