Elevated levels of radioactivity, salts and metals were found in treated water from oil and gas operations discharged into a Pennsylvania creek, scientists say.

Treated wastewater from hydraulic fracturing or "fracking" activities released into the creek in the west of the state was tested, researchers from Duke University and Dartmouth College reported Wednesday in a study published in the journal Environmental Science & Technology.

"Radium levels were about 200 times greater in sediment samples collected where the Josephine Brine Treatment Facility discharges its treated wastewater into Blacklick Creek than in sediment samples collected just upstream of the plant," Duke geochemist Avner Vengosh said.

High concentrations of some salts and metals were also detected in the stream water, he said.

"The treatment removes a substantial portion of the radioactivity, but it does not remove many of the other salts, including bromide," Vengosh said. "This is significant because bromide increases the risks for formation of highly toxic disinfection byproducts in drinking water treatment facilities that are located downstream."

Blacklick Creek is a tributary of the Conemaugh River, which flows into the Allegheny River, a water source for numerous western Pennsylvania cities, including Pittsburgh.

Also of concern were the elevated levels of radiation, the researchers said.

"The radioactivity levels we found in sediments near the outflow are above management regulations in the United States and would only be accepted at a licensed radioactive disposal facility," Duke environmental scientist Robert B. Jackson said.

Vengosh agreed the levels of radioactivity could be a problem.

"Although the facility's treatment process significantly reduced radium and barium levels in the wastewater, the amount of radioactivity that has accumulated in the river sediments still exceeds thresholds for safe disposal of radioactive materials," he said. "Years of disposal of oil and gas wastewater with high radioactivity has created potential environmental risks for thousands of years to come."

"It is clear that this practice of releasing wastewater without adequate treatment should be stopped in order to protect freshwater resources in areas of oil and gas development," Vengosh said.