Posted on 26 June 2023 by Guest Author

This is a re-post from Yale Climate Connections by Sarah Wesseler

Within the past few years, scientists have found that gas stoves are a major source of air pollution within homes, responsible for almost 13% of all childhood asthma in the United States. But a new study from Stanford’s Doerr School of Sustainability and PSE Healthy Energy, a nonprofit research institute, warns that these appliances are even worse for our health than previously believed.

“This study presents data that is deeply troubling to anyone concerned about the health of their families in their homes,” Gaurab Basu, a primary care physician and the director of education and policy at the Center for Climate, Health, and the Global Environment at Harvard’s T.H. Chan School of Public Health, wrote in an email. Basu was not involved in the study.

The research, which was published on June 15 in the peer-reviewed journal Environmental Science & Technology, was the first to focus on the relationship between gas stoves and benzene, a carcinogen. 

“We’ve known for a long time that gas stoves emit some harmful pollutants, including nitrogen dioxide and carbon monoxide,” said lead researcher Yannai Kashtan, a Ph.D. student at Stanford. “This study shows that in addition to those known pollutants, gas stoves can also emit amounts of benzene that can lead to indoor concentrations that exceed health benchmarks.”

Kashtan and his team analyzed air from 87 homes in California and Colorado, finding dangerous levels of indoor benzene pollution while gas stoves were in use. In some cases, levels were higher than those caused by cigarette smoke, which the World Health Organization has called the main source of indoor benzene contamination.

The researchers also found that benzene emissions from cooking often spread throughout homes, sometimes leading to hourslong periods of elevated readings in bedrooms. 

Turning on range hoods vented to the exterior made little difference in indoor pollution levels, the testing showed. 

Health impacts of benzene

Jan Kirsch, a retired medical oncologist, and hematologist who practiced at the California Cancer Center and was not involved in the research said that the fact that such high concentrations of benzene lingered in interior air as a result of burning gas came as a surprise. “I think the study is amazing,” Kirsch said. “I’m sure it’s going to save lives.”

Benzene, which is a colorless or yellow liquid at room temperature, occurs both naturally and as a result of human activities. It’s present in crude oil and in emissions from volcanoes and forest fires, and is widely used in industry. Long-term exposure can lead to leukemia and other blood-related cancers, while high levels of short-term exposure can affect the nervous system. The World Health Organization has called exposure to benzene unsafe at any level; Kirsch said it’s the most potent chemical leukemogenic, or leukemia-causing substance, that she’s aware of.

Health impacts typically occur when benzene particles are inhaled. Cigarette smoke, gasoline, and industrial processes are common sources of airborne benzene pollution, with tobacco smoke accounting for approximately half of all exposure in the United States, according to the American Cancer Society. 

Kirsch noted that benzene can be more carcinogenic at lower levels of exposure than it is at higher levels, such as those encountered in the petroleum or chemical industries. A growing body of evidence shows that a more potent change in gene expression occurs after the absorption of lower quantities of the chemical. “At higher doses, it’s more risky, but per each unit dose, it’s more toxic at lower doses,” she said.

As medical knowledge about benzene’s effects on the body has grown, ideas of who’s most at risk have changed, she said. Historically, the chemical was thought to have the most significant impact on industrial workers. But over the last few decades, this has changed as researchers have recognized that children and others who spend much of their time breathing contaminated air inside the home can also face significant hazards. 

Cooking with gas (and getting more than you bargained for)

Another study published in 2022 by PSE Healthy Energy linked gas stoves to benzene pollution within homes, but its focus was on gas that leaks from appliances while they’re not in use. This work highlighted the fact that, while natural gas consists mainly of methane, it contains traces of benzene and other chemicals that can seep into homes through gas lines and appliances.

By contrast, Kashtan said that his team, which included several individuals who contributed to the gas-leaks study, decided to focus their research on benzene produced in the kitchen while cooking fuel is burned.

Methane consists of one carbon atom and four hydrogen atoms. When it’s burned in the air in a perfectly calibrated setting such as a laboratory, the carbon is converted to carbon dioxide, and the hydrogen is converted to water. But with garden-variety kitchen stoves, the conditions under which this combustion occurs can vary considerably, resulting in different byproducts. “If something happens in the flame — the temperature isn’t ideal, the fuel-to-air-ratio isn’t perfect, etc. — you can get all of this panoply of products that are basically in between methane and carbon dioxide,” Kashtan said. “So those include carbon monoxide, they include benzene.” 

Since gas stoves are already known to generate carbon monoxide during the cooking process, the researchers reasoned that they might also be creating benzene. Recent improvements in technology for the analysis of airborne chemicals allowed them to confirm this hypothesis.

The study also showed that cooking with gas produces significantly more benzene pollution than gas leaks alone. “When you’re using the stove, if you have a median stove, you’re getting hundreds of times more benzene emissions than just when the stove is off,” Kashtan said.

Kashtan also noted that another health-damaging chemical associated with gas stoves, nitrogen dioxide, is generated when methane is burned even under perfect circumstances for combustion.

Politics in the kitchen

The new research is likely to feed into heated debates about how to regulate gas stoves in the United States. Over the past few years, many cities have banned these and other appliances in new buildings, citing their climate impact — methane is a potent planet-warming gas — as well as their health risks. Earlier this year, New York State became the first stove to ban gas stoves in most new buildings. 

But the issue has become highly politicized, with Democrats generally in favor of policy action to reduce the use of gas stoves and Republicans generally opposed. “Don’t tread on Florida, and don’t mess with gas stoves!” tweeted Florida governor and Republican presidential candidate Ron DeSantis earlier this year. Republican-led states like Ohio and Texas have passed legislation prohibiting cities within their borders from banning the appliances.

The uncertainty over the future of gas stove policy was heightened in April when a federal appeals court overturned Berkeley, California’s ban on gas hookups in new buildings, which was the first of its kind when passed in 2019. 

The Biden administration has shown strong support for electrifying stoves, most notably through the Inflation Reduction Act, which was signed into law in August 2022. This legislation provides generous rebates for electric purchase stoves for households meeting certain income requirements. But since individual states are responsible for implementing the rebate program, the specifics of the timeline and funding could vary significantly in different parts of the country. 

This political backdrop aside, Jan Kirsch said that the study points to a clear solution for individuals wanting to avoid cancer risk from gas stoves in their own homes. “The best thing to do is transition to something all-electric,” she said.

But Gaurab Basu noted that not all households have the ability to purchase and install an electric stove on their own. In particular, renters and lower-income people may have little choice but to continue to live with high benzene exposure in the absence of policy levers to assist with stove electrification.

“This is a matter of health equity,” he wrote in an email.