Distribution characteristics of microplastics in urban rivers of Songjiang District, Shanghai

Plastic products are widely used for their low price, light weight and convenience for carrying. Meanwhile, more and more discarded plastic trashes enter water bodies. They can break down to smaller fragments by physical and chemical factors. Plastic debris whose sizes are smaller than 5 mm can be defined as microplastics. Microplastics can be ingested by organisms that take them as size-similar food. They can be transferred to human body through food chain by bioaccumulation and cause health crisis. Though there are plenty of researches focusing on marine microplastics, little attention is paid to microplastics in urban rivers. The urban rivers are closer to human residents and are largely influenced by human activities. So to understand the status of microplastics in urban rivers is urgent for human health. Shanghai, as an international economic, financial, trade, shipping, science and technology innovation center, is with dense population and strong human activities. Located in the Yangtze River Delta area, Shanghai is in the east of China, and near the Yangtze River Estuary and the East China Sea. Songjiang District is located in the southwest of Shanghai, about 40 km away from the urban area. The main rivers are Huangpu River, Dianpu River and Sijingtang River. The industry, agriculture and tourism are relatively developed in Songjiang District, so the pillar industries are diversified. In order to reveal the distribution and influencing factors of microplastics in urban rivers in Songjiang District, Shanghai, the contents, particle size range, sources and influencing factors of microplastics in four rivers which flow through different functional areas in Songjiang District were studied by means of surface sampling, density suspension separation, optical microscope and Laman spectroscopy. Results showed that the content of microplastics in the four rivers in Songjiang area was 2-5 pieces · m-3, and the content of microplastics was negatively correlated with the runoff (R2=0.81, P<0.05). The river with slow flow was more likely to hold the microplastics in the water. The particle size of microplastics in the river ranged from 0.5 mm to 5.0 mm, and the particle size was relatively large. Microplastics mainly came from human life plastic waste and plastic packaging in industrial and agricultural production. The research results can provide a reference for the analysis of the current situation of urban river microplastic pollution, and lay a foundation for further prevention and control of urban microplastic pollution.