Microplastics (plastic particles < 5 mm) are ubiquitous in our environment, and rainfall acts as a conduit for transporting microplastics from land to aquatic ecosystems. In this study, the impact of rainfall on microplastic abundance within a canal ecosystem was investigated. During the first flush of a rainfall event, we measured and collected runoff from two outlets originating from the busiest and least busy parking lots on a university campus. Among the land-based microplastic sources, parking lots are an important source as the wear and tear of vehicle tires, fragments of parking lot construction materials, litter, and plastic road sign markings accumulate in a parking lot. Rainfall runoffs carry these accumulated microplastics, alongside other pollutants, into the nearest water body (e.g., a canal). Furthermore, to comprehensively evaluate the overall impact of rainfall on microplastic pollution in a canal, we examined four canal cross-sections, focusing on water concentrations, bed load, and suspended sediment load. Our findings revealed that the rainfall intensity, duration, and time interval since the last rainfall events significantly influenced the transport of microplastics. Microplastic concentration varied significantly between summertime (university off period) and fall (regular class period). Moreover, based on a risk assessment, the impact of transported microplastics was characterized. This study aims to provide a scientific reference on the impact of rainfall on microplastic pollution in the aquatic environment as well as the migration of land-based microplastic to canal ecosystems.
