Unravelling land-based discharge of microplastics in River Basantar of Jammu & Kashmir, India: Understanding sinking behaviors and risk assessments.

Microplastics (MPs) are ubiquitous and are increasing globally, but there is limited information available on their presence in freshwater ecosystems. This research work aims to investigate the abundance, sinking behavior, and risk assessment of MPs in the freshwater River Basantar, Jammu & Kashmir, India. Microplastic abundance in sediments was recorded in the range of 1-6 items g^-1, with a mean abundance of 3 ± 1.594 item g^-1, whereas MPs in surface water ranged from 200 to 850 items L^-1 with a mean abundance of 530 ± 218.4 items L^-1 among 12 sites for sediments and 10 sites for surface water. Besides, the sinking behavior of MPs was analyzed through portioning coefficients (K_d) at sediments-surface water interface, which ranges from 0.71 to 2.50 L Kg^-1 for River Basantar. The most common shapes identified were fragments, fibres, and films, followed by pellets, foams, and lines. ATR-FTIR polymeric characterization reported polyethylene, polypropylene, polystyrene, polyethylene terephthalate, and polyvinyl chloride, and thus, polymeric risk assessment analysis was also evaluated and normally distributed in the River Basantar. Polymer Hazard Index was calculated across all the sites which observed to be polluted under risk categories "III" and "IV" for both the sediments and surface water samples. Pollution Load Index (PLI) calculated across all the sites was >1 depicting all the sites for both sediments and surface water sampling to be polluted. Pollution Risk Index was assessed and majority of surface water and sediment samples were observed to be under "Very high" risk category. The study, using principal component analysis and heatmap analysis, found that MPs are primarily a result of urbanization and anthropogenic actions, like industrial discharges, household wastes, and agricultural runoffs. This study highlights the significance of more investigation and coordinated efforts to solve the worldwide problem of plastic pollution in freshwater environments. Results data provide insight into the current state of MP contamination and will help government authorities implement strict rules and perform management interventions to reduce and monitor pollution levels in River Basantar. Future studies on the partitioning of MPs in sediments and surface water must be focused on aggregation, biofouling, plastic density & size, salinity, and flow behaviors to understand transport and deposition in rivers.