River Microplastic Contamination and Dynamics upon a Rainfall Event in Hong Kong, China

Microplastic pollution is a global environmental crisis because of the persistence of plastics in the environment and their direct and indirect threats to a wide spectrum of wildlife. The marine environment is a major sink of plastic debris and rivers are believed to be an important source. However, the microplastic contamination levels and their dynamics in rivers remain poorly understood. This study aims to quantify microplastic abundance and the properties of the microplastics at the surface of an urban river after a rainfall event in Hong Kong. Plastic samples were collected at the river surface after a 3-day rainfall event. The microplastic abundance was 7.428 pieces/m3 (1,615,506 pieces/km2), which was nearly double of that observed on coastal sea surface of the same area (3.973 pieces/m3). Microplastic abundances were found to decrease over ten times (from 14.015 to 1.298 pieces/m3) within 2 hours, suggesting that the temporal distribution of river microplastics was highly dynamic after rainfall. To better understand the microplastic dynamics in river with respect to the rainfall-runoff process, further studies are needed to capture microplastic abundances before, during and after a rainfall event.