High Level Arsenic Found In US Rice

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Rice grown in the USA has low levels of arsenic. But those levels are up to five times higher than those found in rice grown in Europe, India and Bangladesh, says a report in the August edition of Environmental Science and Technology.

Researchers from the School of Biological Sciences at the University of Aberdeen in Scotland found an average of 0.26 micrograms of arsenic per gram of U.S. rice. By contrast, Indian basmati rice had 0.05 micrograms per gram. (There are 1 million micrograms per gram of rice and about 16 grains of short-grained rice in one gram.)


Researchers calculated that of those 0.26 micrograms of arsenic in U.S. rice, 42% were an inorganic form that is potentially harmful. While these are tiny amounts, arsenic levels are monitored because long-term intake is associated with increases in some cancers. Low doses are not known to cause acute illness.


Despite its poisonous reputation — it is deadly in very high doses — arsenic is a naturally occurring chemical in soil. It can also cme from pesticides. However, researchers don't yet know why levels in the U.S. are as high as they are.


The results are surprising because Bangladesh struggles with severe arsenic-contaminated ground and irrigation water. Arsenic levels as high as 0.95 micrograms per gram of rice have been reported there in the past, the researchers wrote.
Someone eating a "subsistence" diet of 4½ cups of cooked U.S. rice a day — not an unco_mmon amount in Asia — would most likely be taking in more arsenic than reco_mmended by the World Health Organization, the researchers say.


But other scientists dispute the findings. While the Scottish team bought seven samples of rice in supermarkets in Aberdeen, Cornell University scientists tested 25 samples and found arsenic levels of 0.18 micrograms per gram of U.S. rice. In Bangladesh rice, the Cornell team found 0.35 parts per billion arsenic.


The average American only eats about one ounce of uncooked rice a day or a little more than half a cup of cooked rice, says John Duxbury, a professor of soil chemistry at Cornell University. That puts U.S. arsenic intake far below WHO standards, he says. "So it's pretty clear that we probably don't have a problem."


Rice is the agricultural product most likely to contain high levels of arsenic because it's grown in flooded paddies. That watery, oxygen-free environment causes naturally occurring arsenic in the soil to be freed and thus more readily taken up by the plant, Duxbury says.

The Aberdeen sample isn't large enough to be scientifically valid, says David Coia of the U.S. Rice Foundation, a producers group. "There's been no incident (in which) arsenic and rice have led to any reported human health problem."




Rice grown in the United States contains an average of 1.4 to 5 times more arsenic than rice from Europe, India and Bangladesh, according to a survey of grains from around the world.


This means that people eating a 'subsistence' diet of 500 grams of dry American rice a day are probably consuming more than the maximum intake of arsenic provisionally reco_mmended by the World Health Organization (WHO), says Andrew Meharg, a biogeochemist from the University of Aberdeen, UK, and a member of the survey team.

Although no one knows whether this level and type of arsenic is dangerous, Meharg himself has decided to stop eating American grains.

"When we're all paranoid about what's in our food, the question to ask is, 'Would you like your rice to be grown on arsenic contaminated soil?'," he says.

Low doses of arsenic such as these do not cause acute illness. "It's more about long term intake that can elevate levels of cancer," says Meharg. Research in Taiwan has linked arsenic-contaminated rice to an increase in bladder cancer, for example1.

Poison legacy

The survey team thinks that the contamination is a legacy of cotton farming, which relies on arsenic-based chemicals to kill boll weevils and to remove plants' leaves before harvest. Quite a lot of land in Mississippi and Arkansas that previously grew cotton is now used for rice cultivation, says Meharg.


When rice was first grown in these soils, the crop often failed owing to an arsenic-induced disease known as straighthead. So new, straighthead-resistant rice varieties were bred that could withstand the arsenic.

However, this means that they are more likely to accumulate arsenic in apparently healthy grains, says Meharg, who is now calling for change in farming methods. "I don't think they should be growing rice on old cotton fields," he says.

Of the rice eaten in the United States, the vast majority is home-grown. About half of all US-grown rice is exported.


Gram for gram


Meharg tested rice bought from markets in Aberdeen that had been grown in America, Europe, India, and Bangladesh. He found an average of 0.26 micrograms of arsenic in each gram of US rice. Indian rice hit a low of 0.05 micrograms per gram, whereas Bangladesh, which has had recurring problems with arsenic contamination owing to naturally high levels of the poison in groundwater, and Europe had about 0.15 micrograms per gram. The results are published in Environmental Science and Technology2.

John Duxbury, a soil chemist at Cornell University in Ithaca, New York, points out that there are still many gaps to fill in before we will know whether an overdose of US rice might be bad for you. "The work is fine as far as it goes, but you can't draw broad conclusions from such a limited survey," he says.

Others point out that there is no epidemiological evidence that anyone with a high rice diet, such as those of Asian descent, for example, is experiencing ill effects. "There simply are no known negative health issues with US rice," David Coia, spokeman for the USA Rice Federation in Washington DC.


All tied up

The rice may not be particularly toxic, because of the form that the arsenic takes in the plants. Health effects are diminished if the arsenic atoms are bound up with carbon-based molecules. Inorganic arsenic (the form found in drinking water) is estimated by Duxbury to be five to ten times more toxic.

Meharg found that just 42% of arsenic in US rice was inorganic, co_mpared with 81% of arsenic in Indian rice. But Meharg points out that organic arsenic can still cause problems3, and could convert into the inorganic form in the body4.

The health effects of arsenic in food are hard to verify because the increase in cancer risk is small. Meharg estimates that if 10,000 people were exposed to the WHO limit over their lifetime, this would result in an extra 92 cases of bladder cancer.

Given the uncertainties, regulations are few. Even the WHO has not ratified its provisional guidelines. Australia is the only country that has a safety limit for arsenic in food.



Under review


There are a few different types of arsenic pesticides and herbicides licensed for use in the United States. All are undergoing safety reviews at the moment, says Enesta Jones, a spokeswoman for the Environmental Protection Agency, and decisions are planned for next year.

Duxbury cautions that arsenic in US rice might co_me from natural, geological sources. It may be that the arsenic in pesticides is in a form that is harder for the plants to take up, he adds, which could lower concerns about the chemicals themselves.

Although Duxbury doesn't share Meharg's health concerns, he says the work serves as a good base from which to work out how crops can be contaminated. This could help to breed plants that tend not to store arsenic in an inorganic form, he suggests. "There's potential for a lot of follow up from this."


Source: USA Today and Nature.co_m