Assessment of polychlorinated biphenyls and polybrominated diphenyl ethers in Tibetan butter

The Tibetan plateau is considered a potential cold trap for persistent organic pollutants (POPs) and plays an important role in the global long-range transport of these compounds. This present work surveyed the concentrations of polychlorinated biphenyl (PCBs) and polybrominated diphenyl ethers (PBDEs) in Tibetan butter samples collected from different prefectures in Tibet autonomous region (TAR). ∑25PCB concentrations ranged from 137 to 2518 pg g−1 with a mean value 519 pg g−1, which were far lower than those in the butter from other regions in the world. The highest level was found in butter from Sichuan province, which is located to the east of the Tibetan plateau and the lowest value was in samples from southeast TAR. The average concentration of ∑12PBDE was 125 pg g−1. The sample with highest and lowest ∑12PBDE concentration (955 and 18.0 pg g−1) was from the south and southeast part of the plateau, respectively. Back trajectory model implied that the sources of these two groups of POPs were by atmospheric deposition in south, whereas the western plateau was mainly influenced by the tropical monsoon from south Asia. Air currents from Sichuan and Gansu province are further responsible for the atmospheric transport of PCBs and PBDEs to the eastern and northern side of the plateau. Local air concentrations of ∑5PCBs predicted using air–milk transfer factor were at the lower end of published global levels.