As the oil and gas drilling technique known as fracking, or hydraulic fracturing, grows in this country, scientists are becoming increasingly concerned about the potential health risks some of these toxic fracking fluids pose to mammals, a new study describes.

Of the 200 commonly used compounds shot into the ground during this process, eight of them are toxic to mammals, according to the researchers.

Fracking involves injecting water with a mix of chemical additives into rock formations deep underground to promote the release of oil and gas. The practice seems to have expanded overnight in the United States, but consequently it has also stimulated major opposition and troubling reports of contaminated well water, as well as increased air pollution near drill sites.

"The industrial side was saying, 'We're just using food additives, basically making ice cream here,'" lead author William Stringfellow said in an American Chemical Society (ACS) news release. "On the other side, there's talk about the injection of thousands of toxic chemicals. As scientists, we looked at the debate and asked, 'What's the real story?'"

To figure out for themselves who is right, Stringfellow's team at Lawrence Berkeley National Laboratory and University of the Pacific analyzed a list of substances commonly used in fracking. They include gelling agents to thicken the fluids, biocides to keep microbes from growing, sand to prop open tiny cracks in the rocks and compounds to prevent pipe corrosion.

What they found was that some fracking fluids do indeed contain many nontoxic and food-grade materials, but just because something is edible or biodegradable doesn't necessarily mean that it can be easily disposed of, Stringfellow notes.

"You can't take a truckload of ice cream and dump it down the storm drain," he explained. "Even ice cream manufacturers have to treat dairy wastes, which are natural and biodegradable. They must break them down rather than releasing them directly into the environment."

Most fracking compounds require treatment before being released. They also identified eight compounds, albeit not thousands, which are reportedly toxic to mammals.

"We can't let shale development outpace our understanding of its environmental impacts," Morgan Tingley, co-author of a recent study published in the journal Frontiers in Ecology and the Environment, said in a statement. "The past has taught us that environmental impacts of large-scale development and resource extraction, whether coal plants, large dams or biofuel monocultures, are more than the sum of their parts."

The scientists presented their findings Aug. 13 at the ACS's 248th National Meeting & Exposition.