Cytochrome P450 1A and related measurements in juvenile chinook salmon (Oncorhynchus tshawytscha) from the Fraser River

Juvenile chinook salmon (Oncorhynchus tshawytscha) were captured at six sit es on the upper Fraser, Nechako, and Thompson rivers, British Columbia, Can ada. Biological responses were measured in the liver to assess the effects of contaminants on the fish before they began migration downstream. Both et hoxyresorufin-O-deethylase (EROD) activity and CYP 1A concentrations were s ignificantly enhanced, being two- to three-fold higher in Fraser River samp les compared with those fish from reference sites on the Nechako River. DNA adduct concentrations were two- to four-fold higher in Fraser River fish, although liver histopathology appeared unaffected. Polychlorinated dibenzo- p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinat ed biphenyls (PCBs) in the carcasses contributed to total contaminant burde ns of less than 1 pg,g(-1). Polycyclic aromatic hydrocarbon (PAH) metabolit es were undetectable in nearly all samples of bile. There were strong corre lations between EROD activity, CYP 1A induction, and DNA adduct concentrati ons but no clear correlation between these responses and PCDD, PCDF, or PCB concentrations.