Microplastic pollution in the seas around Great Britain has been found at significantly higher concentrations than previously recorded by a joint project between the University of Portsmouth and GB Row Challenge.
Data collected during the summer of 2024 shows an average concentration of 59 microplastic particles per cubic metre of seawater (59 MP/m³) - more than double the levels reported in comparable surveys conducted in 2022 and 2023, which recorded averages of 23 and 20 MP/m³ respectively.
In some locations, concentrations were more than twice those previously measured, with the highest level - 418 MP/m³ - recorded in the Irish Sea, the greatest concentration observed across the three years of monitoring.
This is a substantial change in what we're measuring, but it's important to be careful about how we interpret it. Rougher seas and poorer weather in 2024 may have mixed microplastics more thoroughly through the water column, making them easier to detect. It's possible these concentrations have been there all along.
Professor Fay Couceiro, School of Civil Engineering and Surveying
Researchers stress that the findings do not necessarily show a sudden deterioration in marine conditions. Differences in weather, sea state and sampling conditions between years may have influenced the results, potentially stirring up microplastics that would otherwise remain below the surface.
"This is a substantial change in what we're measuring, but it's important to be careful about how we interpret it," said Professor Fay Couceiro , from the School of Civil Engineering and Surveying and member of the Revolution Plastics Institute at the University of Portsmouth. "Rougher seas and poorer weather in 2024 may have mixed microplastics more thoroughly through the water column, making them easier to detect. It's possible these concentrations have been there all along."
The data was collected during the GB Row Challenge , a 2,000-mile rowing event circumnavigating Great Britain. Two teams of rowers gathered samples while at sea, using specialist equipment to collect data on microplastics, temperature, noise pollution, and biodiversity. The samples were later analysed at the University of Portsmouth using microRaman spectroscopy.
The two teams, Coastal Odyssey and Sea Change, endured relentless low-pressure systems, challenging weather fronts, and strong winds along the way.
Team Coastal Odyssey completed the full circumnavigation in 49 days, one hour and 29 minutes, setting a new Guinness World Record for fastest mixed team. They rowed two hours on and two hours off for most of the journey, except for when they had to sit on anchor to wait out bad weather.
As our methods improve, we're getting a clearer and often more troubling picture of what's actually in the water. Smaller particles are more abundant and potentially more harmful, because they're more easily ingested by marine life.
Laura Fantuzzi , PhD student at the University of Portsmouth.
Patrick Deacon, Skipper of Coastal Odyssey, said: "To come away with a Guinness World Record is something we're incredibly proud of, but what matters just as much is knowing that every mile we rowed helped collect crucial data on the state of Britain's coastal waters."
Unfortunately, Sea Change had to withdraw, but the environmental samples they collected along the South Coast remain a valuable contribution to the multi-parameter dataset.
This is the third national report to emerge from the GB Row Challenge, which aims to build a long-term picture of environmental pressures on British coastal waters.
The data from this race and previous races will be hosted on The Crown Estate's Marine Data Exchange , one of the world's largest collections of marine industry data, and will be accessible to scientists worldwide.
In 2024, researchers analysed microplastic samples from 23 sites around the British Isles. Each sample involved pumping seawater through ultra-fine filters with a pore size of 0.04 mm for up to 3.5 hours per day, allowing scientists to capture particles far smaller than those typically detected in earlier national surveys.
Nearly all of the microplastics identified were smaller than 0.3 mm, helping to explain why concentrations appear much higher than figures published in earlier offshore monitoring, including a 2017 study by Cefas (the Centre for Environment, Fisheries & Aquaculture Science), which reported between 0 and 1.5 MP/m³ using larger mesh sizes.
"As our methods improve, we're getting a clearer and often more troubling picture of what's actually in the water," said Laura Fantuzzi, a PhD student at the University of Portsmouth who analysed the data. "Smaller particles are more abundant and potentially more harmful, because they're more easily ingested by marine life."
With this in mind, samples of eDNA to monitor biodiversity are being taken alongside the microplastic samples to determine which species are being exposed to these higher concentrations.
While the distribution of microplastics varied between years, consistent regional patterns are beginning to emerge. High concentrations were repeatedly found around the Thames estuary and the Irish Sea/North Channel, while lower concentrations were observed along parts of the east coast of England, particularly between Newcastle and Hull.
Further research is underway to assess how weather conditions, water circulation and marine heatwaves may influence year-to-year variation and the accumulation of plastics in certain regions.
2024 was an exceptionally tough year for the crews from a weather perspective. They faced volatile weather fronts and unseasonable headwinds, yet both teams still collected invaluable empirical data that will contribute to ongoing ocean research. The wider GB Row Challenge team and our partners are extremely grateful for their determination and efforts.
William de Laszlo, GB Row Challenge Founder
Microplastics - plastic particles smaller than 5 mm - have been documented in the marine environment for almost 50 years. Laboratory and field studies increasingly show that ingestion of microplastics can harm marine organisms, causing effects ranging from reduced growth to cellular toxicity.
"Ocean pollution remains one of the defining environmental challenges of our generation," said Professor Couceiro. "Projects like the GB Row Challenge allow us to gather vital data from places that are otherwise difficult to sample, helping us understand not just how much plastic is out there, but how it moves and accumulates."
The findings build on earlier GB Row Challenge research, which found that UK seas were on average 0.39°C warmer in 2023 than in 2022, with parts of the Celtic and Irish Seas experiencing temperature increases of more than 2°C during a marine heatwave.
The researchers say continued long-term monitoring will be essential to distinguish between genuine increases in pollution and changes driven by sampling conditions and to understand what these trends mean for marine ecosystems around the UK.
GB Row Challenge Founder, William de Laszlo, has completed the challenge twice. He said: "2024 was an exceptionally tough year for the crews from a weather perspective. They faced volatile weather fronts and unseasonable headwinds, yet both teams still collected invaluable empirical data that will contribute to ongoing ocean research. The wider GB Row Challenge team and our partners are extremely grateful for their determination and efforts."
Two more teams are busy preparing to take on the GB Row Challenge in 2026, which starts at Tower Bridge, London, on Sunday 14 June.
You can access the full report here: 29948 GB Row impact Report 2024.pdf
