Pavillion resident Louis Meeks, whose well is polluted, at home with John Fenton. (Angus M. Thuermer Jr./WyoFile)

A study has found that polluted groundwater near a fracked Wyoming oil and gas field is more disruptive to human cells than tainted groundwater sampled near conventional oil and gas operations.

The study by researchers at the University of Missouri and other institutions is believed to be the first to compare the effects of fracking-linked pollution to those of conventional oil and gas development pollution. Research found evidence for groundwater contamination from both types of drilling, but more insidious effects from groundwater in areas where nearby wells are stimulated with hydraulic fracturing, the scientific paper says.

Some chemicals reportedly used in fracking act as endocrine disruptors that “can interfere with any aspect of hormone action” and “disrupt development and contribute to disease in both humans and animals,” the paper says. The endocrine system is key to fetal and infant development – turning on and off production of various growth hormones. Its disruption can cause everything from birth defects and miscarriages to low sperm counts.

“Potential endocrine disrupting contaminants were found in the 22 groundwater samples taken near both conventional and unconventional oil and gas development in Wyoming,” said Susan C. Nagel, an associate professor of obstetrics, gynecology and women’s health in the University of Missouri School of Medicine.

That’s not good for people, added lead author Christopher Kassotis, now engaged in post-doctoral work at Duke University. “Ultimately… we’d like to think any alteration of endocrine signaling is adverse,” he said. 

The endocrine system, as portrayed by the U.S. Environmental Protection Agency (EPA)

A citizens’ group that has worried about such pollution hailed the paper as a significant warning. Titled Endocrine-Disrupting Activities and Organic Contaminants Associated with Oil and Gas Operations in Wyoming Groundwater, it was published April 5 online by the peer-reviewed journal Archives of Environmental Contamination and Toxicology.

“This study has major ramifications health-wise,” said Mary Lynn Worl, the chairwoman of the Pinedale-based group Citizens United for Responsible Energy Development. CURED invited Nagel to address residents in her county several years ago. “Across the U.S. this study should be raising red flags wherever there are unconventional oil and gas developments,” or fracking, she said.

But both a state representative and an industry advocate said the study has holes in it and criticized researchers for jumping to conclusions.

“There’s no way to tell me that what they found wasn’t there prior to development,” said John Robitaille, vice president of the Petroleum Association of Wyoming, after reviewing the 12-page paper.

Rep. Lloyd Larsen (R-Lander), who owns a construction company that works in the oil and gas industry, said he was “a little disappointed,” with the study’s thoroughness.

“If that was a prospectus and I was a banker lending money, I wouldn’t lend a penny,” he said. “They’ve not convinced me they’ve done their homework.”

Water from Pavillion and Clark were compared

The study collected groundwater samples from Fremont County’s Pavillion, a community where fracking has been employed, and Park County’s Clark, which researchers say is the site of conventional oil and gas fields. Researchers tested groundwater samples from 22 sites for their effects on the human endocrine system. Oil and gas wells were within a mile of most Pavillion groundwater sample sites, and within five miles of those in Clark.

Hydraulic fracturing, or fracking, is the practice of pumping large quantities of water, chemicals and “proppants” into an oil or gas well to increase or stimulate production. The procedure is performed under high pressure and usually in oil and gas reservoirs in “low-permeability” geologic formations where the resource is tightly held.

Groundwater samples, most of them collected from taps, were processed in a lab and applied to human cells in a procedure that indicated when parts of the endocrine system were stimulated or retarded.

The paper showed that samples from Pavillion exhibited a trend of greater disruption to progesterone than samples from Clark, Kassotis said in an interview. Progesterone is key to healthy conception and pregnancy. 

This diagram shows how an endocrine disruptor could block a hormone from simulating biological functions. (Max Liboiron)

“There are really no other known progesterone antagonists [disruptors] in the environment,” than those from fracking fluids, Kassotis said. “The only other is RU 486 – the morning after pill. Traces [of RU 486] might show up in sewage water, but that’s not at high levels and that’s not common.”

The endocrine system employs glands, starting with the pituitary gland in the brain, to produce hormones that signal through the bloodstream when growth and other functions should start and stop. Other glands, including the ovaries and testes, pancreas and adrenal and thyroid glands, are part of the complex and delicate system. 

“Life requires precise hormonal messaging at precise levels at specific times,” Kassotis said. “Pregnancy, early life, the period of sexual development are some of those critical periods. It’s important to think about the endocrine system and disruption during those sensitive windows.”

It doesn’t take much of some chemicals to disrupt life’s delicate balance, Worl said. “These chemicals, in very small amounts can have a major impact on the body,” she said. “If they get into the body they are going to disrupt not only the hormone production but release of enzymes.”

