Computing riverine inputs of macrolitter into the Central Tyrrhenian Sea (Western Mediterranean Sea) from the Tiber River during the 1st post-pandemic year

This study addresses the critical knowledge gap on riverine macroplastic inputs to marine litter, focusing on changes in waste composition in a post-pandemic context. While marine plastic pollution has been widely documented, data on floating macrolitter from urban rivers remain limited. The first comprehensive, year-round assessment of floating macrolitter at both branches of the Tiber River mouth were conducted, using the harmonized RIMMEL approach using a dedicated android App. The simultaneous monitoring conducted at two sites (TIB2 and TIB3), recorded abundance, material composition, size and common item types, revealing an estimated annual transport rate of 9 × 10⁵ items/year from the Tiber River to the Mediterranean Sea. Specifically, the transport rate was 104 ± 87 items/h and density of 1170 ± 151 items/km². The litter transport rate exhibited seasonal variability, with the highest peak observed in autumn and the lowest in summer. Findings reveal a post-pandemic reduction of <34 % in total macrolitter items, countered by a rise in single-use items, such as plastic cups, plastic bottles label and lids plastic stick from cotton bud and lollies, sanitary towel and condom. COVID-19-related items such as single-use face masks and gloves were also recorded. Over half of the items were under 10 cm, suggesting fragmentation before reaching the sea. This study enhances understanding of riverine litter in a big European capital, providing a post-pandemic dataset to identify pollution patterns and track the evolution of COVID-19-related waste.