Text/Yu Mengqi Contributing Writer of CC Intelligence Bureau of Phoenix.com
Editor's note:
斯坦福大学罗伯特· B·杰克逊团队继去年6月15日发布文章称，燃气灶煮饭时会产生一种与白血病和其他血细胞癌风险增加有关的化学物质苯，引发主妇们对使用燃气灶的恐慌后，今年五月初，这个团队又在《科学进展》杂志上，发表了最新的研究文章《美国炉灶燃烧产生的氮氧化物暴露、健康后果及其与人口统计学差异的关联》（Nitrogen dioxide exposure, health outcomes, and associated demographic disparities due to gas and propane combustion by U.S.stoves）。
The study proves that half of the households in the bedroom away from the kitchen can exceed the one-hour environmental benchmark of the US Environmental Protection Agency and the one-hour exposure limit of the WHO guideline if the indoor room is not closed and the range hood is not turned on during the use of the gas stove in half of the households.
The study also found that the nitrogen dioxide level in the bedroom was still higher than the health guideline within 2~3 hours after the gas stove was turned off, and even up to 4 hours in a small house.
The study provides data that people living in houses with an area of less than 75 square meters are exposed to nitrogen dioxide twice as much as the average in a year, four times as many as those living in houses over 280 square meters, and experience up to 10 times more days than 100 ppbv.
Also, range hoods are largely ineffective at reducing nitrogen dioxide concentrations.
In addition to nitrogen dioxide, the harmful substances emitted by gas stoves include carbon monoxide, benzene, formaldehyde and ultrafine particles.
According to a U.S. statistic, gas and propane stoves could be the culprits of 2 million cases of pediatric asthma, costing about $1 billion a year in social costs. In 2020, the social cost of deaths due to natural gas and propane was $25 billion, broken down to about $4,500 per household. Moreover, long-term exposure to NO2 from indoor gas and propane stoves has caused up to 40% of deaths from secondhand smoke.
At present, the gas penetration rate in China has reached 98%. At a high level in the world. In 2021, the number of people using urban gas in China reached 550 million. There are also about 200 million gas users in rural areas, and there should be about 700 million gas users in China. After this series of studies by Stanford was reported by the media, it caused some people to panic and question.
What's behind this series of studies from Stanford University on the risk of gas burndowns? What do the average person think of this study?
Key Takeaways:
1. On June 15 last year, researchers at Stanford University published a paper saying that when people turn on the gas stove to cook, the high concentration of benzene produced will stay in the house for a long time, and prolonged exposure to high concentrations of benzene may lead to leukemia and other blood cell cancers.
2. As early as 1992, American scholars found that children living in households with gas stoves had an increased risk of respiratory diseases by about 20%, and boiling water alone could cause indoor carbon dioxide concentrations to soar. This doesn't mean that having a gas stove in your home will make you sick, but ventilation is the best way to reduce the damage caused by harmful substances.
3. In the U.S., environmental groups don't want experts to come to this conclusion because they want to completely replace gas stoves with induction cookers to reduce emissions. In opposition to this is the gas industry, and banning gas stoves is a catastrophe for them. The debate between the two sides reached the U.S. Congress, and finally ended with the Biden administration not supporting the ban on gas stoves. The incident has already caused economic and political confrontation in the United States.
4. The gas penetration rate in China has reached 98%. After the Stanford study was reported by the media, it caused panic among some people. But we don't have to panic because of this, the rational use of range hoods and timely ventilation can minimize the risk of exposure to harmful substances.
Stanford Blockbuster Study: Can Chemicals from the Combustion of Gas Stoves in Your Home Cause Leukemia?
On June 15 last year, researchers at Stanford University sparked panic in a paper published in the journal Environmental Science & Technolog. Whenever residents light a gas stove to cook rice, they produce a chemical linked to an increased risk of leukemia and other cancers of blood cells: benzene, according to the research article.
The risks of benzene have long been known. The U.S. Centers for Disease Control and Prevention has issued a warning that high doses of benzene can cause leukemia.
