Microplastic in sedimentary archives of the Rhône River: a 35-year record of the impact of the Lyon urban area

Although microplastics (MP) archiving processes are suggested in river sediments, few studies have analysed temporal records of MP in sediment cores. However, sediment cores give access to past anthropogenic contamination on basin and multi-decade scales. This work focus on the MP contamination (25 – 5 000 µm) in sedimentary archives of the Rhône River, recovered in 2021 upstream and downstream of Lyon. Sediment cores were described and sampled by 4 cm slides. Based on radionuclides analysis age-models were proposed. MP were extracted from about 10 g ww of sediment sieved at 5 000 µm, using density separation and oxidative degradation of organic matter, and then filtered on aluminum oxide membrane filters for µFTIR imaging analysis. 25 µm pixel resolution maps were performed and MP were characterised using siMPle. Results revealed a significant impact of the Lyon metropolis on MP content from 1986 to present with range between 800 and 3'750 particles/kg/year in the upstream station and between 3'180 and 73'000 particles/kg/year in the downstream station. Furthermore, results show a significant difference in the polymers composition between stations. In the upstream one, polypropylene (PP) and polyethylene (PE) are the most abundant polymers with respectively 70% and 20% of the MP, whereas in the downstream one, most represented polymers are PP (53%) and polyvinyl chloride (PVC) (33%). Over the recorded period, the MP content is maximum around 2010 in both stations. In the downstream station, PVC content shows a decreasing trend since the mid-1980s. Using well-dated and well-described sediment cores we reconstituted temporal evolution of MP pollution along a river section crossed by a highly industrialized and urbanized area. We highlighted contrasted trends and MP abundances and the diversity of polymers in relation with the influence of the urban area. Also see: https://micro2022.sciencesconf.org/426792/documentIn MICRO 2022, Online Atlas Edition: Plastic Pollution from MACRO to nan