Arsenic, benzene, formaldehyde, lead and mercury are among more than 200 toxins found in fracking fluids and wastewater that may pose serious risks to reproductive and developmental health, according to a paper published on Wednesday.

And that list may just be just the tip of the iceberg, said Nicole Deziel, an environmental health expert at the Yale School of Public Health and senior author of the new study.

Many more chemicals known to be used in fracking could pose similar risks, yet remain unstudied, Deziel said. Other substances involved in oil and natural gas production remain undisclosed by fracking companies.

In their study, Deziel and her team investigated more than 1,000 chemicals used in and created by the controversial drilling process, which shoots a mix of pressurized water, sand and chemicals into shale rock to unlock hydrocarbon reserves. The U.S. Environmental Protection Agency used the same list in its assessment of the available science, which found no evidence that fracking has led to widespread, systemic contamination of drinking water.

For most of the chemicals, insufficient information thwarted the researchers' efforts to determine potential toxicity.

"That's not really surprising," said Deziel. "There are thousands of chemicals in commerce that people are routinely exposed to and for which we have limited data." (Hence, the major push to overhaul the 1976 Toxic Substances Control Act, which environmentalists argue doesn't give the EPA enough authority to study and regulate chemicals.)

Of the 240 chemicals for which the Yale team did have adequate data, they found that 157 were associated with some kind of reproductive or developmental problem, such as adverse birth outcomes, derailed brain development or infertility.

And, of course, these health concerns come in addition to worries over air pollution, noise, greenhouse gas emissions and even earthquakes, which have also been linked to fracking.

The fracking industry was quick to note that the study doesn't prove a link to any such health risks.

"The real question is whether people are actually being exposed to those chemicals at concentrations that would be harmful. There is nothing in this study that suggests that is occurring," Steve Everley, senior adviser for Energy in Depth, the oil and gas industry's education and public outreach arm, told HuffPost in an email.

It's a point that Deziel acknowledged, while again lamenting the significant gaps in understanding the science of fracking and its potential consequences. Some previous research does, however, suggest that even tiny doses of chemicals released during phases of oil and natural gas production could pose serious health risks -- especially to developing fetuses, babies and young children.

Andrea Gore, an expert in hormone disruption at The University of Texas at Austin, co-authored a scientific statement in September that underscored that point. Combine these chemicals -- just as fracking fluid and wastewater naturally does -- and the risks may become more unpredictable and worrisome, according to the statement from the Endocrine Society, a professional medical organization.

Gore praised the new paper. "This was a good first step to identify some chemicals that give cause for concern, and to draw attention to the lack of knowledge about hundreds of chemicals getting into the environment, and from there, into our water sources," said Gore, who was not involved in the study.

Zacariah Hildenbrand, a researcher with Inform Environmental, an environmental consulting group, co-authored a separate paper published this week that he said builds on findings from his group and others that fracking chemicals can make their way into the water. While simply living close to a gas or oil well doesn't mean a person faces contamination, living in an area with a high density of wells could indeed raise that risk, he said.

"We found a number of things that shouldn't be in the water," said Hildrenbrand.

"This research needs to be done. In my opinion, it's one of the most important issues in terms of climate science," Hildrenbrand added. "We're looking at shale energy as a kind of bridge towards more renewable sources, so it's best for us to understand what the risks are."

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