Organotin and osmoregulation : quantifying the effects of environmental concentrations of sediment-associated tri-n-butyltin and triphenyltin on osmoregulatory processes in the European flounder Platichthys flesus (L)
The disruption of physiological and morphological aspects of osmoregulatory processes in freshwater-adapted 0-group European flounders, Platichthys flesus (L.), caused by exposure to environmental concentrations (150 ng triorganotin g"1 dry weight sediment) of sediment-associated tri-o-butyltin chloride (TBTCl) and triphenyltin chloride (TPhTCl), was examined and quantified. Radiotracers were used to measure hydromineral fluxes, the water balance and passive sodium efflux of chronically (35 days) exposed fish. The water permeabilities of exposed flounders varied during the course of the experiment and were significantly lower than the corresponding controls, that did not change significantly with time. It was found that the maximum change in water permeability of TBTCl- and TPhTClexposed fish occurred after 14 days and 21 days, respectively; thereafter there was an increase towards control values, suggesting adaptation to compensate for the effects of the organotin exposure. Drinking rates increased significantly in both organotin groups but urine production rates did not change. The effects of organotin exposure on the passive sodium efflux and Na+/K+-ATPase activity showed an inverted relationship in the TBT group, where the Na7K+-ATPase activity was reduced and the passive sodium efflux was increased. TPhT had no inhibitory effect on Na7K+-ATPase activity and the passive sodium efflux increased only gradually. The overall effect of these changes in these components of hydromineral regulation was to reduce the mean blood osmolalities of the organotin groups compared to the control values. The effects of chronic exposure to sediment-associated triorganotin compounds during sea water adaptation was examined and quantified by measuring the active sodium efflux, Na+/K+-ATPase activity and structural changes to the gill epithelium usually encountered in euryhaline fish during adaptation to sea water. Following the transfer to sea water, the Na+/K+-ATPase activity and the active sodium efflux were decreased in the TBT group but increased significantly in both the TPhT and control groups. Similarly, the morphological changes to the gill epithelium, involving chloride cell distribution, associated with sea water adaptation, took place in the control group and only partially in the TPhT group but were significantly inhibited or delayed in the TBT group. The exposure to organotin caused the mean blood osmolalities in fish of the TBT and TPhT to rise beyond the expected values that were observed in the control group. The results presented in this study lead to the conclusion that tri-tt-butyltin chloride and triphenyltin chloride in sediments are capable of significantly disrupting both the physiological as well as morphological components of osmoregulatory functions of an estuarine fish, at concentrations currently found in local sediments.