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Natural gas — just by nature of being the most common residential energy source in the U.S. — has the sheen of being a relatively safe and clean kind of power. But increasingly, researchers are concerned we don’t have a firm enough handle on its potential health effects.

Research suggests somewhere around 1% of natural gas — which is mostly methane — wafts out of stovetops unburned and untouched. Cooking or heating with natural gas also releases potentially toxic compounds into the air. A new study, published Tuesday in Environmental Science & Technology, underscores the scope of those concerns: In natural gas samples collected from 69 homes in the Boston area, researchers detected 21 federally-regulated hazardous air pollutants.

“A fossil fuel pipeline literally ends where the kitchen begins. This is a direct conduit to a gas well far away, deep underground,” said Drew Michanowicz, first author of the study and a public health researcher at Harvard, in a call with reporters. Natural gas “is so widely used in our indoor spaces, where we spend up to 90% of our time,” he said, that “any small leaks of these hazardous air pollutants in our homes can potentially impact our health.”

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The study wasn’t designed to detect whether the hazardous pollutants are harming people’s health, or exactly how heavily people are exposed ambiently in the home. Rather, researchers were examining the range of chemicals that might leak at the source of natural gas. They collected samples by placing tubing directly next to the gas outlet of stoves, which sampled a higher concentration of the gas and its components than a person would be exposed to naturally.

In particular, they found benzene, a known carcinogen, in 95% of samples at an average level of 165 parts per billion. That’s not to say levels are that high in the rest of a person’s home. But certain chemicals can infiltrate the area at troubling levels. In certain kitchens, nitrogen dioxide emissions can surpass the Environmental Protection Agency’s air quality standards within minutes of a stove being turned on.

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“I was taken aback,” said Timothy Collins, a University of Utah professor who studies environmental hazards and environmental justice issues. “It’s surprising no one’s looked at this before. It’s both disturbing and surprising,” added Collins, who was not involved in the research.

Zeyneb Magavi, a co-author of the study and co-director of the Cambridge-based nonprofit Home Energy Efficiency Team, said “it’s the potential for it leaking in a closed environment that begins to raise the question of a health impact.” Nearly half of U.S. households use natural gas, and a third of all U.S. energy demands are met by natural gas. Another study of natural gas infrastructure in Boston drives home the concern, estimating that 4% of natural gas is lost between the well and the stove, 2.5% of which leaks out after the gas has arrived in urban areas.

But additional research is needed to confirm the extent to which residents are exposed to these potentially concerning compounds.

“There’s a real question that we have to pursue about what does this mean for health,” said Curtis Nordgaard, an author of the study and environmental health researcher at the nonprofit Physicians, Scientists, and Engineers for Healthy Energy. “We think there probably is some risk, but that risk may be less than other really well-established environmental health hazards like tobacco smoke.”

Recent studies have suggested natural gas burned to power both residential and commercial buildings contributes to health harms. But despite that, experts say the potential health impacts of natural gas have received relatively little attention. “People are just a little bit more familiar with water systems than they are with the natural gas system,” said Frankie Wood-Black, a division chair at Northern Oklahoma College who was not involved with the study, citing examples such as the Flint water crisis.

Experts are also worried that the public doesn’t always know when a natural gas leak needs to be fixed. Sharp odors are added to methane as a warning sign, but the study authors raised the concern that the odorizing process is inconsistently applied, and that illnesses that rob people of the sense of smell could also make it hard for people to detect concerning levels of natural gas in their homes.

To curb their risk, the study authors say residents can regularly open windows to increase ventilation, purchase a relatively cheap induction cooktop, and make a plan to replace gas-powered appliances with electric ones when possible. Wood-Black added that homeowners can consult consumer safety data sheets for natural gas, which companies are required to provide, as well as drinking water reports that the government provides online.

Experts also say there’s a clear need for more research that challenges what Michanowicz, the first author, said is a “quite sincere assumption of natural gas as clean and non-toxic.” They’ve already sampled 16 California and a dozen other North American cities; that research is now under review. That study, they say, will look at actual exposures too, which would better inform policy changes that may be necessary. “From a sustainable city and quality of life issue, we’re going to have to look at those infrastructure questions,” said Wood-Black. “Having more knowledge will let us know, hey, do we really need to address our infrastructure.”

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