For years, the controversy over natural gas drilling has focused on the water and air quality problems linked to hydraulic fracturing, the process where chemicals are blasted deep underground to release tightly bound natural gas deposits.

But a new study reports that a set of chemicals called non-methane hydrocarbons, or NMHCs, is found in the air near drilling sites even when fracking isn't in progress.

According to a peer-reviewed study in the journal Human and Ecological Risk Assessment, more than 50 NMHCs were found near gas wells in rural Colorado, including 35 that affect the brain and nervous system. Some were detected at levels high enough to potentially harm children who are exposed to them before birth.

The authors say the source of the chemicals is likely a mix of the raw gas that is vented from the wells and emissions from industrial equipment used during the gas production process.

The paper cites two other recent studies on NMHCs near gas drilling sites in Colorado. But the new study was conducted over a longer period of time and tested for more chemicals than those studies did.

"To our knowledge, no study of this kind has been published to date," the authors wrote.

The researchers took weekly air samples at a site that's within one mile of 130 gas wells in Garfield County, Colo., with little other industry aside from natural gas production. They detected more than 50 chemicals between July 2010 and October 2011, including 44 with reported health effects. The highest concentrations were measured after new wells were drilled, but the concentrations did not increase after the wells were fracked.

Carol Kwiatkowski, one of the study's authors, said that because of limitations on funding and access to drilling sites, the study doesn't definitively link the gas fields to the air pollutants. But because the research was conducted in a region with few people and roads, "natural gas drilling would be the first thing anyone would look at."

What the study shows, she said, is that more research is needed on all stages of gas production. "It's not all about fracking. ... Air pollution needs more focus and scrutiny."

Kwiatkowski is executive director of the Endocrine Disruption Exchange (TEDX), a nonprofit research organization in Colorado that studies the impact of environmental pollutants on the endocrine system, a network of hormone-producing glands that affects nearly every organ in the body. TEDX has spent years studying the health effects of natural gas drilling, and its reports are routinely criticized by the industry.

Kathleen Sgamma, vice president of government and public affairs at Western Energy Alliance, which represents oil and gas drillers in the American West, said the TEDX scientists have produced "a study that clearly doesn't come up with the results they're trying to show." Sgamma questioned the scientists' qualifications, as well as the quality of the journal that published their findings. "This was clearly not a well-thought out and well peer-reviewed study," she said.

But Robert Jackson, a professor of energy and environmental studies at Duke University who was not involved in the research, said the study is valuable because it shows that more study is needed about how drilling affects communities near gas fields.

"There's the question of whether there are long-term health effects," he said. "It warrants a follow-up [health] study."

Many residents of the sparsely populated area live within a mile of active wells. As gas drilling expands throughout the nation, production is moving closer to populated areas, with wells in some states now being drilled within a few hundred feet of schools and homes.

All of the chemicals TEDX detected were at levels well below the limits the federal government recommends to protect workers from dangerous chemicals. However, those standards are usually designed for healthy adult males who are exposed to the chemicals on and off for 40 hours a week. Scientists say the risks would likely be different for people—including pregnant women, children and the elderly—who live near gas fields and are exposed 24 hours a day, seven days a week.

"We've been overlooking these non-methane hydrocarbons until now," said Theo Colborn, president of TEDX and the paper's lead author. "They've been measured before in cities ... otherwise, no one has looked at [them] as related to natural gas drilling in rural areas."

What the Scientists Found

Non-methane hydrocarbons are emitted by industrial equipment and also by unprocessed natural gas.

When an operator drills a new well, most of the raw gas that flows out of the ground is methane—the target compound that's collected and sold. The gas also contains water and dozens of NMHCs, including the carcinogen benzene. On average, NMHCs account for 18 percent of the unprocessed gas and are released into the air at various stages of production.

John Starck, an engineer and president of EGL Resources, a Texas oil and gas company, said very little raw gas escapes during the initial drilling phase, because the gas-bearing rock is so impermeable. Once the well has been fracked, the quantities of NMHCs released would be on the order of parts per thousand or parts per million, unless there is a leak, he said.

The NMHCs in the study were detected at levels of parts per million, parts per billion and parts per trillion, but the endocrine system is so sensitive that even tiny doses can lead to large health effects. Federal safety standards rarely consider the impacts of low dosage testing, an omission that scientists say should be addressed.

The study's authors detected thirty NMHCs that affect the endocrine system. Several belong to a class of compounds called polycyclic aromatic hydrocarbons (PAHs) and were detected at levels that other scientists have found are high enough to impact child development. In those studies, clinical researchers gave pregnant women living in cities personal air monitors, then tracked their children's development. Women exposed to a certain level of PAHs were more likely to have children with lower birth weight and lower IQ scores.

One chemical found at surprisingly high levels was methylene chloride, a common laboratory solvent. It's not a component of raw gas and doesn't appear on any of the public disclosure forms of chemicals used during drilling and fracking. "However, residents and gas field workers have reported that methylene chloride is stored on well pads for cleaning purposes," the authors wrote.

Robert Howarth, a Cornell University scientist who wasn't involved in the study, said the presence of methylene chloride points to a need for better chemical disclosure laws. "Methylene chloride is a surprise...We need a lot more information on what's used at drilling sites overall."

While drilling companies are required to disclose many of the chemicals used for fracking, they are usually allowed to keep proprietary chemicals secret. Drilling and cleaning compounds are rarely, if ever, subject to public disclosure.

Sgamma, the industry representative, said she was not aware of methylene chloride being used on well pads. She said the samples were probably contaminated in the lab.

Kwiatkowski said TEDX considered that possibility and ran blank samples to test for contamination. They didn't find methylene chloride in the blanks, but found it "over and over again" in the collected air samples.

