Plastic pollution could linger at ocean surfaces for over a century

Even if all plastic inputs into the ocean were stopped immediately, fragments of buoyant plastic debris would continue to pollute the ocean surface and release microplastics for more than a century.

Those are the conclusions of a study by researchers at Queen Mary University of London.

Using a model that simulates the slow breakdown of large plastic particles and their interaction with marine snow (sticky organic material that helps transport debris to the deep sea), the researchers show that the degradation process is the limiting factor in removing plastic from the surface.

Dr Nan Wu, the paper’s lead author from the Department of Geography and Environmental Science at Queen Mary University of London, said:

“People often assume that plastic in the ocean just sinks or disappears. But our model shows that most large, buoyant plastics degrade slowly at the surface, fragmenting into smaller particles over decades. These tiny fragments can then hitch a ride with marine snow to reach the ocean floor, but that process takes time. Even after 100 years, about 10 percent of the original plastic can still be found at the surface.”

The findings help explain the persistent mismatch between the amount of buoyant plastic entering the ocean and the relatively small amounts observed at the surface. This is often referred to as the ‘missing plastic’ problem.

The model also shows that the biological pump, the ocean’s natural conveyor belt for carbon and particles, may become overwhelmed as plastic production increases. If microplastic concentrations continue to rise, there is a risk they could interfere with ocean biogeochemical cycles.

Paper details

Wu, N., Grieve, S., Manning, A. & Spencer, K.L “Coupling fragmentation to a size-selective sedimentation model can quantify the long-term fate of buoyant plastics in the ocean.” Philosophical Transactions A.