According to the article, "A gas stove set to high or a gas oven set to 350°F (about 177°C) can cause indoor carcinogen benzene levels to be higher than those found in secondhand tobacco smoke." Benzene also wafts throughout the room and stays in the air for hours. Gas stove flames produce higher concentrations of benzene indoors than secondhand smoke. ”
The authors of the paper are three professors at Stanford University. The article points out that tobacco smoke, oil and gas development, refining, gasoline pumping, and gasoline and diesel combustion have all been identified to produce benzene, a carcinogen, and after the first quantitative testing, benzene can also be produced indoors when burned on a gas stove, which means that exposure to cooking gas flames can have health effects.
Between January and December 2022, the researchers tested 87 homes in California and Colorado, including homes, apartments, and Airbnb rentals with kitchens. In the test, kitchens were divided into three categories, those with doors and windows fully closed and isolated from other rooms with plastic materials were called "closed", those with doors and windows closed but not isolated were called "semi-closed", and those with doors and windows open were called "open". After complex conversions and calculations, the final conclusions are mainly three:
1. Natural gas and LPG stoves emit benzene, and in some homes and in certain categories of kitchens, indoor benzene concentrations are above established exposure benchmarks that may lead to chronic health problems.
2. High-temperature natural gas and LPG burners, as well as ovens set to 350°F (about 177°C), have an average benzene emission of 2.8-6.5 μg/min, which is 10-25 times higher than that of electromagnetic burners.
3. Neither the cooker nor the food being cooked itself emits detectable benzene, which means that benzene can only come from the combustion of natural gas or LPG.
The paper also cites a series of previous studies showing that gas stoves can affect climate change and health. A previous study led by Stanford University showed that methane leaks from U.S. home gas stoves have the same climate impact as carbon dioxide emitted by about 500,000 gasoline-powered cars; A large sample analysis in 2013 concluded that children living in households with gas stoves had a 42% higher risk of asthma than children living in households without gas stoves; A 2022 analysis calculated that 12.7% of childhood asthma in the U.S. may be attributable to gas stoves.
▎As early as October 2022, Environmental Science and Technology released a similar study, saying that gas stoves can be dangerous even when turned off, and it is possible to leak twelve potentially carcinogenic chemicals including benzene, cyclohexane, nitrogen dioxide and other chemicals in the home, and people can hardly smell it.
For the average reader, since few people closely follow the ins and outs of the gas stove health dispute in the United States, it may be a little difficult to sit still when they see a few information keywords such as Stanford, scientists, and carcinogenicity. In fact, the novelty of this study is only that it introduces exposure to carcinogen benzene as a new perspective, and before that, gas stoves were most often accused of emitting pollutants such as nitrogen dioxide (NO2), carbon monoxide and formaldehyde. Over the past few years, research in favour of abolishing gas stoves has focused on nitrogen dioxide, with a narrative based on the Environmental Protection Agency's claim that "nitrogen dioxide is a toxic gas that can cause breathing problems in people with asthma or chronic obstructive pulmonary disease even in very low concentrations." ”
Children living in households with gas stoves have an increased risk of respiratory diseases by about 20%?
As early as 1992, studies showed that children living in households with gas stoves had an increased risk of respiratory diseases by about 20 percent. In October 2021, NPR approached the author of that study, Josiah Kephart, an environmental epidemiologist at Drexel University in Philadelphia who studied indoor air pollution caused by traditional stoves in Latin America, and then conducted a field experiment at his home to prove his theory.
At first, air monitors showed that the carbon dioxide concentration in the Copathga kitchen was about 24 parts per billion (24 ppb). This is normal for households with gas stoves, but is still above the World Health Organization's (WHO) average annual health guidance of 5ppb. When Copat boiled a pot of boiling water on a gas stove and baked blueberry muffins in an oven at 375 °F (about 191 °C), the detector showed that the carbon dioxide concentration had soared to 168 ppb, which was more than 50 percent of the WHO's hourly health guidance of 106 ppb. At this point, Copat explains, "if you have children or have any type of lung disease, then according to the scientific literature, their lungs will start to change that could make them have more severe symptoms or make their disease worse." "After another half hour, the air monitor showed a value of 207 ppb, almost double the WHO's hourly health guidance standard.
