Friday, December 17, 2010

Alternate wetting and drying of rice paddies in Bangladesh cuts arsenic contamination

Janet Pelley in Chemical & Engineering News: Rice is the staff of life for millions of Bangladeshis, but it could also damage their health. The well water drawn for irrigating rice in Bangladesh is naturally high in arsenic, a carcinogen with no safe dose. Now a study shows that a simple farming practice promoted to save water could also help cut exposure to arsenic (Environmental Science & Technology (DOI: Environ. Sci. Technol., DOI: 10.1021/es102882q).

Rice usually grows in perpetually flooded fields that provide a reducing and anoxic environment. In such an environment, arsenic becomes bioavailable and gets released from the soil. Plants can then readily take it up. Rice in a typical Asian diet can lead to daily arsenic exposures equivalent to drinking 2 L of water that is at or above the World Health Organization's limit for arsenic of 10 µg/L. Researchers have found that growing rice on dry fields cuts arsenic levels in the grains by 90% but also slashes yields.

A different farming method has been catching on fast in Bangladesh as a way to save water. In it, farmers irrigate their fields and then wait up to 10 days to let their paddies dry out before irrigating again. Stephan Hug, an aquatic geochemist at the Swiss Federal Institute of Aquatic Science and Technology, and colleagues in Switzerland and Bangladesh wondered if intermittent irrigation could also lessen plant exposure to arsenic….

Drying rice in the sun in Bangladesh, shot by Shahnoor Habib Munmun, Wikimedia Commons, under the Creative Commons Attribution 3.0 Unported license

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