ALTERATION OF [C-14]-TESTOSTERONE METABOLISM AFTER CHRONIC EXPOSURE OF DAPHNIA-MAGNA TO TRIBUTYLTIN

Tributyltin (TBT) is a marine biocide that has been shown to alter the activity of cytochrome P450 monooxygenases and elicit toxicity indica tive of androgenization in some species. The present study was conduct ed to determine whether TBT altered P450-, reductase-, and transferase -mediated testosterone metabolic processes in Daphnia magna at subleth al exposure concentrations. Two generations of daphnids were continuou sly exposed for 21 days to nominal TBT concentrations ranging from 0.3 1 to 2.5 mu g/L TBT. The highest TBT concentration (2.5 mu g/L) was le thal to 60% of the exposed organisms. Lower TBT concentrations elicite d no adverse effects on molting or reproduction of the daphnids. No di fferences were observed in the response of the first-and second-genera tion daphnids to the toxicity of TBT. The ability of daphnids to metab olize [C-14]-testosterone in vivo was assessed following exposure of e ach generation to TBT. Production of hydroxylated, reduced/dehydrogena ted, and glucose-conjugated metabolites of testosterone were all eleva ted following exposure of both generations to 1.25 mu g/L TBT. These f indings indicate that, under these conditions, TBT elicits no discerni ble effects on molting and reproduction of daphnids at sublethal conce ntrations, and testosterone metabolism is enhanced at concentrations a pproaching those that are lethal to organisms. Alterations of steroid metabolism by xenobiotics can be used as a more sensitive indicator of sublethal exposure in daphnids than reproductive endpoints.