Concentrations variation trend and potential sources of PFASs in Lake Nam Co, Qinghai-Tibet Plateau

Per- and polyfluoroalkyl substances (PFASs) are one of emerging pollutants of international concern. They are ubiquitous worldwide, even in remote polar and alpine regions. Benskin et al. (2011) proposed that direct long-range atmospheric transport (LRAT) of PFASs, atmospheric transport and degradation of their precursors are the main sources of PFASs in remote regions. Chen et al. (2019) found in their study of PFASs in the water and surrounding runoff of Lake Nam Co in the Tibetan Plateau that the release from glacier melting is the second largest source after LRAT. As the continuous production and use of PFASs, combined with the impact of glacier melting, the concentrations of PFASs in Lake Nam Co are likely to rise rapidly. In this study, a total of 38 lake water samples were collected from Lake Nam Co in August 2023, and a total of 30 runoff water samples from glacial and non-glacial runoff flowing into Lake Nam Co were collected and the concentrations of 9 PFASs were analyzed. By comparing with the results of 2020, the temporal trend of PFASs in Lake Nam Co was studied, and their potential sources were analyzed. The results show that the mean concentration of PFASs in the water samples collected from the shores of Lake Nam Co in 2023 is 7724 pg/L, which is a 120% increase from the level observed in 2020. Within the PFASs, the short-chain PFASs (4-6 carbon atoms) exhibit the fastest growth, increasing by 150% compared to 2020. This may be due to the widespread production and use of short-chain PFASs as substitutes for long-chain PFASs, which arrive in Lake Nam Co via LRAT, resulting in a more significant increase in the concentrations of short-chain PFASs in the lake water. It is also found that the concentrations of PFASs in glacial runoff are significantly higher than in non-glacial runoff, with the greatest concentration difference found for PFBA, which is approximately twice as high in the glacial runoff compared to non-glacial runoff. In addition, the concentrations of PFASs in the southern side of Lake Nam Co, which receives multiple glacial runoff inputs, are higher than those in the northern side, with PFBA showing the greatest difference between the two sides. Several studies have speculated that PFBA may be an indicator of ice and snow melting. The observed spatial heterogeneity of PFBA implies that the release of PFASs due to glacier melting could be one of the main sources contributing to the increasing concentrations of PFASs in the water of Lake Nam Co. Under the influence of global warming, the glaciers surrounding Lake Nam Co may experience further melting in the future, which implies that the melting of glaciers could release more PFASs into Lake Nam Co in the coming years. Given that the concentrations of PFASs in the water of Lake Nam Co have shown an increasing trend, it is necessary to conduct continuous tracking monitoring and environmental risk assessments for Lake Nam Co and other ecologically vulnerable environments such as alpine and polar regions.