Microplastic pollution in the glaciers, lakes, and rivers of the Hindu Kush Himalayas: Knowledge gaps and future perspectives

The Hindu Kush Himalayas (HKH), often referred to as the Third Pole and the Water Tower of Asia, represents a vital geo-ecological asset, providing essential services to millions of people. However, this once-pristine environment is increasingly threatened by the influx of microplastics. This study provides a comprehensive overview of the current state of microplastic pollution in the HKH region, identifies key research gaps, and highlights areas for future research. A review of existing literature reveals the lack of standardized protocols for microplastics analysis, which hinders cross-study comparisons. The reported microplastic abundances vary widely across environmental matrices including 0.14-31,200 MPs m in river water, 0.072-26,000 MPs kg in river sediments, 180-5500 MPs kg in lake sediments, 55-2380 MPs kg in lake shoreline sediments, 30-871.34 MPs L in glaciers, and 2.23-130 MPs L in lake surface water. Polymer characterization using spectroscopic techniques has identified 54 polymer types across different environmental matrices in the HKH region with polypropylene (PP) being the most dominant, followed by polyethylene (PE), and polystyrene (PS). The sources of microplastics in the HKH region include both local activities and long-range atmospheric transport. Although research on microplastics in the region has gained momentum in recent years, significant knowledge gaps remain regarding their fate, degradation mechanisms, and environmental impacts. Further studies are essential to investigate the role of microplastics as light-absorbing impurities that may accelerate glacier melting, as well as their implications for biodiversity and human health in the region.