From historical plastic pollution to environmental remediation scenarios. A case study in the Seine estuary

The Seine River basin, home to a quarter of the French population, faces the generation of around one million tons of plastic waste each year in the Paris region. Despite efficient plastic waste management, some of it escapes the systems and ends up in the Seine River, contributing to its pollution. Recent studies show that plastic debris remains in the river due to tides. This promotes the accumulation of plastic debris on the riverbanks, particularly during floods, creating historical accumulation zones in some areas. In this way, these plastics along with their chemical substances, pollute all environmental compartments. The aim of the TEDiPLAST project is to better understand the sources, stocks, fluxes, and dynamics of plastic debris in historical accumulation zones. How they build up and what do they become? First, innovative clean-up techniques will be tested to ensure effective collection of plastic debris, including those as small as preproduction industrial pellets. Second, adapted sampling and treatment protocols will be implemented to obtain representative results along a size class continuum, from macroplastics to coarse microplastics (> 500 µm), while considering their respective characteristics. Third, macroplastics will be sorted according to the OSPAR/TSG ML, whereas smaller plastic debris will be analysed by ATR-FTIR. Additionally, all data related to tracing debris sources and their lifespan in the environment will be recorded (dates, brand names, logos, etc.). One of the challenges consists in combining analytical techniques and sampling protocols to cover a large continuum of plastic sizes, while remaining representative of extensive and heterogeneous accumulation zones where up to 4 kg of plastic per square meter accumulates. Furthermore, preproduction industrial pellets will also be a focus, as they are one of the main plastic wastes found in these zones due to the vicinity of some producers and converters along the Seine River. At the end, remediation scenarios will be suggested to support mitigation policies and strategies.