Identification and quantification of new polybrominated dimethoxybiphenyls (PBDMBs) in marine mammals from Australia

Marine mammals from Queensland, Australia, are bioaccumulating elevated concentrations of a range of polybrominated natural products. In this study, we detected three new polybrominated dimethoxybiphenyls (PBDMBs) in the blubber of selected marine mammal samples which were identified as 2,6′-dimethoxy-3,3′,5-tribromobiphenyl (2,6′-diMeO-BB 36), 2,2′-dimethoxy-3,3′-dibromobiphenyl (2,2′-diMeO-BB 36), and 6,6′-dimethoxy-3,3′-dibromobiphenyl (6,6′-diMeO-BB 11). These three PBDMBs are structurally related to the known natural product 2,2′-dimethoxy-3,3′,5,5′-tetrabromobiphenyl (2,2′-diMeO-BB 80). In the first part of this study, 2,2′-diMeO-BB 80 was photochemically debrominated under UV irradiation. This resulted in seven of eight possible mono- to triBDMBs as debromination products. In the second part of this study, the structure of all PBDMBs debromination products was investigated. This was supported by synthesis of two diBDMB and one triBDMB via bromination and subsequent methylation of 2,2′-biphenyldiol. Structures of the remaining PBDMBs were tentatively assigned by considering the retention times, mass spectra and amounts formed during UV irradiation of 2,2′-diMeO-BB 80 .In the third part of this study, blubber of marine mammals from Australia was analysed for PBDMBs using gas chromatography in combination with electron ionization mass spectrometry (GC/EI-MS) in the selected ion monitoring mode. In these samples, 2,2′-diMeO-BB 80 was found at concentrations of 200–1800 ng g−1 lipid weight (lw). The latter represents the highest concentration reported for this compound in environmental samples. 6,6′-diMeO BB 11, 2,2′-diMeO BB 36, and 2,6′-diMeO BB 36 were present at ∼7 ng g−1 lipids, or 0.43–1.5% of diMeO-BB 80. No further PBDMBs were detected in the samples. The di- and triBDMBs identified in marine mammal blubber have not been reported as natural products. They may represent either new natural products or transformation products of 2,2′-diMeO-BB 80.