Polychlorinated biphenyls (PCB), man-made industrial chemicals, have been identified in tissues of polar bears (Ursus maritimus), ringed (Phoca hispida) and square flipper (Erignathus barbatus) seals, and Arctic char (Salvelinus alpinus) of the Canadian arctic and subarctic. All tissues from each species examined contained these compounds. PCB content in tissue, both absolute and relative to the concentration of DDT (p,p′-DDE + p,p′-DDD + p,p′-DDT), generally increased from seals to adult polar bears to polar bear cubs and young. Polar bear milk contained high concentrations of PCB and is the most probable source of the high concentrations in polar bear cubs. Chromatograms revealed a greater accumulation of higher chlorinated PCB isomers in polar bears than in seals, their main food. Residue data suggest that polar bear subpopulations in the eastern Canadian arctic and subarctic have been exposed to higher levels of PCB and DDT than western subpopulations.

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Abstract. An electrometric system for determination of carbfonic anhydrase activity was constructed. Enzyme

Retention times of 15 authentic standards of chlorinated dibenzofurans containing from three to six chlorine atoms were determined relative to dieldrin on gas chromatograph columns of four different polarities (3% OV-1; 5% SP-2401; 1.5% OV-17/1.95% QF-1; and 3% OV-1/5% OV-210/6% OV-225). On the basis of coinjections of the standards with extracts from American (Aroclor) and Japanese (Kanechlor) polychlorinated biphenyls (PCB), two of the compounds in those extracts have been identified as 2,3,7,8-tetra-and 2,3,4,7,8-pentachlorodibenzofuran. The concentrations of the compounds were estimated to range from 0.08 to 0.83 *ig/g of PCB.Vos et al. (1970) have identified toxic components of European polychlorinated biphenyls (PCB) as two chlorinated dibenzofurans. Subsequently, several additional chlorinated dibenzofurans were found in the German preparation examined by Vos et al. (Bowes et al., 1973). Further investigations have led to the detection by high-resolution mass spectrometry of those contaminants in American (Aroclor) PCB (Bowes et al., 1975). A recent study reports unidentified tri-, tetra-, and possibly pentachlorodibenzo-

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