Source apportionment of polychlorinated dibenzo-p-dioxin/furans and polychlorinated biphenyls in soil from the Gyirong Valley in the Himalayas.

The Tibetan Plateau is an important area for persistent organic pollutants (POPs) research because of high-altitude condensation and global distillation. However, the sources of the POPs in remote regions have not been quantified, which is critical for global control of POPs. The Gyirong Valley in the Himalayas bordering Nepal serves as an important pathway for cross-border transport of POPs to the Tibetan Plateau. In this study, the occurrences of polychlorinated dibenzo-p-dioxin/furans (PCDD/Fs) and polychlorinated biphenyls (PCBs) as typical POPs were investigated in surface soil samples collected along the Gyirong Valley. The PCDD/F and PCB congener profiles and positive matrix factorization were used to identify sources and quantify their contribution to PCDD/Fs and PCBs in the valley. The main source of PCDD/Fs was long-range atmospheric transport (LRAT), while the main sources of PCBs were domestic burning of coal and wood (27.3 %), LRAT (23.7 %), by-products from pigments, paints, and dyes (42.4 %) and industrial activities related to maintenance, disassembly or accidental releases of electrical equipment (6.5 %). A backward trajectory simulation indicated that the Indian monsoon played a dominant role in facilitating the transport of POPs from Nepal through the Gyirong Valley to the Tibetan Plateau. These results for the occurrences, distribution characteristics, and primary sources of PCDD/Fs and PCBs in the Himalayas will be helpful for POPs risk assessments and control in remote regions.