Scientists identify 1.9 million pieces of microplastic in one square meter of ocean floor

Researchers writing on Science have reported the highest levels of microplastics observed on the seabed to date, finding up to 1.9 million fibers and fragments per square meter of seabed.

For some time, scientists have struggled to find the 99 percent “lost” plastic that ends up in our oceans: the polyethylene bags and polypropylene straws that accumulate on the surface and represent a small fraction of total waste. Now, an international team of scientists says they have identified a mechanism that transports and dumps at least part of the remaining 99 percent to the seafloor.

While floating plastic islands, such as the large Pacific trash patch, estimated to be twice the size of Texas, have attracted a lot of media attention, researchers have identified what they call “microplastic hot spots.” , which are formed in a not too different fashion, only thousands of feet below the sea surface.

“So far we have not understood where the microplastics missing in the ocean end up and how they are transported,” said Mike Clare of the National Center for Oceanography. Newsweek. “We know that there are concentrations of plastic on the ocean surface, but this represents less than one percent of the plastic that reaches the ocean.”

He added: “Until now, the rest were supposed to settle slowly, like rain or snow in the deep sea. We discovered instead that currents in the deep sea act as conveyor belts, moving plastic around, locally creating points on the seabed. “

The researchers reached these conclusions after analyzing sediment samples collected from the bed of the Tyrrhenian Sea in the Mediterranean, near the west coast of Italy. The team studied the content of the samples, identifying the different types of plastic, and compared the results with models of ocean currents.

The results suggest deep-water ocean currents driven by temperature and salinity fibers that transport fibers and plastic fragments, as well as nutrients and hydrogen peroxide, through the seabed. The formation of these currents can cause these plastics to accumulate in certain areas, described in the document as “microplastic hot spots”.

According to the study, the concentration of plastics found in some areas is more than double that registered in submarine canyons. The highest concentrations revealed about two million plastic particles per square meter, a lead author of the finding, Ian Kane, of the University of the United Kingdom at Manchester, who described it as “astonishing”.

The vast majority of microplastics that accumulate at these critical points are fibers found in clothing and large pieces of plastic waste. The researchers found no correlation between microplastic concentrations and proximity to land-based plastic sources.

While the research is entirely focused on one site in the Mediterranean, these currents are spread throughout the world, and the study authors suggest that the process will play an important role in the distribution of plastic elsewhere. However, more research is needed to determine exactly what kind of effect they are having in other parts of the world.

“Our study focuses on the Mediterranean, where currents create circular turns (or vortices) that can explain why microplastics are so concentrated, it is as if plastics are caught in a whirlpool,” Clare said. “Elsewhere, where the ocean margins do not create such confinement, such as in the Atlantic and Pacific oceans, these ocean floor currents can disperse microplastics.

“There is still a lot of work to do to understand how these currents control microplastic concentrations on a global scale. But now we know that these currents are very important.”

It is largely unknown what kind of impact these hotspots could have on marine ecosystems. But if microplastics are filled with currents that carry hydrogen peroxide and nutrients through the ocean, there is concern that they may affect organisms that ingest or absorb these plastics. Previous studies have suggested that the consumption of microplastics can change the behavior of animals, making periwinkles more vulnerable to attack by predators. Other research suggests that microplastics could have a detrimental effect on fish health.

Kane told him Newsweek The researchers hope their work will help turn the intangible “99 percent lost” into something “real” by showing where and how it accumulates on the seabed.

“For me, that makes these hotspots a tangible or ‘real’ feature, and the hope is that just like the trash patches on the sea floor, they can capture the public’s imagination and result in the same kind of push for responsible plastic production and more effective policies for treating wastewater, “he said.

“Very little can be done to deal with these critical points as they are: deep cleaning of the seabed is not a viable option for several reasons,” Clare said.

“Therefore, the solution must start at the source. We need to limit the pathways that plastics take to the ocean, switch to more sustainable materials whenever possible, and maintain the mantra of reduce, reuse, and recycle.”