Synthesis and tentative identification of novel polybrominated diphenyl ether metabolites in human blood

Abstract

Hydroxylated polybrominated diphenyl ethers (OH-PDBEs) are exogenous, bioactive compounds that originate, to a large extent, from anthropogenic activities, although they are also naturally produced in the environment. In the present study nine new authentic OH-PBDE reference standards and their corresponding methyl ether derivatives (MeO-PBDEs) were synthesised and characterised by NMR spectroscopy and mass spectrometry. Seven of the authentic reference standards prepared were thereafter tentatively identified in a pooled human blood sample. The tentatively identified OH-PBDEs were 3-hydroxy-2,2′,4,4′,6-pentabromodiphenyl ether, 3′-hydroxy-2,2′,4,4′,6-pentabromodiphenyl ether, 3-hydroxy-2,2′,4,4′,5-pentabromodiphenyl ether, 3-hydroxy-2,2′,4,4′,5,6′-hexabromodiphenyl ether, 3′-hydroxy-2,2′,4,4′,5,6′-hexabromodiphenyl ether, 3-hydroxy-2,2′,4,4′,5,5′-hexabromodiphenyl ether and 4-hydroxy-2,2′,3,4′,5,5′,6-heptabromodiphenyl ether. An additional seven OH-PBDEs were tentatively identified in the pooled human blood sample, of which one OH-PBDE, 4′-hydroxy-2,2′,4,5,5′-pentabromodiphenyl ether, has not been identified in human blood before. The identification was performed using gas chromatography–mass spectrometry (GC–MS) recording the bromine ions m/z 79, 81. The tentative identification was supported by the peaks relative retention times (RRTs) compared to authentic references on two GC columns of different polarities for the hexa-, and heptabrominated OH-PBDEs, and three different GC columns for the pentabrominated OH-PBDEs. The OH-PBDE congeners most likely originate from human metabolism of a flame retardant, i.e. polybrominated diphenyl ethers (PBDEs), due to the relatively high concentrations of PBDEs in the same human blood sample and the fact that these PBDEs could form the tentatively identified OH-PBDEs via metabolic direct hydroxylation or via 1,2-shift.