At least six million Americans in 33 states are being exposed to unsafe levels of industrial perfluorooctanoic acid (PFOA) chemicals in their drinking water, found a study published Tuesday in the journal Environmental Science and Technology Letters.

"And the available water data only reveals the tip of the iceberg of contaminated drinking water," said study co-author Dr. Philippe Grandjean of the Harvard School of Public Health to the Charleston Gazette-Mail.

The Washington Post details the researchers' findings:

194 of 4,864 water supplies across nearly three dozen states had detectable levels of the chemicals. Sixty-six of those water supplies, serving about six million people, had at least one sample that exceeded the EPA's recommended safety limit of 70 parts per trillion for two types of chemicals — perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA).

PFOA and PFOS chemical compounds—including C8, popularly known as the Teflon chemical—are extremely dangerous to human health, and despite an EPA advisory released earlier this year and increasing calls for action, research shows they are near-ubiquitous in the United States.

"Virtually all Americans are exposed to these compounds," said Xindi Hu, the study's lead author and a doctoral student at Harvard's Department of Environmental Health, to the Post. "They never break down. Once they are released into the environment, they are there."