Induction of mfo enzymes and production of bile metabolites in rainbow trout (Oncorhynchus mykiss) exposed to waste crankcase oil

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Abstract
It is difficult to assess the toxicological significance of complex mixtures of contaminants in the environment because of paucity of dose‐response studies. Rainbow trout (Oncorhynchus mykiss) were exposed per os to waste crankcase oil and analyzed for hydrocarbon classes, 26 polycyclic aromatic compounds (PACs) and 66 elements. MFO enzyme activity, measured as 7‐ethoxyresorufin O‐deethylase (EROD) was induced in liver, kidney, and heart. The threshold level for induction in liver was approximately 3 mg of PACs (sum of 26 PACs) per kilogram fish. A dose‐response relationship was obtained for liver and kidney but not for the heart. In a time‐response study, liver, kidney, and heart MFO activity increased (14‐, 5‐, and 3‐fold, respectively), reaching a maximum between days 1 and 4, then decreased to basal levels by day 12. Analysis of bile metabolites, as gluc‐uronide and sulfate conjugates, showed a pattern similar to that displayed by MFO induction, possibly with a slight delay. This study establishes time‐ and dose‐response relationships for MFO enzyme induction and appearance of bile metabolites in fish exposed to an environmentally important source of PACs.