At one time it was used as an aftershave because of its sweet smell.聽聽It was even used to decaffeinate coffee.聽聽Oh my, how times change!聽聽Today we worry about a few parts per billion of benzene in our drinking water, in our soft drinks, in our antiperspirants or sun protection products.聽聽Why?聽聽Because benzene is an established carcinogen and should be avoided.聽聽But benzene also happens to be one of the building blocks of our society.聽聽Traces of it are everywhere.聽聽Given that eliminating benzene from the environment is impossible, what we need is a reasonable risk analysis.聽聽That鈥檚 quite a challenge, but let鈥檚 give it a shot.聽
Not all appearances of benzene are due to human activity.聽聽It is one of the numerous compounds formed when organic matter decomposes, and therefore it can be found in petroleum.聽聽It also forms when organic matter burns, so volcanoes and forest fires produce benzene.聽聽So does burning coal.聽聽In fact Michael Faraday, the brilliant English chemist, first isolated benzene from 鈥渋lluminating gas鈥� in 1825.聽聽Back then combustion of coal or peat produced the gaslight that illuminated homes and streets.聽聽The molecular structure of benzene, though, remained a mystery for some forty years.聽聽Chemists could not figure out how the six carbon atoms and six hydrogens that made up benzene were joined together.聽聽At least not until August Kekule supposedly had a dream in which a snake seized hold of its own tail.聽聽This vision led him to suggest a structure for benzene in which the six carbons were joined in a ring.聽聽Kekule may have dreamt of a structure for benzene, but he could have hardly imagined the role this compound would play in building the industrialized world.聽
Today benzene is produced in huge amounts by various processes that rely on petroleum as a feedstock.聽聽It serves as the raw material for making plastics such as nylon, polystyrene and polycarbonate, as well as adhesives, detergents, dyes, insecticides, synthetic rubber, explosives and drugs.聽聽Without a doubt, benzene makes our life easier, but does it also make it shorter?聽聽聽
The first hint of potential health problems appeared when workers exposed to benzene vapours complained of dizziness, headaches, tremors and even delirium, all symptoms of neurotoxicity.聽聽This led to the implementation of measures to reduce benzene exposure in the workplace, but lingering concerns about long-term exposure to small amounts remained.聽聽And it turned out that these concerns were justified because epidemiological studies eventually revealed a higher rate of leukemia in workers who inhaled benzene over a period of many years.聽聽The connection is not an overwhelming one, it is estimated that since 1928 when the association was first noted, there have been about 150 cases of leukemia worldwide that can be linked to occupational benzene exposure. Estimates are that breathing workplace air at a level of 50 ppb over a 40-year career will result in an increased risk of leukemia.聽
Most of us don鈥檛 have to worry about occupational exposure.聽聽But what is the risk associated with benzene that shows up in our food and drink and in the air that we breathe?聽聽In theory, no amount of a carcinogen is safe, because a single molecular insult to DNA can lead to cancer.聽聽But in practice, elimination of the numerous carcinogens to which we are exposed, both natural and synthetic, is impossible.聽聽In the case of benzene, most authorities have set a maximum allowable level in drinking water of 5 parts per billion (ppb).聽聽This is not because amounts in excess of this are known to be a health hazard, it is because water treatment systems cannot realistically be expected to reduce levels below 5 ppb.聽聽聽
Now let鈥檚 put some numbers into the benzene-cancer equation.聽聽We have two sources of information, human exposure data and animal feeding studies.聽聽When workers are exposed to less than 0.1 parts per million (ppm) of benzene in the air, there is no evidence of increased risk of leukemia.聽聽Since we know the average human inhales about 20 cubic meters of air a day, this translates to exposure to 6 milligrams a day.聽聽Animal feeding studies have confirmed that at such doses there is no increased cancer risk.聽聽So how much benzene are we exposed to?聽聽When it comes to beverages, the issue is the reaction of sodium benzoate, a preservative, with vitamin C, which is present in many drinks.聽聽It seems clear that in the presence of trace amounts of metals that catalyze the reaction, vitamin C produces free radicals that can convert benzoate into benzene.聽聽That鈥檚 why some beverages have been found to contain as much as 50 ppb of benzene, ten times what is allowed in drinking water!聽聽But when we make the calculation, we find that a litre of such a drink contains 50 micrograms of benzene, which means that even at an impossible consumption rate of 120 litres a day, we would be below the amount that has no effect on occupational workers.聽
Of course, soft drinks are not our only exposure to benzene.聽聽When the U.S. Food and Drug Administration carried out a survey of 70 foods over five years, benzene was found in every item except for American cheese and vanilla ice cream.聽聽A hamburger, for example, has 4 micrograms, but this is only one-tenth of the amount of benzene in the smoke inhaled from a cigarette.聽聽A banana can harbour up to 20 micrograms.聽聽When you use a deodorant spray or sun protection aerosol you may produce a temporary cloud that contains 28 ppb of benzene. Still, when all exposures are added up, we are well below the levels that have been linked with leukemia.聽聽聽
Is the risk zero?聽聽No.聽聽In some unlucky person, a trace of benzene may start a cascade of events that leads to cancer.聽聽Therefore all efforts should be made to minimize exposure to carcinogens, particularly in the workplace, but traces of benzene in soft drinks do not appear to be a serious risk聽聽In any case, these can be eliminated by switching to preservatives other than sodium benzoate.聽聽As far as personal care products go, not all deodorants or sunscreens contain benzene so it is certainly possible to produce these without benzene as a contaminant.聽
If you want to worry about something, worry about the lack of nutrition in soft drinks.聽聽Or about the benzene you鈥檙e inhaling (20 micrograms) when you鈥檙e pumping gas or inhaling city air (25 micrograms per hour) or smoking a cigarette which can expose you to 3,000 micrograms a day.聽 The bottom line here is that manufacturers and food producers should do their best to reduce levels of benzene in their products but in the grand scheme of risks, non-workplace exposure to benzene does not rank very high.
