Plastic pollution has often been described as one of humanity’s most persistent environmental threats — and now, scientists have a clearer sense of just how persistent. A new study from Queen Mary University of London (QMUL) predicts that it could take more than a century to remove buoyant plastic waste from the ocean’s surface, even if all new pollution were stopped today.
Published in Philosophical Transactions of the Royal Society A, the research represents the third and final installment in a trilogy exploring the long-term fate of microplastics in the world’s oceans.
The Research Behind the Century-Long Forecast
Led by QMUL’s Department of Geography and Environmental Science in collaboration with HR Wallingford Ltd, the study combines marine geochemistry, fluid dynamics, and environmental modeling to explore how plastics move and degrade through the ocean.
Researchers used a simulation model to track the breakdown of large buoyant plastic particles as they interact with marine snow — sticky, organic material that forms naturally in seawater and helps transport debris from the surface to the seafloor.
According to Dr. Nan Wu, the study’s lead author, most large plastics do not immediately sink when discarded into the ocean. Instead, they remain near the surface, slowly fragmenting into microplastics over several decades.
Why the Oceans Still “Hide” Most Plastic Waste
For years, scientists have puzzled over the so-called “missing plastic” problem — the discrepancy between the enormous volume of plastic entering oceans and the relatively small amount visible on the surface.
This new model offers an answer. As plastics fragment, the pieces become small enough to stick to marine snow and sink, but the breakdown happens slowly. “People often assume that plastic in the ocean sinks or disappears quickly,” said Dr. Wu. “Our model shows that even after 100 years, around 10 per cent of the original plastic could still be floating and breaking down.”
This gradual degradation and transport process means that ocean plastic pollution isn’t just a short-term issue but a multi-generational environmental legacy.
Understanding the Role of Marine Snow
Marine snow consists of organic particles like plankton, fecal matter, and dust, acting as a natural conveyor belt for materials in the ocean. It gradually sinks toward the seabed, taking with it carbon, nutrients, and, now, microplastics.
The researchers observed that fragmented plastics attach to this “sticky” network, allowing even buoyant plastic types — such as polyethylene and polypropylene — to descend over decades.
However, the model also revealed bottlenecks. Plastic degradation itself remains the limiting factor in how fast the ocean surface can clear, as the breakdown of large debris takes far longer than the sinking process that follows.
The Scale of the “Missing Plastic” Issue
While millions of tonnes of plastic enter oceans annually, surveys detect only a fraction of that mass floating near the surface. The new simulation clarifies this mystery by showing that degradation and downward movement take decades, resulting in a delayed accumulation on the seafloor.
This delay means that plastic pollution continues to appear “missing,” even though it is still in slow motion through the deep ocean cycle.
The researchers noted that improving the tracking of plastic degradation rates could help refine global models and ocean cleanup strategies.
The Ocean’s Natural Conveyor Belt Could Become Overwhelmed
The findings also raise concerns about how rising microplastic concentrations could affect the biological pump — the process by which carbon is naturally transported from the surface to the deep ocean.
If microplastics increasingly clog this system, they could interfere with vital biogeochemical cycles that control Earth’s climate.
“Plastics don’t just stay where we drop them; they move through the system and interact with every level of the marine environment,” said Professor Kate Spencer, co-author and supervisor of the project.
She added that the persistence of microplastics illustrates the intergenerational nature of the crisis. “Even if we stopped all plastic dumping tomorrow, our grandchildren would still be cleaning up the oceans.”
Environmental Consequences Beyond the Surface
As plastics fragment into nanoplastics, their ability to infiltrate marine life increases dramatically. These particles can enter food webs, disrupt nutrient cycles, and even alter water chemistry.
The researchers warn that smaller debris forms a nearly invisible layer of pollution that persists for generations, raising complex ecological and human health challenges.
Moreover, ongoing breakdown continuously releases chemical additives — including bisphenols and phthalates — that have known toxic effects on aquatic organisms.
A Call for Long-Term Thinking
Professor Andrew Manning, Principal Scientist at HR Wallingford and co-author, stressed that quick cleanups cannot solve the broader issue.
“This study helps explain why expectations to find large plastic accumulations at the ocean surface often fall short,” he said. “As large plastics degrade, they become microscopic and sink slowly. Tackling this problem requires long-term thinking, not just surface-level cleanup.”
The research reinforces the need for centuries-scale waste planning and stricter measures to reduce plastic production and improve material recycling.
How the Model Works
The team’s model couples fragmentation kinetics — how plastics break apart — with size-selective sedimentation, determining how particles of different shapes and sizes interact with the water column.
By calculating how long particles take to transition from macroplastics to microplastics, the simulation provides perhaps the clearest timeline yet of plastic pollution’s persistence.
The method demonstrates that even though the rate of input might slow, the ocean’s existing pollution will linger for over a century. This conclusion is based on physics, degradation chemistry, and empirical data from previous QMUL studies in Nature Water and Limnology & Oceanography.
Funding and Collaborative Effort
The study was supported by the Lloyd’s Register Foundation, with project backing from QMUL, HR Wallingford Ltd, and the EU INTERREG Preventing Plastic Pollution programme.
It reflects years of interdisciplinary collaboration among geochemists, oceanographers, and fluid mechanics specialists working to understand plastic transport from the coast to the deep sea.
This combination of empirical data and theoretical modeling offers a balanced perspective on how plastics evolve over time in marine environments and how humanity might best mitigate the consequences.
The Urgent Need to Manage Plastic at Its Source
The scientists emphasize that prevention remains more effective than any cleanup technology. With plastic production projected to triple by 2060, the window to act is closing.
Global treaty negotiations to end plastic pollution, including the UN Environment Assembly’s draft international agreement, will depend on accurate scientific understanding like this model provides.
Early measures to curb plastic production, promote recycling innovations, and strengthen waste management infrastructure could prevent hundreds of millions of tonnes from entering oceans in the future.
As Dr. Wu concluded: “Our results show that we can’t rely on natural processes to clean up the mess we’ve already made. The plastic in our oceans today will outlast us unless immediate global interventions begin at the source.”
Looking Toward a Cleaner Ocean
The model’s century-long timescale is sobering, but it also offers a foundation for realistic strategies. Understanding how plastic behaves in different ocean layers provides an opportunity to prioritize mitigation at every stage—from banning single-use plastics to enhancing river filtration systems.
By coupling climate action, environmental monitoring, and waste management, scientists and policymakers can work together to change the trajectory of ocean pollution before the next century begins.
Plastic pollution may be an intergenerational challenge, but science continues to show that with coordinated global will, it is one humanity still has the power to solve.
