By Christopher Joyce, originally posted on August 9, 2016

A study of drinking water supplies throughout the U.S. shows that numerous sources are contaminated with firefighting chemicals.

A team of scientists examined government data from thousands of public drinking water supplies. The water samples had been collected by the federal Environmental Protection Agency.

The scientists were looking for several types of chemicals from a class of fluorinated substances used commonly in firefighting foam.

They found significant amounts of one chemical in 66 water supplies. Two other versions of the chemicals showed up in nearly 200 supplies. In some cases the level was barely above the maximum allowable limit set by the government. Others were far higher. The researchers say some 6 million people in 14 states are served by these water sources.

The chemicals showed up more often near sites where these firefighting chemicals are common, such as airports or military bases. “During firefighting practice drills,” says Arlene Blum, a study co-author from the University of California Berkeley, “large volumes of these chemicals wash into surface and ground waters and can end up in our drinking water.” They are also found often near sites where the chemicals are manufactured.

These chemicals, called poly- and perfluoroalkyl substances, have been in use for decades and are very persistent once they’re out in the environment.

The study, published in Environmental Science and Technology Letters, did not determine people’s actual exposure to the chemicals. And the amounts found in most cases were very low. But the chemicals have been linked to cancer, low birth weight in children born to women who are exposed, and hormonal changes.