A new model reveals that plastics dumped today will haunt the oceans for more than a century, fueling a relentless tide of microplastic pollution.
Image Credit: Parilov/Shutterstock.com
The study was published in Philosophical Transactions of the Royal Society A: Mathematical, Physical, and Engineering Sciences. It introduced a novel model that combines plastic fragmentation with size-selective sedimentation to predict the long-term fate of buoyant plastic debris in marine environments. This model addresses how large floating plastics degrade into microplastics (MPs) and are transported to deep-sea sediments.
The findings highlight that even after 100 years, around 10% of the original plastic will remain at the ocean surface, continuously releasing MPs and contributing to marine pollution.
The Crisis of Plastic Pollution in Oceans
Ocean plastic pollution is a critical global environmental crisis, with an estimated 250,000 metric tons of buoyant plastic debris floating at the surface. Most of these plastics are larger than 5 mm and persist for decades due to their buoyancy. Over time, exposure to sunlight, wave action, and oxidation degrades them into MPs smaller than 5 mm, which pose serious ecological risks across marine trophic levels.
The mechanisms governing the vertical transport of buoyant plastics and their degradation products remain poorly understood, largely because of the gap between estimated plastic inputs and observed surface concentrations.
Recent evidence suggests that marine snow aggregates (MSAs), organic-rich particles formed from planktonic debris, play a key role in the downward transport of MPs. These aggregates capture and embed MPs, facilitating their gravitational settling to deep-sea sediments.
Introducing a Predictive Framework for Plastic Degradation
Researchers developed a one-dimensional (1D) predictive model to simulate buoyant plastic debris's long-term degradation and sedimentation. The model focuses on 10 mm polyethylene (PE) microspheres, representing typical floating plastics. It operates within a 5100 m deep-water column, replicating North Pacific Subtropical Gyre conditions.
Built on over 2,000 measurements and validated with more than 4,000 experimental data points, the framework integrates fragmentation and sedimentation processes. The study modeled degradation through surface erosion at a rate of 0.45 % mass loss per month. Fragmentation follows a negative binomial distribution, redistributing eroded mass into smaller size bins while conserving total mass.
The sedimentation component simulates the incorporation of microplastics into MSAs, with particles smaller than 160 µm having a higher attachment probability. Using flocculation theory and Stokes’ law, the model calculates collision rates and settling velocities, capturing aggregation and disaggregation cycles. Sensitivity analysis was conducted to understand how variations in degradation rates and fragmentation probabilities influence the long-term fate of plastics in the ocean.
Outcomes: Microplastic Dynamics and Persistence
The model showed complex dynamics of plastic degradation and sedimentation. Within the first 10 years, the mass of the original 10 mm plastic particle decreased by nearly 30 %. Over a 100-year simulation, only 31.76 mg of the initial mass remained, indicating a total loss of about 93.7 %. Most degraded material shifted into the smallest size ranges, demonstrating that large plastic fragments effectively break down into microplastics.
The study also tracked the time it takes for small microplastics to reach deep-sea sediments. For example, 25 µm particles required about 80 days to settle to 3000 m below the surface and about 289 days to reach the ocean floor. Smaller microplastics (<160 µm) are more readily attached to MSAs, enhancing their downward transport.
Throughout the simulation, the amount of buoyant plastic at the surface continued to decline, with only 57 mg remaining after a century. The concentration of microplastics suspended in the water column remained low, suggesting that most buoyant debris either persists at the surface or eventually settles in deep sediments.
These findings highlight that even if plastic input into the ocean were to stop today, the effects of existing waste would persist for more than a century, underscoring the urgency of global mitigation efforts.
Applications for Policy and Environmental Management
This research has significant implications for environmental management and policy-making. Clarifying how plastics degrade and settle in marine environments provides a foundation for developing effective strategies to mitigate ocean plastic pollution. The model shows that accelerating plastic degradation could enhance the natural removal of plastics from the ocean surface, reducing long-term ecological harm. It can also support targeted cleanup efforts and help identify pollution hotspots for efficient resource allocation.
The study also emphasizes the crucial role of MSAs in transporting MPs to deep-sea sediments, highlighting the need for further research on how plastics interact with marine ecosystems.
Ultimately, the findings reinforce the importance of reducing plastic production, improving waste management, and addressing pollution at its source.
Conclusion and Future Directions
This study represents a significant advancement in understanding the long-term fate of buoyant plastics in the ocean. By integrating fragmentation processes with sedimentation dynamics, researchers developed a robust framework for predicting the behavior and persistence of plastic waste in marine ecosystems.
Although degradation processes gradually reduce plastic mass, the long-term persistence of plastic pollution remains a major environmental concern.
Click here to download a free PDF copy of this page
Future work should focus on extending the model to incorporate multiple polymer types and variable degradation pathways, and on coupling it with three-dimensional ocean circulation models. Such developments would improve predictions of microplastic distribution across global oceans and support targeted cleanup efforts.
Addressing marine plastic pollution requires a comprehensive approach that combines technological innovation, improved waste management, and effective policy.
Journal Reference
Wu, N., et al. (2025). Coupling fragmentation to a size-selective sedimentation model can quantify the long-term fate of buoyant plastics in the ocean. Philosophical Transactions of the Royal Society A Mathematical, Physical, and Engineering Sciences. DOI: 10.1098/rsta.2024.0445, https://royalsocietypublishing.org/doi/10.1098/rsta.2024.0445
Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.