Assessing macroplastic debris collected from eight diverse river systems across four continents: Insights from synchronous three-year community-led research efforts.

Plastic pollution is an urgent and growing threat to human and planetary health. Rivers transport large volumes of plastic pollution across and between Earth's systems, providing opportunistic and strategic focal points for collection and quantitative assessments of plastic debris. A dearth of empirical, in situ studies of riverine plastic debris in scientific literature highlights the need for more research conducted in rivers across diverse contexts to better understand riverine plastic debris and inform upstream solutions. We present and analyze a dataset on macroplastic debris collected over three years (2020-2023) in a nearly continuous and synchronous fashion from eight diverse river systems in eight countries across four continents. We observed the majority (66 %) of the 3.8M kg of debris collected and analyzed in these river systems to be plastic. The compositions of polymers, single-use plastic items, and end-of-life fates of the collected plastic debris varied substantially between river systems. We discuss how differences in socioeconomic, regulatory, and infrastructure conditions across study sites begin to explain some of the observed variation. From these data insights, we share local and global recommendations for actions that could help reduce the flow of plastic debris into rivers in the first place. This research adds to our growing understanding of plastic pollution locally in these specific river systems as well as globally at a moment when the international community is actively working towards a global policy instrument to end plastic pollution.