Arsenic contamination of groundwater is a major public health problem — threatening the health of millions — in Bangladesh, and high concentrations are also found in drinking water in China, India and parts of South-East Asia.
The toxin is also present in rice and vegetables in parts of Bangladesh (see Tainted wells pose food threat in Bangladesh). But until now, researchers did not know what process led to some plants being contaminated by arsenic and others not.
The Chinese researchers, led by Zhu Yongguan, of the Research Centre for Eco-Environmental Sciences at the Chinese Academy of Sciences, showed that when rice grows in flooded fields, iron deposits — clearly visible as a reddish coating — can form on their roots.
Zhu's team showed that arsenic builds up in the iron deposits, becoming trapped there. The deposits therefore help protect rice plants from arsenic contamination. The scientists found that depending on the rice variety, significantly different amounts of arsenic are trapped in this way.
The researchers also showed that more iron deposits form when phosphorous levels in soil are low. "[This] implies that if a low-phosphorus chemical fertiliser is used, more arsenic may be blocked from moving to rice seeds," says Zhu.
The Chinese scientists have teamed up with colleagues at the University of Aberdeen, United Kingom, to develop arsenic-resistant rice varieties. The researchers will need to assess whether these varieties also have high yields.
Zhu says recent research by Tapash Dasgupta, in India, may help them in their efforts. Dasgupta revealed that a single gene controls root characteristics that affect arsenic uptake, such as growth rate and length.
Arsenic contamination of water or food can lead to serious health problems — ranging from skin lesions to a variety of cancers. The World Health Organisation says contaminated drinking water alone could kill 270,000 Bangladeshis during the next decade.
Research led by Andrew Mehard at the University of Aberdeen, suggests that even for people whose drinking water is moderately contaminated, tainted rice could be the dominant source of arsenic exposure.