Rivers act as temporary sinks of microplastics and a key medium allowing microplastics to enter the ocean. In this study, microplastics pollution in river shore sediment of the Indian Himalaya, including the Brahmaputra River and the Indus River was discussed. Sampling campaigns were performed in years 2018 and 2019. Sample pretreatment was performed using Na₂WO₄·2H₂O for density separation and H₂O₂ for oxidation of organic material. Microplastics analysis was performed by using FTIR microscope. The smaller size of microplastics 20-150 μm were more abundant (531-3485 MP/kg in the Brahmaputra River and 525-1752 MP/kg in the Indus River) than microplastics in size range between 150 μm and 5 mm (20-240 MP/kg in the Brahmaputra River and 60-340 MP/kg in the Indus River). Microplastics were found in sediments of all sampling sites. Fragmented, secondary microplastics were dominant in the river shore sediment of the Indian Himalaya. This study contributes towards filling research gap of microplastics in India's freshwater source and highlights the importance of in-depth complete studies of microplastics in the rivers that act as pathways and sinks for microplastics.

Microplastics pollution is a growing environmental concern. However, microplastics studies in high altitude remote lakes are scarce. In this study, microplastics pollution was assessed in the shore sediment of three high altitude lakes in Ladakh of the Indian Himalaya, namely Pangong Lake, Tsomoriri Lake and Tsokar Lake. Sampling of lakes shore sediment was performed in August 2019. Two different pretreatment methods were implemented with sediment samples from same sites, resulting two sets of samples. One set of samples was pretreated utilizing enzymatic degradation together with Fenton reactions. Another set of samples from the same sites were pretreated with 30 % hydrogen peroxide (H₂O₂) and Fenton reaction. Enzymatically pretreated samples resulted in higher microplastics concentrations than the set of H₂O₂ pretreated samples, which indicated that microplastics concentrations in sediment samples varies even among samples from the same site and that the pretreatment procedure may impact on the reported microplastics concentrations. Considering both sets of samples, microplastic concentration was 160-1000 MP/kg dw in Pangong Lake, 960-3800 MP/kg dw in Tsomoriri Lake, and 160-1000 MP/kg dw in Tsokar Lake. Blank correction based on the limit of detection and the limit of quantification indicated that microplastics concentrations at some sites of the studied lakes are higher than the limit of detection and the limit of quantification. The findings of this study indicated that the studied lakes in the Indian Himalaya are contaminated with microplastics. In addition, the comparison of microplastics using different pretreatment methods illustrated the importance of harmonization of microplastics studies to enable a reliable comparison among microplastics data. Therefore, this study contributes towards an assessment of microplastics in the high-altitude lakes in Indian Himalaya. The findings attributed towards clearer understanding regarding the need of harmonization of pretreatment methods and demonstrated the importance of reporting complete information in microplastics research.

Although microplastics research has received enormous attention in the last decade, both the research practices and the quality of produced data should still be improved. In this study, the identification process of microplastics with Raman imaging microscope was improved by decreasing the time needed for the analysis. To do that, new features, including terrain mosaic and automatic particle selection, were utilized and various ways of handling the produced microplastics data were implemented and discussed. Furthermore, blank correction of microplastic concentrations was demonstrated and its effects on the recovery of spiked microplastics was assessed with aqueous and solid samples. Six types of microplastics, including fragments and fibers, were spiked in triplicates of ultra-pure water and reference sediment samples. The spiked samples were pretreated by a modified method of the universal enzymatic purification protocol. Microplastics were analyzed with Raman imaging microscope, using terrain mosaic combined with automatic particle selection. The microplastics data were subjected to different identification steps to estimate the potential overestimation and underestimation of microplastics counts. With the complete correction of Raman-based data, the average recovery rates of fragments (77-80%) were higher than fibers (20-33%). The decrease in recovery rates of spiked microplastics (49-57%) were observed when blank correction was applied (28-47%). The impact of the blank correction depended on the polymer, causing exclusion of PE, PET, and PP from sediment samples. For the completely corrected Raman-based data, the average recovery rates of microplastics were higher for water than sediment samples both with and without blank correction. The results demonstrated the impact of blank correction on the microplastics recovery rates. To our knowledge, this is the first study to explore the use of automatic particle selection of Raman imaging microscope for microplastics analysis. Hence, potential drawbacks and advantages of the new features of Raman imaging microscope were explicitly discussed.

The Brahmaputra River is the largest tropical river in India that flows along the Himalayan regions and it is the lifeline of millions of people. Metal fractionation in the Brahmaputra River’s surface sediments and its correlation with turbidity are assessed in this study. The interaction between metal fractions and the overlying water is studied using multivariate statistical analyses. The strong positive correlation between NH₄ of the overlying water and the exchangeable fractions in sediments signifies that the metals in the exchangeable fractions can be substituted by NH_4. Subsequently, these metals can be released into the overlying water. The fluctuation in turbidity from 73 to 875 NTU indicates a large variation in the suspended matter concentration, and a higher concentration of suspended matter could provide attachment sites for pollutants such as metals. Significant variation in turbidity manifests a potentially high risk of pollution. In addition, the observation of local people along the Brahmaputra River turning its color to muddy indicates the need for continuous monitoring of water quality and an assessment of pollution is crucial. Although the Brahmaputra River’s risk assessment code is at low risk, the exchangeable fractions of Ni and Zn are present at all sites. Thus, the Brahmaputra River requires early preventive measures and management strategies to control metal pollution. This study contributes to an understanding of the fluctuation of turbidity of a tropical river. We provide baseline data for policymakers, and the importance of further intensive studies on metal pollution in the Himalayan Rivers is highlighted.