Microplastics (MPs) pollution is a global problem in the current decade due to its contamination, persistence, and risks to ecosystems. The present study aims to investigate the ‘occurrence and distribution’, physiochemical characteristics, metal binding with MPs, and their environmental risk in the downstream of the riverine ecosystem (water and sediment/soil). The MPs were observed in the range of 50-5000 μm, with a higher abundance in sediment (1356 ± 13 particles/kg) compared to water (582 ± 12 particles/m3), where the sediments have the potential to act as long-term sinks for MPs. The ‘transparent/white color’ and ‘fragments/fibers’ MPs were dominant in both water and sediment. Chemically, the polypropylene (PP) had the highest abundance (Water: 55.56 ± 2%, Sediment: 57.45 ± 3%) compared to polyethylene (PE) polyethylene terephthalate (PET), and polystyrene (PS) in the riverine ecosystem. All MPs are partially weathered (surface roughness/cracks and degradation), and several elements (e.g., As, Cd, Al, etc.) are attached to the MPs surface, suggesting anthropogenic activities as significant contributors. The risk assessment of the study reflects the moderate types of MPs pollution load; also, the detected particle type represents moderate risk of polymers (PS ' PE ' PET ' PP), resulting in a potential environmental risk on the downstream of the riverine ecosystem. The overall study provides a comprehensive baseline of MPs pollution and risk in the river system, as well as MPs-metal interactions in the aquatic ecosystem, which can help to take proper monitoring strategies and mitigation of plastic-related ecological threats at both regional and global scales, particularly in riverine ecosystems as per SDG-3, 6, 12, and 14.