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Microplastic accumulation in sewer sediments and its potential entering the environment via combined sewer overflows: a study case in Paris
Summary
During heavy rainfall events in Paris, sewer sediments containing densely accumulated microplastics — up to 178,000 particles per kilogram of dry sediment — are resuspended and discharged directly into rivers via combined sewer overflows. This previously overlooked pathway means that stormwater overflow events can rapidly transfer large quantities of microplastics stored in urban sewer networks into freshwater ecosystems.
Abstract During wet weather events, combined sewer overflows (CSOs) transfer large amount of particulate matter and associated pollutants into surrounding water bodies, thereby deteriorating the recipients’ ecological health. Resuspension of sewer sediments during these events contribute significantly to pollution level of these discharges. However, how much this in-sewer process contributes to CSOs’ quality regarding microplastic (MP) pollution is little known. Therefore, an investigation on sewer deposits inside the Parisian combined sewer network was carried out. The study found high MP concentrations stored in this matrix, ranging from 5×10 3 to 178×10 3 particle/kg dry weight. Polymer composition is similar to what found in raw wastewater, containing a high proportion of polyethylene and polypropylene. Thus, the results indicated the retainment of MPs in sewer network during transport during dry weather periods to treatment facilities. Once resuspension of sewer deposits happens, MPs can be released into water flow and get discharged along with CSOs. This highlights another potential pathway of MPs into freshwater environment.