A history of water pollution

Researchers chose Pavillion because of the area’s controversial pollution history. The town became the subject of heated debate — often serving as a stand-in for the larger national conversation about fracking — when  residents experienced everything from tap water that smelled like diesel to the high-pressure blowout of a water well as it was being drilled.

In 2010, a report commissioned by various community groups in the town found that 94 percent of respondents “experienced adverse health effects that were known to be associated with contaminants that [the U.S. Environmental Protection Administration] had reported in area drinking water.”

But Wyoming has contested others’ findings from Pavillion. The EPA conducted the first federal study in 2011 that produced a preliminary report suggesting that groundwater was likely contaminated by unconventional oil and gas operations.

Wyoming took over the review and refuted the initial findings, saying there was no evidence of fracking-related contamination.

A scientist who worked on the initial study then reprised data in a third study in 2016 that “substantiated the original EPA draft report and provided additional evidence of upward migration of [unconventional oil and gas] fluids into groundwater,” Kassotis’ paper says.

Read about Wyoming’s final report in this WyoFile story

There was, Kassotis said, “a lot of back and forth over what’s going on in Pavillion.” Instead of debating the old issue — where did the pollution come from, what was in the water and who was responsible — he sought “an actual health out-point.”

Thus, the study’s conclusion: Groundwater from near a fracked field disrupts human cells in ways that adversely affect the critical endocrine hormone messaging system, and to a more serious degree than polluted groundwater near a conventional oil and gas operation.

“Fracking — the process — adds an additional source of endocrine disrupting chemicals to the environment,” Kassotis said. “We are looking at the biological effect — something in the water to bind to and inhibit the progesterone receptor.” Ovaries, adrenal glands and placentas produce the progesterone hormone that governs various reproductive activities, among other biological functions.

Pavillion is a ranching community on a dead-end road that emerged from obscurity after reports of pollution in domestic water wells. (Angus M. Thuermer Jr./WyoFile)

Putting the new study in perspective, Worl looked back to the 2010 community health survey in Pavillion. “I think [the new study] substantiated some of the health concerns people in the Pavillion area have been expressing for years,” she said.

In Pavillion, a homeowner whose well is polluted sees the research as confirmation of years’-long complaints. “It doesn’t surprise me that they’re finding all these things,” said John Fenton. “You see, smell, taste things that you don’t anywhere else other than in those oil and gas operations. I really don’t see why anybody would be surprised that there would volatile organic compounds and other substances in the groundwater — they inject that stuff into the ground.”

Research doesn’t convince industry, representative.

Industry supporters are not convinced the study is the basis for action, and they criticized elements of the research.

“They’re seemingly blaming the production fields on what they’re finding,” PAW’s Robitaille said. “You can’t make that assumption without more study. Who’s to say this wasn’t happening all along,” without drilling or fracking, he said.

Kassotis agreed the study didn’t include samples from a third area where no development has taken place nearby. “We didn’t have a good non-drilling area in Wyoming to compare to,” he said. “We don’t have a baseline.” Nevertheless, the disrupting effects of groundwater “increase when we move into Pavillion.”

For Larsen, who represents a House district adjacent to Pavillion in the Wyoming Legislature, the study doesn’t properly define the two types of drilling. “There’s hardly any wells that haven’t had some sort of stimulation,” he said. “Virtually all conventional wells have fracking and acidizing. Fracking has been going on since the 1970s.”

The two areas compared have different geological structures, he said, a troublesome variable. There’s also the baggage — conflicting reports of the cause of pollution — that comes along with any discussion of Pavillion.

“They really don’t wrestle with the discrepancy,” among the three Pavillion studies, he said. “I don’t understand why they didn’t do that.”

Larsen also criticized the research for using potentially affected parties in the collection of samples, exposing the research to bias. “You could have somebody there who was very opposed, or somebody very pro-industry, say ‘come and test my water,’” he said. 

Rep. Lloyd Larsen (R-Lander)

“I’m not trying to belittle the University of Missouri,” he said. “I just don’t know if it was done in the manner we’d expect. We wouldn’t see that from the University of Wyoming.”

Kassotis agreed there is “a chance” collected samples were not representative of the region. “We know the community group members that we work with,” he wrote in an email, “and ensure they’re aware that we want as representative a sample as possible — and that skewing sample in one direction or another actually harms the resulting outcomes.” Individual water samples were collected according to “proper procedures,” he said.

He dismissed criticism that stimulation might have taken place at Clark and confounded the comparison between the two fields. In Pavillion, “we know stimulation was routinely used for production whereas there was no need for that in the conventional Clark fields.”

Kassotis also agreed there is different geology in the two areas. “Whether these results are broadly applicable to all unconventional and conventional oil and gas fields has yet to be determined.”

Clark also acted as a control for another variable — consumer products like sunscreen that may contain traces of endocrine disrupting chemicals.

