The research team, led by Rubab Mansoor and Riffat Naseem Malik of Quaid-i-Azam University in Islamabad, together with colleagues at the University of Rhode Island’s Graduate School of Oceanography, analyzed peat cores for a suite of twenty-one PFAS compounds as well as methylmercury. The results were striking in both magnitude and pattern. Total PFAS concentrations ranged from 3.49 to 221.56 nanograms per gram of peat, while methylmercury concentrations spanned 0.27 to 11.24 nanograms per gram, with pronounced spatial variability between the two lakes. Naltar Lake recorded the higher PFAS burdens, whereas Sheosar Lake emerged as the hotspot for methylmercury, a divergence that points to fundamentally different contamination pathways operating at the two sites.

PFAS are a broad family of synthetic chemicals prized for their water and grease resistance, used for decades in textiles, firefighting foams, nonstick coatings and countless industrial applications. Their carbon-fluorine bonds are among the strongest in organic chemistry, which makes them extraordinarily persistent in the environment. Because they can travel vast distances through the atmosphere, attached to particles or as volatile precursor compounds that later degrade, PFAS reach even the most pristine corners of the planet. Previous studies have documented their deposition on Mount Everest, in Svalbard ice cores and across the Tibetan Plateau, but the peatlands of northern Pakistan had remained a blank space on that map until now.

Using source apportionment techniques, the researchers identified long-range atmospheric transport as a dominant pathway delivering PFAS to these mountain lakes, meaning the chemicals likely originated from industrialized regions far away and rode air currents before settling onto the high-altitude landscape. Glacial melt emerged as a second major source. As glaciers retreat under a warming climate, they release contaminants that were deposited and frozen into the ice over decades, flushing them into downstream lakes, wetlands and peat soils. This dual mechanism, atmospheric delivery plus cryospheric release, means that mountains are not merely passive recipients of pollution but active reservoirs that can re-mobilize legacy contaminants as the climate warms.

Methylmercury tells a different story. Unlike PFAS, methylmercury is not emitted directly by factories in significant amounts. Instead, it is produced in situ when microbes, particularly sulfate-reducing bacteria, methanogens and iron-reducing bacteria, convert inorganic mercury deposited from the atmosphere into its organic, methylated form. This biotransformation thrives in waterlogged, oxygen-poor environments, precisely the conditions that peatlands provide. The elevated methylmercury levels at Sheosar Lake therefore reflect local biogeochemical conditions favoring microbial methylation rather than a distinct pollution source, underscoring that even modest inputs of inorganic mercury can be transformed into a far more dangerous compound under the right environmental circumstances.

The distinction matters because methylmercury is the form of mercury that bioaccumulates and biomagnifies through aquatic food webs. It crosses the blood-brain barrier and the placenta, making it a serious neurodevelopmental hazard for humans and wildlife that consume contaminated fish. PFAS, meanwhile, are associated with a range of health concerns including immune suppression, elevated cholesterol, liver damage and certain cancers. The risk assessment conducted by the team found that perfluoroalkyl carboxylic acids and perfluoroalkyl sulfonic acids, the two principal PFAS classes, carried the highest risk quotients at Naltar Lake, while methylmercury was the dominant concern at Sheosar Lake. In other words, each lake faces its own characteristic toxic threat.

Peat itself plays a crucial role in this contamination story. Peatlands are highly organic soils composed of partially decomposed plant material, and their abundant humic substances carry charged surfaces that bind both PFAS and mercury strongly. This makes peat an effective natural archive, preserving a layered record of deposition over time, but it also makes peatlands critical contaminant reservoirs. The vertical profiles in the cores reveal how accumulation has changed with depth, offering a historical dimension to the study. Earlier work has shown that ombrotrophic peat bogs can be imperfect archives for PFAS because of post-depositional movement, yet the strong spatial patterns and source signals recovered here demonstrate that high-altitude peat can still illuminate where and how these chemicals arrive in mountain ecosystems.

The most consequential finding may be what it implies for the future. The Hindu Kush Himalayan region is often described as the water tower of Asia, feeding river systems that sustain hundreds of millions of people downstream. As glacial retreat accelerates across the region, the contaminants stored in ice, snow and alpine peatlands will not stay put. Meltwater can flush PFAS into proglacial rivers and lakes, and warming ground can release inorganic mercury from peat while simultaneously stimulating microbial methylmercury production, a combination documented in boreal peatlands that now appears relevant to the high mountains of South Asia. The authors warn that alpine peatlands may act as secondary sources of contamination to downstream aquatic ecosystems, converting a long-standing sink into an emerging source.

For environmental managers, the study provides a baseline against which future changes can be measured, and a scientific rationale for incorporating contaminant release into models of glacial retreat and water security in the region. It also highlights the value of remote, high-altitude monitoring sites as sentinels of global pollution, since their contamination reflects hemispheric-scale atmospheric transport rather than local emissions. The work was supported by the U.S. Fulbright Senior Scholar Program, with PFAS analyses performed at the University of Rhode Island, illustrating the kind of international collaboration needed to track pollutants that recognize no borders.

Ultimately, the peat cores of Naltar and Sheosar Lakes deliver a sobering message: there is no longer any landscape so high, so cold or so remote that the chemical fingerprints of industrial society cannot reach it, and once there, those fingerprints do not simply fade. They are stored, transformed and, in a warming world, increasingly set in motion again. Understanding the archives that mountains keep, and the risks they hold in reserve, is now an essential part of protecting the water supplies and ecosystems that depend on them.

Subject of Research: PFAS and methylmercury contamination in high-altitude peat archives of glaciated lakes in northern Pakistan

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

Article References: High-altitude peat archives of PFAS and MeHg in Northern Pakistan: vertical distribution, source apportionment and environmental implications. (n.d.). https://doi.org/10.1007/s10653-026-03477-1

Image Credits: AI Generated

DOI: 10.1007/s10653-026-03477-1

Keywords: PFAS, methylmercury, peat cores, high-altitude lakes, glacial melt, long-range atmospheric transport, Northern Pakistan, Hindu Kush Himalaya, contaminant reservoirs, environmental risk assessment, mercury methylation, climate change