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Microplastics retained in rain gardens within different functional areas of Nanjing, eastern China
Summary
Researchers investigated microplastic retention in rain gardens across different functional areas of Nanjing, China, quantifying MP characteristics in these low-impact development stormwater management systems and evaluating their sources, finding that rain gardens can serve as significant sinks for urban microplastic pollution.
Rain gardens, a type of low-impact development infrastructure, are designed to manage stormwater runoff and retain pollutants, such as microplastics (MPs). However, few studies have quantified MPs in rain gardens and evaluated their sources. In this study, we investigated the characteristics of MPs and evaluated their source pathways (stormwater loading and atmospheric deposition) by sampling soils inside and outside (nearby lawns) the boundaries of rain gardens within residential, traffic, and park areas in Nanjing, China. The dominant size of MPs was observed to be < 2 mm, fibers being the major shape. In traffic areas, the average MP concentration was significantly higher in rain gardens than in lawns, especially for MPs < 2 mm. Conversely, in other functional areas, no significant differences in MP concentrations were found. This indicates that stormwater runoff is an important yet not the sole source of MPs in rain gardens, and its contribution to MPs in rain gardens increased in traffic areas. Considering that MP accumulation in rain gardens may affect the function of rain gardens, such as water infiltration, we propose that the media of rain gardens in traffic areas should be replaced more frequently to prolong their longevity.