Plastic debris dataset on the Seine riverbanks: up to 38,000 pre-production plastic pellets reported per square meter

Plastic pollution in rivers is a major source for plastic pollution into the ocean. However, it is now recognized that plastics may accumulate in rivers for years, especially in estuaries, before reaching the ocean. This long residence time favours fragmentation of macroplastics into smaller and smaller pieces, but relative data are still carse. Here we present data from the downstream part of the Seine estuary in a historical deposit full of plastic debris, with the highest concentration of industrial plastic pellet ever reported in France. Plastic debris (down to 6 mm according to sieving limits) were classified using the updated European classification J-list. The sampled site is located close to the river mouth within a national natural reserve, surrounded by international harbour activities and two major industrial plastic producers: Total Energy and Exxon Mobil. A surface of only 1 m² was sampled in a visual maximum of plastic pollution. Over 100,000 plastic debris were counted or estimated when it comes to plastic debris <6 mm. Items were classified and weighted by category for a total mass higher than 4 kg. By mass (count), 24 % (38 %) of total plastic debris were pre-production plastic pellets, 21 % (1 %) were unidentified, colourful, plastic fragments (<i>≥</i> 2.5 cm), and 19 % (33 %) were unidentified, colourful, plastic fragments (<2.5 cm).