“Given the close geographic proximity, we would assume that the residents living in these regions [Pavilion and Clark] likely use [similar] consumer products and have relatively similar [endocrine disrupting chemical] inputs to the environment. It’s very unlikely that someone in Pavilion uses dramatically different personal care products than in Clark.” Kassotis said.

By controlling for that variable, and by determining that the Clark samples contained “no chemicals unique to fracking,” researchers believe they’ve isolated the Pavillion fracking activity as the source of the samples’ disparate results.

What should people do?

Robitaille said his industry is well-regulated. “There are numerous things that need to be done in protecting not only groundwater but everything else,” before and during drilling, he said. “Regulation [and] engineering are definitely more than adequate to protect the environment when we go into these types of operations.”

Larsen agreed. “It’s been established by our [Department of Environmental Quality] the limits [of certain chemicals] and how these liquids need to be disposed of,” he said. “My concern is we have to be careful that were not pulling the fire alarm without there being a fire.”

“This isn’t the last study we’ll see,” Larsen said. “We’re constantly looking out for the welfare of the citizens of our state. I think as these studies come out we have a responsibility to review them and, if they’re valid, to address the concerns that are there.”

Fenton said authorities have it backwards. “The state and all the regulatory agencies that are responsible for allowing and regulating this need to know what could go wrong — before they allow it — instead of having the citizens figure out what is occurring around them,” he said. “By that time, the activity is done. We need to act preventively instead of after the damage has occurred.”

For future studies, it would help to get water samples from a region before development begins, Kassotis said.

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There’s a larger picture being painted across the country, he said. “We have now reported similar endocrine bioactivities across numerous unconventional oil/gas sampling regions, and other researchers are beginning to demonstrate similar effects in cell and animal models,” he wrote in an email. “These, above all else, lend strong support for our findings.”

Residents in such areas need to be informed so they can make their own choices. “What I hope to do is to be able to better communicate my science to those people living in these communities so they can make up their own minds,” he said.

He’ll stop short of recommendations regarding who should live where. “I’d rather let my science speak for itself,” he said.

Angus M. Thuermer Jr. is the natural resources reporter for WyoFile. He is a veteran Wyoming reporter and editor with more than 35 years experience in Wyoming. Contact him at or (307)...

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  1. Thanks for the reporting again Angus, All we have here of value is scenery wildlife, a few people, some water and our air and family, Thank you for reporting on our water problems in northeast Wyoming. If you had not reported on this last fall people would have been brushed off or dismissed for questioning the narrative.

    Good solid reporting makes a difference.. I do believe good debate on the problems you are covering are the only thing stopping stupid moves. By the time the DEQ gets involved in the problem it may already be too late to fix. Please keep up the fine job you are doing and follow up with us over here. There is still no resolution and we need your type of honest journalism.

  2. Well said, Damon. This article, as well, is more sensational and less detailed than I would prefer. (Full disclosure: I’m a Missouri J-school graduate, so I have some expertise in what good reporting should include.) For example, which chemicals, specifically, are considered “unique to fracking”? Naming those chemicals would allow concerned citizens to consult sites like and search for wells in Freemont county and see exactly what chemicals were used in them. But by cloaking which chemicals are suspect, that’s not enabled. In reality, very few if any chemicas are “unique” to frac fluids because the fracturing or pressure-pumping market isn’t large enough to economically sustain their manufacturing.

  3. Your thought process is way off Damon. Pavillion population 249….125 maybe are women…older women have the higher population there….so maybe 50 are on bith control…maybe 40 take the pill….and your saying they are causing disrupters in the water….LOL rolling…

  4. Correlation is not causation. The increase in endocrine disrupting chemicals may be from our societies use of birth control pills which end up in septic tanks and then get in the water and not from hydraulic fracking. It is likely that Pavilion has seen an increase of endocrine disrupting chemicals, just as Maryland and 19 national wildlife preserves have an increase in endocrine disrupting chemicals (“Leftover Birth Control Pills Are Turning US Fish Into Hermaphrodites: Problem Could Affect Human Health,” Maryland has banned hydraulic fracking. Hydraulic fracking does not exist in national wildlife preserves. If Maryland is seeing the same problem and they have no hydraulic fracking, linking the etiology to fracking is highly suspect. The researchers may see a correlation but this certainly does not mean causation. Moreover, Pavilion is nearly impossible to compare conventional drilling and fracking as it has a history of conventional exploration overlaying its fracking history.

    As a University of Missouri alumni we can do better than this.

    1. Yeah right! Let’s continue possibly poisoning our groundwater until it is finally proven poisonous beyond a reasonable doubt. Let’s not hold off on possibly poisoning our groundwater until it is proven safe beyond a reasonable doubt. There’s money and tax dollars to be made. Let’s let science take a back seat to all the money just a few people can make!