The natural gas delivered to homes contains low concentrations of several chemicals linked to cancer, a new study finds. Researchers also found inconsistent levels of odorants — substances that give natural gas its characteristic “rotten egg” smell — which could increase the risk of minor leaks going undetected.
The study, which was published in the journal Environmental Science & Technology, adds to a growing body of research linking natural gas supply and use to adverse public health and climate impacts.
Most previous research has documented the pollutants present where oil and gas extraction takes place, but there are “fewer studies as you work your way through the supply chain,” said Drew Michanowicz, the study’s lead author, looking at “where we actually use it, in our homes.”
Over 16 months, researchers 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 “airborne toxicants” — a 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, can lead to drowsiness, dizziness, headaches and irritation of the eyes and skin, according to the Centers for Disease Control and Prevention. Long-term exposure can increase the risk of blood disorders and certain cancers, such as leukemia.
The highly flammable chemical is colorless or pale yellow and is found in products made from coal and oil, including plastics, resins and nylon fibers, as well as in some types of rubbers, dyes and pesticides. It is also regularly found in vehicle exhaust, tobacco smoke and gasoline.
The concentrations of benzene the researchers found in the natural gas samples were “much lower compared to the amount in gasoline,” said Dr. Michanowicz Friday during a conference call with reporters. Still, he said, the finding is worrisome because “natural gas is so widely used in society and in our indoor spaces.”
Americans spend more than 90 percent of their time indoors, according to the EPA, where concentrations of some pollutants can range from two to five times higher than outdoors.
Benzene is a carcinogen and exposure increases over time, leading some experts to suggest that there is no safe level of exposure.
The researchers said the aim 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 greatest 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 participate in the study. “On the other hand, all the unnecessary benzene in the house is just too much.”
The unburned natural gas also contained inconsistent levels of odorants, or substances that give off a detectable odor, the researchers said. Methane, the main component of natural gas, is odorless, so fragrances are added regularly to help detect leaks.
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“If there is less odorant in the natural gas stream, it is more likely that larger leaks will occur without them smelling,” said Dr. Michanowicz in Friday’s 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 discharges of methane.
Across the country, a growing number of cities are trying to phase out natural gas connections for homes and businesses in favor of electric alternatives, citing the emissions impact of continuing to burn fossil fuels.
The new research suggests that natural gas leaks not only release methane, but also toxic compounds into the air that could be harmful to public health, said Curtis Nordgaard, a pediatrician and co-author of the study. “Maybe we want to rethink those leaks as not just a climate problem, but a health problem,” he said.
dr. Nordgaard is a senior scientist at PSE Healthy Energy, a non-profit research institute focusing on the public health and climate impacts of energy production, like 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, in accordance with recommendations from the North American Energy Standards Board, an industry organization that sets standards for the natural gas and electricity markets.
However, the gas composition tests usually only measure the 16 most common components of natural gas. That list doesn’t include some of the components the researchers identified, such as benzene.