Lake sediments act as a sink of microplastics in the High-Altitude Himalayan Dal Lake, India

Plastic debris is a growing concern in freshwater ecosystems worldwide. This study investigates the presence, characterization, and quantification of microplastics (MPs) in Dal Lake, a known urban Himalayan lake in India, located at an altitude of 1583 meters and covering 24 km². The analysis revealed MP concentrations in surface water ranging from 140±20 to 846±136 particles per liter, and in sediments, from 2616±1016 to 12966±496 particles per kilogram (dry weight). The higher accumulation of MPs in sediments suggests they act as a long-term sink for these particles, trapping them over time. The MPs found exhibited three main morphologies: fragments, films, and lines, indicating the breakdown of larger plastic debris. Around 90% of the detected MPs in both water and sediment were smaller than 500 µm, with polyethylene and polypropylene being the most common polymers identified. Pollution levels were assessed using a count-based index, which indicated higher contamination in sediments compared to surface water, with sediment contamination being approximately 2.05 times higher. This places the lake in hazard category II, suggesting significant ecological risks. The primary sources of MP pollution in Dal Lake appear to be domestic waste, tourism activities, and urban runoff, all of which introduce plastics into the water system. This study highlights the widespread and pervasive nature of MP pollution in high-altitude freshwater ecosystems like Dal Lake.