Microplastics in Urban Environments: Sources, Pathways, and Distribution

Due to high-density anthropic activity, the urban environment is regarded as one of the major sources of microplastics (MPs). MPs can be produced in the process of tire wear, landfill and sewage treatment, construction, industrial activity, household laundry, and so on. According to recent studies, MPs have been widely detected in urban atmosphere, ground surface dust or soil, and municipal rivers. Due to lightweight and low density, MPs can easily float and transform between different environmental matrices in urban ecosystems. Storm-water runoff is regarded as an important pathway of MP from land to urban rivers or coastal waters. By wind transportation, MPs on the municipal ground surface can be transferred to urban rivers or the atmosphere. After treating sewage treatment plants, concentrations of MPs can be extremely reduced in the discharged water but increased in the sludge. MPs have also been found in landfills and may leak into other environmental substrates. It can be concluded that MPs can migrate and transform among multiple urban environments through physical and biochemical drivers. Distribution and transformation of MPs are closely related to the urban ecological environment and also pose a potential risk on the health of urban residents. More research work needs to fully reveal the source and fate of MPs in urban environments.