Co-occurrence of microplastics and heavy metals in a freshwater lake system in Indian Himalaya: Distribution and influencing factors

Abstract

Microplastic (MP) contamination in freshwater systems is a prevalent and persistent environmental issue, yet their occurrence and distribution remain poorly constrained. The present study examines the MPs abundance in sediment and water samples and factors controlling their distribution in the Manasbal Lake, north-western (NW) Himalaya. Additionally, the study investigates the relationship between heavy metals and the distribution of MPs in sediment, as well as their potential interactions. The MPs counts in lake surface sediment and water samples varied from 840 nkg⁻¹ to 4020 nkg⁻¹ and 13 nL⁻¹ to 89 nL⁻¹, respectively. The MPs distribution in Manasbal Lake exhibited spatial heterogeneity, with the greatest abundance observed in the eastern and northeastern areas near lake inlets. Grain size and land use appear to collectively modulate the variability of MPs in Manasbal Lake sediments. Five main MPs types were identified: beads/pellets, fragments, fibres, foams, and films, with beads being the predominant type. Polypropylene, polyethylene, and polystyrene are the dominant constituents of the observed MPs, with domestic sewage suggested as the predominant source for their abundance in the lake. Furthermore, the contamination factor for heavy metals indicated a high level of lead contamination in surface sediments, while copper and cobalt showed moderate contamination near the lake inlet. The SEM-EDS analysis illustrated the presence of toxic elements such as Hg, Zn, Pb, Cr, Cd, Ni, and Cu to the surface of MPs. This study expands the baseline characterization of MPs in freshwater systems and enhances our understanding of the potential sources and factors influencing MP distribution.