Distribution And Chiral Signature Of PCBs And OCPs In Topsoil Of The Central Tibetan Plateau

This study is in Central Tibetan Plateau(CTP), an important background region, which plays an important role in the global fate and distribution of persistent organic pollutants(POPs). Forty-four surface soil samples and grass samples across CTP were collected, with an altitude of 3711 m to 5352 m and the concentrations of 122 congeners of polychlorinated biphenyls(PCBs) were detected. The total concentration of PCBs was 66.98-150.81 ng/kg, and the average content was 100.64 ng/kg. It is found that the total concentration of PCBs was positively related with the sampling altitude and clays content. By further chiral analysis, enantiomeric fraction(EF) was determined for CB-95, CB-136 and CB-149.(+) enantionmer excess was identified for CB-136 and CB-149 in all detected samples. Also, the same trend was also found for CB-95. The dominance of enantiomer-specific excess decreased with the increase of the altitude and congener concentration. The most possible explanation is that the air temperature decreased with increasing altitude, which increased the soil concentration and changed the EFs in soils. The chiral analysis of two organochlorine pesticides(OCPs)was performed for α-HCH and o,p’-DDT in paired soil and grass samples in Central Tibetan Plateau. In the case of α-HCH, 83.3% of the soil samples showed excess of(-) α-HCH and 80% of grass samples showed excess of(+) enantiomer. For o,p’-DDT, 90.9% of grass samples showed excess of(-) o,p’-DDT while 50% of soil samples showed excess of the(-) enantiomer. A correlation between EFs of soil and grass was not observed for either compound. The EFs of both compounds were correlated with soil concentration and the sampling altitude, within EFs being lower than racemic. However, these trends were not found in grass samples.