High levels of carcinogen discovered in European gas supply

(Adapted from PSE press release)

Researchers have discovered high levels of the carcinogen benzene in the domestic gas supply for multiple Western European cities by US researchers. With low level gas leaks common in homes, “hazardous leaks are likely underreported in Europe” concluded a peer-reviewed paper by researchers at the Stanford Doerr School of Sustainability and PSE Healthy Energy, an energy science and policy research institute. The paper was published March 25 in the journal Environmental Research Letters.

“We’re just learning how much benzene enters our homes by burning gas indoors," said study co-author Rob Jackson, a professor of Earth system science at the Stanford Doerr School of Sustainability. "Now we find a second source of dangerous toxins entering our home air. This finding should trouble us all.”

Benzene was found in all 72 domestic gas samples collected by the US researchers in homes in the United Kingdom, the Netherlands and Italy. The substance occurs naturally in oil and gas fields, has no safe exposure level according to the World Health Organization, and is associated with leukemia and other long-term adverse health effects and diseases. The researchers found that UK gas samples had 37 times more benzene than in typical North American gas, on average, while Dutch samples had 66.5 times more. Gas in London was found to contain 64 times and Amsterdam 73 times the benzene concentration of typical North American gas, on average, while Milan, the only Italian city studied, had 8.5 times more.

The researchers also checked homes for gas leaks that occur chronically, when gas stoves were switched off. Gas leaks were found in approximately 40% of the kitchens visited in the three countries. Gas stove leak data and benzene concentrations in gas were combined in household modeling to estimate annual exposure. The researchers conservatively calculated that 9% of homes visited in the UK, Netherlands and Italy had leaks large enough to exceed a UK and EU exposure limit for benzene, while 14% exceeded the more strict World Health Organization lifetime (WHO) guidance level.

Extrapolating to a population level in conservative calculations outside the research paper, hundreds of thousands of people, mostly in the UK and the Netherlands where benzene readings were higher, are likely exposed above the regulatory limit, the researchers estimated. Modeled benzene exposure from the larger leaks measured in these two countries is worse than living with a smoker, in terms of benzene exposure alone.

The researchers also tested gas for sulfur-based odorants, added by gas companies to help people detect leaks and avoid explosions. In all cases outside Italy, odorant levels were too low to alert most people to leaks large enough to lift concentrations of benzene in indoor air above WHO and regulatory limits. Exposure could rise nine times over the national limit in the UK (nearly 40 times in London) and nearly five times the EU limit in the Netherlands (nearly 15 times in Amsterdam) before a gas leak could be smelled at the average odorant level measured in gas, the researchers calculated. 

PSE air quality scientist and lead author of the study, Tamara Sparks, said: “We were surprised by how high the benzene levels were compared to what we’ve seen in our previous studies. Given these high concentrations, a lot of people are likely being chronically exposed to benzene without knowing it. We have little clarity on why gas leaks occur in some homes and not others, making this benzene hazard essentially a lottery. This has so far flown under the public’s radar, but we hope that, by bringing attention to it, action can be taken to reduce this threat. People can reduce their personal risk by opening windows to get more fresh air, but there’s only so much an individual can do when this gas is piped into their home.”  

The research is the first to reveal the widespread presence and risk of benzene in European home gas supplies and follows a similar discovery in North America. It is part of PSE’s Methane + Health Initiative, which assesses air pollution and health risks from known methane sources. PSE and Stanford researchers previously established the rate benzene is created as stoves burn natural gas, the direct health implications, as well as wider leak concerns.

The paper also modeled a spike in benzene following a large UK pipeline leak in 2023. At its peak, this lifted concentrations of the carcinogen four times beyond an EU eight-hour worker safety limit up to 50 meters downwind, the modeling found, with lower levels predicted as far as 10 kilometers downwind, potentially exposing tens of thousands of people in Cheltenham and Bishops’s Cleeve.

PSE executive director Seth Shonkoff, said: “The levels of benzene we found in the distribution system gas in the UK and the Netherlands are frankly eye-popping. That means even a small leak can pose significant health risks quickly indoors and outdoors. Whether it’s leaking from a pipeline or a stove in someone’s kitchen, it’s all the same gas, and health risk travels with it.” 

Research funding came from the European Climate Foundation and the Wellcome Trust.

Wellcome Trust head of mitigation, Rachel Huxley, said: “We expect our homes to be the safest place we spend our time. This study shows that everyday use of gas can put people at unnecessary health risks. Because gas is primarily methane—a powerful super pollutant—even small leaks expose communities to harmful air pollutants and worsen climate change. The findings underscore the significant health impacts from indoor air pollution and air toxics such as benzene. This study shows the importance of science in understanding risks to our health, and in helping governments and businesses to support policies that reduce pollution and promote healthy homes and communities.”

Having established a large, previously unrecognized benzene exposure pathway in Europe, today’s study concluded that safeguarding the public from benzene exposure in Europe will require grappling with our relationship with natural gas.

Jackson is the Michelle and Kevin Douglas Provostial Professor at Stanford, and a senior fellow at the Stanford Woods Institute for the Environment and the Precourt Institute for Energy, which are both part of the Doerr School of Sustainability.