Plastic pellets pollution on the French Atlantic coast: Investigating the Loire estuary

Plastic pellets are among the most frequently microplastics reported in coastal environments. However, their distribution and sources remain poorly documented in metropolitan France, particularly along the Atlantic coast. This study combined a literature review, fieldwork, and model simulations to produce an up-to-date data status on pellet occurrence in metropolitan France, and major potential source areas. First, we conducted a literature survey of the current knowledge on pellet contamination in France, integrating information from peer-reviewed publications, grey literature, and technical reports. To fill the data gap revealed in the Loire estuary, we sampled beach-stranded pellets in the estuary and Bourgneuf Bay (27 beaches). We also mapped the French plastic production and transportation chains, identifying major industrial clusters and port infrastructures potentially associated with pellet loss. Two major industrial hubs structure the French plastic production chain, in accordance with French petrochemical activities: 1) Lyon region along the Rhone River and 2) along the Seine corridor near Le Havre. Six major commercial ports were identified as strategic nodes for the maritime transport of plastic-related goods along the French coastline. Available pellet data are concentrated in areas such as Côte d’Argent , Brest, Le Havre, and Dunkirk. Pellets were widely distributed across the Loire Estuary, with high spatial heterogeneity. Higher levels were observed in the eastern estuary and on the Atlantic coast of Noirmoutier Island (716.2 to 2.9 pellets m -2 ). Our findings fill an important geographical gap in pellet monitoring along the French Atlantic coast and reinforce the need for broad and long-term monitoring programs.