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Instead of helping to tackle the world's staggering plastic waste problem, recycling may be exacerbating a concerning environmental problem: microplastic pollution.

A recent peer-reviewed study that focused on a recycling facility in the United Kingdom suggests that anywhere between 6% to 13% of the plastic processed could end up being released into water or the air as microplastics — ubiquitous tiny particles smaller than five millimeters that have been found everywhere from Antarctic snow to inside human bodies.

"This is such a big gap that nobody's even considered, let alone actually really researched," said Erina Brown, a plastics scientist who led the research while at the University of Strathclyde in Glasgow, Scotland.

The research adds to growing concerns that recycling isn't as effective of a solution for the plastic pollution problem as many might think. Only a fraction of the plastic produced gets recycled: About 9% worldwide and about 5% to 6% in the United States, according to some recent estimates.

The study was conducted at a single plastic recycling facility, but experts say its findings shouldn't be taken lightly.

"It's a very credible study," said Judith Enck, a former senior Environmental Protection Agency official under President Barack Obama who now heads the Beyond Plastics advocacy organization. She was not involved in the research. "It's only one facility, but it raises troubling issues, and it should inspire environmental regulatory agencies to replicate the study at other plastic recycling facilities."

How does plastic recycling work?

While there are many different types of plastic, many experts say only things made out of No. 1 and 2 are really recycled effectively in the United States. At recycling facilities, plastic waste is generally sorted, cleaned, chopped up or shredded into bits, melted down and remolded.

It's unsurprising that this process could produce microplastics, Enck said. "The way plastic recycling facilities operate, there's a lot of mechanical friction and abrasion," she said.

Brown and other researchers analyzed the bits of plastic found in the wastewater generated by the unnamed facility. They estimated it could produce up to 6.5 million pounds of microplastic per year, or about 13% of the mass of the total amount of plastic the facility receives annually.

The researchers also found high amounts of microplastic when they tested the air at the facility, Brown said.

Will filters help?

The study also looked at the facility's wastewater after filters were installed. With filtration, the estimate of microplastics produced dropped to about 3 million pounds a year.

Even with the use of filters at the plant, the researchers estimated that there were up to 75 billion plastic particles per meter cubed in the facility's wastewater. A majority of the microscopic pieces were smaller than 10 micrometers, about the diameter of a human red blood cell, with more than 80% below 5 micrometers, Brown said.

She noted that the recycling facility studied was "relatively state-of-the-art" and had elected to install filtration. "It's really important to consider that so many facilities worldwide might not have any filtration," she said. "They might have some, but it's not regulated at all."

While effective filters could help, Brown and other experts said they aren't the solution.

"I don't think we can filter our way out of this problem," Enck said.

More research and better regulation

Enck and other plastics experts not involved in the research said it underscores the need to look into the issue more deeply.

"The findings are certainly alarming enough that it's worthy of far more investigation and understanding of how widespread of an issue this might be," said Anja Brandon, associate director of U.S. plastics policy at Ocean Conservancy, a nonprofit group.

Unlike other ways microplastic can wind up in the environment, recycling facilities could be identifiable sources, Brandon said.

"We know where the pollution is coming ... and we could take measures to actually do something about it through permitting, through regulation, through all of those kind of rules we have available," she said. "This is an area we could take action on, provided we learn a little bit more."

Many of the environmental permitting requirements in the United States are based on decades-old standards that should be updated to reflect with "the best available science," she added.

Kara Pochiro, a spokesperson for the Association of Plastic Recyclers, an international trade association, said plastic recycling plants don't all have the same water treatment systems. But recyclers, she said, are subject to national, state and local regulations, including environmental laws.

"Every plastics recycling facility works closely with their local municipal plant, including sampling and third-party testing at mutually agreed upon intervals," she said.

The Environmental Protection Agency said it will review the study.

Keep recycling

Despite the study's findings, experts emphasized that the answer isn't to stop recycling.

"What this study does not tell us ... is that we should stop recycling plastic," Brandon said. "So long as we are continuing to use plastic, mechanical recycling is really the best end-of-life scenario for these materials to keep us from needing to produce more and more plastic."

Plastic waste that isn't reused or recycled generally ends up in landfills or incinerated, Enck said. It's important, she and other experts said, for people to continue to try reducing the amount of plastic they use.

"This is not a major reason why we have such a significant problem with microplastics in the environment," she said. "But it's potentially part of it and there's an irony to it because it involves recycling."