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Plastic debris has long been a visible and growing problem in the world’s oceans, with debris littering the shores of once-unspoiled beaches, spreading across a wide expanse of sea in the Great Spot of Trash from the Pacific and they threaten marine life that ingests it.
A new report offers a glimpse of one of the impacts below the ocean’s surface: the scale of microplastics that accumulate on the ocean floor. In what the researchers called the first such global estimate, Australia’s national scientific agency says that between 9.25 million and 15.87 million tonnes of microplastics – fragments measuring between five millimeters and one micrometer – are embedded in the bottom of the sea.
That’s a lot more than on the ocean’s surface, and it’s the equivalent of 18 to 24 shopping bags filled with tiny pieces of plastic for every meter of shoreline on every continent except Antarctica.
It’s an issue activists have long warned about, even as the fight to clean up the ocean has largely focused on eradicating single-use plastic products like shopping bags.
The findings were published Monday in a new study from the Commonwealth Scientific and Industrial Research Organization, or CSIRO.
“It really points to the ubiquity of the problem. It really is everywhere all the time and on the rise, ”said Britta Denise Hardesty, CSIRO lead scientist and study author, in a telephone interview Wednesday.
Microplastics are not limited to the ocean. They are also found in airborne particles and can be spread by the wind. A variety of microplastics were even detected in the human intestine.
In recent years, hundreds of plastic objects have been found in the belly of dead whales around the world.
While cities have banned plastic bags and straws, the use of disposable plastic packaging has increased amid the coronavirus pandemic as consumers become more concerned about hygiene and pollution.
Over time, some plastics break down into smaller pieces and sink into the ocean. The more buoyant types of plastic don’t sink by themselves and wash up on beaches or end up in deep water.
Microbes and mussel colonies growing on floating plastic often cause the entire mass to sag due to the added weight.
Dr. Hardesty said that microplastics could be ingested by smaller plankton and fish on the seabed. Once eaten by fish, microplastics can end up in the human food chain.
The goal of the study, Dr. Hardesty said, was to scale the problem. She described it as the first accounting of its kind.
Using a robotic submarine, scientists collected 51 deep-sea sand and sediment samples in the Great Australian Bight in 2017, hundreds of miles offshore, and determined the global estimate based on the average number and size of the particles.
The study found zero plastic particles in some deep-sea sediments, but up to 13.6 particles per gram in others, up to 25 times higher than what had been found in previous studies of deep-sea microplastics.
The scientists said they made conservative estimates to account for the full range of samples. They also removed fibers or other materials from their count to rule out possible contamination of the samples.
Dr Hardesty said that it was important to prevent the plastic from ending up in the ocean in the first place. He said he was hopeful that pollution awareness would lead to more sustainable policies and behavior changes.
“Most of what ends up in the oceans is in the hands of the people,” he said. “They can see that their behavior, their actions and purchasing power, is very powerful and that can result in a change.”
