Transfer dynamics of macroplastics in estuaries – New insights from the Seine estuary: Part 3. What fate for macroplastics?

Highlights: • Institutional cleaning on riverbanks in the Seine estuary are conducted since 2008. • A tagged litter experiment was conducted to quantify macroplastic emissions. • 28% of the tagged litter were recovered by institutional cleaning in one year. • 100–200 mt/yr (maximum) of macroplastics are emitted to the sea. • Cleaning on riverbanks are the best curative solutions to prevent plastics at sea. Macroplastic emissions from the Seine estuary to the English Channel were estimated using institutional cleaning of riverbanks, combined with a tagged litter experiment. Cleaning were performed between March 2018 and April 2019 by the non-profit company Naturaul'un over 19 sites covering 20 km of riverbanks. A total of 365 tagged litter (90% macroplastics) was released in the estuary in March (n = 200), at the end of the winter/spring flood 2018, in July (n = 58), August (n = 56) and September 2018 (n = 51) during low river flow periods. Over the total tagged litter, 102 (28%) were recovered by Naturaul'un. Relative to the total amount of macroplastics (>5 cm) collected and the estimated amount of smaller/hidden macroplastics (>5 mm) not collected, the maximum macroplastic emission to the English Channel was estimated to be ~100–200 metric tons per year.