Mounting evidence suggests that gas appliances create all sorts of toxic effects on the body-from allergic responses to growth retardation.
In these globally warmed times, we are all being encouraged to get cooking with gas. Gas is so much more eco-friendly, we're told, because it's one of the cleanest-burning alternative fuels, producing fewer smog-producing and greenhouse-gas emissions. When we light the gas burner to boil an egg, we will use far less energy than boiling it using electricity.
But the environment is one thing and environmental medicine another, and what's good for the planet isn't necessarily so for the people on it. Research is now showing that gas appliances may be so toxic that they may even be stunting children's growth.
When Dr Theron Randolph (1906-1995), the great American pioneer of environmental medicine, first started charting his patients' toxic reactions to things in their environment, top of his list were gas appliances. Time and again, he found that his patients' most common chemical sensitivity was to the com-bustion byproducts of natural gas. What's more, he found that gas cookers in the home were often the trigger for multiple chemical sensitivity (see box, page 21), later dubbed by the popular press as 'allergy to the 20th century'.
Today, official surveys have con-firmed that natural gas is one of the major sources of indoor air pollution. That's because cookers produce a cocktail of unpleasant substances, including not only the toxic gases carbon monoxide and nitrogen dioxide, but also particles of poly-cyclic aromatic hydrocarbons (PAHs) and heavy metals.
Although the usual expectation is that these toxic substances will be dealt with by extractor fans, most homes with gas cookers either don't have or don't use extractor fans.
And even if they do, the fans don't appear to work that well anyway.
An in-depth British study carried out about 10 years ago showed that women-and it's still usually they who do the cooking-with extractor fans in their kitchens had just as many respiratory problems as women with unventilated cookers (Lancet, 1996; 347: 426-31).
So, exactly what are the potential health problems that can come from cooking with gas?
Carbon monoxide (CO) is the most obvious hazard. Odourless, tasteless and colourless, this gas binds with the haemoglobin in the blood 200 times better than oxygen and, thus, severely reduces the amount of oxygen transported to the tissues of the body. At very high doses, it can kill, as evidenced by the many cases of fatal carbon-monoxide poisoning in homes that are using faulty, poorly maintained or unvented gas appliances.
But carbon-monoxide poisoning is not all or nothing. Well before it becomes fatal, a continuous low-level exposure to the gas can cause early symptoms of CO toxicity (see box below). In fact, hospital accident and emergency departments estimate that as much as 5 per cent of their cases of severe headaches and dizzi-ness are due to CO poisoning. The problem is noticeably worse in winter because of the lack of ventilation (Lambert WE, Samet JM. Occupational and Environmental Respiratory Disease. St Louis, MO: Mosby-Year Book, 1996: 788).
Nitrogen dioxide (N02) is another odourless gas contained in gas-cooker fumes. It has long been known to be a powerful irritant to the eyes, nose, throat and, particularly, lungs. At high concentrations, it can cause extensive lung damage in both animals and humans, whereas lower levels can result in chronic low-grade disease.
In tests involving young British housewives, doctors at St Thomas' Hospital, in London, showed that women who cooked on gas stoves had significantly reduced lung func-tion, along with an increased risk of wheezing, shortness of breath and asthma attacks (Lancet, 1996; 347: 426-31). Furthermore, N02 has been found to worsen asthma symptoms in general, exacerbating what might just have been a mild reaction to allergens such as house-dust mites (Lancet, 1994; 344: 1733-6).
However, the most alarming evi-dence as to the adverse effects ofN02 concerns children. Researchers in Hong Kong found a direct correla-tion between the amount of gas-stove usage in the home and the incidence of childhood respiratory illnesses.
After surveying the parents of 426 children, aged six and under, on two housing estates, the researchers discovered that the more times a family used gas for cooking, the higher the incidence of allergic rhinitis, asthma, bronchitis, sinusitis and pneumonia in their children-a clear dose-response relationship. In addition, although the Chinese tend to be heavy smokers, the researchers found that passive smoking had far less effect on the children than did cooking with gas (Arch Dis Child, 2004; 89: 631-6).
