Fluorine-based chemicals that can cause cancer, developmental toxicity and numerous other detrimental health effects have contaminated the drinking water of millions of Americans, and the blood of people and animals worldwide. But how did these chemicals get there—and what happens when they’re passed on to future generations?

A series of new, peer-reviewed studies connect the dots from the pollution sources, to drinking water supplies, to women’s blood, and bolster earlier findings that these chemicals can harm the immune systems of fetuses exposed in their mothers’ wombs. Perfluorinated chemicals, or PFCs, are used in Teflon, Scotchgard and hundreds of other products.

A study published recently in Environmental Science & Technology Letters points to military bases, airports, industrial sites and wastewater treatment plants as the major sources of PFCs in drinking water. PFC pollution from industrial facilities has long been known, but the new study found that drinking water contamination, detected by nationwide tests mandated by the Environmental Protection Agency, correlates strongly to military and civilian airports' use of firefighting foams.

“During fire-fighting practice drills, large volumes of these toxic chemicals wash into surface and ground waters and can end up in our drinking water,” said Arlene Blum, co-author of the study and executive director of the Green Science Policy Institute. “Such toxic and persistent chemicals should only be used when essential, and never for training. There are non-fluorinated fire-fighting foams that should be considered for use instead.”

Environmental Working Group collaborated on the study with researchers at Harvard University, the Green Science Policy Institute, Silent Spring Institute, University of California at Berkeley, University of Rhode Island and Colorado School of Mines, as well as the EPA and the California Department of Toxic Substances Control.

In June, a study from the California Department of Toxic Substances Control found elevated levels of two PFCs—PFOA, formerly used to make DuPont's Teflon, and PFOS, formerly an ingredient in 3M's Scotchgard—in the blood of women whose water supply was contaminated with those chemicals. PFOA and PFOS levels were 38 percent and 29 percent higher, respectively, in women with detectable levels in their drinking water.

PFCs can be passed via the umbilical cord from mother to unborn fetus, as well as from mother to baby through breast milk. Another study, published recently in Environmental Health Perspectives, connects early life exposure to PFCs with reduced immune system responses that persist into adolescence. The author, Phillipe Grandjean of the Harvard School of Public Health, said the EPA's non-enforceable health advisory level for PFOA and PFOS in drinking water is much too high to protect against immune system harm. This paper comes just a month after the National Toxicology Program published a draft review of the science indicating that PFOA is presumed to harm the immune system.

And Grandjean said the contamination revealed by EPA's water tests is only the tip of the iceberg, because the tests don't include the small water systems and private wells that serve more than 30 percent of Americans.

“Our research has documented harm to the human immune system from these substances at levels much below those that were detectable in the [EPA tests] and even more water supplies are likely to contaminated at these low levels,” Grandjean said.

In April, EWG submitted a letter to EPA Administrator Gina McCarthy, requesting expedited action on setting an enforceable national drinking water standard, and calling for additional data collection and testing to identify and remediate sources of pollution.

PFOA and PFOS have been phased out, but significant work remains to clean up the legacy of pollution left from decades of their use in hundreds of products. Meanwhile, chemical makers have introduced hundreds of replacement chemicals, many of which share similar characteristics to the ones that have caused such widespread contamination.

This article was originally published by Environmental Working Group.