The Active Soil Layer of Thawing Permafrost Is an Emergent Source for Organic Substances of Concern to Water Resources

The Tibetan Plateau and surrounding area are an important source of freshwater for approximately two billion people. Climate change has aggregated permafrost degradation in the Tibetan Plateau over the last few decades, mobilizing organic substances sequestrated in the permafrost. Of particular concern are the mobilized organic substances that would be considered persistent, mobile, and toxic (PMT) or very persistent and very mobile (vPvM). These PMT and vPvM substances would persist and be widespread in the downstream water distribution system, potentially threatening drinking water sources and groundwater quality. Our study evaluated and identified PMT and vPvM substances among 21 currently available literature reports that reported detected organic compounds in the active soil of permafrost. Our approach combined a standard evaluation scheme and a machine learning model. We reported that 34% of these detected compounds are PMT/vPvM substances; these compounds were of either synthetic, natural, or undefined origin. The impact that further permafrost degradation will have on releasing these PMT/vPvM substances on water resources should be prioritized.