Comparison of dietary and waterborne exposure to benzo[a]pyrene: bioavailability, tissue disposition and CYP1A1 induction in rainbow trout (Oncorhynchus mykiss)

Absorption and tissue distribution of benzo[a]pyrene (BaP)-derived radioact ivity were studied in juvenile rainbow trout following dietary or waterborn e exposure. In order to compare the bioavailability of BaP, the fish were e xposed to 1.5 mCi H-3-BaP kg(-1) fish, either in the diet or in the water a s a 2 days static exposure. Furthermore, tissue levels of BaP-derived radio activity bound to macromolecules in different tissues were studied in non-i nduced fish, and in fish induced by additional treatment with unlabelled Ba P (corresponding to 5 mg kg(-1) fish) in the water. Absorption and tissue d istribution of H-3-BaP were studied by liquid scintillation counting and wh ole-body autoradiography. BaP-derived radioactivity bound to macromolecules in different tissues was studied by autoradiography of solvent-extracted w hole-body sections. The hepatic CYP1A induction was measured as EROD activi ty. Exposure to unlabelled BaP resulted in a marked induction of hepatic ER OD activity in rainbow trout 2 days after the start of the exposure. Signif icant higher concentrations of radiolabelled compound were observed in wate rborne-exposed fish, in contrast to dietary-exposed fish. High concentratio ns of radiolabelling were observed in the gills, liver, bile, intestines, o lfactory organ, kidney and the skin of the waterborne-exposed fish. In the dietary-exposed fish, high levels of radioactivity were observed in the int estines and the bile, whereas lower concentrations were present in the live r. Only traces of radioactive compound were observed in the gills. In contr ast to waterborne-exposed fish, no radioactivity was detected in the olfact ory organ or skin. In autoradiograms of sections extracted with a series of polar and non-polar solvents, a large fraction of radioactivity was still present in the gills, olfactory organ, liver, kidney, skin and intestinal m ucosa of the waterborne-exposed fish, indicating that reactive BaP intermed iates formed by CYP1A-mediated metabolism were bound to macromolecules in t hese tissues.