The total amount of microplastics found at the bottom of the oceans has tripled in the past 20 years, corresponding to the increase in consumption of plastic products, according to a study published in the journal Environmental Science and Technology (ES&T). The team of researchers from the Institute of Environmental Science and Technology of the Universitat Autònoma de Barcelona (ICTA-UAB) and the Department of the Built Environment of Aalborg University (AAU-BUILD) provided the first reconstruction of microplastic pollution from sediments obtained in the northwestern Mediterranean Sea.
Researchers know that microplastics will end up at the bottom of the sea, but what happens when they get there is still a mystery. The new study shows that these microplastics stay unaltered in marine sediments, and the amount accumulated reflects the increased use of plastic products in society from 1965 to 2016. “Specifically, 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,” explains ICTA-UAB researcher Laura Simon-Sánchez.
Worryingly, sediments remain unchanged since they were deposited decades ago. “This has allowed us to see how, since the 1980s, but especially in the past two decades, the accumulation of polyethylene and polypropylene particles from packaging, bottles, and food films has increased, as well as polyester from synthetic fibers in clothing fabrics,” explains Michael Grelaud, ICTA-UAB researcher.
These three types of particles represent 1.5mg for each kg of sediment collected, with polypropylene being the most common, followed by polyethylene and then polyester. Despite awareness campaigns to encourage people to use less single-use plastic, this study shows we’re far from achieving this objective. The authors suggest that new global policies could contribute to improving this problem.
In addition, researchers looked at what happens when plastic gets buried. It turns out that once trapped in the sea floor, microplastics no longer degrade, possibly due to lack of erosion, oxygen, or light. “The process of fragmentation takes place mostly in the beach sediments, on the sea surface, or in the water column. Once deposited, degradation is minimal, so plastics from the 1960s remain on the seabed, leaving the signature of human pollution there,” says Patrizia Ziveri, ICREA professor at ICTA-UAB.
This study took place in November 2019 on board the oceanographic vessel Sarmiento de Gamboa during an expedition from Barcelona to the coast of the Ebro Delta in Tarragona, Spain. The researchers picked this location — in particular, the Ebro Delta — because rivers are known hotspots for several pollutants, including microplastics. In addition, sediment coming from the Ebro River provides better sedimentation rates than in the open seafloor.
Simon-Sánchez L, Grelaud M, Lorenz C, Garcia-Orellana J er al. (2022) , Can a Sediment Core Reveal the Plastic Age? Microplastic Preservation in a Coastal Sedimentary Record. Environ. Sci. Technol. 2022, 56, 23, 16780–16788, https://doi.org/10.1021/acs.est.2c04264