No abstract

The variation in levels of polychlorinated biphenyls (sigma PCBs), chlorobenzenes and chlorinated pesticides was studied in burbot (Lota lota) from eight remote locations along a northwesterly transect from northwestern Ontario to the Mackenzie River delta in Canada. Significant declines in concentrations of PCB congeners, DDT isomers (sigma DDT), lindane, dieldrin, and mirex in burbot liver were found with increasing north latitude. Mean sigma PCB concentrations ranged from 1,290 ng/g (lipid wt) at Lake 625, a remote lake in northwestern Ontario, to 301 ng/g in samples from the Mackenzie River at Arctic Red River, N.W.T. No significant differences in mean concentrations of toxaphene, alpha-HCH, tri- and tetrachlorobiphenyls were observed between southern and northern sampling sites. Toxaphene was the predominant organochlorine residue in northern fish samples averaging 1,400 ng/g (lipid wt) at the three most northerly sites and 1,723 ng/g at Lake 625. Airborne contamination was the only likely source of organochlorines for most of the locations surveyed. The results were consistent with the hypothesis that inputs of semi-volatile organochlorines to northern aquatic ecosystems decrease with increasing north latitude and distance from North American sources.

Accumulation of and hepatic monooxygenase induction by 2,3,4,7,8‐pentachlorodibenzofuran (PnCDF) were studied in juvenile rainbow trout (Onchorhynchus mykiss) by feeding treated food for 31 d followed by a 180 d depuration period. Efficiency of assimilation was 44 and 41% at exposure concentrations of 9.0 and 0.82 ng g−1 PnCDF, respectively. Depuration of PnCDF followed first‐order kinetics with half‐lives (based on toluene extraction of 14C‐radiolabel corrected for growth dilution) of 61 and 69 d at the low and high exposure concentrations, respectively. Monooxygenase enzyme induction measured by ethoxyresorufin‐O‐deethylase (EROD) activity in individual trout livers was 84‐ and four‐fold higher after 31 d of exposure to 9.0 and 0.82 ng g−1, respectively, than in livers of unexposed fish. Sustained EROD activity at the high treatment concentrations was observed during the 180 d depuration phase. Ethoxyresorufin‐O‐deethylase activity declined at approximately half the rate of elimination of PnCDF. No significant differences between growth rates of treated and control fish were found.

No abstract

Juvenile lake trout were intraperitoneally injected with corn oil containing nominal concentrations of 0, 0.6, 6.3, or 25 μg [14C]‐3,3′,4,4′,5‐pentachlorobiphenyl (PCB‐126) per gram of body weight. The PCB‐126 accumulated in liver in a dose‐dependent manner to a sustained concentration by 6 weeks and remained elevated for the 30‐week experimental period. Mixed‐function oxidase (MFO) enzyme activity was elevated in the two highest dose groups relative to the control group, but not in the low‐dose group throughout the 30 weeks. Oxidative stress, measured by the thiobarbituric acid reactive substances test, was correlated with ethoxyresorufin O‐deethylase and was elevated in liver of the two highest PCB dose groups but not the low‐dose group. The activities of the enzymatic antioxidants superoxide dismutase, catalase, and glutathione peroxidase were unaffected by PCB‐126 exposure. The nonenzymatic antioxidant tocopherol was depleted to approximately 75% of the control concentration in liver of all three PCB‐dosed groups. Hepatic ascorbic acid levels were not different in any of the treatment groups. Retinol was depleted by greater than an order of magnitude in liver of the two highest dose groups but not in the low‐dose group. This study demonstrates a correlation between hepatic MFO activity and oxidative stress in PCB‐exposed lake trout. Tocopherol and retinol may be important mediators of oxidative stress but additional study is required to confirm the antioxidant activity of retinol.