Microplastic sources and distribution dynamics across contrasting anthropogenic settings: implications for lake management

Abstract

Microplastic (MP) particles have emerged as a concerning pollutant that interferes with ecological processes and poses risks to human health. A comprehensive understanding of their source, distribution dynamics and controlling factors across diverse freshwater systems is essential for deciphering their environmental impacts. This study investigates the magnitude and spatial distribution of MP contamination in the water and sediment of two contrasting freshwater lakes, Mansar and Sukhna, and elucidates the key environmental drivers governing their variability, including TOC, TN, grain-size characteristics, and water depth. In Mansar Lake, an anthropogenically influenced and unregulated site, exhibited substantially higher microplastic levels, varying between 45–120 particles per L in the water and 390–5720 particles per kg in the sediment. In contrast, Sukhna Lake, which is relatively well managed, microplastic concentrations ranged from 5–75 particles per L in the surface water and 170–2320 particles per kg in the sediment. The markedly lower MPs abundance in Sukhna Lake can be attributed to its ongoing conservation and management interventions, including restrictions on construction activities and bans on single-use plastics within the catchment. The chemical composition of MPs identified in the water and sediment samples comprises polypropylene (PP), polyethylene (PE), polystyrene (PS), and polyethylene terephthalate (PET), predominantly occurring as pellets, fibres, and fragments. The coherent spatial patterns of TOC and TN, along with their strong positive covariance in Mansar Lake, indicate a common source of organic matter. In contrast, the decoupled distributions of TOC and TN in Sukhna Lake suggest multiple and compositionally distinct organic matter sources. The absence of statistically significant relationships between MP abundance and environmental variables, including grain size, water depth, TOC, and TN, implies that MP loading is largely driven by the proximity and intensity of local anthropogenic activities rather than in-lake physicochemical controls. These findings highlight the efficacy of targeted lake-management interventions, including restrictions on specific anthropogenic activities within the catchment, in reducing MP inputs to freshwater systems.