Terrestrial and marine plastic pollution outlook in the Mediterranean region: a box-model approach based on OECD policy scenarios

Abstract. Plastic pollution in the Mediterranean region and Sea raises serious concerns for ecosystem and human health. Plastic dispersal from Mediterranean watersheds in Southern Europe, Northern Africa and Middle-East, and Nile basin is complex due to the different (mis-)managed waste streams, population dynamics and climate. In this study, an environmental plastics mass budget and box-model is proposed for the Mediterranean region based on recent observations. We use this model to explore plastics dispersal under different OECD plastic production and waste management policy scenarios toward the end of the 21st century. We find that the current Mediterranean marine plastic stock (sea surface, water column, sandy beach and sediments) of 7 million metric tons (Mt, median, IQR 3–15 Mt) in 2015 constrains continental plastic runoff to 0.31 Mt y^-1 (median, IQR 0.14–0.57 Mt y^-1). The total marine plastics stock would increase 4-fold by 2060 under a business-as-usual scenario, reaching 26 Mt (median, IQR 13–48 Mt). Implementation of the OECD Global Ambition policy scenario, that targets near-zero new plastics waste leakage, would not significantly lower this stock (25 Mt, median, IQR 12–44 Mt) by 2060. This is because marine litter remote sensing observations attribute most, 0.27 Mt y^-1 (88 %), of recent plastic runoff to Southern Europe, where high rainfall will continue to mobilize legacy plastic waste from land to sea, regardless of low leakage targets. About 1.5 % of all Mediterranean legacy plastic waste reached the marine environment, meaning that most plastic waste still resides on land (361 Mt, 76 %). Moreover, in the marine environment, 83 % of plastic mass resides in shelf sediments (median 6 Mt, IQR 2–14 Mt), which are fragile ecosystems that host most of the Mediterranean Sea biodiversity, and are not easy to clean up. This underlines the necessity to address upstream legacy plastic waste on land. Land-based remediation scenarios modelled here show that total plastic runoff from land to sea can be reduced 2-fold (0.22 Mt y^-1, IQR 0.16–0.27 Mt y^-1) compared to the business-as-usual scenario in 2060, and significantly reduce the total plastic stock in the marine environment.