Low levels of oil and gas production chemicals cause abnormal mammary glands and pre-cancerous lesions in female mice

Female mice exposed to a mixture of 23 chemicals used in oil and gas fracking developed mammary lesions and enlarged tissues—suggesting the chemicals may leave breast tissues more prone to cancer, according to a new study.

The study is the first to examine the potential impact of chemicals used in unconventional oil and gas extraction—such as hydraulic fracturing and directional drilling—on mammary glands and suggests that low levels of the chemical cocktail commonly found near frack sites may spur abnormal development in women’s breast tissue.

“The mammary gland is a hormone-sensitive organ that is responsive to multiple endocrine inputs during development,” the authors wrote in the study published today in the Endocrinology journal.

It’s the latest potential health impact linked to fracking chemicals, which have been associated with low birth weights, birth defects and reduced brain function in children.

The findings are important as more than 17 million people in the U.S live within a mile of an oil or gas well. Hydraulic fractured wells now account for about half of U.S. oil, and two-thirds of the nation’s natural gas, according to the U.S. Energy Information Administration.

In addition, health impacts were seen after exposure to levels of chemicals well within what is found near frack sites. The mixture was just a fraction of the more than 1,000 chemicals used during oil and gas fracking.

Scientists exposed female mice—while in their mothers’ womb—to different levels of 23 chemicals. There were no effects on the mammary glands prior to puberty, but when the exposed mice were adults they developed lesions and a condition called hyperplasia, which causes enlarged organs or tissues.