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Experimental study on transport processes of fragment microplastics during urban road rainfall runoff
Summary
Tiny plastic fragments that accumulate on roads get swept into rivers and lakes when it rains, especially during heavy storms, on flatter roads, and when smaller fragments are involved, according to this study. This matters because these plastics eventually end up in the water bodies that supply our drinking water and support fish and wildlife, and understanding how rain washes them away can help cities design better filtering systems to catch them before they spread further into the environment.
Large quantities of microplastics (MPs) are transported from urban surfaces via runoff to different water bodies, leading to the deterioration of aquatic ecosystems. Fragment MPs have been found to be widely present on urban roads, and their shapes are significantly different from granular ones, which affects their transport mechanism in stormwater. However, the transport process of fragment MPs in urban stormwater is still not well understood. Moreover, whether the traditional exponential wash-off model proposed for particulate matter can be applied to fragment MPs still requires further verification. A series of simulated rainfall experiments were conducted considering various rainfall intensity, slope, initial load, and particle size. It demonstrated that fragment MPs exhibited similar transport processes under various conditions, characterized by first increases to the maximum value and then a decrease to zero in both concentration and transport rate. With the increase of rainfall intensity and the decrease of slope, the peak values of concentration and transport rate as well as the final wash-off fraction all increased significantly. The influence of initial load on the transport process of fragment MPs showed a proportional relation. Furthermore, the larger the size of the fragment MPs, the smaller the transport potential was observed. The first flush effect was obvious during the transport processes of fragment MPs and could be fitted by the power function. The exponential wash-off model could be used to predict the wash-off fraction of MPs fragments effectively. This study advances the understanding of the transport process of fragment MPs in urban areas.