▎In 2017, a five-year lung cancer epidemiological survey conducted by the Cancer Institute of Tongji University in Shanghai found that the risk of lung cancer increased by 2-3 times in middle-aged and elderly women due to long-term exposure to high temperature oil fumes. Among the risk factors for lung cancer in non-smoking women, more than 60% of women are exposed to kitchen fumes for a long time; 32% of women prefer to fry food in high-temperature oil when cooking, and the kitchen doors and windows are closed or poorly ventilated.
However, NPR reporters also noticed that there was no range hood on the stove in Kopat's house, and during the experiment, he turned on the ventilation fan on the wall, but the ventilation fan was more than 2 meters higher than the stove, and turning it on did not seem to have any effect on the concentration of carbon dioxide in the room. Kopat himself admits that having a gas stove in your home doesn't necessarily make you sick or cause asthma, and the study concluded that it was a mathematical calculation of risk, "If you have a big kitchen with really up-to-date ventilation systems, and you're in good health, it's probably not your biggest worry or the biggest risk to your health." Of course, when talking about children, he stressed, "It seems to me that putting this source of pollution in our house increases the risk of asthma or other respiratory diseases for children, which is definitely not good for me." ”
In fact, a closer look at the NPR report and the Stanford University researchers' paper reveals several common points in the debate about whether gas stoves cause illness at all. For example, the two concepts of exposure risk and pathogenic risk are related, but they are obviously not the same thing, and they are strictly defined and qualified in serious academic papers, but they are often blurred intentionally or unintentionally at the media level; For example, is the toxic substance produced by combustion or by heating the food itself? This is the reason why benzene does not come from food in the latest paper, but other substances such as nitrogen dioxide have so far been inconclusive.
▎According to figures released by the National Cancer Center, between 2000 and 2014, the incidence of lung cancer among Chinese women nearly doubled from 27 per 100,000 to 51 per 100,000. Lung cancer ranks second in incidence among female malignant tumors in China, second only to breast cancer, and ranks first in mortality. Since 80-90% of women diagnosed with lung cancer do not smoke, kitchen fumes are considered to be one of the triggers.
Darby Jack, an associate professor of environmental health sciences at Columbia University who has studied indoor air pollution for more than a decade, is a supporter of induction cookers, but in a series of interviews in early 2023, he stressed that there is no reason for people to panic about using gas stoves. "Nobody needs to rush out to take urgent action or worry that they're going to die tomorrow from cooking with gas," he said, adding that ventilation minimizes exposure to harmful substances, "and if you have a good ventilation that can be ventilated outside, it can be of a great help in terms of reducing the risk of nitrogen dioxide exposure, and the key is that you have to turn it on." ”
Jack mentions a more important point: Does effective ventilation dramatically reduce the concentration of toxic pollutants produced by cooking? The latest paper by researchers at Stanford University also has a quote, "Good ventilation helps reduce pollutant concentrations, but we found that exhaust fans are often not effective in eliminating benzene exposure." In this case, should a good range hood also be part of the response recommendations? The U.S. Environmental Protection Agency (EPA) has recommended that indoor gas stoves have more ventilation than electric stoves, and that larger gas stoves should be installed with more power than smaller kitchen spaces.
However, environmental groups that support the study do not want experts to come to this conclusion, because the reason why environmental groups are eyeing the health problems of gas stoves is not to get people to buy range hoods, but to induce consumers to change to induction cookers, and the reason why they are eyeing induction cookers is because the stove is considered to be the entrance to determine what type of energy a family chooses, and when the stove generally uses electricity, it means that most families in the United States are likely to change their heating, bathing and other equipment from gas to electricity. And behind this change, ordinary people also know how huge the impact it will have on the distribution of benefits. According to statistics, in the United States, 46% of households currently use natural gas as the main heat source, 40% use electricity, 10% use other fuels such as heating oil or liquefied petroleum gas, and 4% do not have heating. For water heating, the percentages are 47% gas, 47% electricity, and 6% other fuels.
