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.
Keywords: Flood; Institutional cleaning; Macroplastic emissions; Riverbanks; Tagged litter.
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