Sediment-associated tri-n-butyltin chloride and its effects on osmoregulation of freshwater-adapted 0-group European flounder, Platichthys flesus (L.).

The disruption of osmoregulatory processes was examined in European flounders exposed to environmental concentrations (150 ng TBTCl g(-1) dry weight sediment) of sediment-associated tri-n-butyltin chloride (TBTCl), by using radiotracers to measure changes in hydromineral fluxes and water balance. The water permeabilities of TBTCl-exposed fish varied during the course of the experiment and were significantly lower than those of the corresponding controls that did not change significantly with time. It was found that the maximum decrease in water permeability of TBTCl-exposed fish occurred after 14 days; thereafter there was an increase towards control values. However, there was a differential reduction of the diffusional (P(d)) and osmotic (P(os)) permeability coefficients, where the former decreased more rapidly than the latter, reflecting the reduction of diffusional membrane permeability and the increasing importance of osmotic permeability. In fish exposed to TBTCl sodium efflux and drinking rates were significantly increased but Na(+)/K(+)-ATPase activities and urine production rates were not affected. The effects of TBTCl exposure are also manifested at the level of the whole organism by a reduction in the increase of the body length of exposed fish, when compared to controls. It was concluded that tributyltin-n-chloride in sediments is capable of significantly disrupting the osmoregulatory functions of a benthic estuarine fish, at concentrations found in the sediments of Southampton Water and the River Itchen.