What's your poison?

Thursday, 17 September 2015

I'm reading a really interesting book at the moment by Kathryn Harkup called A is for Arsenic: The poisons of Agatha Christie. It's a fascinating insight into Christie's life, both as a chemist and as an author and is peppered with facts about various toxins and the murderers who used them, both in her novels and in real life.

Reading the chapter on arsenic reminded me of this story of great problem solving:

Arsenic is a real problem for countries where there are large deposits in the soil and where rice is a staple of the population's diet. Like many toxins, it accumulates in the body and will eventually cause sickness and, if levels get high enough, death.

So how do you remove arsenic from rice without expensive lab equipment?

Get a coffee machine.

The standard method for making rice — boiling it in a pot until it soaks up all the liquid — binds into place any arsenic contained in the rice and the cooking water. Andrew Meharg, a plant and soil scientist at Queen’s University Belfast, UK, wondered whether cooking the grain in a different way might help to lessen the health risk.

On the basis of earlier work, Meharg and his colleagues knew that arsenic levels drop when rice is thoroughly rinsed and then cooked in an excessive amount of water. The method helps even when the cooking water contains arsenic.

Meharg and colleagues found that using this method with increasing proportions of water removed progressively more arsenic — up to a 57% reduction with a ratio of 12 parts water to one part rice. That result confirmed that the arsenic is 'mobile' in liquid water, and thus can be removed.

The team then cooked rice in an apparatus that continually condenses steam to produce a fresh supply of distilled hot water, and in an ordinary coffee percolator with a filter, which allows cooking water to drip out of the rice. Testing the rice before and after cooking showed that coffee-pot percolation removed about half the arsenic, and that the lab apparatus removed around 60–70%.  In some cases, the technique removed as much as 85% of the substance, depending on the type of rice used.

Meharg does not expect people to start cooking rice in their coffee machines. “We just took something that’s in everybody’s kitchen and applied it to show a principle,” he says. He sees the research as a proof of concept that could feed the development of simple, inexpensive rice cookers that can lower arsenic concentrations.

The same technique could also help companies elsewhere to lower arsenic levels in baby cereals and other products that use pre-cooked rice. Rice-based baby foods often contain high levels of arsenic, a double-whammy for small children, who consume proportionately more of the substance for their body size.

In the long term, the best strategies for removing arsenic from rice will come from ongoing efforts to breed low-arsenic strains and alter growing techniques, says Margaret Karagas, an epidemiologist at Dartmouth College in Hanover, New Hampshire. But, she says, “This is really interesting because it is offering a short-term solution to the problem. It’s giving people an opportunity to reduce the arsenic burden of their rice.”

Source: Nature.com

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