Occurrence, spatial heterogeneity, and risk assessment of perfluoroalkyl acids (PFAAs) in the major rivers of the Tibetan Plateau

The Tibetan Plateau (TP) is home to the headwaters of major rivers in Asia, yet their water quality security on a large spatial scale is scarcely studied, especially in regard to emerging organic pollutants. In this study, a systematic field campaign was carried out along Yarlung Tsangpo River, Nu River, Lancang River and Jinsha River, and 13 perfluoroalkyl acids (PFAAs) were analyzed. The total concentrations of PFAAs in the river waters of the TP were in the range of 0.58-7.46 ng/L, containing a high proportion of perfluorobutanoic acid (PFBA) and perfluorobutane sulfonate (PFBS) with average values of 56.7 %. Elevated PFAA loadings were found for the midstream of Yarlung Tsangpo River in central Tibet. Geodetector results indicated that precipitation, solar radiation and vegetation type were the top three influential factors contributing to the observed spatial heterogeneity. When interactions with human activities were taken into account, the explanatory power was significantly enhanced and rose above 0.70, highlighting the increased risks for TP rivers from the combined effects of natural environments and anthropogenic activities. Risk assessments suggest a low risk is posed to the alpine aquatic ecosystems and human health. The discharge fluxes of PFAAs via riverine export were estimated at 94-425 kg/year, which is one to two orders of magnitude lower than their mass loadings in major rivers worldwide. Our study underlined the need for further attention to the increased risk of water resource quality on the central TP in the context of long-range transport, increased cryosphere melting and local emission.