Plastics long shadow: legacy and fate of plastic pollution in the oceans

Based on our modeling, more than 10 million tonnes of plastic have entered the oceans, yet their ultimate fate and long-term impacts remain uncertain. We developed a multimedia model constrained by observations from beaches, seawaters, and seabeds to reconstruct the size (≥>0.2 mm), source, age, and storage of marine plastics since 1950. We find that beaches are the primary mass reservoir, while most particles remain suspended in the water column or sink toward the deep ocean.  Continental emissions primarily contaminate nearby regions, whereas maritime sources disperse particles widely across ocean basins. Global mean ages of plastics range from 14 (10–16) years at the surface to 26 (20–32) years on beaches and 38 (35–42) years on seabeds on a mass-weighted basis, and are generally higher when weighted by particle numbers, highlighting the enduring legacy of historical plastic emissions. Persistent fragmentation of older plastics, combined with accelerating new inputs, produces a numerical dominance of small plastic fragments  (<1 mm) despite their negligible contributions to total mass (<5%). These findings establish a quantitative framework for the ocean plastic cycle,  facilitating the quantification of its ecological and climatic impacts. This underscores the urgent necessity for proactive measures to mitigate the environmental and socio-economic repercussions.