Rain, sleet, snow and freezing temperatures. This time of year seems a lifetime away from the balmy summer evenings when we were lounging outside enjoying the delights of a barbecue. The smell of grilled meat and smoky charcoal wafting through the air is the essence of summer to many people.
The best position at an outdoor barbecue is a few feet upwind, so that the smoke is drifting away but odours of the cooking food still manage to percolate the area. The macho position in control over the barbecue is reckoned by some to be the worst of all, as it is accompanied by a surplus of heat from the equipment and frequent lungsful of smoke.
These considerations are not without foundation. Not only are the smoke particles a health hazard, but they are accompanied by harmful series of compounds originating from the cooking food and the charcoal itself. Outdoors, these will quickly disperse after they have blown over the chef but indoors, they can accumulate in the air and reach dangerous concentrations.
The indoor problem is not as odd as it sounds. In Asia, there are special barbecue-style restaurants where the customers cook their own food at their tables. It is likely that any volatile compounds will remain in the restaurant and be inhaled by the patrons. Carbon monoxide, toxic carbonyl compounds and aromatic hydrocarbons are some of the potential pollutants.
The emission of these groups of compounds from charcoal has been investigated by scientists from Sejong University and Korea University in Seoul and was described by senior reporter Ki-Hyun Kim in the Journal of Hazardous Materials. The team studied 16 barbecue charcoals originating from Korea, Indonesia, China and Malaysia, all of which are commonly available in Korea.
Samples of each charcoal were burned in a combustor and the emissions were collected in a Tedlar bag. For volatile hydrocarbons, the trapped gases were passed to a cold trap before thermal desorption and GC-FID analysis. The levels of benzene, toluene, ethylbenzene, m/p-xylene and styrene were measured.
For carbonyl compounds, the gases were passed through a dinitrophenylhydrazine cartridge to convert them to hydrazones, before elution with acetonitrile. The mixtures were analysed by HPLC with UV detection at 360 nm. A C18 column was used to separate the hydrazones with an isocratic mobile phase of aqueous acetonitrile and they were quantified from calibration curves. The detection limits ranged from 0.92 to 1.16 ppb for formaldehyde, acetaldehyde, acrolein, acetone, propionaldehyde, crotonaldehyde, butyraldehyde, benzaldehyde and valeraldehyde.
Smokes from all of the charcoals contained large amounts of aromatic hydrocarbons. The amounts varied with the country of origin with Korean charcoal the highest emitter, having a total of all C6-C16 hydrocarbons of 7160 ppb, compared with 3270, 510 and 315 ppb for Indonesian, Chinese and Malaysian charcoal. Toluene and benzene were the most abundant hydrocarbons at mean levels of 116 and 98.7 ppb.
With the carbonyl compounds, formaldehyde, acetaldehyde and acetone were consistently above the detection limit for all samples, the other carbonyls being present in some, but not all, samples. Formaldehyde and acetaldehyde, at mean levels of 275 and 126 ppb, were the most abundant. The pattern of emissions differed to that of the hydrocarbons, with Chinese charcoal the worst emitter.
The mean levels of nearly all of the compounds tested were below the permissible exposure levels (PELs) for short-term exposure set by the US Occupational Safety and Health Administration (OHSA). The exception was formaldehyde, for which 11 of the 16 samples exceeded the PEL.
The VOC and carbonyl content will be dependent upon the type of wood used to manufacture the charcoal and the presence of other constituents. For instance, vegetable wastes, paper mill residues and scrap wood from furniture or wood flooring are often employed. In addition, coal dust is added as a heat source, along with sodium nitrate to improve ignition and lighter fuel in quick-light brands.
Bearing in mind the acute irritation caused by low levels of formaldehyde and acetaldehyde, and the carcinogenicity of aldehyde, the researchers recommended the introduction of controls on the use of barbecue charcoal to reduce potential health risks. This is especially the case for charcoals produced from improper materials, such as furniture or wood panelling, which may have been painted or lacquered and will release extra pollutants upon combustion.
Related links:
* Journal of Hazardous Materials 2010, 174, 492-499: "Barbecue charcoal combustion as a potential source of aromatic volatile organic compounds and carbonyls"
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