Across the US, towns warn of toxic PFAS chemicals in drinking water. Here's what to know.

The U.S. Environmental Protection Agency in June issued nationwide health advisories for four PFAS chemicals commonly found in drinking water. Short for per- and polyfluoroalkyl substances, the quartet are part of a larger class sometimes referred to as “forever chemicals,” due to their strength and failure to degrade in the environment.

The EPA's new advisories startled many observers because the safety levels for two of the chemicals -- perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) -- are extremely low. Thousands of drinking water utilities across the country likely have PFOA or PFOS in their system above the EPA's new advisories. Studies have linked the chemicals to serious health effects like cancer, low birthweight babies and immune system effects.

In the wake of EPA's action, cities such as Mobile, Alabama, sent notices to their customers confirming the presence of PFAS in drinking water and alarming many residents.

If you're concerned about PFAS in your drinking water, here's what to know:

How dangerous are PFAS?

There are thousands of PFAS chemicals, hundreds of which are used in the U.S. for things like nonstick coatings and waterproofing in products such as kitchenware, clothing, furniture and food packaging. 

The chemical industry argues that it has phased out the varieties of PFAS known to be hazardous, such as PFOS and PFOA, and replaced them with safer alternatives. But environmental groups and some scientists say the common characteristics of PFAS make them all dangerous.

More:What are PFAS? A guide to understanding chemicals behind nonstick pans, cancer fears

The potentially toxic effects of most PFAS chemicals have not received robust research. But large studies have found links between PFOA and PFOS and a variety of health effects, including high cholesterol, ulcerative colitis, thyroid disease, testicular cancer, kidney cancer and pregnancy-induced hypertension. Many researchers also worry about reproductive and developmental harms, such as low birthweight and decreased immune response.

Exactly how much PFOA or PFOS it takes to harm someone is unknown. PFAS chemicals do not cause sudden illnesses like a poison would. Instead, they accumulate in the body over time, where scientists say they can begin to impact systems. The EPA says its new advisories are designed to protect even pregnant women, young children, and the elderly over a lifetime of constant exposure.

“This means that these advisory levels are very conservative, or protective, of your health,” the EPA told USA TODAY in an email.

How do I know if I or my family are in danger?

Scientists say there is little anyone can do to assess individual risk. In highly contaminated communities, people have had blood tests to determine how much PFAS they've been exposed to, which can then be compared with national averages. But blood tests are expensive, can be difficult to obtain, and will not definitively tell someone what danger they face, health experts say.

Instead, many scientists assess the potential health impacts of PFAS at a population-level. Most recently, researchers estimated that exposure to some PFAS may have played a role in about 6.5 million deaths in the U.S. from 1999-2018, primarily those caused by cancer and heart disease. Annually, that's about the same mortality rate as COVID-19.

More:Do you know what's in your blood? New EPA docs show widespread risk from common chemicals

But virtually all Americans have some level of PFAS in their bodies, and the blood levels of the most problematic chemicals, PFOS and PFOA, have declined ever since an industrywide phaseout over the past two decades. In one way, that means the EPA advisories for PFOS and PFOA are part of an effort to further drive down a risk that has already been decreasing for many Americans.

How do I know if PFAS is in my drinking water?

At present, there is no national rule to test for PFAS in public drinking water, and many water utilities do not. Some, like Mobile, have tested and notified the public even when PFOA and PFOS are found in small amounts, just above the level that can be detected by advanced equipment.

Other states have tested water utilities across their jurisdiction. A Chicago Tribune investigation published this week reviewed state data that showed PFAS in water utilities across the state, with at least one PFAS chemical detected in water supplies collectively serving 8 million people, about 62% of the state's population.

Private testing in North Carolina has found PFOA and PFOS in the water sources for dozens of utilities across the state. Officials in Raleigh, Durham and Chapel Hill confirmed the presence of the chemicals above the EPA's new advisories, adding that they are studying the problem, the Raleigh News & Observer reports.

While the EPA is planning on sampling thousands of water authorities across the country for PFAS in the years ahead, there is no official, central database where the public can check every system.

Residents can inquire with their water supplier or state environmental agency about whether testing has been performed on their system. The Environmental Working Group, a national environmental nonprofit that advocates for strict limits on PFAS, maintains a map of all known locations where PFAS have been found in drinking water.

The American Water Works Association, a nonprofit representing water utilities nationwide, told USA TODAY its members “want to make the right decisions to quickly and efficiently reduce potential exposure to PFAS through water and protect their communities.”

But the association said members questioned the “scientific underpinnings” of the new advisories and the timing of their release and worry they create pressure for water utilities to make the “wrong investments.” They also want regulators to do more to find PFAS polluters and halt the contamination of water sources.

Regardless, the group said it is urging transparency among members.

“We encourage our members to speak openly and honestly with their communities about PFAS, discussing both what they know and do not know," said Steve Via, director of federal relations for the association. “Although there’s a great deal of uncertainty out there, the act of having that conversation can be helpful in strengthening public trust.”

What is being done about this? 

The EPA's new advisories are not formal regulations. The agency says it plans to announce draft regulations this fall, which, if approved, would then likely take effect in coming years.

Until then, action will continue to vary from community to community and state to state. In some places, such as highly contaminated towns in southeast Pennsylvania, officials adopted “zero tolerance” plans in which they installed carbon filtration systems to remove PFAS entirely from drinking water. But such plans can cost tens of millions of dollars for a typical water utility to implement.

Other cities have adopted a wait and see approach, reluctant to make such investments before seeing what the EPA's regulations might be.

Individuals can install filters in their homes, which can protect an entire house or can go under the kitchen sink to remove most PFAS from water used to cook and drink. Scientists say PFAS do not readily pass through the skin, making showering and bathing safe.

The Environmental Working Group says individuals can also lower their exposure to PFAS by purchasing commercial products that are PFAS-free.

The EPA offers a guide on reducing exposure to PFAS and recommends that those with concerns or questions about PFAS in commercial products contact the Consumer Product Safety Commission. The agency also promotes its own Q&A page around the new health advisories and says it has released the first $1 billion of $5 billion in funding to help water utilities address PFAS contamination.

Kyle Bagenstose covers climate change, chemicals, water and other environmental topics for USA TODAY. He can be reached at kbagenstose@gannett.com or on Twitter @kylebagenstose.