The uptake, distribution and metabolism of benzo[a]pyrene in coho salmon (Oncorhynchus kisutch) during the parr-smolt transformation

Benzo[a]pyrene (BaP) uptake, distribution, and metabolism patterns were investigated from February to June during the transformation of freshwater coho salmon (Oncorhynchus kisutch) parr to smolts. At a BaP concentration of 5 μg/L, uptake rates increased significantly from 0.01 ± 0.000 μg/g/h in February to 0.04 ± 0.003 μg/g/h in May and declined to 0.035 ± 0.004 μg/g/h in June. Following a 24-h exposure to BaP, the highest percent of body burden of BaP was found in the liver, gills, skin, and bile. The proportion of BaP in the liver and gills increased in fish from February to May and declined in June, whereas the proportion of BaP in the bile continued to rise until June when it reached a maximum of 49% of the body burden. The percent body burden of BaP in tissues such as the stomach, intestine, visceral fat, muscle, and brain did not show significant changes through the duration of the study. An analysis of bile suggests that both coho salmon parr and smolts are capable of metabolizing BaP via phase I and II biotransformation reactions to glucuronide, sulfate, and other conjugated metabolites. No significant changes occurred in the proportions of metabolite classes during the parr–smolt transformation process.