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Microplastics have tripled on the seafloor in the past 20 years

Although the seafloor is considered the final sink for microplastics floating on the sea surface, the historical evolution of this major source of pollution in the sediment compartment – and especially the sequestration and burial rate of smaller microplastics on the ocean floor – has been unknown until recently. Now, a new study published in the journal Environmental Science & Technology has found that the total amount of microplastics deposited on the seafloor has tripled over the past two decades, mimicking the progression of the global plastic production 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,” said study lead author Laura Simon-Sánchez, a researcher at the Institute of Environmental Science and Technology of the Universitat Autònoma de Barcelona (ICTA-UAB).

The analysis of sediments obtained in the northwestern Mediterranean Sea has revealed that the microplastics that reached the seafloor have remained unaltered since they were deposited decades ago, most likely due to lack of erosion, oxygen, and 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,” explained study senior author Patrizia Ziveri, a marine biologist at ICTA-UAB.

“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,” added study co-author Michael Grelaud, an oceanographer at the same institute.

According to the scientists, the amount of these three types of particles reached a critical level of 1.5mg per kilogram of sediment collected, with polypropylene being the most abundant, followed by polyethylene and polyester. 

Regardless of the increasing number of awareness campaigns on the necessity of reducing single-use plastic, data from annual marine sediment analyses show that we are very far from achieving this goal. To solve this major problem, policies at the global level addressing this issue are urgently needed in order to protect the health and functioning of a vast number of currently endangered ecosystems.

By Andrei Ionescu, Staff Writer

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