In drinks, the combination of sodium benzoate or potassium benzoate (212) and ascorbic acid (vitamin C, both naturally occurring and the additive 300) can result in the formation of benzene, a known carcinogen. Heat or light during transport or storage can boost the amount of benzene formed.
FSANZ tested 68 flavoured drinks, including flavoured mineral waters, cordial, fruit juice and fruit drinks, and found 38 of the samples contained trace levels of benzene. While the majority had benzene levels below WHO guidelines for drinking water (10 ppb — parts per billion), a number contained levels of 1 ppb and above — up to 40 ppb. 1 ppb is the reference level for benzene in Australia’s more stringent drinking water guidelines.
Additionally, the most recent national diet survey found that young children who have lots of drinks that contain a form of benzoate (non-cola soft drinks, orange juice and cordial, for example) could be exceeding the acceptable daily intake (ADI) for benzoates.
The food preservatives sodium nitrite (250) and sodium nitrate (251) — typically found in processed meats — are both listed as "probably carcinogenic to humans" by WHO’s International Agency for Research on Cancer, because they can be converted to cancer-causing nitrosamines in the stomach. Nitrosamines can increase the risk of gastric cancer, although this risk is small. In processed foods, however, sodium nitrite and nitrate prevent the growth of bacteria that cause botulism poisoning, which can be deadly.
Calcium propionate (282) prevents mould growth on bread and is most heavily used in humid, tropical areas. It’s been linked to migraines and behavioural and learning problems, but reports are largely anecdotal.
Wine and dried fruit
Preservatives that contain sulphur (220-228), including sulphur dioxide (220), which is used in wine and dried fruit, can trigger asthma attacks. The most recent national diet survey found that young children who eat lots of foods that contain sulphites, such as dried apricots, sausages and cordial, could be exceeding the ADI for sulphites.
Additional exposure to benzene in food and drink products may be small when compared with breathing air that contains benzene from traffic pollution or tobacco smoke, but it’s unnecessary. So it makes sense to avoid drinks that contain benzoates and ascorbic acid.
The benefit of adding nitrites and nitrates to food far outweighs the risk they present. Even so, the WHO advises us to "moderate consumption" of preserved meat (including sausages, salami, bacon and ham).
Sulphur dioxide should be avoided by people who have asthma.