While almost all the world’s oceans are contaminated with microplastics, the Mediterranean Sea has become a hotspot for microplastic pollution. The sea is surrounded by three continents with dense populations that act as a trap for plastic debris and now, a study has warned that the problem is getting worse, with more plastic than previously thought accumulating in the seabed.

Researchers from the Universitat Autònoma de Barcelona and Aalborg University found the amount of microplastics deposited on the bottom of the Mediterranean Sea has tripled in the past two decades. It’s the first high-resolution reconstruction of microplastic pollution from sediments taken from the northwestern Mediterranean Sea.

“The results show that, since 2000, the amount of plastic particles deposited on the seafloor has tripled and that, far from decreasing, the accumulation has not stopped growing mimicking the production and global use of these materials,” Laura Simon-Sánchez, study author and researcher at Barcelona University, said in a statement.

Microplastics in the Mediterranean

The researchers collected a sediment core from the Mediterranean Sea and then used advanced imaging technology to study the microplastics. This allowed them to fill an important gap around the accumulation of the small particles in the marine sediment, and better understand how they are altered, or not, after becoming embedded in the material.

In fact, they found that the microplastics remain preserved in the seabed after reaching it – something the researchers link to a lack of erosion, oxygen, or light. “Once deposited, degradation is minimal, so plastics from the 1960s remain on the seabed, leaving the signature of human pollution there,” study author Patricia Ziveri said in a statement.

The scientists were able to produce a timeline of plastic pollution in the seabed and found the amount of microplastics has tripled since 2000, with the nature of plastics building up mirroring global production and use of plastics. This has allowed them to see the growing accumulation of particles from packaging, bottles, and food films.

The sediment core was collected in November 2019, on board the vessel Sarmiento de Gamboa, in an expedition that went from Barcelona to Tarragona in Spain. The researchers selected the western Mediterranean Sea as a study area as rivers in there are recognized as hotspots for several pollutants, from microplastics to chemicals.

A study in 2020 found about 229,000 tons of plastic leak every year into the Mediterranean Sea, equivalent to over 500 shipping containers each day. This is expected to double by 2040. Egypt, Italy, and Turkey were found to be the countries with the highest plastic leakage mainly due to mismanaged waste and large coastal populations.

The study was published in the journal Environmental Science and Technology.