Effects of Biotreated Bleached Kraft Mill Effluent on Fingerling Chinook Salmon (Oncorhynchus tshawytscha)

Fingerling chinook salmon (Oncorhynchus tshawytscha) were chronically exposed in the laboratory to nonlethal biologically treated bleached kraft mill effluent (TBKME) at concentrations and temperatures typical of the Fraser River. Laboratory exposure was for 144 d in freshwater followed by 66 d in seawater without TBKME. Exposed fish bioconcentrated chlorophenols, chloroguiacols, and extractable organochlorine substances in proportion to the aqueous concentrations of the substances. Polychlorinated dibenzo-p-dioxins (PCDD's) and polychlorinated dibenzofurans (PCDF's) were also bioaccumulated, but the low body burdens compared with wild fingerling chinook indicated that the laboratory environment did not account for biomagnification via the food chain. Growth, mortality, hematocrit, protein and fat content, liver somatic index, sorbitol dehydrogenase, and tolerance to hypoxia were not affected by TBKME exposure. Increased nuclear diameters of interrenal cells among TBKME-exposed fish indicated that these fish were experiencing chronic stress. Hepatic and renal granulomas of Bacterial Kidney Disease origin were observed in some TBKME-exposed fish, but there was only a tenuous link between TBKME exposure and disease resistance. Hepatic ethoxyresorufin-O-deethylase (EROD) activity was correlated with dioxin toxic equivalency (TEQ). From this analysis, we estimated a threshold for EROD induction between 0.3 and 1.0 ng TEQ∙kg−1.