Histopathological study of Poecilia reticulata (guppy) after long-term exposure to bis(tri- n-butyltin)oxide (TBTO) and di- n-butyltindichloride (DBTC)

Abstract

The histopathologic effects in the small fish species Poecilia reticulata (guppy) were investigated after exposure to the biocide bis(tri- n-butyltin)oxide (TBTO), a contaminant of the aquatic environment. At the age of 3–4 wk animals were exposed to concentrations ranging from 0.01–32 μg TBTO/l over 1 and 3 months. In a comparative study young guppies were exposed to di- n-butyltindichloride (DBTC) for 1 month at a concentration range of 320–3200 μg/l. Both compounds induced thymus atrophy, hyperplasia of hemopoietic interstitial tissue of the kidney, and increase in number of free peritoneal cells in the body cavity, which were probably neutrophilic granulocyte analogs. In the liver vacuolation was increased, predominantly due to accumulation of fat and of glycogen; also muscle glycogen was increased. Effects of DBTC occurred at concentrations which were almost three orders of magnitude higher than of TBTO, and there were no indications that the TBTO-induced thymus atrophy is caused by the DBT-metabolite. In addition, at the higher concentrations of TBTO epidermal hyperplasia and keratitis occurred, as well as changes in the rods and cones layer of the retina. The ‘no-observed-effect’ concentration of TBTO was 0.01 μg/l, based on thymus atrophy, liver vacuolation or hyperplasia of the hemopoietic tissue, and this was 30-fold lower than when based upon classical toxicological criteria (growth). In the DBTC study, thymus atrophy was still present in the lowest concentration tested (320 μg/l) whereas the NOEC for mortality and behavior was 1800 μg/l. Atrrophy of the thymus, keratitis and skin irritation seem to be similar effects as found in mammals. It is concluded that long-term low dose TBTO-exposure of guppies causes thymus atrophy, increase in granulocytes, accumulation of glycogen and fat in the liver, and changes in cornea, retina and skin; except for the changes in the eye and skin, similar effects were induced by DBTC, although at manyfold higher concentrations.