U.S. researchers studying the surface water near a hydraulic fracturing wastewater disposal facility in West Virginia have identified high levels of chemicals that can cause hormonal changes.

The University of Missouri said on Wednesday that the endocrine disrupting chemicals (EDCs) found at the wastewater injection well may be associated with negative health effects in aquatic organisms, other animals and humans.

“Surface water samples collected on the disposal facility site and immediately downstream exhibited considerably greater EDC activity than surface water samples collected immediately upstream and in a nearby reference stream,” said Susan C. Nagel, director of the study and an associate professor in the Department of Obstetrics, Gynecology and Women’s Health in the School of Medicine, and an adjunct associate professor of biological sciences in the university’s College of Arts and Science. “The level of EDC activity was within the range or higher than the level known to impact the health of aquatic organisms.”

The fracking process results in large volumes of wastewater that contains chemicals used to drill and frack the well and may also contain radioactive compounds and heavy metals released from deep underground.

Approximately 1,000 different chemicals are thought to be used across the fracking industry, and more than 100 of these are known or suspected to be EDCs.

Disposal wells like the one analyzed in the University of Missouri study are used only to dispose of fluids associated with oil and natural gas production.

“Approximately 36,000 of these disposal wells are currently in operation across the U.S., and little work has been done to evaluate their potential impacts on nearby surface water,” said Christopher Kassotis, a former graduate student in Nagel’s laboratory and a current postdoctoral fellow at Duke University. “Given the large number of disposal wells in the U.S., it is critical for further investigation into the potential human and environmental health impacts.”

The study, titled “Endocrine Disrupting Activity in Surface Water Associated with a West Virginia Oil and Gas Industry Wastewater Injection Disposal Site,” will be published online in Science of the Total Environment.