Irrigation may produce arsenic-tainted rice in Bangladesh

December 09, 2002

The arsenic that has contaminated much of Bangladesh's drinking water supply is also getting into its rice, according to a new study. Irrigating rice fields with tainted well water could be jeopardizing the country's staple food, which provides more than 70 percent of the population's daily intake of calories.

The findings will appear in the Jan. 15 print edition of Environmental Science & Technology, a peer-reviewed journal of the American Chemical Society, the world's largest scientific society. The article was initially published Nov. 20 on the journal's Web site.

Shallow wells, known as tubewells, are commonly used in Bangladesh to avoid the region's surface water, much of which contains bacteria that can cause waterborne diseases. Beginning in the 1970s, international aid organizations dug millions of tubewells, and the program was basically successful in providing bacteria-free water. But officials soon found that the tubewells were reaching groundwater containing high levels of arsenic.

The World Health Organization has called the tubewell crisis in Bangladesh the largest mass poisoning of a population in history. WHO predicts that as many as 270,000 may die from drinking arsenic-contaminated water in the Ganges Delta region.

"There has been a considerable research effort on the effects of drinking arsenic contaminated water in Bangladesh," says Andrew Meharg, Ph.D., a biogeochemist at the University of Aberdeen in Scotland and lead author on the paper. "However, the tubewell water is not just used for drinking water, it is also used for irrigation."

Farmers in Bangladesh use tubewell water for irrigation so that rice can be grown during all six months of the dry season. If the arsenic that is building up in the soil from irrigation moves into rice crops, Meharg says, the exposure of people to arsenic in Bangladesh will be much greater than previously thought.

Meharg and his colleagues took 71 soil samples from 27 districts throughout Bangladesh and collected rice grains from various regions. "We've shown that rice collected from the areas of Bangladesh with the most contaminated fields have arsenic levels 10-fold higher than rice from uncontaminated areas," Meharg says. They calculated that rice could be the main source of arsenic for people in these highly contaminated areas.

Three of the Bangladesh rice samples contained more than 1.7 milligrams of arsenic per kilogram of rice. Arsenic is a slow poison; studies have linked long-term exposure to several types of cancer, according to the U.S. Environmental Protection Agency.

While there is currently no international standard for arsenic levels in food, WHO advocates a maximum arsenic level in water of 10 micrograms per liter, which is the standard currently used by the EPA. But many developing countries still use a standard of 50 micrograms per liter.

"These findings cause considerable concern and suggest that ingestion of rice is a major source of arsenic exposure in Bangladesh and elsewhere in regions with subsistence rice diets," the researchers write. A number of countries in the region have similar problems with tubewell contamination. Two areas --Vietnam and West Bengal, India -- are particularly likely candidates for finding arsenic in rice, Meharg says.

This study comes on the heels of another recently published Environmental Science & Technology research paper about arsenic in southern Asia. Researchers studied tubewells in Bangladesh and West Bengal, India, and found that the arsenic test kits used by field workers are frequently inaccurate, producing scores of incorrectly labeled wells. [Ed. note: A press release about the arsenic test kits can be viewed at ACS News Service site.]
-- Jason Gorss

American Chemical Society

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