Even if all plastic inputs into the sea were stopped today, surface plastics could continue to pollute the world’s oceans for more than a century, according to new research from Queen Mary University of London (QMUL).
The study, published in Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences on October 23, 2025, presents a new model explaining how buoyant plastics slowly break down and settle through ocean layers. It shows that plastic pollution in oceans is far more persistent than previously estimated, with fragments continuing to degrade and circulate near the surface long after their release.
Led by Dr Nan Wu from QMUL’s Department of Geography and Environmental Science, the research team worked with collaborators from HR Wallingford Ltd to simulate how plastic debris moves from the surface to the deep ocean. The model incorporates fragmentation dynamics and the role of marine snow. That is sticky organic material that binds to microplastics and carries them downwards, which can be used to predict the long-term fate of floating plastic.
How plastics linger for a century at the ocean’s surface
The study reveals that large, buoyant plastic items degrade slowly at the surface under sunlight and wave action, fragmenting into smaller particles over decades. These microfragments then attach to marine snow, which gradually sinks, carrying plastics toward the seabed. The degradation process, rather than sedimentation, is the main factor limiting how quickly plastics disappear from surface waters.
“People often assume that plastic in the ocean just sinks or disappears,” said Dr Wu. “But our model shows that most large, buoyant plastics degrade slowly at the surface, fragmenting into smaller particles over decades. Even after 100 years, about 10 per cent of the original plastic can still be found at the surface.”
This slow breakdown helps explain the “missing plastic” problem — the gap between the amount of buoyant plastic entering the ocean and the smaller quantities observed floating at the surface. While some sinks over time, much of it persists unseen as suspended microplastics that continue to fragment and cycle through marine ecosystems.
A global challenge that demands long-term thinking
Co-author Professor Kate Spencer, also from QMUL’s Department of Geography and Environmental Science, said the findings confirm that plastic pollution in oceans is an intergenerational problem.
“Our research shows how important fine and sticky suspended sediments are for controlling microplastic fate and transport. It also tells us that microplastic pollution is a problem our grandchildren will still be managing, even if we stop plastic waste today.”
The model also highlights how increasing plastic production could overwhelm the biological pump — the ocean’s natural system that transports carbon and particles to the deep sea. As microplastic concentrations rise, they may begin to interfere with this process, disrupting carbon cycling and marine nutrient balance.
Professor Andrew Manning, Principal Scientist at HR Wallingford and Associate Professor at the University of Plymouth, said addressing the issue requires sustained global cooperation.
“This study helps explain why so much of the plastic we expect to find on the ocean surface is missing. As large plastics fragment, they become small enough to attach to marine snow and sink. But that transformation takes decades. To tackle the problem properly, we need long-term thinking that goes beyond just cleaning the surface.”
Towards better models of marine plastic fate
The paper concludes a trilogy of studies that together provide the most comprehensive framework yet for understanding how buoyant plastics behave in marine environments. Earlier work by the same team, published in Nature Water and Limnology & Oceanography, examined microplastic dispersion and sedimentation processes, forming the foundation for this final global-scale model.
Funded by the Lloyd’s Register Foundation and supported by QMUL, HR Wallingford, and the EU INTERREG Preventing Plastic Pollution project, the research underscores the need for more robust predictive models to inform policy and management decisions.
As Dr Wu noted, “Our results show that plastic pollution in oceans cannot be solved by surface clean-ups alone. The persistence of buoyant plastics means we need strategies that prevent fragmentation at the source and consider how plastics interact with ocean processes over decades.”