A new study suggests fracking wastewater can endanger drinking water even after it has passed through treatment plants and been diluted.

Hydraulic fracturing, or fracking, is the process by which natural gas is extracted from shale deposits by blasting the underground rock with highly pressurized water mixed with chemicals. At the end of the process, drillers are left with tanks full of natural gas; but they're also left with highly radioactive wastewater laden with heavy metals and with halide salts like bromide, chloride and iodide.

Most fracking operations store their wastewater in holding ponds. Eventually, that water is filtered through municipal or commercial treatment plants and emptied into rivers, lakes and ponds.

But new research suggests that wastewater contaminants, when subjected to traditional treatment methods like chlorination or ozonation, encourage toxic byproducts.

Researchers with the American Chemical Society found that even extremely diluted wastewater can still produce these byproducts during the treatment process. Scientists say their findings suggest regulators and energy officials should be more careful about which surface waters treated wastewater is emptied into. They also say new water treatment methods should include halide-removal techniques.

"The potential formation of multiple disinfection byproducts (DBPs) in drinking water utilities in areas of shale gas development requires comprehensive monitoring plans beyond the common regulated DBPs," researchers wrote in the newly published study.

The research was detailed this week in the ACS journal Environmental Science & Technology.