The natural gas used in homes in the Greater Boston area contains varying levels of toxic chemicals, including benzene and toluene, according to a new study, upending the long-held idea that natural gas is a “clean” fossil fuel.
In a first-ever look at the chemical makeup of gas coming into homes, scientists found benzene — a carcinogen for which there is no known safe level of exposure — in 95 percent of the samples, which were collected between December 2019 and May 2021, according to the study, published in the journal Environmental Science & Technology.
The authors cautioned that their investigation had not looked into the potential threat to public health. But their findings, coupled with recent information that methane can leak from gas stoves even when they are off, suggest a troubling new indicator of the safety of indoor air.
“We found that unburned natural gas delivered to homes contains numerous air toxics . . . that can cause cancer and other serious health effects,” said lead author Drew Michanowicz, a visiting scientist at the Center for Climate, Health, and the Global Environment at Harvard T.H. Chan School of Public Health and a senior scientist at PSE Healthy Energy.
The findings come at a time when the everyday kitchen stove has become a new pressure point in the fight against global warming by shifting to cleaner energy. The gas industry has heavily promoted the idea that good cooking equates to cooking with gas, but it has been fighting local initiatives from the Boston suburbs to Southern California that aim to restrict the use of fossil fuels in new buildings.
Recent studies have shown that natural gas — which consists of up to 90 percent methane — is leaking at far higher rates than expected, even when stoves are turned off, and that it contains other health-damaging pollutants such as nitrogen oxides.
Robert Jackson, a scientist at Stanford who has studied methane leaks and was not involved in the new study, said he was surprised by the findings, because these compounds would not be expected to be found in natural gas. He considered it a call for more study of the potential health impacts of these toxins, and added that it was another reason to stop using fossil fuels.
“The climate implications of gas use mean that we have to electrify our homes eventually, and eventually is pretty soon — 2040 or 2050, if you want to stabilize the climate at 1.5 to 2 degrees Celsius,” he said. “The potential health implications in this study, and in our work, provide an additional reason to support the electrification of homes and buildings.”
The new study identifies the full spectrum of chemicals that can leak into homes, finding 21 different chemicals designated by the Environmental Protection Agency as hazardous air pollutants.
The scientists collected more than 200 samples from 69 kitchen stoves and building pipelines in the region from customers of both Eversource and National Grid.
“Historically, natural gas has been described as a clean, or cleaner, fossil fuel,” said Zeyneb Magavi, co-executive director of HEET, a nonprofit that promotes geothermal heat, and a coauthor of the study. “Now that we know there are small quantities of VOCs present in the gas supply in the Greater Boston area, it is reasonable to conclude that our gas supply is not as clean as we thought it once was.”
Those pollutants were found in the gas fed into kitchen stoves, before it’s burned. While the authors of the study said it was significant to see so many toxins in the samples, they stressed that their work had not necessarily uncovered a public health emergency.
“We have to really emphasize that at this point, we can’t make any statement like that, because this study was really about identifying what’s in the natural gas,” said coauthor Dr. Curtis Nordgaard, an environmental health scientist at PSE Healthy Energy.
What they know for now, Nordgaard said, is that based on the toxics they discovered, “there is probably some risk,” but it may be less than other known hazards, like tobacco smoke.
Charles Crews, president of the Northeast Gas Association, said the presence of low levels of volatile organic compounds in natural gas is something the industry is aware of, but noted that “VOCs are emitted by a wide array of products in a household, including disinfectants, cosmetics, and many more according to the EPA.”
Spokespeople for Eversource and National Grid said they have just begun their review of the study.
“The research tells us that VOC emissions in natural gas at the low levels identified in the Harvard Study and confirmed by industry studies and the USEPA do not present a hazard in the home,” said Christine Milligan, of National Grid, noting the need for more research.
For climate advocates, though, the study provides another argument to speed the transition off natural gas. A study released in October found six times more methane leaking into the air around the Boston area than the state’s most recent estimate from three years ago.
“We just keep getting more evidence that having combustion in our homes, like in our stoves, leads to a lot of bad air quality,” said Maryann Racine Sargent, an atmospheric scientist at Harvard University’s John A. Paulson School of Engineering and Applied Sciences, and the lead author of the October study.
She was not involved in the new study, but said it underscores the need for more investigation into how these toxins can impact health. Researchers on the study echoed that call, and noted they hope to soon publish another study that involves natural gas samples from 16 cities in California, and ongoing work in a dozen other North American cities.
In addition to the presence of the toxins, the scientists also found that there was variation in the amount of pollutants depending on the location and time of year a sample was collected. In winter, for instance, the researchers found much higher peaks — three times higher than what they measured in spring, and about eight times higher than summer. They don’t yet know why that is, Michanowicz said.
They also found that small leaks of methane inside homes were often going undetected. Because natural gas does not have a smell, an odorant is added to it, to help alert people if there is a leak. But the scientists found that while all of the samples met federal standards of odorant so people would be able to smell a large leak, the inconsistent levels of odorant makes it possible for small leaks of methane to go unnoticed.
Andrea Honoré, a Weymouth graphic designer and mother of two, was among the study’s volunteer participants. “We just assume that because these stoves are sold to us and we use them, that everything is totally cool,” she said. When she and her husband bought their home in 2007, the gas stove was a selling point. Like many, Honoré preferred cooking with gas. Now, that has changed.
“I don’t want this in my house,” said Honoré, who is also a climate activist who regularly protests the Enbridge-owned Weymouth Compressor Station, a yearslong effort that has made her more aware of the potential harms of natural gas. She added that she’s looking into replacing her stove with an induction stove.