In recent years, many studies have shown that microplastics pose a potential threat to human health and are widely detected in aquatic organisms such as fish and shellfish in river ecosystems. As an emerging pollutant, microplastics exist in large quantities in the watershed environment and have the ability to adsorb pollutants, which intensifies the threat to the watershed ecological environment. Therefore, it is important to deeply study the distribution characteristics and source analysis of microplastics in different types of urban water environment. However, there are few studies on microplastic pollution in small watershed areas such as Nandu River and Wanquan River in Hainan Province.
In this study, a systematic survey was carried out in the Nandu River and Wanquan River basins in April and August 2023 by using the bucket sampling method to explore the occurrence characteristics, migration routes and potential sources of microplastics. The results showed as follows: 1) Microplastics were detected in Nandu River and Wanquan River, and the main components were polyethylene, polypropylene and polyester fiber. 2) The spatial heterogeneity of microplastics in water is affected by unique hydrological characteristics, which can be attributed to the variation of water flow velocity in different sampling areas caused by topographic differences, which affects the distribution uniformity of microplastics. 3) The differences in the abundance and morphology of microplastics at different sampling sites indicate that they have different pollution sources. The abundance of microplastics was the lowest in the sampling points of reservoir, and their morphology was similar, and they came from upstream input. The abundance of microplastics in sampling sites in densely populated areas is the highest, and the forms are diverse, which is related to nearby sewage discharge, industrial wastewater and gas discharge. Although the level of microplastic pollution in Nandu River and Wanquan River is low, it is still necessary to strengthen the management of plastic waste. The results of this study provide a scientific basis for monitoring, prevention and control of microplastic pollution in river basins.

Microplastics; Occurrence characteristics; Source analysis; Nandu River; Wanquan River