Chiral PCB methyl sulfones in rat tissues after exposure to technical PCBs

PCB methyl sulfones (MeSO2-PCBs) are lipophilic PCB metabolites known to exhibit selective tissue retention properties in wildlife and humans. The aim of this study was to investigate the presence of atropisomers of MeSO2-PCB congeners in tissues of rats exposed to a technical PCB product, Clophen A50. Changes in the enantiomer fractions (EFs) of the MeSO2-PCB atropisomers after exposure were also determined. Liver, lung, and adipose tissue from rats dosed with Clophen A50 were analyzed for the MeSO2-PCB atropisomers of 3-methylsulfonyl-2,2',4',5,6-pentachlorobiphenyl (5-MeSO2-CB91), 4-methylsulfonyl-2,2',3,4',6-pentachlorobiphenyl (4-MeSO2-CB91), 3-methylsulfonyl-2,2',3',4',5,6-hexachlorobiphenyl (5'-MeSO2-CB132), 4-methylsulfonyl-2,2',3,3',4',6-hexachlorobiphenyl (4'-MeSO2-CB132), 3-methylsulfonyl-2,2',4',5,5',6-hexachlorobiphenyl (5-MeSO2-CB149), and 4-methylsulfonyl-2,2',3,4',5',6-hexachlorobiphenyl (4-MeSO2-CB149). In all tissues analyzed, especially lung, the para-MeSO2-PCBs were more abundant than the meta-MeSO2-PCBs. The concentration ratio was higher for 4-MeSO2-CB149 versus 5-MeSO2-CB149 than for the corresponding ratio 4-/5-MeSO2-CB91 and 4'-/5'-MeSO2-CB132. Enantioselective MeSO2-PCB analysis of the lung samples showed an excess and dominance of the second eluting atropisomer of 4-MeSO2-CB149. In both lung and adipose tissues, small amounts of the first eluting atropisomer of 5-MeSO2-CB149 was present, but this atropisomer was not detected in the liver. No significant time-dependent changes in the EFs of 4-MeSO2-CB91, 5'-MeSO2-CB132, 4'-MeSO2-CB132, 5-MeSO2-CB149, and 4-MeSO2-CB149 atropisomers were found for either lung, liver, or adipose tissue. The results of the present study suggest that enantioselective formation occur for both meta- and para-MeSO2-PCBs.