Knowledge is limited regarding methylsulfone (MeSO₂)-polychlorinated biphenyl (PCB), and especially MeSO₂–2,2-bis(chlorophenyl)-1,1-dichloroethylene (DDE), metabolites in cetacean species. We hypothesized that the ability of beluga whale (Delphinapterus leucas) to biotransform PCB and DDE compounds, and to form and degrade their MeSO₂ PCB and -DDE metabolites, is related to the capacity for xenobiotic metabolism. Adipose biopsies were collected from male and female beluga whale from distinct populations in the St. Lawrence River estuary (STL) and western Hudson Bay (WHB), Canada, which are contrasted by the exposure to different levels of cytochrome P450 enzyme-inducing, chlorinated hydrocarbon contaminants. The PCBs, DDTs, DDEs, 28 MeSO₂ metabolites of 14 meta-para chlorine-unsubstituted PCBs, and four MeSO₂ metabolites of 4,4′- and 2,4′-DDE were determined. The mean concentrations of total (Σ-) MeSO₂-PCB in male STL beluga (230 ng/g), and ratios of Σ-MeSO₂-PCB to Σ-PCB (0.05) and Σ-precursor-PCB (0.17) were approximately twofold higher, whereas the Σ-precursor-PCB to Σ-PCB ratio was approximately twofold lower, than in male WHB beluga. Both populations had a low formation capacity for MeSO₂-PCBs with ≥six chlorines (<4% of Σ-MeSO₂-PCBs). The congener patterns were dominated by trichloro- and tetrachloro-MeSO₂-PCBs, and tetrachloro- and pentachloro-MeSO₂-PCBs in WHB and STL animals, respectively. In addition to 2- and 3-MeSO₂-4,4′-DDE, two unknown MeSO₂-2,4′-DDEs were detected. The mean 3-MeSO₂-4,4′-DDE concentration in STL beluga (1.2 ng/g) was much greater than in WHB (<0.01 ng/g) animals. The concentrations of 4,4′-DDE, and not 3-MeSO₂-4,4′-DDE, increased with age in male STL animals. We demonstrated that sulfone formation and clearance is related to metabolic capacity, and thus PCB, DDE, and MeSO₂-PCB and -DDE toxicokinetics differ for STL and WHB beluga. In the past, the capacity of odontocetes for PCB and DDE biotransformation leading to persistent sulfone metabolites has been underestimated. More information is needed for other cetacean species and marine mammals. The results of this study indicate that MeSO₂-PCBs and -DDEs need to be included in the toxicologic risk assessment of PCB and DDT exposure in odontocetes, and perhaps for cetaceans in general.

R.J. Letcher, R.J. Norstrom, D.C.G. Muir, C.D. Sandau, K. Koczanski, R. Michaud, S. De Guise, P. Beland. 1999. Methylsulfone polychlorinated biphenyl and 2,2‑bis(chlorophenyl)-1, 1 dichloroethylene metabolites in beluga whale (Delphinapterus leusus) from the St. Lawrence river estuary and Western Hudson Bay, Canada. Environmental Toxicology and Chemistry Vol. 19, No. 5, p. 1378-1388.

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