Hepatic 7-ethoxyresorufin-O-deethylase activity, plasma steroid hormone concentrations, and liver bioassay-derived 2,3,7,8-TCDD toxic equivalent concentrations in wild white sucker (Catostomus commersoni) caged in bleached kraft pulp mill effluent

Prespawning male white sucker (Catostomus commersoni), captured near Jackfish Bay, Lake Superior (exposed to bleached kraft pulp mill effluent (BKME)), and Mountain Bay (reference) were caged in the BKME receiving area for 2, 4, and 8 d. Initially, the hepatic 7-ethoxyresorufin-O-deethylase activity was similar in fish from both BKME and reference sites and, upon BKME exposure, increased 20-fold at both sites after 2 d. The H4IIE cell culture bioassay was used to measure 2,3,7,8-tetrachlorodibenzo-p-dioxin toxic equivalent concentration (TEC) in sucker liver extracts. H4IIE bioassay-derived TECs from Jackfish Bay sucker showed no significant treatment differences; combined TECs for all treatments averaged 51.1 pg∙g −1 . Mountain Bay sucker liver TECs were initially significantly less (4.64 pg∙g −1 ) than the Jackfish Bay TECs but did show a significant, fivefold increase when fish were exposed to effluent. Mountain Bay and Jackfish Bay 8-d BKME-exposed fish showed no uptake of TECs calculated from directly measured polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) during this exposure. The results suggest that PCDDs and PCDFs are not responsible for the mixed function oxidase induction observed. Handling stress caused rapid reduction of the plasma steroids testosterone and 11-ketotestosterone, confounding any possible BKME effect.