Natural gas used in homes may contain hazardous air pollutants: study

Natural gas used for powering household stoves, furnaces and water may contain levels of cancer-linked compounds that are toxic to residents when leaked, a new study has found.

The research, published in Environmental Science & Technology on Tuesday, investigated the composition of greater Boston’s “unburned” household gas, or the gas that comes out of kitchen stovetops when switching on the appliance.

While sampling natural gas supplies in more than 200 homes, the authors detected varying concentrations of volatile organic compounds (VOCs) — known not only to be carcinogenic, but also to generate secondary air pollutants such as particulate matter and ozone. 

Though most related research has focused on methane — the primary component of natural gas — and its impacts on climate change, the degree to which other air pollutants are present in natural gas at household “end use” remains largely unexplored, according to the study. 

“When we talk about natural gas, we just talk about methane,” lead author Drew Michanowicz, a visiting scientist at the Harvard T.H. Chan School of Public Health, told reporters in a call prior to the study’s release.

Considering gas beyond its methane contents therefore requires “a paradigm shift” that is critical to understanding the potential health impacts of household exposure, according to Michanowicz, who is also a senior scientist at the PSE Healthy Energy research institute. 

“Natural gas is mostly methane like pizza sauce is mostly tomatoes,” Michanowicz explained. “There’s other trace ingredients in pizza sauce. You need salt, oregano, pepper.”

From December 2019 through May 2021, Michanowicz and his colleagues collected 234 unburned natural gas samples from 69 kitchen stoves and building pipelines across the Boston region, according to the study.

Within these samples, they detected 296 unique chemical compounds — 21 of which are designated by the federal government as hazardous air pollutants.

“Historically, natural gas has been described as a clean or cleaner fossil fuel,” said co-author Zeyneb Magavi, co-executive director at the Boston-based Home Energy Efficiency Team.

“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,” Magavi said.

One VOC that the scientists found in 95 percent of the samples was benzene, which is classified by the National Toxicology Program as a known carcinogen. The wintertime concentration of benzene was nearly eightfold greater than that of the summertime, according to the study.

Several other VOCs that are considered “hazardous” by the Environmental Protection Agency also appeared in most samples. Among those compounds were hexane, found in 98 percent of samples; toluene, found in 94 percent; heptane, found in 94 percent; and cyclohexane, found in 89 percent.

“Benzene is concerning because it’s a known human carcinogen that affects white and red blood cells and leads to anemia and decreased immune function,” Michanowicz said.

“Because of that, it’s strongly regulated,” he added, acknowledging, however, that the benzene levels found in the samples were relatively low.

Over the course of the study, Michanowicz said that the team uncovered five leaks — or about one in 20 homes — that were large enough to necessitate a follow-up with an expert. 

Michanowicz reiterated that their study focused on hazard identifications only and therefore did not assess human exposure or potential associated health effects. 

“It’s really the first step,” he said. “There’s more research that needs to be done.”

Nonetheless, he stressed that any such effects would likely be mirror the known impacts already linked to the combustion of natural gas, such as the formation of nitrogen dioxide, particulate matter, carbon monoxide and formaldehyde.

“We think there probably is some risk, but that risk may be less than other really well-established environmental health hazards like tobacco smoke,” said co-author Curtis Nordgaard, an environmental health scientist at PSE Healthy Energy.

Adding up low-level leaks across a large metropolitan area like Boston could end up being significant, Nordgaard suggested. Also worth considering are those individuals exposed to higher concentrations of gas due to their occupations, such as commercial kitchen or pipeline workers, he said.  

Even prior to determining the precise health impact of exposure, the authors stressed that there are proactive measures residents can take to minimize potential harm.

Increasing filtration and ventilation in buildings is an effective step, as is finding and fixing indoor gas leaks, Magavi explained.

“A fossil fuel pipeline literally ends where a kitchen begins,” Michanowicz said. “This is a direct conduit to a gas well, far away, deep underground.”

“Cooking over a natural gas flame is probably the most intimate connection with climate change that we never think about,” Michanowicz added.