Plastic pollution outlook in the mediterranean sea: a box-model approach based on OECD policy scenarios.

The Mediterranean Sea is pressured by numerous anthropic factors, among which plastic pollution raises serious concerns for ecosystems and human health. In this study, an environmental plastics mass budget is proposed for the Mediterranean region based on recent observations, allowing the formulation of a first order plastics cycle box-model that simulates plastics dispersal and fragmentation in the land-ocean-atmosphere system. We use this model to explore 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 3-13 Mt) in 2015 constraints continental plastic runoff to 0.44 Mt y-1 (0.20-0.82 Mt y-1). The total marine plastics stock would increase 9-fold by 2060 under a business-as-usual scenario, reaching 60 Mt (29-100 Mt). Implementation of the OECD Global Ambition scenario would lower this stock to 49 Mt (25-81 Mt) by 2060. Most of the plastic runoff from land to sea is attributed to the Northern Africa and Middle-East modelled region, with 0.34 Mt y-1 (78%). This indicates that efforts to implement efficient collecting and treatment systems should focus on these regions. About 1.4% of all the plastic waste generated in the Mediterranean Sea catchment between 1950 and 2015 reached the marine environment, meaning that most of the plastic waste generated is still terrestrial (362 Mt, 76%). Moreover, in the marine environment, most of the plastic mass is concentrated in the shelf sediments (5 Mt, 76%), which are fragile ecosystems that host most of the Mediterranean Sea biodiversity, making downstream plastic unrealistic to clean up. Terrestrial remediation of legacy plastic pool could reduce total plastic runoff from land to sea by half of the current value toward the end of the 21st century.