Over the past two decades, the total amount of microplastics accumulating on the ocean floor has tripled. The study provides the first high-resolution reconstruction of microplastic pollution from sediments recovered in the northwest Mediterranean.

Although the seabed is considered the final sink for microplastics floating on the sea surface, the historical evolution of this source of pollution in the sediment compartment, particularly the rate of sequestration and burial of microplastics on the ocean floor, is unknown. “Plastic accumulation has not stopped growing, mimicking the production and global use of these materials,” explains ICTA-UAB researcher Laura Simon-Snchez. Microplastic Pollution in Deep-Sea Sediments The researchers explain that the sediments analyzed have remained unchanged on the sea floor since they were deposited decades ago. “This allowed us to see how the accumulation of polyethylene and polypropylene particles in packaging, glass and food films, as well as polyester from synthetic fibers in clothing, has increased since the 1980s, but especially in the last two decades.” ICTA-UAB researcher Michael Grelaud explains. The amount of these three types of particles reaches 1.5 mg per kilogram of accumulated sediment, the most abundant is polypropylene, followed by polyethylene and polyester. Despite campaigns to raise awareness of the need to reduce single-use plastic, data from annual records of marine sediments show that we are still a long way from achieving this. In this regard, policy at the global level can contribute to ameliorate this serious problem. Despite the abundance of small microplastics in the environment, limitations in analytical methods have limited robust evidence of levels of microplastics in previous studies targeting marine sediments. In this study, they were characterized using state-of-the-art imaging to quantify particles up to 11 ┬Ám in size. The degradation status of the buried particles was investigated and it was found that they do not deteriorate further due to either erosion, lack of oxygen or lack of light after being trapped on the seabed. “Degradation occurs mostly in beach sediments, the sea surface, or the water column. Once deposited, degradation is minimal, so plastics from the 1960s remain at the bottom of the sea, leaving traces of human pollution there,” says Patrizia Ziveri, ICREA professor at ICTA-UAB. The studied sediment core was collected aboard the oceanographic vessel Sarmiento de Gamboa in November 2019 on an expedition from Barcelona to the coast of the Ebro Delta in Tarragona, Spain. The research team chose the western part of the Mediterranean Sea, specifically the Ebro Delta, as their study area because the rivers are known to be hotspots for a number of pollutants, including microplastics. In addition, the sediment flux from the Ebro provides a higher sedimentation rate than the open ocean.

Source: Eurekalert

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