Occurrence and distribution of microplastics in domestic, industrial, agricultural and aquacultural wastewater sources: A case study in Changzhou, China

The extensive application of plastic in human life brings about microplastic (MP) pollution in the environment. Identifying the potential sources of MPs is necessary to diminish its pollution. In this study, the occurrence, composition and distribution of MPs in the influents and effluents from 9 domestic wastewater treatment plants (WWTPs), 5 industrial WWTPs, wastewater of 10 industrial plants, 4 livestock farms and 4 fish ponds in China were investigated. Water samples were enzymatically treated followed by digestion with hydrogen peroxide and density separation. MPs were characterized using micro-Raman spectroscopy and were categorized by shape, size and color. Results showed that MP abundance in the influents and effluents of domestic WWTPs was 18-890 and 6-26 n·L-1, respectively, with the removal efficiency ranging from 35 to 98%. The effluents of industrial WWTPs contained 6-12 n·L-1 and the levels of MPs in the wastewater of industrial plants, livestock farms and fish ponds were in the range of 8-23, 8-40 and 13-27 n·L-1, respectively. No significant differences of MP abundance were demonstrated among effluents or wastewater of different sources, indicating they all constitute sources of MP pollution. Polyethylene (PE), polypropylene (PP) and polystyrene (PS) made up almost 83% of the total MPs. Fragment and film were the most abundant shapes and the majority of MPs were smaller than 500 μm. Polymer type and shape in different sources did not vary statistically, however, there were slight differences among different sources concerning size and color of MPs. This study could fill MP data gaps regarding different sources, guide future monitoring work and policy making.