Macro and Microplastics in Stormwater and Combined Sewer Overflows in Paris Megacity

Abstract

Stormwater and combined sewer overflows (CSO) might represent an important source of macro and microplastics in the environment, but such fluxes are poorly investigated. In order to fill this knowledge gap, macro and microplastic concentrations were investigated (i) in stormwater and grid refusals at the outlet of a runoff water pipe located in Sucy-en-Brie (Paris suburb, France) and (ii) in CSO discharges at the Clichy outfall (Paris suburb, France). Macroplastics were sorted, weighted and classified. To study microplastics during rain events, 500 litres of water were filtered using plankton net with 80 μm mesh size. Microplastics were then extracted using H2O2 30% digestion followed by NaI density separation (d = 1.6 g.cm−3). A microscope and Fourier Transformed Infrared spectroscopy were applied to identify microplastics. Preliminary results from stormwater outlet of Sucy-en-Brie showed that macroplastic mass percentages were in the range of 1.5 to 37.5%. Moreover, 8 main plastic categories were found to contribute to 95% of total macroplastics and were identified as sanitary textiles, plastic bags or films, food packaging, bottles, cigarette buds, garbage bags, and polystyrene fragments. Macroplastic concentrations in stormwater from March to June 2018 ranged from 3 × 10−5 kg/m3 to 1 × 10−4 kg/m3. Three rain events were sampled at Sucy-en-Brie to study the concentration of microplastics. Microplastics with size of 1 to 5 mm during first rain event were analysed. Results indicated that microplastic concentrations were in the range of 4.6 × 10−2 and 9.3 × 10−3 fragments/L, in which polyamide and polyethylene predominated.