The natural gas delivered to homes contains low concentrations of several chemicals linked to cancer, a new study found. Researchers also found inconsistent levels of odorants — substances that give natural gas its characteristic “rotten egg” smell — which could increase the risk of small leaks going undetected.
The study, which was published in the journal Environmental Science & Technology, adds to a growing body of research that links the delivery and use of natural gas to detrimental consequences for public health and the climate.
Most prior research has documented the pollutants present where oil and gas extraction takes place, but there are “fewer studies as you work your way down the supply chain,” said Drew Michanowicz, the lead author of the study, looking at “where we actually use it, in our homes.”
Over 16 months, researchers led by the Harvard T.H. Chan School of Public Health collected 234 samples of unburned natural gas from 69 homes in the Boston metropolitan area that received natural gas from three suppliers. They found 21 “air toxics” — an Environmental Protection Agency classification of hazardous pollutants known or suspected to cause cancer, birth defects or adverse environmental effects — including benzene, which was detected in 95 percent of the samples.
Short-term exposure to high levels of benzene in particular could lead to drowsiness, dizziness, headaches and irritation of the eyes and skin, according to the Centers for Disease Control and Prevention. Longer-term exposure can increase the risk of blood disorders and certain cancers like leukemia.
The highly flammable chemical is colorless or light yellow, and is found in products made from coal and oil including plastics, resins and nylon fibers, and also some types of rubbers, dyes and pesticides. It is also regularly found in vehicle exhaust, tobacco smoke and gasoline.
The concentrations of benzene that the researchers found in the natural gas samples were “much lower compared to the amount in gasoline,” Dr. Michanowicz said on Friday during a conference call with reporters. Even so, he said, the finding is concerning since “natural gas is used so widely in society and in our indoor spaces.”
Americans spend more than 90 percent of their time indoors, according to the E.P.A., where concentrations of some pollutants can range from two to five times as high as outdoor concentrations.
Benzene is a carcinogen, and exposure over time adds up, leading some experts to suggest that there is no safe level of exposure.
The researchers said that the goal of their study was to identify the presence and concentration of certain hazards, and that more research is needed to understand the health risks.
“The largest sources of benzene in most people’s lives are gasoline from cars and smoking,” said Rob Jackson, an earth scientist at Stanford University who did not work on the study. “On the other hand, any unnecessary benzene in your home is just too much.”
The unburned natural gas also contained inconsistent levels of odorants, or substances that give off a perceptible smell, the researchers said. Methane, the main component of natural gas, is odorless, so odorants are routinely added to help detect leaks.
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“If there’s less odorant in the natural gas stream, there is a higher potential for larger leaks to exist without a smell to them,” Dr. Michanowicz said in the Friday call.
When released into the atmosphere unburned, methane is a particularly potent greenhouse gas. It can warm the planet more than 80 times as much as the same amount of carbon dioxide over a 20-year period. Oil and gas companies have come under fire in recent years for often large-scale, invisible releases of methane.
Across the country, a growing number of cities are trying to phase out natural-gas hookups to homes and businesses in favor of electric alternatives, mostly citing the emissions impact of continuing to burn fossil fuels.
The new research suggests that natural gas leaks aren’t just releasing methane, but also air toxics that could be detrimental to public health, said Curtis Nordgaard, a pediatrician and study co-author. “We might want to rethink those leaks as not just a climate issue, but a health issue,” he said.
Dr. Nordgaard is a senior scientist at PSE Healthy Energy, a nonprofit research institute focused on the public health and climate effects of energy production, as is Dr. Michanowicz.
With this study, the researchers said they hoped to fill a gap in the availability and transparency of gas composition data. Pipeline operators and gas suppliers in the United States generally test the composition of gas, consistent with recommendations from the North American Energy Standards Board, an industry organization that sets standards for the natural gas and electricity marketplace.
However, the gas composition tests usually measure only the 16 most abundant constituents of natural gas. That list doesn’t include some of the components the researchers identified, like benzene.