Photo by Jay Alexander

New data from a national survey of British coastal waters has found average microplastic concentrations of 59 particles per cubic metre of seawater, more than double the levels recorded in comparable surveys in 2022 and 2023, which found averages of 23 and 20 MP/m³ respectively. The highest single reading, 418 MP/m³, was recorded in the Irish Sea, the greatest concentration observed in three years of monitoring.

The data was collected during the 2024 GB Row Challenge, a gruelling 2,000-mile unsupported rowing circumnavigation of Great Britain, during which two teams, Coastal Odyssey and Sea Change, gathered seawater samples while at sea using specialist equipment. Samples were subsequently analysed at the University of Portsmouth using microRaman spectroscopy. Team Coastal Odyssey completed the full circumnavigation in 49 days, one hour and 29 minutes, setting a new Guinness World Record for the fastest mixed team.

Researchers from both the University of Portsmouth and the University of Surrey are urging caution in interpreting the year-on-year increase. Professor Fay Couceiro, from the School of Civil Engineering and Surveying and the Revolution Plastics Institute at the University of Portsmouth, said: “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.”

Methodological advances also help explain the striking figures. Researchers used ultra-fine filters capable of capturing particles far smaller than those detected in earlier national surveys – nearly all of the microplastics identified were smaller than 0.3 mm. For context, a 2017 Cefas study using coarser filters measured between 0 and 1.5 MP/m³ in offshore trawls, making some of the 2024 readings appear up to 100 times higher, though the difference is largely attributable to the improved detection of smaller particles.

Nonetheless, Hannah Davies, Senior Lecturer in Veterinary Clinical Practice at the University of Surrey, who rowed as part of Team Coastal Odyssey, stressed that the findings carry real significance regardless of how long these particles have been present: “Current levels are worrying and are detrimental to sea life. Not only do they cause physical harm to marine animals, but they also contaminate seawaters, potentially impacting the safety of humans who use the waters for leisure and work activities.”

Laura Fantuzzi, a PhD student at the University of Portsmouth who analysed the data, highlighted both the improving resolution of the research and its implications: “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.”

Consistent regional patterns are emerging from the three-year dataset. High concentrations were repeatedly found around the Thames Estuary and in the Irish Sea and North Channel, while lower concentrations were consistently recorded along stretches of England’s east coast between Newcastle and Hull. Researchers are currently working to assess how weather conditions, water circulation and marine heatwaves may drive year-to-year variation and cause accumulation hotspots.

Alongside the microplastic sampling, the teams collected environmental DNA (eDNA) to track marine biodiversity and identify which species are being exposed to the highest plastic loads. The data, which also covers underwater noise, temperature and salinity, will be made available to scientists worldwide via the Crown Estate’s Marine Data Exchange.

GB Row Challenge Founder William de Laszlo 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.” Professor Couceiro added: “Ocean pollution remains one of the defining environmental challenges of our generation. 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.”

This is the third annual report to emerge from a five-year collaboration between the University of Portsmouth and the GB Row Challenge. Two new teams are preparing to take part in the 2026 race, which is due to start at Tower Bridge on 14 June.