Rice studies highlight inconsistent arsenic standards

Measurements of potentially dangerous amounts of arsenic in rice show food regulations in the EU and US are outdated and lag far behind the stricter controls on arsenic in water, say UK chemists.   

In studies that made media headlines this month, researchers led by Andrew Meharg at the University of Aberdeen, UK, found what they called ’concerning’ levels of arsenic in pre-cooked baby rice and in rice milk.[1,2] The findings were the latest in a series of analytical studies on rice, which readily takes up poisonous inorganic arsenic compounds - such as arsenates and arsenites - from water and soils.   

It is not clear how much inorganic arsenic is acceptable in food. The UK Food Standards Agency (FSA), for example, has found the same or higher doses of arsenic in rice for decades, yet says that there is no need for concern for the average consumer. ’At the current time there is insufficient evidence to indicate an immediate need to increase arsenic standards in foods,’ says Richard Loeppert, a crop sciences expert at Texas A&M University, US. 

Meharg agrees that most adults probably don’t need to worry but thinks people who eat lots of rice may be at risk. He points out that a baby eating one serving of rice a day takes in more arsenic, per kilogram of body weight, than an adult exposed daily to the maximum allowed levels of arsenic in drinking water. But though there are tough controls on arsenic in drinking water, where it’s known that long-term exposure can cause cancer, no agency has called for matching rules for food. 

’We seem to have thrown the precautionary principle out of the window on this one. EU and US food regulations on inorganic arsenic are non-existent,’ Meharg says. 

Differing standards

International regulations on arsenic in food are certainly haphazard. The World Health Organization established a provisional tolerable weekly intake of arsenic from the diet in 1988 - but when the FSA reviewed this in 1993, an independent committee could find no reason for the level that had been chosen.   

So the UK’s arsenic food regulations are still the same as those set in 1959, long before inorganic arsenic was shown to be a potent carcinogen. In 2006 China enforced its own stricter arsenic standards specifically for rice - but neither the FSA nor the US Department of Agriculture understand the rationale for this decision either. Some of the rice samples examined by Meharg and the FSA would fail the Chinese standards. 

Without clear regulations to work from, the FSA thinks it has got dietary exposure to arsenic as low as reasonably practicable, explained an FSA spokesman. 

’Nevertheless it would be desirable to bring this down further and we are commissioning further research on the levels of arsenic present in rice and rice products. We have started discussions at the EU level on legislation for maximum levels of arsenic in food in order to harmonise standards of food safety,’ the FSA says.   

The slow progress irritates Meharg. ’By switching rice sources, you could cut inorganic arsenic in baby rice to a fifth of its present level right now,’ he says. Long-term arsenic reduction plans are also being studied - including selectively breeding arsenic-poor rice varieties.   

According to the FSA, another difficulty is that it is hard to measure levels of arsenic species reliably - especially when methods must be validated to work across many laboratories. ’Inorganic arsenic is not an easy analyte to look for,’ agrees chemist Erik Larsen, who works at the National Food Institute, Technical University of Denmark. His team are starting an EU-funded project to establish analysis methods for inorganic arsenic, based on atomic absorption spectroscopy. Meharg and his colleague Jorg Feldmann think the analysis is not difficult - and point out that chemicals currently regulated in food, such as dioxins and methyl mercury, require similar analytical sophistication. 

Unfair reports

While inorganic arsenic in food is grabbing the headlines, analytical chemist Kevin Francesconi, of the University of Graz, Austria, cautions that the effects of other arsenic compounds are unknown. Though fish contains much more arsenic than rice, it’s viewed as harmless because its greatest arsenic component, arsenobetaine, is rapidly excreted by the body. Francesconi says seafood can contain other organic arsenic compounds whose toxicity is unknown.[3] He has recently identified new arsenic-containing fatty acids in cod-liver oil.   

Working out the toxicity of organic arsenic species in foods is a long but necessary slog, Francesconi thinks. Otherwise, he says, doubts over arsenic in foods will remain unresolved, and ’recurrent reporting of foods "discovered" . to be high in arsenic . would be continually and unfairly damaging for products and of no tangible benefit to the consumer’. 

Richard Van Noorden

This article is a preview from the June 2008 edition of Chemistry World magazine