Study Limitations

The TEDX study was inspired by years of complaints about headaches and respiratory problems the researchers had heard from people living near gas wells. Many of the symptoms began the moment drilling started, long before the wells were fracked, Kwiatkowski said.

That prompted the scientists to study air quality before and after drilling. They identified a well pad slated for drilling and set up an air sampling station near a home 0.7 miles from the well pad. There were 130 active gas wells within one mile of the site.

Kwiatkowski said the ideal sampling station would have been located directly on the well pad, but TEDX has had little success persuading the industry to cooperate with its research, so the researchers didn't ask for access to the well pad. They also didn't want to draw unwanted attention to their work. Local residents are divided when it comes to the benefits and risks of gas drilling, and Kwiatkowski said they didn't want to cause trouble among neighbors. Their choice of location was further constrained by the need for a constant source of electricity and the need to protect the station from possible vandalism.

The scientists took a partial set of baseline data on July 2010, before any wells had been drilled on the pad. On October 19, after residents called to report activity on the well pad, the scientists rushed in to take a full set of baseline readings. The first well was drilled three days later.

Air sampling continued weekly until October 2011. All samples were analyzed in EPA-certified labs. The scientists tested for more than 100 chemicals and found over 50 at levels high enough to be detected by their instruments.

When the dates of the drilling and fracking activity were posted online, in accordance with Colorado's disclosure laws, the scientists learned that the company had drilled 16 wells on the well pad between October 2010 and March 2011. Two other well pads were drilled starting in April and July. Fracking followed the drilling. About 100 other wells within a mile already were producing gas and were neither fracked nor drilled during the study period.

The data showed a major spike in chemical concentrations after the first 16 wells were drilled, but not after fracking. The increase was significant when compared with the baseline samples collected before the drilling, as well as samples from most of the year after drilling stopped.

Colborn said that suggests the increased emissions are linked to the raw gas released from drilling—but she said there's no way to tell for sure, because they couldn't directly sample emissions from the well pad. Colborn said TEDX and other scientists are already making plans for a follow-up study to chemically fingerprint the source of the pollutants.

Jackson, the Duke University scientist, said the paper hasn't convinced him that the increased emissions are directly tied to the well pad it studied instead of the combined effect of the region's natural gas operations.

He said the evidence is weak because the spikes occurred only during the middle two months of the five-month drilling period, and because the emissions could have originated from the 130 other wells in the region.

There's no question the study "is documenting air quality in that valley," he said, "and that's still valuable," especially when it comes to health implications for local residents.

Industry Questions Study's Credibility

Sgamma, the industry representative, said the TEDX study "has all the problems you'd expect when a zoologist and psychologist attempt to conduct an air quality study."

The "zoologist" refers to Colborn, who helped pioneer the field of endocrine disruption in the 1980s and served on numerous government science panels. Colborn describes herself as an "environmental health analyst"—a term that reflects her multidisciplinary background in zoology, epidemiology, toxicology, freshwater ecology and water chemistry.

Kwiatkowski has a Ph.D. in experimental psychology and specializes in statistical analysis. She is a former assistant professor at the University of Colorado School of Medicine.

According to the TEDX website, the organization runs on three basic principles: rigorous scientific analysis, promoting education on endocrine disruption and advocating policy to protect public health and the environment. Kwiatkowski said she wasn't surprised by Sgamma's criticism, because TEDX has been willing to tackle issues that other scientists "might typically not want to go out on a limb for."

"What industry does is attack your reputation as a scientist," Kwiatkowski said. "Young scientists in particular can't afford to have their reputations challenged."

The TEDX study cites two recent studies with similar research goals—a Health Impact Assessment (HIA) from the University of Colorado School of Public Health and a pilot study led by the National Oceanic and Atmospheric Administration.

The HIA was commissioned in 2010 to examine the potential health affects of a pending gas drilling project in Garfield County, the same county Colborn's group examined, but the county commissioners cut its funding before it could be completed. A draft of the HIA from Feb. 2011 cited a 2007 air monitoring report that identified oil and natural gas production as the largest contributor of benzene in Garfield County.

The NOAA study, published in February by the Journal of Geophysical Research, found that oil and gas operations released more methane and benzene than previously thought. It used a chemical fingerprint to pinpoint drilling operations as the source of the contaminants, but it examined far fewer non-methane hydrocarbons than the TEDX paper.

Researchers from the Health Impact Assessment and a co-author of the NOAA study declined to comment on the TEDX paper. The lead author of the NOAA paper did not return requests for information.

Sgamma also questioned the researchers' decision to publish the paper in Human and Ecological Risk Assessment, which she said is not a "typical" destination for air quality studies.

Kwiatkowski said they chose the journal because they wanted it to reach scientists who study risk assessment.

Barry L. Johnson, the journal's editor-in-chief for the past 12 years, said the publication's first priority is the quality of the science in the manuscripts it receives. He said it has published papers written by industry researchers and that industry scientists serve on the journal's board. Johnson has worked for the EPA and the federal Agency for Toxic Substances and Disease Registry, and is an adjunct professor of public health and environmental policy at Emory University.

The TEDX paper was processed like any other study, Johnson said. It was sent to two scientists for peer review, both of whom have published widely on issues of air quality. The reviewers' names are kept private, he said, because his journal operates under a double-blind review system, where authors and peer reviewers are unaware of each others' identities in order to avoid potential conflicts of interest.

Johnson said his publication "deemed the [TEDX] paper, as we have deemed others dealing with air quality, as being relevant to the aim, purpose and scope of our journal." He said that Sgamma is welcome to submit formal comments on the paper.

The TEDX study is "clearly labeled and presented as an exploratory study," he said. "It has strengths and limitations—I don't know of any studies that don't. That's just how science works ... and this may contribute towards a better understanding of what's happening around gas operations."