Occurrence, Characterization, and Potential Ecological Risks of Microplastics in the Himalayan Riverine Systems

Microplastic (MP) pollution is a prevalent environmental concern, omnipresent in soil, water, and air. The Indian Himalayan riverine systems are increasingly threatened by MP contamination, seeking dire attention. This study investigates not only the occurrence, abundance, and characterization of MPs in the rivers of Dehradun, focusing on two tributaries of the Ganges (Rispana and Bindal) and the Yamuna (Tons), but also on their temporal variation during pre- and post-monsoon seasons. A difference in the presence of MP pollutant in the upper Ganges (Rishikesh) versus its lower tributaries-Rispana and Bindal was observed, which was almost nil in the upper regions and detectable in the latter. Water chemistry, including physicochemical analysis and heavy metal analysis, along with Carbon, Nitrogen, and Phosphorus, was estimated and compared at each site. MP abundance ranged from 0.1 to 10.95 particles/L and was consistently higher in the pre-monsoon period. Colored MPs were dominant across sites (65.66%, 86.57%, and 91.72%), with fibers being predominant, followed by fragments and films. FTIR and Raman of MPs revealed primarily polyethylene, polypropylene, polystyrene, and polyvinyl chloride. A glimpse of the presence of heavy metals and microorganisms on the MPs' surface (plastisphere) was depicted via light microscopy and SEM-EDS. Raman spectroscopy revealed MPs were laden with detergent, as hinted by pigmosol detection-a detergent component. Thus, MPs act as carriers for contaminants and microbial colonization, potentially altering the riverine ecosystem dynamics. Overall, the study underscores the ecological risks of MPs in Himalayan riverine systems and calls for targeted mitigation and management strategies.