Biological transport and mammal to mammal transfer of organochlorines in Arctic fauna

Ringed seal (Phoca hispida) is assumed to be the most important and common prey of polar bears (Ursus maritimus). However, during a scientific survey in the ice area of the northern Barents Sea east of Svalbard in June 1995, an unexpectedly high number of polar bears were observed feeding on harp se al (Phoca groenlandica) carcasses. Samples of both harp and ringed seals we re obtained and organochlorine (OC) occurrence and pattern in these two pot ential polar bear prey species were determined. Significantly higher OC con centrations were found in harp seals, as compared to the ringed seals. All animals in the northern harp seal group were lean specimens in late moult. The industrial chemicals, polychlorinated biphenyls (PCBs) and hexachlorobe nzene (HCB), and the OC pesticides bis-2,2,(chlorophenyl)-1,1,1-trichloroet hanes (DDTs), hexachlorocyclohexanes (HCHs), and chlordanes (CHLORs) were a nalysed in blubber. The concentrations of Sigma PCB (sum of concentrations of 16 PCB congeners) and Sigma DDT (sum of concentrations of p,p'-DDT and p ,p'-DDE) in the northern harp seal group ranged from 2093 to 20,382 and 146 0 to 10,381 ng g(-1) lipid weight, with mean concentrations of 11,133 and 6 847 ng g(-1) lipid weight, respectively. The mean concentrations of the CHL ORs, oxychlordane and trans-nonachlor, were 1311 and 3743 ng g(-1) lipid we ight, respectively, while the mean concentrations of HCB and HCH isomers (a lpha-, beta- and gamma-HCH) were all < 500 ng g(-1) lipid weight. No signif icant difference was found in the mean total blubber mass between the two s eal species when collected in June. This indicates that polar bears preying on harp seals instead of ringed seals at this time of the year could accum ulate significantly higher PCB concentrations. We suggest that polar bears feeding along the ice-edge east of Svalbard in May and June preferentially prey on harp seals instead of ringed seals, and that this may partly explai n the variation in PCB concentrations among polar bears from the Norwegian Arctic. An hypothesis is that the harp seal may function as a transport vec tor of OCs into the high Arctic environment. (C) 2000 Elsevier Science Ltd. All rights reserved.