Causes of spatial heterogeneity of PFASs in the Nam Co Lake and surrounding runoff on the Qinghai Tibet Plateau

Nam Co Lake, located in the Tibet Plateau region, is the highest and second-largest enclosed salt water lake in China, and is a representative area for the study of long-range atmospheric transport (LRAT) and climate change of perfluoroalkyl and polyfluoroalkyl substances (PFASs). We analyzed the causes of spatial heterogeneity of 18 PFASs in 17 lake samples, 7 glacial runoff samples, 8 non-glacial runoff samples and 9 sediment samples in or around the Nam Co Lake in 2023. The results showed that the distribution of PFASs in various environmental media around Nam Co Lake can be influenced by glacial melting, salinity, pH, carbon chain length and human activities etc. Due to the melting of glaciers caused by global warming, PFASs deposited in the glaciers over the years flowed into the runoff in large quantities through the meltwater, making the PFAS concentrations in the runoff higher than those in the water of Nam Co Lake. The concentrations of short-chain PFASs in lake water were significantly negatively correlated with pH, possibly because the stronger alkalinity can change the structure and soil chemistry of PFASs and thus reduce their concentration. In contrast to the lake water, there is no significant correlation relationship between the concentration of PFASs in the runoff and the salinity and pH, so the influencing factors of the runoff concentration may be more complex compared to the closed Nam Co Lake, affected by human activities and other factors. The short-chain and long-chain PFASs accounted for the largest and the smallest proportion for both runoff and lake water samples, respectively, while the opposite for sediment samples, indicating that the long-chain PFASs with better hydrophobicity could be easily distributed to sediments. Considering for the irreversible accumulation and aquatic ecotoxicity, the concentrations and partition coefficient of TFA in the water and sediment of Nam Co Lake on the Tibet Plateau were firstly detected and analyzed. The results showed that TFA was the substance with the highest concentration, and the concentration of TFA in lake water, sediment, glacial runoff and non-glacial runoff accounted for 32.09%, 34.39% of ∑PFAS, respectively. Therefore, it was necessary to continuously track the concentration and environmental risk of TFA.