There is little information available to scientists about which compounds are used during hydraulic fracturing. What they do know is that at least eight commonly used fracking chemicals are toxic to mammals.

Fluid used by the oil and gas industry during hydraulic fracturing — also known as fracking — contains chemicals that are highly toxic to mammals, along with many compounds that are either undisclosed or have unknown health effects, according to two recent studies.

Many environmental groups have focused on the potential dangers of toxic chemicals, such as formaldehyde and benzene, used to extract oil and gas trapped within shale rock formations. But it is the unknowns that have some scientists worried that energy development is outpacing our understanding of its environmental and health impacts.

Because fracking fluid recipes are closely guarded industry secrets, scientists are groping in the dark in an attempt to study them.

“There are hundreds of other chemicals that are being used for fracking, and thousands of wells in operation,” said Kimberly Terrell, a wildlife biologist for the Smithsonian Conservation Biology Institute. “So understanding the health risks that are associated with that is challenging enough, but when you don’t have access to basic chemical information, it’s really impossible to accurately predict these risks.”

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Terrell is co-author of a study published in the August issue of Frontiers in Ecology and the Environment. Based on a review of 150 oil and gas wells in three of the top oil producing states in the U.S., an international group of researchers found that two-thirds of the wells were fractured with fluid containing at least one undisclosed chemical.

This lack of information makes it difficult for scientists to determine the risks associated with fracking fluid if it should leak into groundwater or surface water.

“Without knowing the full ingredient list of these fracturing fluids, scientists can’t really predict the toxic effects of the fluid on humans or wildlife,” Terrell said.

The results are similar to another study presented this month at the meeting of the American Chemical Society. Researchers from Lawrence Berkeley National Laboratory and the University of the Pacific found that of 200 compounds commonly used in fracturing, doctors don’t know the health risks of about one-third. In addition, eight substances in fracking fluid are already known to be toxic to mammals.

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During hydraulic fracturing, chemicals — including gelling agents, anti-corrosives, and antimicrobials — are mixed with large amounts of water and sand and injected into wells, fracturing rock formations deep within the earth. Industry supports the use of these chemicals for extracting oil and gas reserves, including those substances known to be toxic.

“It’s not the presence [of certain chemicals],” said Steve Everley, national spokesman for Energy In Depth, a research and public education arm of the Independent Petroleum Association of America, in an email to Healthline, “it’s the concentration, and even more importantly it’s a question of whether it’s being handled properly under strong regulations — which, in the case of oil and gas, there are plenty.”

One aspect of industry regulations is building wells that adequately contain the fracking fluid. But strong wells are only one part of an extremely complicated process.

“It’s definitely important to construct these wells as safely as possible,” Terrell said, “but we have to recognize that fracking chemicals are entering our land and waterways through several other routes.”

In addition to well failure, chemicals can end up in the environment through leaks from tanks, valves, or pipes, improper storage or disposal of fracking fluids, and abandoned wells that have not been sealed.

“It’s not just about the well itself and how it’s constructed,” Terrell said. “There are a lot of other stages of the process that could potentially go wrong.”

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Safe energy development depends on knowing more about the compounds used during hydraulic fracturing, including understanding how the individual ingredients act when combined.

“From a human and an environmental health perspective,” Terrell said, “it’s important to understand exactly what ingredients are in fracturing fluid, because chemicals can have different effects when they occur in mixtures, compared to when they’re pure.”

Even in the face of health concerns, it’s likely that hydraulic fracturing will continue, especially given the need for new sources of energy. But it is also important, said Everley, to “mitigate and control risks so we can actually have a vibrant and healthy economy.”

This is why scientists are calling for more research on the nature of the compounds used in hydraulic fracturing. This will help all parties — industry, scientists, legislatures, and the public — make better-informed decisions.

“Most human activities do have environmental trade-offs,” Terrell said, “but it’s important that the public be informed of the risks, so that they can decide if the costs are worth the benefits.”