Accelerated release of PFASs from glacier melting on the Qinghai-Tibet Plateau caused by global warming

Due to the characteristics of persistence, bioaccumulation, potential for long-range environmental transport and adverse effects, the emissions and pollution characteristics of long-chain, short-chain and ultra-short-chain polyfluoroalkyl and polyfluoroalkyl substances (PFASs) are affected by International attention, especially in the Arctic, Antarctic and the third pole Qinghai-Tibet Plateau region. The Tibetan Plateau is the highest plateau in the world (averaging over 4,000 metres) and has the largest ice reserves (approximately 7,481 cubic kilometres) except for the polar regions, and is known as the water tower of Asia. Kwok et al. (2013) found that glaciers can act as temporary reservoirs for PFASs, which are released by melting glaciers under the influence of global warming. Chen et al. (2019) found that melting glaciers have become the second major source of PFASs in Lake Nam Co. Since the 1980s, global warming has led to the retreat of more than 80% of the glaciers and the expansion of more than 50% of the lakes on the Tibetan Plateau, which may intensify the release of PFASs from the glaciers. In this study, 17 water samples, 12 sediment samples and 12 soil samples were collected in the east, south, west or north direction, or in the center of Lake Nam Co in August 2020. Moreover, 23 water samples were collected from glaciers and non-glacial runoff around the lake that flow into Lake Namco. 19 PFASs (C2-C18), and their nine isomers and one main precursor FHxSA were analyzed by solid-phase extraction (two-fraction elution) and ultra-high performance liquid chromatography/tandem mass spectrometry. The results showed the concentrations of PFASs in water bodies such as lake water, glacial runoff and non-glacial runoff were the highest, with average concentrations of 3603 pg/L, 9,823 pg/L and 4,089 pg/L, respectively, which were 4 times, 7.4 and 5.6 times those of 2017. The concentrations of PFASs in soil and sediment were significantly lower than those in water bodies, 1.86 and 0.616 ng/g (dry weight), respectively. It was estimated that the PFASs input flux of surface runoff to lake reached 18,926.5mg/d, of which the glacial runoff reached 11,326.2mg/d (7.7 times that of 2017). It is very likely that the melting of glaciers accelerated the release of PFASs from glacier runoff into the water of Lake Nam Co. For all the three media, the linear chain was the most important isomer of PFOA and PFOS, and the order of the proportion of branched chain isomers was consistent (iso->5m->4m->3m-PFOS/PFOA). The PFBA concentrations were highest in lakes and surface runoff, accounting for 55.2% and 81.2% of total PFASs, respectively. PFBA and other PFASs in lake water were poorly correlated, and Cai et al. (2012) found similar results in polar glaciers, suggesting that the PFBA in the Lake Nam Co probably mainly came from the melting of glaciers. In the future, global warming may further accelerate the melting of glaciers and the release of PFASs in glaciers, and the changing trend of PFASs concentrations in water bodies on the Tibetan Plateau should be continuously tracked.