Dufault had discovered levels of mercury ranging from 0.005 to 0.570 micrograms (mcg)/g of HFCS and, as the average daily consumption of the sweetener is around 50 g in the US, consumers are very likely - and unwittingly - ingesting every day up to 28.5 mcg of mercury, the most toxic metal known to man.

As the standard 20-oz bottle of Coca-Cola contains around 17 teaspoons' worth of HFCS, it's easy to see why processed snack foods and soft drinks are easily a far higher source of mercury than are fish (Environmental Health, 2009; 8: 2; doi: 10. 1186/1476-069X-8-2).

But how did the mercury get into the HFCS amples in the first place? Although its advocates describe HFCS as 'natural' and even 'organic', it's nothing of the sort. While other sweeteners are based on cane and beet sugar, HFCS is a derivative of corn starch-and it comes about only as a result of various industrial processes.

In 1957, scientists discovered an enzyme that could convert the glucose in corn syrup into fructose, a process that was finally perfected only in the 1970s, thereby paving the way towards mass production of HFCS.

The process involves several steps and three different enzymes, and the result is a syrup with a 90-percent fructose content. This is then blended down with untreated, glucose-only syrup into a mix that is either 42-per-cent or 55-per-centfructose.

Around 50 processing plants around the world, including eight in the US and three in the UK, are currently producing HFCS. And some of these plants-more correctly known as 'industrial chlorine' or 'chlor-alkali' plants - still use caustic soda (sodium hydroxide) in the manufacture of HFCS, although it's an outmoded form of manufacturing and some plants have replaced it with safer technology. Other food ingredients, such as citric acid, are also manufactured at these plants.

The caustic soda is referred to as 'mercury-grade' or 'rayon-grade', which indicates that these plants are reliant on mercury for part of the process. Astonishingly, the plants regularly report that some of the mercury mysteriously disappears. In the year 2000, for example, the four plants in the US that still use caustic soda each reported an unaccountable loss amounting to around seven tons of mercury.

What's more, the three UK plants report a similar story, although the environmental lobby group Oceana believes that the mercury loss isn't so mysterious, and that it's pumped out into the air and into the general water supply.

In fact, according to the group's report Poison Plants, published in January 2005, these three plants are responsible for a third of all mercury emissions in the air and nearly half of all emissions in the water supply of the UK.

Nevertheless, the release of mercury into the environment accounts for only a mere fraction of the total mercury 'lost'. In 2003, nine of the mercury-using plants around the world reported that eight tons of the stuff had been emitted into the air and water supply. Nevertheless, they still could not explain the disappearance of a further 30 tons to the US Environmental Protection Agency for its 2003 report [68 FR (Federal Register) 70904].

In light of these facts, it's not an enormous leap of imagination or judgement to suspect - given such cavalier safety procedures - that some of the so-called missing mercury may well be getting into the HFCS itself, as Dufault and her colleagues discovered.

Snacking on Mercury
Alerted by Dufault and her colleagues' findings, Dr. David Wallinga and other researchers at the Institute for Agriculture and Trade Policy (IATP), an independent lobby group based in Minneapolis, MN, went out and bought a range of commonly consumed soft drinks and snack foods sweetened with HFCS, and tested them for mercury.