Attorney General Lori Swanson had no doubt that 3M endangered Minnesotans by dumping waste from perfluoroalkyl and polyfluoroalkyl substances.

Swanson sued 3M for $5 billion.

She settled the case for $850 million in February 2018. The company never admitted guilt.

One reason it did not have to was the lack of a national toxicity standard for the chemicals involved.

The absence of mandatory, enforceable limits on the substances, known as PFAS, complicates and sometimes cripples attempts by governments and individuals to hold producers accountable for what has become a national pollution problem, legal and scientific specialists say.

“Until the federal government says it is hazardous, there is no need to admit guilt,” said Alexandra Klass, an environmental law professor at the University of Minnesota.

PFAS help make products heat-, stain-, water- and grease-resistant. Decades of use have spread the chemicals throughout the environment and alarmed public health groups and regulators. They worry about animal tests and epidemiology that link PFAS to cancer, liver problems and developmental issues in rodents, as well as weakened immune and vaccine responses in humans.

Despite two decades of study by the EPA, no mandatory limits exist for any type of PFAS. There are only advisory drinking-water limits on two major types. Companies do not have to follow these recommendations and cannot be held legally accountable if they breach them.

Companies such as 3M, Chemours, DuPont and Daikin that have been accused of deceiving government and the public about the risks of PFAS steadfastly maintain their innocence. They say they stopped using two common forms of PFAS — PFOA and PFOS — when they learned of their potential health risks and replaced them with safer kinds of chemicals.

In February, the EPA announced a program to propose official drinking-water standards for those two types of PFAS by the end of the year. The agency did not lay out groundwater pollution-cleanup guidelines. The regulatory process the EPA outlined will take months, and likely years, of legal wrangling.

Environmental and public health groups said that the EPA already has enough evidence to set mandatory limits and cleanup criteria for PFOS and PFOA. Failure to do so, they said, puts people at risk.

“You need the hazardous designation [to get] funding to do something,” Klass explained. “That’s very critical to abatement and prevention.”

In a statement to the Star Tribune, the EPA said it can sufficiently enforce clean-water laws and hold polluters accountable while continuing the regulatory process.

Deborah Swackhamer, former chair of the EPA’s Science Advisory Board and its Board of Scientific Counselors, said she thinks “delays in setting new regulations such as drinking-water standards for PFAS are weakening public health protections.” She declined to comment on the legal impact a lack of standards has on punishing polluters.

“PFAS has been shown to be a widespread contaminant throughout the US [and world] and not just a problem in a few localized places,” Swackhamer, a professor emeritus at the University of Minnesota, said in an e-mail. “This national problem warrants prompt action from the EPA, which we have not seen.”

Writing in the peer-reviewed journal PLOS Biology, Gloria Post of the New Jersey Department of Environmental Protection warned of a “rapid increase in evidence” for “adverse health effects” of PFAS, which turned up in 194 public water systems serving 16.5 million people in 36 states during a 2013-2015 EPA survey.

Fears about PFAS contamination have spawned dozens of legal actions against companies such as 3M, DuPont, Chemours and Daikin that make and use the chemicals.

The U.S. House conducted a PFAS hearing last week. A Department of Defense official testified that in 2017, 36 drinking-water systems the department manages or purchases water from had PFAS levels higher than the human health safety level recommended — but not mandated — by the EPA. The military uses firefighting equipment that contains PFAS.

The level of chemicals the EPA now recommends to avoid health problems — 70 parts per trillion in drinking water for PFOA and PFOS — is far too low for the chemical industry and far too high for public health officials.

The American Chemistry Council, a trade group that includes 3M, wants the U.S. to set PFAS safety levels identical to those just agreed to in Canada — 200 parts per trillion for PFOA and 600 parts per trillion for PFOS.

Public health specialist Alan Stern pushed back in the other direction. “Seventy parts per trillion is not protective,” said Stern, who recently retired from New Jersey’s Department of Environmental Protection. The EPA “clearly missed the mark” for immune-system problems that researchers have noted in clinical and epidemiological studies, Stern explained.

Minnesota has nonbinding recommended levels of 35 parts per trillion for PFOA and 27 parts per trillion for PFOS.

At 3M, officials said they agree with the EPA setting a “maximum contaminant level” for PFOS and PFOA in drinking water. But the company will not say what that level should be.

“We support regulation rooted in the best available science, which considers peer reviews and scientific rigor,” 3M said in a statement to the Star Tribune. “The science behind these legacy compounds is complex. Indeed, different regulatory agencies around the world have looked at the same body of scientific evidence and have established very different standards for drinking water. We believe this is an area where the National Academy of Sciences could play an important role resolving some of the underlying uncertainty among regulatory agencies.”

The company phased out use of PFOA and PFOS beginning in 2000. It now makes or uses two different kinds of PFAS — PFBS and ADONA, which current research shows are less toxic.

A 3M spokeswoman said the company would not comment on PFAS litigation.

The American Chemistry Council also backs “best available science” and opposes laws by Congress or state legislatures that set maximum PFAS limits. The trade group believes it is “inappropriate” to regulate all PFAS by a single standard. Instead, it wants different classes of PFAS to go through separate regulatory processes “because it will allow all stakeholders, including our industry, the opportunity to provide comments and important scientific information, which a legislative approach would not.”

Administrative law specialist Mehmet Konar-Steenberg of Mitchell Hamline School of Law said the term “best available science” is so vague it could “define away our ability to reach scientific conclusions.”

In legal filings, then-AG Swanson charged that 3M manipulated the science around PFAS by “funding friendly research ... while simultaneously paying money to ensure that less-favorable research would be suppressed.” She claimed that 3M knew in the 1970s that the PFAS it dumped into unlined pits and trenches in the east metro area of the Twin Cities were toxic, but “concealed this critical fact from government regulators and the scientific community for decades.”

The company and other producers of PFAS accused of similar coverups steadfastly maintain their innocence.

It is a pattern with plenty of precedent, said Klass, the environmental lawyer.

“Companies said for a long time that lead emissions from gas were not harmful,” she pointed out. “Now we know that lead poisoning causes harm.”

Determining the toxicity for PFAS will be more complicated than lead emissions because scientists must deal with a family of chemicals that has thousands of members. Finding common denominators among the most frequently used PFAS has become a crucible for the EPA.

In the end, it could come down to will and resources. Klass said few government agencies other than the EPA have the means to do testing necessary to determine toxicity of various kinds of PFAS. If the federal government won’t test or ignores existing evidence, the standard set for the country could be more hindrance than help. It will be hard, she said, to win a state lawsuit based on PFAS levels that are stricter than a national standard.

The EPA under President Donald Trump has generally taken an anti-regulatory approach, Stern added.

“Somebody has to be out there setting a standard for others to rely on,” he said. “In the political climate in which we live, that’s unfortunately not going to be the EPA.”