Understanding the fate and control of road dust-associated microplastics in stormwater

Microplastics (MPs) pollution in the water environment is recognized as an important environmental risk. Among the diverse sources of MPs pollution, road dust is a major contributor via stormwater runoff. Roaddust mainly originates from degradation of vehicle tyres, road marking paints, polymer-modified bitumen and the broken plastics on the surface of the road. The objective of this study is to provide a comprehensive understanding of the fate and control of MPs in the open water environment. This review critically discusses the characteristics and pathways of road dust-associated MPs in stormwater and common stormwater treatment processes used for removing MPs, and provides insight into the technical challenges of these technologies. Constructed wetland is widely used for stormwater management; however, it is found that this process is only removing 28 % MPs as they usually remain suspended or settle down very slowly in the sedimentation basin of constructed wetlands. This is because of the low density of MP particles as well as the low retention time of the wetland. Thus, untreated stormwater, rich in MPs, is released into open waterbodies. This study concludes by providing an outlook of the future opportunities of installing membrane- or flotation-based technologies in the outlet of the constructed wetland for removing 90-95 % MPs and other remaining contaminants. Such a process can produce clean water either for use in households, for sanitation, and for industrial and agricultural usage, or alternatively, for safe discharge into open waterways. (c) 2021 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.