Seasonal variations of microplastics in surface water and sediment in an inland river drinking water source in southern China

The aim of this study was to examine microplastic (size distribution of 0.05-5 mm) occurrence and distribution in drinking water source of XJ River during both flooding and dry periods. Surface water and sediment samples were collected from the CS City section of the river in August and December 2020. During the flooding period, microplastic abundances were observed at 0.72-18.6 (7.32 ± 2.36) items L in surface water and 26.3-302 (150 ± 75.6) items kg dry weight (dw) in sediment. In the dry period, abundances were slightly higher at 2.88-17.7 (11.0 ± 3.08) items L and 27.0-651 (249 ± 182) items kg dw, respectively. Microplastics were found in higher concentrations in urban areas and downstream of wastewater treatment plants, suggesting anthropogenic sources. The diversity in shapes, colors, and types of microplastics in surface waters and sediments indicates specialized enrichment processes and persistent sources of microplastic pollution. Approximately 60 % of the microplastic particles identified fall within the 50-100 μm range. Furthermore, a significant correlation was observed between these smaller-sized particles and the overall prevalence of microplastics. Fourier-transform infrared spectroscopy and scanning electron microscopy indicated that the microplastics had been subjected to weathering in the environment, contributing to the production of oxygen-containing functional groups and surface cleavage features. The utilization of energy dispersive spectroscopy revealed the presence of microplastics associated with various heavy metals, highlighting the intricate nature of microplastic pollution. Moreover, the high abundance of microplastics may pose a potential ecological risk to the aquatic environment of the XJ River. The results of this study demonstrate concerning levels of microplastics in the XJ River, despite its status as a high-quality water source.