Understanding the distribution of marine litter in the Bay of Biscay

The challenge

Plastics and other marine litter are considered by the European Union to be one of the main threats to the oceans, due both to their environmental impact and the economic costs they generate in coastal regions. Every year, around 10 million tonnes of waste end up in the sea.

Despite the seriousness of the problem, knowledge about the origin and actual distribution of this waste is still limited, especially in coastal areas of the Bay of Biscay, where studies had focused mainly on offshore waters. Reliable and detailed data are essential to design effective prevention, management, and plastic reduction measures in the marine environment.

The solution

AZTI led a four-year comprehensive research programme aimed at characterising the spatial distribution of marine litter in the Bay of Biscay.

The study simultaneously addressed all key factors influencing the presence of marine litter, including:

• Analysis of microplastics, mesoplastics, and macroplastics.

• Study of riverine environments as pathways for waste entering the sea.

• Assessment of floating litter and its dynamics.

• Analysis of waste generation by different economic sectors.

• Research into biodegradation processes.

• Examination of the relationship between marine litter and fishing and aquaculture activities.

The results

• Microplastics are by far the dominant fraction: 93% of detected particles (equivalent to 28% by weight).

• Mesoplastics account for 7% of particles (26% by weight), while macroplastics represent only 1% of items but 46% of total weight.

• Recorded average abundances range between 739,395 and 2,625,271 plastic items per km², with an average of 232,227 items per km².

• French waters show significantly higher contamination levels, with five times more plastics than Spanish coastal waters.

These results provide, for the first time, a comprehensive and comparative overview of plastic pollution in the Bay of Biscay, delivering an essential scientific basis for designing reduction policies, improving waste management, and moving towards a cleaner and healthier marine environment.