A chemical health story that has been bubbling for several years came to a head earlier this year, as consumers learned that their soft drinks could be contaminated with levels of benzene far higher than national and international drinking water standards allow.

According to food and drinks authorities in the UK, Germany, and elsewhere, numerous products were found to contain higher than recommended levels of benzene. Indeed, on March 31^st, the UK's Food Standards Agency (FSA) published results showing that some 4 of 150 soft drinks available in the UK contained benzene at higher than World Health Organization (WHO) acceptable levels. In other words, benzene was not detectable in the majority of products sampled. An FSA spokesman explained that while the levels of this putative carcinogen are very low, it is prudent for the sake of public confidence that products that contain more than the acceptable level suggested by the WHO should not be sold.

Ironically, the source of the benzene is thought to be a product of the reaction between vitamin C (ascorbic acid or ascorbate salts) with salts of benzoic acid added as a preservative to many soft drinks. The reaction occurs to different degrees depending on length of exposure of the product to heat and light. Ironically, certain fruits, such as cranberry, contain benzoate naturally, but are very low in natural vitamin C. As such, cranberry drinks often contain added vitamin C.

However, while this issue has reached the attention of the public only recently, the industry was allegedly first made aware of a potential problem with benzoate and ascorbate preservatives in their products in the early 1990s. The US Food and Drug Administration is thought to have alerted manufacturers but it seems that it did not insist that the industry address the problem and it has apparently persisted ever since.

The effects of low level but chronic exposure to benzene on human health are not clear, however, the Environmental Protection Agency errs on the side of caution and requires public notification of water supply contamination when levels reach just 5 parts per billion. Levels of benzene in soft drinks have been found at 10-20 ppb. According to the EPA, "relatively short periods" of exposure can produce "temporary nervous system disorders, immune system depression [and] anemia." It is long-term exposure that worries the EPA most as laboratory tests reveal "chromosome aberrations [and] cancer." There is also the much wider context of "background" benzene sources, such as vehicle fuels and exhausts, and cigarette smoke, to which a lot of people are exposed on a daily basis, which may have an effect on total exposure.

According to Cambridge University chemist Jonathan Goodman, one would have to drink almost a litre (800 ml) of soft drink containing five times the WHO limit to match exposure from a single car journey. And even then, Jacob Zabicky of Ben Gurion University, Israel, is on record as explaining that benzene's relative solubility in water and its volatility would suggest that once opened, most of the benzene present in a can of soda should be lost with the fizz.