COMPARISON OF P-4501A1 MONOOXYGENASE INDUCTION IN GIZZARD SHAD (DOROSOMA-CEPEDIANUM) FOLLOWING INTRAPERITONEAL INJECTION OR CONTINUOUS WATERBORNE-EXPOSURE WITH BENZO[A]PYRENE - TEMPORAL AND DOSE-DEPENDENT STUDIES

The objective of this study was to compare the dose-response and time-course for hepatic P-4501A1 induction in gizzard shad (Dorosoma cependianum) following intraperitoneal (i.p.) injection or waterborne-exposure to benzo[a]pyrene (B[a]P). P-4501A1 activity was measured as ethoxyresorufin-O-deethylase (EROD) activity. To investigate the i.p. dose-response, fish were injected with a range of B[a]P concentrations (0.1, 1.0, 10 and 50 mg/kg) and sacrificed 72 h post-injection. In comparison, waterborne dose-response fish were exposed to a range of B[a]P concentrations (0.14, 0.24, 0.44 and 0.76 mu g/L) and sacrificed after 10 d. The amount of B[a]P removed from the water by fish was estimated with a one-compartment linear clearance model. Maximum EROD activity was reached after fish were either injected with or cleared approximately 10 mg/kg. The injection doses (10 and 50 mg/kg) and waterborne concentrations (0.44 and 0.76 mu g/L) that caused EROD induction were used to evaluate the time-course for EROD induction. Maximum EROD activity for both injection doses was reached by day 3 and for both waterborne concentrations by day 10. Although i.p. injections are adequate for rapid screening of potential P-4501A1 inducers over a wide dose range, continuous waterborne-exposures simulate a significant route of exposure and provide improved predictive capabilities for monitoring the time-course for P-4501A1 induction under environmentally realistic conditions.