Distribution of PCBs and PBDEs in soils along the altitudinal gradients of Balang Mountain, the east edge of the Tibetan Plateau

Surface soils were collected in Balang Mountain to explore the environmental process of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) during air transport. The average concentrations of ∑25PCBs and ∑13PBDEs in soils were 163 pg/g and 26 pg/g, respectively. The significant correlations between the concentrations of pollutants and total organic carbon (TOC) indicated the importance of TOC in accumulation potential of POPs. The slopes from fitted curves of PCBs were highly related with logKoa, demonstrating that TOC dominates the soil-air exchange of PCBs. The TOC-normalized concentrations of contaminants in samples from below-treeline were higher than those from alpine meadow, probably due to the forest filter effect. The increasing trends of the concentrations with altitude from the alpine meadow samples, could be attributed to the mountain cold-trapping effect. And the weak cold-trapping effect of POPs might be due to the less precipitation in 2008 when comparing with those in 2006.

► Total organic carbon plays an important role in accumulation potential of POPs.
► Forest filter effect might enhance the chemical levels for below-treeline soils.
► Precipitation was the key factor of mountain cold-trapping effect in this area.
► The reduction of precipitation might lead to a weak cold-trapping effect of POPs.
► Higher level of BDE-153 at Site 7 probably resulted from the human disturbance.