Abstract. The effects of environmental salinity on the distribution, metabolism, and elimination of benzo [a]pyrene (B[a]P) were examined in mature rainbow trout. Trout acclimated to either fresh water (0 ppt, FW) or sea water (20 ppt, SW) for 3 weeks received a single 10 mg/kg intra-arterial injection of [ 3 H]-benzo[a]pyrene (B[a]P) at their acclimation salinity or when subjected to an acute salinity change. Statistically significant differences in the percent body burden of B[a]P-derived radioactivity in various tissues were seen between fish in FW versus SW. Significant differences in the distribution of B[a]P and its metabolites were also noted when fish were subjected to an acute salinity change after chemical injection. Modulation of B[a]P metabolism by environmental salinity included: (1) significant differences in the proportions of Phase I metabolites in the bile of FW-(2.3%) versus SW-acclimated (14.1%) fish, and (2) alterations in the accumulations of specific metabolites (predominantly t-9, 10-dihydrodiol-B[a]P in FW fish, and 3-hydroxy-B[a]P in SW fish). The percentages of the [ 3 H]-B[a]P dose eliminated by 48 h was similar in FW and SW fish, but decreased in fish subjected to an acute salinity change (FW 98.8% eliminated, FW:SW 90.4%, SW 98.1%, and SW:FW 93.1%). Pharmacokinetic modeling confirmed that acute salinity changes can result in longer terminal half-lives and slower total body clearances of B[a]P
