Seasonal variation and risk assessment of microplastics in surface water of the Manas River Basin, China

The ubiquity of microplastics in the environment has caused great influence to ecosystems and seriously threatened human health. To better understand the variation in microplastics in different seasons in an inland freshwater environment and determine the sources of microplastic pollution and its migration features, this study investigated the characteristics of microplastic pollution during dry (April) and wet (July) seasons in surface water of the Manas River Basin, China. The size, color, shape, area distribution and compound composition of microplastics were studied. Moreover, the risk of microplastic contamination was explored based on risk assessment models. The results demonstrated that the degree of pollution caused by microplastic abundance was minor in this study area. The average abundance of microplastics in April (17 ± 4 items/L) was higher than that in July (14 ± 2 items/L). The range in the abundance of microplastics in April and July were 22 ± 5-14 ± 3 items/L and 19 ± 2-10 ± 1 items/L, respectively. Highly hazardous polymers such as Polyvinyl chloride (PVC) and Polycarbonate (PC) have a significant impact on the results of the evaluation of the presence of microplastics. This study is an important reference for understanding the characteristics of the seasonal variation in microplastics in inland freshwater environments and has practical significance, as it will allow relevant agencies to accurately assess the pollution level of microplastics in different seasons. It is of practical significance to understand the sources and sinks of microplastics in inland freshwater environment.