Yesterday (Sept. 6), a US House of Representatives hearing convened to ask why federal authorities haven’t regulated PFAS, a little-known class of chemicals that has sparked one of the biggest drinking-water contamination revelations in recent decades. The US Environmental Protection Agency has known for decades it could have a PFAS problem on its hands, and now hundreds of communities across the US are finding the chemicals in their water.

“How do we create that sense of urgency?” representative Debbie Dingell, a Michigan Democrat, asked the head of the EPA’s office of drinking water. “PFAS in Michigan is scaring people more than the Flint water crisis.” In Battle Creek, Michigan, PFAS levels in the groundwater were recently found to be up to 757 times higher than the recommended limit—and the recommended limit was found to be as much as 10 times higher than what could really be considered safe. That’s just one case; Department of Defense and Northeastern University data tally 172 known contaminated sites, and those numbers do not account for contaminated public water systems, which the Environmental Working Group estimates could add up to over 1,500 additional sites.

The situation contains shades of a now-famous disaster: In the 1950s and 1960s, nearly everyone on the planet was exposed to the pesticide dichlorodiphenyltrichloroethane. DDT is a household name, synonymous with chemical dangers at first ignored and then revealed to be damaging generations of life, both human and animal.

DDT is still ubiquitous, showing up in food, water, and nearly everyone’s blood, even though it was banned in most countries more than 40 years ago. Today, studies link elevated exposure to it to heightened cancer risks, infertility, developmental delays, and most recently, to autism.

Now a similar scenario is playing out with PFAS, a class of widely used chemicals that should also be a household name by now. They’re the compounds that give us nonstick pans, waterproof shoes, firefighting foams, and a long list of other products. And they are likely contaminating the water supplies of tens of millions of people in the US. PFAS contamination cases outside the US—particularly in Australia—are also beginning to emerge.

The health risks of PFAS exposure

At this point, most people in the US have been exposed to chemicals in the PFAS family. The most common are PFOA (perfluorooctanoic acid, an ingredient in Teflon, the chemical used to make non-stick cookware) and PFOS (perfluorooctane sulfonate, often used as a firefighting foam, especially at airports and on military bases). The compounds leach into the water supply from sites where PFAS industries dumped their manufacturing waste, or where firefighting foam is allowed to seep into the ground.

The number of PFAS contamination discoveries keep piling up. Just last month, news broke that the residents of Flint, Michigan weren’t just exposed to elevated lead levels from the Flint River—they were likely also exposed to hightened levels of PFAS, too, and the state of Michigan knew about it before the city began using the river as its water source in the first place.

PFAS chemicals have been linked to a range of health risks including cancer, immune-system issues, and developmental problems in fetuses. Communities in states as far-flung as West Virginia, New York, Michigan, Illinois, Pennsylvania, and Wisconsin have already dealt with water-contamination emergencies from the chemicals. The crisis isn’t contained to the US; at least 90 sites across Australia are contaminated with PFAS, mostly due to use of firefighting foam, and reports emerged last month that new PFAS contamination sites were identified in Western Australia.

Outside of affected communities, PFAS is still little-known. But that is no accident; for years, the US government and industry leaders obscured and downplayed evidence of the compounds’ harm and ubiquity in the environment. For example, Sharon Lerner at the Intercept recently reported that 3M, makers of Scotchguard and firefighting foam made from PFOS and PFOA, knew by the 1970s that the compounds were harmful to people’s health and accumulating in people’s blood, and yet continued manufacturing the compounds and withheld the information from the US Environmental Protection Agency until turning over documents and ceasing production in 2000. In turn, EPA fined 3M $1.5 million for violating toxic-substance regulations, yet did nothing further to stop the spread of PFAS in the environment.

It has still not enacted any rule to regulate the compounds. Under the Safe Drinking Water Act of 1974, the EPA is responsible for determining when a chemical needs to be regulated in the US water supply. Despite tens of thousands of new chemicals arriving on the market, the EPA hasn’t added a new toxin to its list since 1996. (Even the Government Office of Accountability thinks that’s a sign of a broken system.)

But the news around PFAS is reaching a critical mass that is impossible to ignore.

Why isn’t the government doing anything about PFAS?

In 2013, in an effort to decide whether to regulate certain PFAS compounds, the EPA ordered nationwide testing. It hired three labs to do the job. Based on those results, the EPA estimated that PFAS only contaminates about 1% of the US water supply—too low an amount to make an urgent case for new regulations. But last year, a reanalysis by one of those labs found that if the EPA had used more granular verification methods, they would have found PFOA in 20% of the national water supply.

This year, in January, EPA and White House staffers attempted to block publication of a US Department of Health and Human Services study that showed PFAS could harm human health at exposure levels far below EPA’s current recommended thresholds. In emails obtained by the Union of Concerned Scientists under the Freedom of Information Act, a Trump administration aide warned other staffers that the study would cause a “public relations nightmare.”

“The public, media, and Congressional reaction to these numbers is going to be huge,” one unidentified White House aide said in an email forwarded to another federal staffer on Jan. 30. “The impact to EPA and [the Department of Defense] is going to be extremely painful.”

The staffer was likely referring to the defense department because PFOS is used to make a firefighting foam widely used on military bases during training and ammunition testing. Water supplies near at least 126 military bases across the US have been found to be highly contaminated with PFAS.

The US government made headlines in May by initially keeping journalists out of a meeting about its findings on public water contaminated with the compounds. In June, the stalled Health and Human Services report was finally released. It concluded that the EPA’s recommended threshold for PFAS weren’t even close to being adequate to protect human health—they should be set at levels seven to 10 times lower than they currently are, the HHS wrote.

It may be no accident that most people still don’t know what PFAS are—but as more and more communities begin finding it in their water supplies, and as our scientific understanding of its impact matures, PFAS could emerge as the chemical tragedy of this generation.