Lead isn’t the only toxin threatening the safety of community drinking water. A recent study on water located downstream from a West Virginia fracking disposal site uncovered levels of endocrine-disrupting chemicals high enough to adversely impact the aquatic animals living there. And that means human health could be at risk too.

“We can’t make any direct (human health) assumptions about this particular water,” said study co-author Susan Nagel, an associate professor in the University of Missouri School of Medicine’s Division of Obstetrics, Gynecology and Women’s Health. “But we certainly know that humans are sensitive to endocrine-disrupting chemicals — we know (these chemicals) negatively affect human reproduction and fetuses.”

The study, published earlier this month in Science of the Total Environment, focused on four sites associated with a fracking disposal well near Fayetteville, West Virginia: one upstream from the well, one near the well and two downstream from the well. The study didn’t test the actual wastewater stored in the disposal site. These disposal wells contain the wastewater that returns to the surface after drilling for oil and gas at fracking extraction sites. About 1,000 different chemicals are used in the fracking industry, with more than 100 being known or suspected endocrine disruptors. About 36,000 such disposal wells have been permitted throughout the U.S., though little is known about their potential to contaminate nearby water sources.

To conduct the study, which is part of a larger U.S. Geological Survey (USGS) study in the region, researchers collected surface water samples and sent them to Nagel and her colleagues in Missouri, where they used a process known as solid-phase extraction to isolate the chemicals and test them in human cells. The tests revealed greater endocrine-disrupting chemical activity on and downstream of the fracking disposal site, compared to samples taken upstream from the site. Nagel told me that in exposing both female and male mammalian sex hormones to the water, researchers found that the water blocked the hormones’ normal processes. She noted that while the study did not examine drinking water, the tested surface water was collected from a creek that eventually flows into a drinking water source.

“I wasn’t surprised to see the elevated (endocrine-disrupting) activity,” Nagel told me. “But I was surprised at the amount of the activity.” She said the activity she found in the West Virginia samples were at least 10-fold higher than similar surface water testing she’s conducted near fracking sites in Colorado.

Nagel and study co-authors Christopher Kassotis, Luke Iwanowicz, Denise Akob, Isabelle Cozzarelli, Adam Mumford and William Orem write:

As a class II injection well, this site is permitted to accept wastewater from unconventional oil and natural gas extraction. However, this site may accept wastewater and fluids from other industries as well, and the hormonal activity profile exhibited may be due in part to other sources. As such, caution should be taken in the extrapolation of these results to unconventional oil and gas activities specifically. To address this concern, research performed concurrently describes in detail the analytical and geochemical profiling that identified inorganic and organic constituents indicative of (unconventional oil and natural gas) wastewater at these sites. Specifically, elevated conductivity, sodium, chloride, and barium concentrations, and strontium isotopes suggest that the contamination profile is specifically due to the handling of (unconventional oil and natural gas) wastewater from shale gas and coal bed methane production. In addition, numerous organic chemicals were identified in water and sediments downstream of the injection facility, many associated with (unconventional oil and natural gas) operations.

The study found chemical activities well within range to affect the health of aquatic animals — in fact, chemical activities found downstream of the fracking disposal site were well above levels linked to adverse health effects in such animals. Researchers noted that “even with considerable dilution,” the levels of endocrine-disrupting chemicals in the sampled water would still be capable of disrupting normal development in fish and aquatic animals. Nagel added that “fish are actually very good sentinels — we do have a lot of the same hormone receptors that control a lot of the same processes.”

Nagel emphasized that the study doesn’t pinpoint the source of the surface water contamination — in other words, the study does not make a conclusive link between the contaminated water and a leak or spill from the nearby fracking wastewater site. Though she said there have certainly been previously confirmed cases of drinking water contamination linked to fracking disposal wells.

“We don’t know how (the endocrine-disrupting chemicals) got there,” she said. “But it’s absolutely essential to find out where this is coming from. We need a national dialogue that is very specific about looking into the human health impact, and we need a systematic approach to do that.”

Nagel has also been involved in research in Colorado, where she and her colleagues concluded that fracking activities may be contributing to elevated levels of endocrine-disrupting chemical activity in surface and groundwater. In another 2014 study, Nagel and colleagues found that fracking byproducts in the air and water may be linked to infertility, miscarriage, impaired fetal development, birth defects and diminished semen quality.

To request a full copy of the study, visit the University of Missouri newsroom. For more on USGS fracking research, visit http://toxics.usgs.gov/investigations/uog.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for nearly 15 years.