The Environmental Protection Agency proposed strict limits on six types of "forever chemicals" in drinking water Tuesday. The announcement caps a years-long campaign from scientists, environmentalists and public health advocates who have urged the agency to stop the industrial chemicals from invading Americans' bodies by way of their taps.

PFAS, short for per- and polyfluoroalkyl substances, have been linked to an array of health problems, including some cancers, immune issues and developmental risks. Two of the oldest and best-studied, PFOS and PFOA, are regularly found in the environment even though U.S. manufacturers no longer produce them. The forever chemical moniker comes from their tendency to linger in human bodies and resist breaking down.

The chemicals first became a public concern in Minnesota in 2004, when it was revealed that Maplewood-based 3M had disposed of large volumes of the chemicals in leaky landfills in the eastern Twin Cities metro. Today, the state has its own standards for four of the six chemicals to be regulated by the EPA, as well as two more not covered by the EPA, and officials were optimistic that Minnesota would be able to carry out the federal rules.

"We've had this almost two decades of head start, and we've built a framework in Minnesota of existing data," said Sandeep Burman, the section manager for drinking water protection at the state Department of Health. "It's unfortunate, but we're used to dealing with PFAS."

The announcement marks the first time the EPA has proposed drinking water limits on PFAS chemicals that can be enforced with fines or other measures. The other two chemicals covered by the EPA's proposal but unregulated at the state level haven't been found in Minnesota, Burman said.

The levels proposed by the EPA for PFOS and PFOA are at 4 parts per trillion, or nearly at the limit of what can be detected, though MDH's lab can turn up slightly smaller concentrations. For the other four PFAS, the EPA proposes combining them to create one standard — in an acknowledgement that the chemicals, even in small amounts, may do more harm mixed together than in individual doses.

3M, which pioneered the chemicals and used them for decades in products like Scotchgard, has announced it will stop making any type of PFAS by the end of 2025. But in a statement Tuesday, spokesman Sean Lynch wrote that the EPA's proposed water rules "lack a sound scientific basis," and that the agency didn't show the rules "are necessary to protect public health or the environment."

But at a news conference in North Carolina announcing the new rules, EPA Administrator Michael Regan said that the drinking water limits would "prevent thousands of deaths and prevent tens of thousands of serious PFAS-related illnesses."

Public health officials have spent decades unwinding the toxicology of the chemicals, said Sarah Fossen Johnson, supervisor of MDH's Health Risk Assessment Unit. She was skeptical of the claim that the chemicals are causing thousands of deaths, but she said serious exposures are potentially causing health problems "for some of our most vulnerable populations, such as infants and children."

"We're really starting to see that now that the epidemiology studies are becoming stronger and giving us better evidence," Fossen Johnson added.

The EPA will accept public comments on the proposed rules for 60 days and hold an online hearing May 4. The final limits could change based on the input the agency receives.

The regulations would come with a significant cost. Smaller water systems, in particular, may face large bills for granular activated carbon filters or pressurized reverse osmosis.

Adam Olson, a spokesman for the Minnesota Pollution Control Agency, wrote in an email that the state's costs could top $1 billion to implement treatments, test for PFAS sources and clean up the chemicals.

One affected city is Woodbury, which as of December had higher levels of PFOA and PFOS than the EPA's proposed limits. Woodbury is one of several east metro communities affected by PFAS that leached out of 3M's disposal sites from its Cottage Grove chemical plant and into groundwater.

Woodbury Mayor Anne Burt said Tuesday the limits will have no immediate impact on the city's water system. "Moving forward, our years of proactive work on temporary water treatment for PFAS and our progress on permanent treatment solutions position the city well for mitigating PFAS impacts," Burt said in a statement.

Woodbury has closed drinking water wells in the past, and it rapidly built a temporary treatment plant in 2020 for six other wells after it found the chemicals in water pulled from deep below ground.

The city has begun work on a treatment plant to take in all of the city's water and treat it for PFAS before it's piped to homes and businesses. The massive project — the largest in city history — is not expected to be completed until 2027.

Star Tribune staff writer Matt McKinney and Wisconsin Watch reporter Bennet Goldstein contributed to this report.