Accumulation pattern and biotransformation enzyme induction in rainbow trout embryos exposed to sublethal aqueous concentrations of 3,3',4,4 '-tetrachlorobiphenyl

Accumulation pattern of 3,3',4,4'-tetrachlorobiphenyl (PCB 77) and the expo sure time needed to activate the monooxygenase (EROD) and conjugation (GST) enzyme systems of fish at the advanced embryonic stage were studied. Eyed stage embryos of rainbow trout (Oncorhynchus mykiss) were exposed to sublet hal doses (0, 1, 10, and 100 mu g/l) of PCB 77. Results indicated direct ac cumulation of the chemical into the eggs, but the exposure time was not lon g enough for PCB 77 to reach constant steady state. However, at the two low est test concentrations (1 mu g/l and 10 mu g/l) a temporary plateau at che mical accumulation was reached at the third exposure day (185 and 1221 ng P CB/g egg w.w). At the highest concentration (100 mu g/l) the decrease in th e accumulation rate was already evident after the first day (2182 ng PCB/g egg w.w). The chemical uptake increased again at day 7 in all the exposure groups. That event could have been caused by the increased metabolic rate o f the embryos in preparation for the upcoming hatching event. The microsoma l CYP1A monooxygenase system (EROD) was shown to be a sensitive indicator o f embryonic exposure, being induced at the low (1 mu g/l, 182 ng/g egg) PCB concentration and after a short (3 day) exposure time. The conjugation enz yme system (GST) was shown to be functioning already at the advanced embryo nic stage, although no response to the studied chemical stress was detected . (C) 1999 Elsevier Science Ltd. All rights reserved.