High-altitude peat archives of PFAS and MeHg in Northern Pakistan: vertical distribution, source apportionment and environmental implications.

Per- and polyfluoroalkyl substances (PFAS) can reach remote environments mainly through atmospheric transport and deposition, whereas methylmercury (MeHg) is formed primarily through in-situ microbial methylation of inorganic mercury (Hg). However, their occurrence in high-altitude environments is still poorly understood. This study provides the first assessment of the vertical distribution, source apportionment, and risk implications of PFAS and MeHg in peat cores from two alpine glaciated lakes in northern, Pakistan. Total ∑21PFAS concentrations ranged from 3.49 to 221.56 ng/g, while MeHg concentrations ranged from 0.27 to 11.24 ng/g, with pronounced spatial variability. Naltar lake had higher PFAS concentrations, whereas Sheosar Lake showed higher MeHg concentrations. Long range atmospheric transport (LRAT) and glacial melt were identified as major PFAS sources, while MeHg was primarily associated with in-situ methylation of Hg. Risk assessment identified Perfluoroalkyl Carboxylic acids (PFCAs) and Perfluoroalkyl Sulfonic acids (PFSAs) as the compound classes with the highest risk quotients at Naltar lake, while MeHg was the main concern at Sheosar lake. Alpine peatlands serve as critical contaminant reservoirs and may act as secondary sources to downstream aquatic ecosystems amid ongoing glacial retreat. This study improves understanding of PFAS and MeHg accumulation in high-altitude ecosystems and provides useful information for assessing contaminant sources and supporting future environmental management.