Benzene in soft drinks

Benzene in soft drinks is of potential concern due to the carcinogenic nature of the benzene molecule. This contamination is a public health concern and has caused significant outcry among environmental and health advocates. Benzene levels are regulated in drinking water nationally and internationally, and in bottled water in the United States, but only informally in soft drinks. The benzene forms from decarboxylation of the preservative benzoic acid in the presence of ascorbic acid (vitamin C) and metal ions (iron and copper) that act as catalysts, especially under heat and light.

The major cause of benzene in soft drinks is the decarboxylation of benzoic acid in the presence of ascorbic acid (vitamin C, E300) or erythorbic acid (a diastereomer of ascorbic acid, E315). Benzoic acid is often added to drinks as a preservative in the form of its salts sodium benzoate (E211), potassium benzoate (E 212), or calcium benzoate (E 213).Citric acid is not thought to induce significant benzene production in combination with benzoic acid, but some evidence suggests that in the presence of ascorbic or erythorbic acid and benzoic acid, citric acid may accelerate the production of benzene.

The proposed mechanism begins with hydrogen abstraction by the hydroxyl radical, which itself is produced by the Cu²⁺-catalysed reduction of dioxygen by ascorbic acid:

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