River Plastic Retention and Export across Europe

Rivers play a central role in the global distribution of plastic pollution. Despite recent research showing that the majority of plastic is not transported to the sea, most plastic transport models have not explicitly included plastic retention in rivers. We propose a new model to quantify micro- and macroplastic retention on land and in rivers, and export toward the sea. Of the 3.55 Mt year-1 of plastics emitted to the environment, only 0.1% of microplastics and 0.5% of macroplastics are exported from the river outlet. This results in 16.9 (15.7-35.1) kt year-1 of microplastic and 3.2 (1.4-12.1) kt year-1 macroplastic export. Rivers store plastic, retaining 159.0 (147.8-330.6) kt year-1 of microplastics (5.3%) and 67.4 (29.7-255.4) kt year-1 of macroplastics (2.5%), while the greatest proportion of plastic remains on land. Although large basin size and high plastic emission to land characterize high absolute micro- and macroplastic retention and export, large basin size is a weaker predictor for high plastic retention and export per capita. By aggregating ranks for plastic export and retention, we provide a new and comprehensive outlook on the most polluting rivers of Europe. This work provides crucial baseline estimates for plastic pollution in light of missing plastic reduction quotas to guide future prioritization and assessment of mitigation actions.