The fate of missing ocean plastics: Are they just a marine environmental problem?

The fate of mismanaged plastic waste released into oceans (ocean plastics) remains a topic of debate, where the mass imbalance between the leakage and abundance in the world's oceans appears paradoxical. In the present study, a budget for ocean plastic mass was estimated based on a combination of numerical particle tracking and linear mass-balance models, both validated using a worldwide ocean plastic dataset. Integrating the time series of worldwide macroplastic emission from both rivers and the fisheries industry over the period 1961-2017 yielded a total mass of 25.3 million metric tonnes (MMT). Macro- and microplastics currently floating in the oceans, and microplastics on beaches, each account for 3-4% of the ocean plastics emitted worldwide to date. Overall, 23.4% of ocean plastics were macroplastics on beaches. Meanwhile, 66.7% of ocean plastics were heavier than seawater or microplastics removed from the upper ocean and beaches, which are difficult to monitor under current observation frameworks adopted worldwide. However, the present study on ocean plastics suggested that the whole ocean plastics accounted for only 4.7% of mismanaged plastic waste (542.2 MMT) generated between the 1960s and today.