It's the same story in Australia, where researchers have confirmed that even relatively low levels of N02 can cause respiratory problems in children. It's been calculated that cooking on a gas stove can expose people to air containing as much as 1000 parts per billion (ppb) of N02, which can linger for up to an hour in the room after the cooker has been turned off. Even levels as low as 80 ppb can be hazardous to children (Int J Epidemiol, 1997; 26: 788-96). And, as N02 is heavier than air and, thus, sinks, children are likely to receive higher doses of it than do adults.
Gas stoves also make life more difficult for children who already have asthma. A recent study from Yale University found that asthma symptoms more than doubled in homes with gas stoves, even when N02 levels were low. An average of just 25 ppb of N02-well below the US official safety guidelines of 53 ppb-could cause breathing difficul-ties among children (Am J Respir Crit Care Med, 2006; 173: 297-303).
There's also evidence that N02 may not only worsen asthma, but actually cause it. An eight-year follow-up study in Tasmania came up with the alarming finding that, if a child is exposed to a gas stove in the first month of its life, it will have twice the risk of developing house-dust mite allergy by the age of eight (Clin Exp Allergy, 2001; 31: 1544-52).
And gas stoves don't just produce gases-they also release particles, mainly, polycyclic aromatic hydro-carbons (PAHs), which researchers are only just beginning to realize can also be hazardous to health.
One of the earliest alerts came from Australia, where researchers at Monash Medical School in Victoria, even after adjusting for the effects of N02, found that children from homes with gas cookers still had an increased risk of respiratory disorders. "This suggests an additional risk apart from the nitrogen dioxide exposure associated with gas stove use," they said (Am J Respir Crit Care Med, 1998; 158: 891-5).
The added risk could be due to PAHs, or perhaps even heavy metals. It's now known that toxic compounds of mercury, arsenic and lead can accumulate on the burners of gas stoves. Although the precise health consequences of this have not yet been ascertained, it's known that these substances are highly poison-ous and readily accumulate in body tissues (Nature, 1993; 363: 680). Indeed, people suffering from multiple chemical sensitivity have problems with gas rings, even when they're not being used.
The most worrying findings, however, come from Kuwait, where doctors made a comparison of the general health of 130 children from homes that used either electric or gas ranges. These were middle-class children from prosperous Kuwaiti and European families who could afford the luxury of air-conditioning and mechanical ventilation.
In spite of this, there were significant differences between the two sets of children. The researchers were astonished to find that children from the gas-cooker homes not only had impaired lung function, but were also around 3 cm-more than an inch-shorter in height (Arch Environ Health, 1991; 46: 361-5).
The lead author, Professor Wieslaw Jedrychowski of Krakow University, describes these Kuwait results as only "a pilot survey", a preliminary investigation. And certainly, so far, neither he nor anyone else appears to have followed-up these growth-rate findings in other youngsters. Yet, could these Kuwait children be the canaries down the mineshaft?
Look out for these signs
- Early carbon-monoxide poisoning
- dull headache
- ringing in the ears
- pounding heart.
- Nitrogen-dioxide poisoning
- abdominal pain
- difficulty breathing.
- Chemical sensitivity
- runny nose
- itchy eyes
- scratchy throat
- scalp pain
- mental confusion
- heart palpitations
- nausea and/or diarrhoea
- abdominal cramps
- aching joints.
Note: These symptoms often appear to
be unrelated and may occur in a cluster. Having more than three at one time could indicate a problem.
Reducing your gas-cooker risk
- Keep your kitchen well ventilated
- Turn the extractor fan on before you start cooking as most fumes are given off in the first few minutes
- Have the gas hob and extractor fan regularly serviced
- Consider installing carbon-monoxide and methane detectors.
A whiff of a problem
Natural gas is primarily made up of methane and, because it has no smell, odours are added to the gas to help detect leaks by scent. The usual added odours are sulphur-based compounds, which are believed to be non-toxic. Most people can detect them before they reach significant levels but, for chemically sensitive people, even the slightest of gas leaks may constitute a serious health problem.