How do you destroy pollution so stubborn it's nicknamed "forever chemicals"?

That's a question researchers and companies across the country are eager to answer, as regulation tightens on PFAS — per- and polyfluoroalkyl substances — and the chemicals' producers face a mountain of lawsuits.

The chemicals are in fast-food wrappers, firefighting foams, nonstick cookware and dental floss. They don't break down readily in the environment, they flow easily with water and research has linked them to health effects like immune and fertility problems and some cancers.

Getting rid of the harmful chemicals is "a multibillion-dollar elephant in front of us," said Corey Theriault, a technical expert focused on PFAS treatment at the engineering and consulting firm Arcadis.

PFAS have been destroyed via incineration, but there are questions about how thoroughly burning works. The Defense Department halted the practice of burning these chemicals last year.

Everyone from municipal water providers to Fortune 100 companies have shown interest in the technologies, Theriault said. The U.S. Army Corps of Engineers is offering a contract to handle, destroy and replace firefighting foam that is rich in PFAS, worth some $800 million, according to the government's solicitation document.

PFAS became so popular in consumer goods because of the durable carbon-fluorine bond that makes up the links in "short-chain" and "long-chain" versions of the chemicals. These bonds help repel stains, water and grease, and cut off oxygen to dangerous blazes.

But that chemical bond also is exceedingly hard to break.

Many methods being tested to eliminate PFAS have been used in other chemical cleanups. Engineers are trying to burst the molecules in modified pressure cookers, split them with UV light and energized additives, rupture the PFAS chains with electricity or strip apart atoms with cold plasma, a charged and reactive gas.

No technology has yet been deployed on a large scale, but Theriault said those furthest along in development could be ready in the next six to 18 months.

However, none of these technologies will directly treat a contaminated water source. First, the water would have to be filtered so that the PFAS ends up in a concentrate that is more cost-effective to treat. The state of Minnesota already uses a machine that sucks PFAS out of contaminated groundwater by repeatedly stirring the groundwater into a foam, where the chemicals tend to collect.

"The cost per volume of liquid to treat for these destructive approaches is much higher," said Timothy Strathmann, a professor of civil and environmental engineering at the Colorado School of Mines. He is developing a destruction method called hydrothermal alkaline treatment, or HALT, that he described as "a pressure cooker on steroids."

The need for a concentrated chemical soup for experiments has led at least a dozen companies to pitch their products to Minnesota, because the state already is creating it with its filtering machine, said Drew Tarara, a geologist and program manager with AECOM, an engineering firm.

"It does feel like everybody's trying to get their foot in the door," Tarara said.

Minnesota is partnering with AECOM to investigate new technologies. The first six months of this pilot study cost $500,000, Minnesota Pollution Control Agency spokeswoman Andrea Cournoyer wrote in an email.

Next, Minnesota will use the De-Fluoro system, an electrochemical approach marketed by AECOM, to try to destroy the PFAS in its foamy concentrate.

The state faces a decades-long PFAS contamination problem in the east metro area, where Maplewood-based 3M Co., one of the original PFAS developers and manufacturers, polluted groundwater with leaky landfills and disposal sites. Money from a lawsuit the state settled with 3M in 2018 is paying for the work being done today with AECOM.

3M recently announced it would stop using the chemicals in its products by 2025. But the challenge of cleaning up what's already in the environment remains.

The De-Fluoro unit is "still very much in field testing," Tarara said. It will be tested at the Washington County landfill for up to six weeks, where it will process the state's collected PFAS concentrate, but Tarara and state officials have been cautious in describing what De-Fluoro may do. Rebecca Higgins, a senior hydrogeologist at the MPCA, previously told the Star Tribune that De-Fluoro may only be able to snap long-chain PFAS into shorter segments rather than destroy them.

State officials have said they want to test other technologies, too. Cournoyer wrote that any additional systems would be selected in accordance with state procurement rules, and officials also will be monitoring scientific literature for reports on other technologies.

The world of PFAS destruction is rife with proprietary methods and nondisclosure agreements, making it hard to assess what actually works. One notable exception is a study published in the journal Science last year that saw researchers boil the chemicals with two other compounds on low heat. But that method still is in lab testing.

Companies like Claros Technologies, a Minnesota-based startup, are mostly mum about who exactly owns the PFAS waste they're experimenting on, because those partners may have legal liabilities. That makes it hard to validate the company's stated results: 99.9% to 99.99% destruction of PFAS, when treated with UV light and an additive.

Those Claros tests aren't being verified in peer-reviewed scientific journals either because the process is proprietary.

John Brockgreitens, the director of research and development for Claros, said the company hopes one day to treat tens of thousands of gallons of liquid daily. But he admitted it's hard to answer detailed questions about the results of the company's photochemical method.

"We talk to teams of scientists, and they ask us the same thing," he said. "Walking that line is a challenge."

Theriault, who said his firm remains agnostic on what technologies it recommends to its clients, said Arcadis had partnered with Claros and that their method "has definitely shown its promise" to be useful in more applications than other methods.

"There is no one technology that's going to crush it across the board," Theriault said.

But for the communities facing pollution, the technologies can't come soon enough, because current waste-handling methods aren't containing the chemicals.

"Any landfill will fail. It doesn't matter how they're built," said Rainer Lohmann, director of the University of Rhode Island's STEEP lab and an authority on PFAS contamination.

Many landfills no longer accept waste known to be contaminated with PFAS, sources said.

And until a regulator, such as the Environmental Protection Agency, sets standards for how thoroughly PFAS need to be destroyed, no official benchmark exists for new technologies, Lohmann said.

"Does it destroy 95 percent, 99 percent? What do you do with the rest?" he said.

This story is a product of the Mississippi River Basin Ag & Water Desk, an editorially independent reporting network based at the University of Missouri School of Journalism in partnership with Report For America and the Society of Environmental Journalists, funded by the Walton Family Foundation.