More than 15 million Americans live within a one-mile radius of unconventional oil and gas (UOG) operations. UOGs combine directional drilling and hydraulic fracturing, or "fracking," to release natural gas from underground rock. Scientific studies, while ongoing, are still inconclusive on the potential long-term effects fracturing has on human development.

Researchers at the University of Missouri have released a study that is the first of its kind to link exposure to chemicals released during hydraulic fracturing to adverse reproductive and developmental outcomes in mice. Scientists believe that exposure to these chemicals also could pose a threat to human development.

"Researchers have previously found that endocrine-disrupting chemicals (EDCs) mimic or block hormones - the chemical messengers that regulate respiration, reproduction, metabolism, growth and other biological functions," said Susan C. Nagel, Nagel, an associate professor of obstetrics, gynecology and women's health in the School of Medicine. "Evidence from this study indicates that developmental exposure to fracking and drilling chemicals may pose a threat to fertility in animals and potentially people.

Negative outcomes were observed even in mice exposed to the lowest dose of chemicals, which was lower than the concentrations found in groundwater at some locations with past oil and gas wastewater spills."

Researchers mixed 23 oil and gas chemicals in four different concentrations to reflect concentrations ranging from those found in drinking water and groundwater to concentrations found in industry wastewater. The mixtures were added to drinking water given to pregnant mice in the laboratory until they gave birth.

The female offspring of the mice that drank the chemical mixtures were compared to female offspring of mice in a control group that were not exposed. Mice exposed to drilling chemicals had lower levels of key hormones related to reproductive health compared to the control group.

"Female mice that were exposed to commonly used fracking chemicals in utero showed signs of reduced fertility, including alterations in the development of the ovarian follicles and pituitary and reproductive hormone concentrations," Nagel said, who also serves as an adjunct associate professor of biological sciences in the MU College of Arts and Science.

"These findings build on our previous research, which found exposure to the same chemicals was tied to reduced sperm counts in male mice. Our studies suggest adverse developmental and reproductive health outcomes might be expected in humans and animals exposed to chemicals in regions with oil and gas drilling activity."