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 Sea and catchment raises serious concerns for ecosystem and human health. Plastic dispersal from Mediterranean watersheds in southern Europe, northern Africa, the Middle East and the Nile basin is complex due to the different (mis)managed waste streams, population dynamics, and climates. In this study, an environmental macroplastics and microplastics (hereafter "plastics") mass budget and box model is proposed for the Mediterranean region based on recent observations. We use this model to explore the dispersal of plastics under different plastic production and waste management policy scenarios of the Organisation for Economic Co-operation and Development (OECD) 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 7×106 metric tonnes (megatonne, Mt; median, IQR 3-15 Mt) in 2015 constrains continental plastic input to sea to 0.31 Mtyr-1 (median, IQR 0.14-0.57 Mtyr-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). The implementation of the OECD Global Ambition policy scenario, which 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 remote sensing observations of marine litter attribute most, 0.27 Mtyr-1 (88 %), of recent plastic input from land to sea 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 the plastic mass resides in shelf sediments (median 6 Mt, IQR 2-14 Mt), which are fragile ecosystems that host most of the Mediterranean Sea's biodiversity and are not easy to clean up. This underlines the necessity of addressing upstream legacy plastic waste on land. Land-based remediation scenarios modeled here show that total plastic input from land to sea can be reduced 2-fold (0.22 Mtyr-1, IQR 0.16-0.27 Mtyr-1) compared to the business-As-usual scenario in 2060 and can significantly reduce the total plastic stock in the marine environment.