Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: thedoc on 26/06/2015 21:50:01
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Russ Madden. asked the Naked Scientists:
I am trying to find out how many chemicals there are in tobacco smoke, there are a lot of different answers coming up. I discovered on your website, Laura Goss's question about thousands of chemicals in tobacco smoke which made me ponder, how many chemicals are there in one of those lovely open log fires that we find so attractive when visiting a pub in winter. One can immediately smell the presence of a log fire when entering the draughty old pub, the smoke obviously lingers. Now in those very pubs the law states that 'smoking' is illegal, should this ban also apply to those delightful open fires, I am guessing that it is only the nicotine that is significantly absent and that the law has missed a trick.
What do you think?
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There are probably a similar number of chemicals in a log fire as there are in tobacco smoke.
But I expect the ratios to be rather different, as the log fire operates at a very high temperature, burning most of these chemicals to carbon dioxide, plus oxides of nitrogen, sulphur and hydrogen (water). Most of this goes up the chimney, with a some ash left in the bottom of the fireplace.
Compare that with smoking a tobacco cigarette (or, worse, a hand-rolled "reefer" with no filter). The hot gases pass through the dried leaves, volatilising the chemicals and partially burning them. Instead of pumping this noxious mixture up a chimney, you suck it into your lungs, along with some of the ash that makes its way through the filter (if there is a filter).
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A few points:
(1) There are many variables that contribute to the "number of chemicals" in smoke: the composition of what is being burnt, the amount of air that is available to burn it, and the temperature at which it is burnt are probably the most important. The diversity and ratio of elements in the material being burnt will necessarily be retained in the diversity and ratio the elements that end up in the smoke and ash (no atoms are destroyed in the process of combustion, so if there is arsenic in the wood, there will be arsenic in the smoke). If the temperature is very high, and there is plenty of oxygen for the fire to burn with, there would not be much smoke, and the gaseous products should be a fairly simple mixture of H2O, CO2, NOx, SO2 and various oxides of other elements (could still be dozens of chemicals).
At lower temperatures where smoke is produced, I would not be surprised if there were millions (or more) of distinct compounds produced. Some of the nasties to be aware of are polycyclic aromatic hydrocarbons (PAHs), many of which are known carcinogens, fine particulate matter (mostly carbon soot and simple metal oxides like potassium oxide), dioxins (which are formed if there is enough chlorine or chloride around), and if there is not enough oxygen for them to be converted to carbon dioxide, formaldehyde and carbon monoxide...
(2) The number of chemicals in something doesn't really correlate very well with how dangerous that something is. The identities and amounts of the components are what really matter. Your body, and any fairly unrefined food you eat likely contains billions, if not trillions, of different compounds (actually, the refined foods that contain far fewer compounds, are more likely to be unhealthy, because they contain very high concentrations of those few compounds, and as good as sucrose or fructose taste, in high enough doses, they are not so healthy...)
(3) There are significantly higher concentrations of nitrosamines (really bad for you) in cigarette smoke, as well as hydrogen cyanide (only slightly more poisonous than nicotine on a mass basis) and oxides of nitrogen. These are all due to the fairly high concentrations of nitrogen in tobacco, so when it gets burnt, there are more nitrogen-containing products in the smoke.
(4) I can't imagine the smoke from a fireplace is very good for humans (that's one reason we have them outside or use chimneys). Actually one of the first reported instances of occupation-related cancer was in chimney sweeps (https://en.wikipedia.org/wiki/Chimney_sweeps%27_carcinoma).
(5) Ultimately, I bet that if you smoked a pack of sawdust-filled cigarettes a day, the health effects would not be all that dissimilar from smoking cigarettes at the same rate...
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(4) I can't imagine the smoke from a fireplace is very good for humans (that's one reason we have them outside or use chimneys). Actually one of the first reported instances of occupation-related cancer was in chimney sweeps (https://en.wikipedia.org/wiki/Chimney_sweeps%27_carcinoma).
I seem to remember a campaign by either Oxfam or Save the Children to replace wood burning stoves in huts in Africa. These huts are poorly ventilated and there is a high mortality rate from cancer among mothers cooking over these fires.