A national survey has found that microplastic pollution in seawater around Great Britain may be more than double previously recorded levels, according to new data collected during the 2024 GB Row Challenge.

Seawater samples gathered along more than 2,000 miles of coastline recorded an average concentration of 59 microplastic particles per cubic metre (59 MP/m³). Comparable surveys conducted in 2022 and 2023 reported average levels of 23 MP/m³ and 20 MP/m³, respectively.

The highest concentration measured during the challenge was 418 MP/m³ in the Irish Sea — the highest level observed across three years of monitoring.

The data were collected as part of a 50-day rowing expedition around the seas of Great Britain. Participants gathered seawater samples while also recording underwater anthropogenic sound, water temperature, salinity, and biodiversity indicators. Laboratory analysis was conducted at the University of Portsmouth.

Microplastics are plastic fragments typically smaller than five millimetres. They originate from the breakdown of larger plastic waste or from manufactured sources such as synthetic fibres and microbeads. Once in the marine environment, they can remain suspended in the water column or settle into sediments.

How the Survey Was Conducted

The GB Row Challenge involves crews rowing unsupported around Great Britain. During the 2024 expedition, researchers integrated environmental sampling into the journey, creating a continuous dataset along the coastline.

Sampling conditions can influence results. Researchers noted that sea state and weather conditions may affect the distribution and detectability of microplastics. Rougher seas can mix particles more thoroughly throughout the water column, potentially increasing measured concentrations.

Despite these variables, the average recorded concentration exceeded recent baseline measurements.

Regional Differences

Microplastic levels were not uniform across all sampling points. Some locations recorded concentrations more than twice previous measurements.

The Irish Sea showed the highest concentration at 418 MP/m³. While the study did not identify a single cause for regional differences, enclosed or semi-enclosed waters can accumulate pollutants more readily than open coastal areas.

Data from this and earlier expeditions will be made available through The Crown Estate’s Marine Data Exchange, a repository of marine industry and environmental information accessible to researchers.

Environmental and Human Impacts

Microplastics can pose risks to marine ecosystems. Small particles may be ingested by fish, shellfish, and other marine organisms, potentially causing physical harm or transferring contaminants through the food chain.

Researchers involved in the survey stated that microplastics can contaminate seawater and may affect both marine life and human activities in coastal waters. The long-term ecological and health impacts remain under investigation; however, sustained exposure is considered a concern by marine scientists.

Monitoring programmes aim to establish consistent baselines to track changes over time. Variations in methodology between surveys can complicate direct comparisons, but repeated sampling in similar regions helps build a clearer understanding of pollution trends.

Broader Monitoring Efforts

The 2024 data contribute to ongoing assessments of marine pollution around Britain’s coastline. Previous research has documented the widespread presence of microplastics in UK waters, sediments, and marine species.

By combining endurance sporting events with scientific data collection, the survey expanded geographical coverage while maintaining sampling continuity.

The findings indicate that microplastic concentrations in coastal waters may be higher than recent estimates suggested. Continued monitoring will be necessary to determine whether the 2024 results represent a short-term fluctuation linked to environmental conditions or part of a longer-term upward trend.

As marine plastic pollution remains a global issue, consistent measurement and transparent data reporting are essential to understanding the scale and distribution of contamination in coastal ecosystems.