Composition, distribution and migration processes of Cu-Cd in various environmental media of the glacial watersheds in Tibetan Plateau

The Tibetan Plateau (TP), known as the “Water Tower of Asia”, is the source of many major rivers in Asia and an important ecological security barrier in western China. It's environmental sensitivity and unique high-altitude conditions make researching heavy metals critical. Copper (Cu) and Cadmium (Cd), as typical potentially toxic heavy elements, significantly influence biogeochemical processes in watershed ecosystems. This study systematically summarizes the composition, distribution, and enrichment characteristics of Cu and Cd in snow/cryoconite, soil, and river water within the TP. The results indicate that Cu-Cd in snow/cryoconite on TP shows moderate to heavy enrichments, which is mainly affected by local inputs and long-range pollutants via atmospheric circulation. Besides, the concentration and distribution patterns of Cu-Cd in river water of glacial watersheds varied considerably across regions, with both elements exhibiting notable enrichment. The Yarlung Zangbo River in particular, exhibited obvious impacts from anthropogenic activities. Moreover, the estimated atmospheric wet deposition fluxes of Cu and Cd in the glaciers of the TP are 127.62 μg m⁻² a⁻¹ and 2.56 μg m⁻² a⁻¹, respectively; while the corresponding release fluxes from glacial meltwater runoff are 10.52 ∼ 3.9 × 10 ³ kg a⁻¹ for Cu and 0.23 ∼ 12.72 kg a⁻¹ for Cd. The Cu-Cd concentrations in the topsoils of the TP were unevenly distributed, with higher value in the east and lower in the west. The sources of heavy metals were complex and influenced by multiple factors, and the risk of Cd pollution in soil is widespread. Finally, we present a conceptual model illustrating the multi-source origins and migration dynamics of Cu and Cd in the glacial basins. While the TP is generally less polluted than many other global regions, Cu-Cd in glacial environments shows evident anthropogenic influence and elevated enrichment levels, potentially endangering downstream oasis ecosystems and human populations under the pressure of intensified glacier ablation.