Webinar of Dr Johnny GASPERI
November 20th 2024
Microplastics in continental sediments and sedimentary cores: Sedi-PLAST project
Home institution: Université Gustave Eiffel, LEE, Bouhuenais, FranceSynopsis
The Sedi-PLAST project - Microplastics (MP) in continental sediments and sediment cores, 2020-2024 - is funded by the French Research Agency (ANR). This project aims to investigate, using various sedimentological approaches, the contamination of river sediments by MP (> 25 µm) in order to understand the relations between depositional environments (mineralogical composition, texture and residence time of the sediment) and the concentrations, and size and polymer distribution of MP found in the sediments. Results first confirm that sediments are major reservoirs of microplastics. On the scale of the three rivers studied, concentrations range from a few thousand to several tens of thousands of microplastics per kilogram of sediment. Among the factors explaining, the fraction of fine sediments (< 63 µm) and the total organic carbon content appear to be the most important factors in explaining the spatial variability observed between stations, but they alone cannot explain this variability. The geomorphology of the sampling sites and, ultimately depositional environments and the connectivity of these environments with the river also influence the concentration of microplastics in sediments. On the Loire, for example, it has been shown that semi-active channels are contaminated than the banks and sandbanks of the minor bed. Similarly on the Rhone River between sediments collected in the main channel and those collected in the hydraulic appendages.Through a study of sedimentary cores, which is particularly innovative and original, the project objective includes evaluating the temporal trajectories of plastic pollution at the scale of anthropized watersheds. A total of six cores were sampled, upstream and downstream of Paris (J.S. Barbier's thesis), upstream and downstream of Lyon (Dhivert et al., 2024) and two archives in the downstream Loire (C. Croiset's thesis) in different depositional environments (a high bank and a river annex). Spatial comparison of sediment records reveals a sharp increase in contamination levels and polymer diversity downstream of urban areas (Paris and Lyon). For these stations, however, sediment records show a decrease in PM levels since the 2000s for polymers associated with industrial sources, and since the 2010s for ubiquitous polymers. This trend diverges from global assessments, which assume uncontrolled pollution. It suggests that European wastewater directives and regulations on industrial discharges have had a positive influence on water quality with regard to microplastics. Trends in the Loire archives are currently being studied.