Quantifying Microplastics Abundance and Their Implications as Vectors for Heavy Metal Adsorption in Freshwater Aquatic System of Kashmir Himalaya

Microplastic (MPs) contamination in the freshwater systems has recently attracted widespread attention but, the distribution, morphology and interaction of MPs with heavy metals on freshwater aquatic systems has remained elusive and poorly understood. The present study examines the MPs abundance in sediment and water samples and factor controlling their distribution in Manasbal Lake, north-western (NW) Himalayas. The MPs abundance ranged from 13 n·L−1 to 89 n·L−1 (average=46.88 particle/L) in lake surface water samples, while their concentration varied from 840 n·kg−1 to 4020 n·kg−1 in sediment samples, with an average abundance of 2177.6 particle/kg in the dry sediments. Five main types: beads/pallets/granules, fragments, fibres, foams and films were found, wherein beads dominate the quantity accounting 92.24 % of the total microplastics in the sediments. Polypropylene, polyethylene and polystyrene were observed dominant polymers suggesting the pathway through domestic sewage effluents, tourist and fishing activities. No significant correlation was observed between microplastic abundance in surface water and sediment samples. The MPs abundance in Mansabal Lake were closely related to distance from the lake inlet. Furthermore, we also looked into the role of MP morphology in heavy metal adsorption. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) results indicated that the presence of eleven heavy metals (Cu, Cd, Zn, Ni, Co, Fe, Mn, Cr, Bi, Hg and Pb) on the surfaces of different MPs in the lake. We conclude that MPs in sediments act as carriers of heavy metals and activate their bioavailability, hence posing a potential threat to the ecological security of water body.