A recent study of air quality around unconventional oil and gas extraction sites — more commonly referred to as fracking — found high levels of benzene, hydrogen sulfide and formaldehyde, all of which pose risks to human health. But what makes this study particularly interesting is that the air samples were collected by the very people who live near the extraction sites, and the collection times were specifically triggered by the onset of health symptoms.

Published yesterday in the journal Environmental Health, the study involved residents living near 11 unconventional extraction sites in five states: Wyoming, Arkansas, Pennsylvania, Colorado and Ohio. The residents involved in the study were trained to take a “grab air” sample using an inexpensive bucket outfitted with a battery-operated vacuum pump that sucks in air over two to three minutes. (The study authors noted that the bucket device has been subjected to numerous validation tests by public agencies and independent labs.) In addition to the grab air samples, residents were also given a device to measure formaldehyde levels. (That device is called the UMEx100 Passive Sampler and almost looks like an USB flash drive with a clip on it — here’s a picture.) In all, residents put out 41 formaldehyde badges near production facilities and compressor stations.

Residents ended up collecting 35 grab air samples in areas of particular community concern and “under conditions that would lead them to register a complaint with relevant authorities such as a county public health department or state oil and gas commission,” the study stated. Twenty-nine of the samples were taken in direct response to health symptoms, with the most common symptoms being headaches, dizziness, irritated, burning or running nose, nausea, and sore or irritated throat. Air samples were then tested for 74 volatile organic compounds, and formaldehyde samples were analyzed using a method recommended by the U.S. Environmental Protection Agency.

Ultimately, the study found that 16 of the 35 grab air samples and 14 of the 41 formaldehyde tests surpassed minimal risk levels set by EPA and the U.S. Agency for Toxic Substances and Disease Registry, with the three chemicals most commonly found to exceed such levels and which are linked to human disease being benzene, hydrogen sulfide and formaldehyde. Benzene, in particular, was detected at sample locations in Pennsylvania and Wyoming in concentrations that exceeded recommended safe levels “by as many as several orders of magnitude,” wrote the authors, who noted that benzene is a known human carcinogen.

In fact, some air samples had benzene levels that ranged from 35 to 770,000 times higher than background levels (defined as levels that researchers would expect to find naturally), according to a news release about the study. To put that in perspective, the study found benzene levels that were up to 33 times the concentration exposure a person gets when pumping gas. Here’s another comparison from the study’s authors: The benzene exposure a person would experience at one study site in Wyoming would be equal to the exposure of a person living in Los Angeles for two years or Beijing for nearly nine months.

For hydrogen sulfide samples that exceeded recommend levels, study results ranged from 90 to 60,000 times higher than background levels — concentrations that can cause eye and respiratory tract irritation, fatigue, loss of appetite, headache, irritability, poor memory and dizziness. In analyzing the formaldehyde samples that exceeded recommended safe levels, the study found that they were 30 to 240 times higher than background levels. In some cases, the formaldehyde concentrations were more than twice the concentrations found in rooms in which medical students dissect cadavers.

The study authors did note that while the samples taken during the study may reflect a “worst-case concentration,” engaging residents who are directly affected by unconventional oil and gas extraction can benefit long-term research on the topic.

“Community-based monitoring near unconventional oil and gas operations has found dangerous elevations in concentration of hazardous air pollutants under a range of circumstances,” said study author David Carpenter, director of the Institute for Health and the Environment at the University of Albany. “In this study, we have shown that community-based research can improve air quality data while adhering to established methods. Our findings can be used to inform and calibrate state monitoring and research programs.”

To read the full study, visit Environmental Health.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for more than a decade.