Microplastics Found in UNESCO-Protected Basque Estuary for First Time

A recent study published in the journal Marine Pollution Bulletin suggested that protected status and upstream water treatment offer limited defense against plastic particle accumulation in coastal sediments.¹ This study, conducted by researchers at the University of the Basque County, investigated microplastic contamination in the sediments of the Urdaibai estuary reportedly for the first time.¹

What is the Urdaibai Estuary?

The Urdaibai Estuary is a large coastal wetland and estuarine ecosystem in the Basque Country of northern Spain, where the Oka River flows into the Bay of Biscay.² It is widely regarded as one of the most important natural areas in the region and forms the heart of the Urdaibai Biosphere Reserve, which was designated by UNESCO in 1984.²

What did the researchers do in their study?

Over a period of one year, the researchers collected sediment samples from five sites along the estuary of the Oka River every three months. Using Raman imaging microscopy paired with chemometric data analysis, the team identified microplastic concentrations ranging from 16 to 165 items per kilogram of dry sediment.¹

What were the polymers the researchers found in the Urdaibai estuary?

At Urdaibai, the researchers identified that the most dominant polymer types were polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), and polystyrene (PS).¹ These are plastics closely associated with everyday consumer goods, packaging, and textiles. In the study, only fragments and fibers were detected; PET appeared exclusively in fiber form.¹

Although the researchers collected a lot of samples over the course of their study, they also estimate that the figures cited in their study could be an underestimation. Because their methodology excluded particles smaller than 250 micrometers, as well as blue and green particles whose polymer composition could not be confirmed, both these factors suggest a conservative final tally.¹

Did any seasonal trend emerge during the sampling period?

According to the researchers, no consistent seasonal trend emerged across the estuary over the 12-month sampling period. However, one of their sampling sites recorded significantly elevated microplastic levels compared to the other four. The authors attribute this to local geomorphic and hydrodynamic conditions.¹

However, because the researchers only conducted four sampling rounds over the course of a 12-month period, no firm conclusions could be drawn regarding temporal patterns and their impact on microplastic contamination.¹

What methodology did the researchers use in their study?

The team employed an optimized micro-Raman methodology developed within their research group, using a 785-nm laser and imaging-assisted chemometrics to process large volumes of spectral data.¹ Rigorous contamination controls were applied throughout: all sampling equipment was made of glass or metal, solutions were pre-filtered, and procedural blanks detected no microplastic contamination.¹

What are the implications of this study for policy and practice?

The authors frame their findings as a call for structured monitoring of microplastics in coastal and estuarine environments, arguing that consistent data collection is a prerequisite for informed plastic waste management policy, regulatory frameworks governing plastic manufacture and use, and public awareness initiatives.¹

For the marine science and environmental management communities, the Urdaibai study adds to a growing body of evidence that microplastic contamination is now a baseline condition in European estuaries, including those under the highest levels of environmental protection.¹ The question for regulators is no longer whether protected coastal environments contain microplastics, but at what concentrations and from what sources.¹ These questions should form the basis for future studies.

References

1. Maupas, T.; Cossio-Ruiz, M.; Gomez-Laserna, O.; et al. Raman Imaging Spectroscopy Approach for the Microplastics Detection in the Oka Estuary in the Urdaibai Biosphere Reserve (Basque Country, Spain). Mar. Pollut. Bullet. 2026, 225, 119239. DOI: 10.1016/j.marpolbul.2026.119239
2. UNESCO, Urdaibai – General Information. UNESCO.org. Available at: https://www.unesco.org/en/mab/urdaibai (Accessed June 11^th, 2026)