© Hatchingfuture via Wikimedia Commons
A fracking site in the Midwestern United States offers safety warnings.
Fracking — a process in which water, sand and chemicals are pumped into the earth to crack open deposits of gas and oil — has created an energy boom in the United States, but a lot of people are worried about whether it's contaminating our underground supply of drinking water.

The energy industry contends that the risks are minimal, but an EPA report released in June contained a more guarded assessment. The report conceded fracking had contaminated the water supply in some parts of the United States, but the impact "was small compared to the number of hydraulically fractured wells." Another potential danger, however is detailed in a new study that suggests fracking chemicals lead to male sterility.

The study by researchers from several different universities, published in the scientific journal Endocrinology, found that prenatal exposure to a mixture of fracking chemicals, at levels found in the environment, lowered sperm counts in male mice when they reached adulthood.

The scientists tested 24 chemicals used in fracking and determined that all but one of them were endocrine-disrupting chemicals, or EDCs, which interfere with hormones, sometimes by mimicking or blocking them.

Almost all of those chemicals disrupted the functions of estrogens, which are primarily female hormones but also are found in men. The chemicals also disrupted androgens, a group of primarily male sex hormones such as testosterone. In addition, more than 40 percent of the chemicals interfered with progestogens, another type of reproductive hormone, and glucocorticoids, which are involved in metabolism and stress

"In addition to reduced sperm counts, the male mice exposed to the mixture of chemicals had elevated levels of testosterone in their blood and larger testicles," University of Missouri-Columbia researcher Susan C. Nagel said in a press release. "These findings may have implications for the fertility of men living in regions with dense oil and/or natural gas production."

The scientists found mice that were exposed to the chemical mixtures prenatally had decreased sperm counts, smaller testes and increased testosterone levels compared to the control group.

"It is clear EDCs used in fracking can act alone or in combination with other chemicals to interfere with the body's hormone function," Nagel said. She called for more research to assess the reproductive impact of fracking chemicals.