Investigating the Occurrence of Riverine Microplastic Pollution in Western Himalayan region

The Himalayas are critical geographical regions, recognized for their remarkable beauty; however, plastic littering in the Himalayas is increasing exponentially due to ignorance in every matrix. Due to long-term nescience, the degradation of microplastics has been observed and found ubiquitous. Microplastics (MPs) belong to plastic particles less than 5 mm in size. The MPs are one of the critical environmental contaminant reported by various studies, such as oceans, rivers, lakes, and estuaries. Yet, their distribution in western Himalayan river systems are poorly understood. To understand this knowledge gap in research, this study provides a brief quantification, characterization, and its fate in selected western Himalayan rivers: Beas river, Parvati river, Uhl river, and Suketi river, originating from high altitude. Sediment samples were collected from 25 locations, while sampling, field images were taken to understand the source of contamination. The established protocol was performed for pre-treatment process involving sediment sieving: coarse sand (4.75 mm-2.36 mm), medium sand (2.36 mm-0.3 mm), fine sand (0.3mm-0.075mm), siltyclay (<0.075mm) and their organic digestion, and density separation for MPs. Afterward, isolated MPs were followed for visual identification, Raman spectroscopy and Fe-SEM analysis represented polymer specification and surface weathering. The results reveal notable spatial variations with highest MPs concentration 185±14 MPs/gm in Beas river followed by 182±15 MPs/gm in Suketi river due to direct waste disposal. The trend followed by MPs concentration in sediment fraction were siltyclay> fine sand> medium sand, including remote locations. All the samples resulted transparent MPs within the size range of 10-20 µm mainly belonging to PVDF (polyvinylidene fluoride), followed by PEG (polyethylene glycol), PE (polyester), and others prevailing types of MPs. The MPs was notably higher in siltyclay sediment fraction, which are easily transported from higher altitude to lower altitude. This study offers novel insights into the fate of MPs in fragile mountain ecosystems and emphasizes the role of sediments as an important reservoir influencing pollutant transport.

Keywords- Himalayas, Microplastics, Sediment fraction, Raman Spectroscopy, Fe-SEM