中文摘要：

南亚排放的多氯联苯类污染物（PCBs）可随大气传输到西藏南部,并沉降到农田等区域。农田中的PCBs能够经食物链进入人体,从而可能对人体健康产生影响。但目前尚无西藏农田PCBs环境过程和农作物健康风险评估的研究。本研究通过同步采集西藏农田土壤和农作物,发现西藏农田土壤、青稞和油菜PCBs的浓度均值分别为5.1 pg·g-1dw、13.5 pg·g-1dw和10.9 pg·g-1dw,低于全球其他地区。青稞和油菜对PCBs的生物富集系数都大于1,说明PCBs在农作物中发生了生物富集现象。模型模拟结果显示,农田土壤中99.6%的PCBs都富集在土壤有机质中,只有0.38%的PCBs进入了植物根系。因此,青稞直接从大气中吸收PCBs是其对PCBs积累和富集的主要途径。基于饮食结构（青稞、牛肉、牛奶和酥油）,西藏人群PCBs摄入均值为0.75 ng·kg-1bw·d-1,低于安全阈值约一个数量级。PCBs的食物摄入不会对西藏居民健康状况产生明显影响。

英文摘要：

Polychlorinated biphenyls（PCBs） emitted in South Asia can undergo long-range atmospheric transport to reach the southern Tibetan Plateau. Once PCBs are deposited into the agricultural soil of this region they have the potential to accumulate in the human body via food chains, and ultimately increase the health risk for those consuming the produce from these lands. However, despite this important issue, few studies have examined the environmental processes involved, or assessed the health risk, of PCBs in agricultural soil and crops. In the present study, agricultural soil and crops were collected from the southern Tibetan Plateau. The average concentrations of PCBs in the soil, in hulless barley（Hordeum vulgare L. var nudum Hook. f）, and in rape（Brassica campestris L.） were found tobe 5.1, 13.5 and 10.9 pg·g-1dw, respectively, which are at the low end of global levels. The bio-concentration factors of all the vegetation were greater than 1, suggesting PCB accumulation. Results from a fugacity model showed that 99.6% of soil PCBs accumulated in the soil organic matter, while only 0.38% of PCBs were taken up by the roots of crops, implying that the main source of PCBs in the crops was atmospheric deposition. The dietary intake of non-dioxin-like PCBs in the southern Tibetan Plateau was found to be 0.75 ng·kg-1bw·d-1, which is more than one order of magnitude lower than the ＂guidance value＂. In conclusion, the health risks of PCBs via dietary exposure in the southern Tibetan Plateau are low.