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Assessment of microplastic contamination in the Karnali River: A baseline study in remote region of western Nepal
Summary
Researchers surveyed 16 sites along the Karnali River in remote western Nepal and found microplastics at every location, with fiber-shaped particles making up 94% of what they detected — suggesting that even rivers far from cities are not protected from plastic pollution. The findings call for urgent long-term monitoring across Nepal's freshwater systems, most of which have never been studied for microplastic contamination.
• Microplastics (MPs) were found at all 16 sites along the Karnali River in Nepal. • MPs concentration ranged from 0.12 to 0.64 particles/L; average 0.29 ± 0.03 MPs/L. • Blue color (52 %) and fiber shape (94 %) were the most common microplastics. • Polyethylene and Polypropylene were common polymers recorded. • Weak correlations found between MPs and pH, EC, TDS, and Turbidity. Microplastic (MP) contamination is an emerging global environmental problem, however, its status in the freshwater systems of Nepal is not fully understood. Most studies have concentrated on urbanized and easily accessible areas, with remote riverine systems under-examined. This work attempts to address this gap by presenting the abundance, distribution and characteristics of the MPs in the river, a large but isolated river course located in western Nepal. The land use types were the basis for the selection of 16 sampling sites. The microplastic detection method was based on hydrogen peroxide digestion, density separation and stereomicroscopic identification of water samples. Moreover, the study tried to show the association between abundance of microplastic and water quality parameters (pH, Electrical Conductivity, Total Dissolved Solids and Turbidity) Results showed that microplastics were present in all sampling sites of Karnali River, occurring at concentrations ranging between 0.12 and 0.64 particles/L with an average of 0.29 ± 0.03 MPs/L, and revealed the absence of a consistent (increasing or decreasing trend) upstream-to-downstream gradient in microplastic distribution. The blue colored microplastic (52 %) and fiber shaped (94 %) were the dominant morphological form found, varied in size from 296–3135 µm. Spearman’s correlation analysis revealed weak to moderate correlations between microplastic abundance and water quality parameters. The strongest association was observed with turbidity (ρ = 0.389), followed by EC (ρ = 0.262), TDS (ρ = 0.260), and pH (ρ = –0.324), though none were statistically significant at p < 0.05. This study makes evident the widespread and complicated distribution of MPs even in some of the more distant freshwater environments, and demands an immediate response with respect to long-term monitoring and possible interventions in Nepal’s numerous hydrological systems.