High levels of carcinogen discovered in European gas supply

High levels of the carcinogen benzene have been discovered 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 PSE Healthy Energy, an energy science and policy research institute, and the Stanford Doerr School of Sustainability. The paper was published today in the journal Environmental Research Letters. 

Benzene was found in all 72 domestic gas samples collected by the US researchers in homes in the UK, 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 leukaemia 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 64x and Amsterdam 73x the benzene concentration of typical North American gas, on average, while Milan, the only Italian city studied, had 8.5 times more [1].

The researchers also checked homes for gas leaks that occur chronically, when cookers 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 modelling to estimate annual exposure. The researchers conservatively [2] 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% exceed the more strict World Health Organization lifetime (WHO) guidance level [3]. 

Extrapolating to a population level in conservative calculations outside the research paper [4], 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. Modelled 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 odourants, added by gas companies to help people detect leaks and avoid explosions. In all cases outside Italy, odourant 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 40x in London) and nearly five times the EU limit in the Netherlands (nearly 15x in Amsterdam) before a gas leak could be smelled at the average odour level measured in gas, the researchers calculated. 

PSE air quality scientist and lead author of the study, Tamara Sparks, PhD, 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 [5] 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 cookers burn fossil gas, the direct health implications, as well as wider leak concerns. 

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

Today’s paper also modelled 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 8 hour worker safety limit up to 50 metres downwind, the modelling found, with lower levels predicted as far as 10 kilometres downwind, potentially exposing tens of thousands of people in Cheltenham and Bishops’s Cleeve.

PSE executive director Seth Shonkoff, PhD, MPH 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, PhD, 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.

Notes to editors

The paper will be published in Environmental Research Letters here: https://doi.org/10.1088/1748-9326/ae499f while a summary and links to the paper will be available at PSE's website here: www.psehealthyenergy.org/work/gas-stove-benzene-emissions-europe

[1] See today’s paper for the full methodology. The collected samples were analysed under contract by the ISO 17025 accredited lab Tera Environnement. Comparisons with North American gas are based on recent research by PSE and Stanford. 

[2] Exposure calculations were kept conservative. Further to this, potential additional benzene exposure from when cookers were in active use were excluded, as were potential leaks from other gas appliances in homes.

[3] The WHO considers benzene a “major public health concern” for which “no safe level of exposure can be recommended”, though it has set guidance for lifetime exposure, above which “excess” cancer cases can be expected. Governments (EU, UK) have set weaker limits for annual average exposure outside. While regulators have been tightening outdoor exposure limits, the study shows that indoor exposure also creates significant health risks. Benzene was the most toxic and prevalent of six hazardous pollutants identified by the researchers. 

[4] The extrapolation of the modelled over-exposure rate to a population level is stated as an order of magnitude, rather than a precise figure, to reflect the uncertainties involved. It assumes that the range of observed leaks in homes is representative of those found in the larger population and is paired with statistics on gas usage and an estimate of typical window-opening behaviour for ventilation. Follow up research is needed to reach precision. 

[5] This is the first study to sample gas for benzene in European homes, the first to measure gas leaks in those homes and the first to model benzene exposure from these sources in indoor and outdoor air.

About PSE Healthy Energy

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