▎A 2022 analysis noted that 12.7% of childhood asthma in the United States can be attributed to gas stoves.
Should the gas stove be replaced with an induction cooker? Why does Biden not ban gas stoves? Why is the health problem of gas stoves so controversial?
In fact, the Stanford researchers' latest paper is sponsored by an organization called the High Tide Foundation, which is backed by Overlook Investments Group, a Hong Kong-based hedge fund management firm that sponsors many research projects related to climate change. At the same time, the gas utility industry is also engaged in a special study on "stoves and health", because it sees the claim that gas stoves are harmful to health as an existential threat. The American Gas Association (AGA) continues to push back against research. For example, the group made it clear in a statement last January that a December 2022 report in the International Journal of Environmental Research and Public Health linking natural gas cooking to asthma had no credible scientific evidence.
The report, funded by nongovernmental organizations, aims to remove consumers' autonomy from energy options, specifically to induce people not to opt for natural gas, the statement said. "The authors did not make any measurements or tests based on real-life appliance use and ignored literature data, including a study of data collected from more than 500,000 children in 47 countries, which showed that 'no necessary association was found between the use of natural gas as a cooking fuel and asthma symptoms or asthma diagnosis'. Any allegation that gas stoves exceed the standards set by the Environmental Protection Agency and the World Health Organization is patently false. ”
"Regulators, such as the CPSC, should rely on real data and science to make their claims, not unsubstantiated claims by proponents of a particular school of thought. Attempts to create consumer fear with baseless accusations to deny people access to natural gas are a misguided protocol that will not improve the environment or consumer health, and will come at a huge cost to vulnerable groups. ”
The statement was not only in response to the study, but also to a debate that was reignited on Jan. 9 last year. Richard Trumarca, Jr., a member of the U.S. Consumer Product Safety Commission at the time, told Bloomberg that the agency planned to consider regulating gas stoves due to concerns about the health effects of them, and that "products that cannot be guaranteed to be safe may be banned." As a result, conservative politicians are extremely outraged, comparing ownership of gas stoves to the right to bear arms and freedom of religion. Alexander Hoehn-Saric, the chairman of the U.S. Consumer Product Safety Commission, hastened out to explain that "there is no intention to ban gas stoves" and that his agency "has not taken relevant action", and the White House spokesman also clarified that the Biden administration does not support the ban.
Despite this, Republicans in Congress have launched a massive counterattack, introducing the Protect American Stoves Act (Gas Act) and the Stop Trying to Denigrate Energy Act (Stove Act). As these bills move through Congress, reports and media reports supported by environmental groups continue to appear. The Stanford study's publication came a day after the U.S. House of Representatives passed the Gas Act, and AGA immediately praised that "strong bipartisan support for this common-sense legislation is encouraging," that it would "prevent the U.S. Department of Energy from imposing effective bans on all categories of appliances under the guise of energy-saving standards," and that "customers have the right choice of appliances that are right for them and their families."
In short, gas stoves and health, which is a scientific issue that is ambiguous at least for now, is a clear issue of economic interests and politics in the United States.
▎In 2020, there were about 181 million urban natural gas users in China, and about 47 million households in the United States currently use natural gas or propane-fired stoves and ovens.
It is understood that China's current global gas penetration rate has reached 98.00%, which is at a high level in the world. In 2021, the number of people using urban gas in China reached 550 million. There are also about 200 million gas users in rural areas, and there should be about 700 million gas users in China.
The Stanford study, after being reported by the mainland media, caused panic among some people. The number of users who have asked about gas safety has increased significantly, and some people have posted on the Internet and even stopped using the gas stove. At present, as a Chinese user who uses gas stoves, there is no need to be nervous, turn on the range hood and ventilation system when cooking, and try to reduce the indoor air to a healthy level.
After all, in the United States, the health problem of gas stoves is not a simple medical issue, but a question of environmental protection, and it is also a question of who can dominate the future interests of the two major energy industries of electricity and natural gas/LPG, and ultimately a political issue between the left and right.