Polychlorinated biphenyls in surface soils of the Central Tibetan Plateau: Altitudinal and chiral signatures

The soils in the Central Tibetan Plateau (CTP), which is a unique background region, play an important role in the fate of the global cycling of polychlorinated biphenyls (PCBs). Forty-four soil samples from across the CTP were collected at altitudes between 3711 m and 5352 m, and the concentrations of 122 PCB congeners were measured from 66.98 to 150.81 ng/kg. The concentration of PCBs was positively correlated with the sampling altitude and clay content. Furthermore, enantiomeric fractions (EFs) of CB-95, CB-136 and CB-149 in soils of CTP were first determined. A (+)-enantiomer excess was identified for CB-136 and CB-149 in all of the samples investigated. Additionally, enantiomer-specific excess was found for CB-95. The dominance of enantiomer-specific excess decreased with increased the sampling altitude and congener concentration. It is likely that the addition of enantiomeric mixtures of PCBs from the atmosphere changed the EFs in the soils according to the altitude.