Study of plastic debris and anthropogenic fibers during transient events: rainfall episodes in urban environments and flood dynamics

Plastics are an important environmental issue. These debris range from macroplastics to microplastics. Moreover, anthropogenic fibers were identified in different environmental compartments. The urban environment represents a major source for this pollution.This thesis presents new data regarding plastic waste and anthropogenic fibers in the Seine river basin as well as in Greater Paris during transitory events. Firstly, methodological questions were addressed regarding the digestion protocols for fibers analyses. Then, inter and intra event variability of the macro and microplastic concentrations in stormwater of Greater Paris were assessed. The 2018 flood event and the urbanization gradient impact on the microplastic concentration in the Seine river basin were also evaluated. Finally, plastic waste and anthropogenic fibers fluxes were estimated in Greater Paris and in the Seine River.To address the first question, the impact of five commonly used digestion protocols on the seven most produced fibers in traditional textile were studied. 10% KOH 60 °C and 30% H2O2 40°C protocols should be avoided for synthetic fibers analyses. Diluted NaClO at room temperature for 15 h, 10% KOH at 40 °C for 24 h and Fenton's reagent are more appropriate to maintain fibers integrity.The second question was addressed by studying the occurrence, abundance, and composition of the macrolitter, microplastics and anthropogenic fibers from stormwater at a small residential suburban catchment (Sucy-en-Brie, France) in Greater Paris for one year (macroplastics) and for four rain events (microplastics). For this sampling site, macroplastics and microplastics have the same order of magnitude. When extrapolated to the Greater Paris area, the estimated amount of macroplastic debris discarded into the environment through untreated stormwater of separate sewer systems ranges from 8 to 33 tons yr-1, while microplastic and anthropogenic fiber fluxes ranges from 3 to 48 tons yr-1 and from 0.3 to 0.8 tons yr-1.Finally, fiber and microplastic concentrations, size and polymer distributions, and mass fluxes were evaluated in the Seine river during contrasted hydrological conditions: low flow conditions versus a flood event. The median fiber and microplastic concentrations is 2.6 and 15.5 items/L with an interquartile range of 1.6 and 4.9 items/L (n=10), respectively. High flowrates did not significantly change the concentrations. However, microplastic mass fluxes are strongly impacted by the high flowrates during the flood. Fiber and microplastic fluxes show an increasing gradient from upstream to downstream. The flood event, which lasted 52 days (approximately 15% of the year), contributed to 40% of the annual microplastic flux in the Seine river. These events strongly contribute to these fluxes.Plastic mass fluxes in urban compartments and freshwater systems are still sparse. This PhD contributes to the estimation of these fluxes by providing new insights on the role of transitory events