Microplastic in Surface Water and Lake Shoreline Sediments of Phewa Lake, Nepal

Abstract

Microplastic is an emerging environmental pollutant receiving growing concern worldwide. Lakes in Nepal provide a variety of ecosystem services. However, the microplastic pollution in freshwater lakes of Nepal remains unknown. Therefore, this study was carried out to investigate the abundance and characteristics of microplastics along with the spatial and temporal distribution of microplastics in surface water and shoreline sediments of Phewa Lake. In addition, the objective of this study was to analyze the water quality status of Phewa Lake. Thirty-two water samples and twenty shoreline sediment samples were collected from Phewa Lake from various locations for the uniform distribution of sampling sites. National Oceanic and Atmospheric Administration (NOAA) protocols were followed for the isolation of microplastics with minor changes. The water quality of Phewa Lake was analyzed according to the standard methods for the examination of water and wastewater. The mean abundance of microplastic for the whole study period (2021) in Phewa Lake was 1.97 microplastics/L and 88.5±50.32 microplastics/kg dry weight for water and sediment samples respectively. The mean abundance in winter season > rainy season > autumn season for both water and sediment samples. Significant spatial variation of microplastic abundance was observed in water and sediment samples which was driven by population density and topographic factors. Seasonal variation in the mean abundance of microplastic was only observed in water samples (H=22.34, p<0.01). Fibers were the most common type of microplastics accounting for 93.04%, 96.69%, and 85.0% for winter, rainy, and autumn seasons respectively in water samples. Similarly, fibers in sediment samples accounted for 78.11%, 62.03%, and 41.26% for winter, rainy, and autumn seasons respectively. Different types of color were observed in Phewa Lake where transparent was the dominant color in water for all three seasons. But in sediment samples, white color dominated in the autumn season. A maximum abundance of microplastics was found in size class < 1 mm in water and sediment samples for all three seasons in Phewa Lake. FTIR analysis of visible microplastic (size 1-5 mm) reveals polypropylene (PP) and polyethylene (PE) as the main polymer types found in the shoreline sediments of Phewa Lake for all three seasons. The water quality of Phewa Lake was good with regard to the water quality index but is polluted with heavy metals as indicated by the heavy metal pollution index. The findings of this study demonstrate the presence of microplastics in the water and sediments of Phewa Lake. Moreover, this study provides the first baseline data on microplastics in freshwater lakes of Nepal. Keywords: Microplastics, Phewa Lake, shoreline sediment, water, abundance