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Experts detail how rice absorbs arsenic from the soil

(18.07.2008)


Background:
Arsenic occurs naturally in the environment and also is used as a pesticide, wood preservative and feed additive for swine and poultry. Human exposure to arsenic, like in drinking water, has been linked to cancers of the lung, bladder and skin, numbness, cardiovascular disease and diabetes. Arsenic poisoning is especially serious in places such as Bangladesh and West Bengal in India, where arsenic-contaminated groundwater is used for irrigating rice crops, resulting in arsenic accumulation in soils and grain.

Results of a new study:
In a recent scientific achievement, researchers in Japan have found the cause of rice absorbing so much arsenic from the soil. In their report published in the Proceedings of the National Academy of Sciences, they said they had identified two proteins in rice plants that appeared to transport arsenic from the soil to the grain.

Using mutant plants that did not have these two proteins, the experts found sharply reduced levels of arsenic. "We used mutant paddy (in which) these two transporters were knocked out and we saw decreased arsenite in both the stalk and rice grain," said Ma Jianfeng at Okayama University's Research Institute for Bioresources.

However, Ma's team found the absence of the two transporter proteins reduced the absorption of silicon from the soil. Silicon occurs naturally and is important for the growth and productivity of rice plants. It also protects rice from pests and disease. "Silicon concentration was also decreased. So in future we have to try to change the selectivity, to allow silicon to be transported but not arsenic. That's what we have to do in future," Ma told Reuters in a telephone interview. Ma also recommended that more silicon fertilisers be used. "Silicon and arsenic use the same transporters ... (using) more silicon fertilisers in paddy fields (will result in) more silicon uptake and less arsenic," Ma said.


The new Study

Jian Feng Ma, Naoki Yamaji, Namiki Mitani, Xiao-Yan Xu, Yu-Hong Su, Steve P. McGrath, Fang-Jie Zhao, Transporters of arsenite in rice and their role in arsenic accumulation in rice grain, Proc. Natl. Acad. Sci. U.S.A., 2008. doi: 10.1073/pnas.0802361105


Related Studies

B.M. Dahal, M. Fuerhacker, A. Mentler, K.B. Karki, R.R. Shrestha, W.E.H. Blum, Arsenic contamination of soils and agricultural plants through irrigation, water in Nepal, Environ. Pollut., 155/1 (2008) 157-163.

Wang-da Cheng, Guo-ping Zhang, Hai-gen Yao, Wei Wu, Min Xu, Genotypic and environmental variation in cadmium, chromium, arsenic, nickel, and lead concentrations in rice grains, J. Zhejiang Univ. Sci. B , 7/7 (2006) 565-571. doi:10.1631/jzus.2006.B0565

Yong-Guan Zhu, Paul N. Williams, Andrew A. Meharg, Exposure to inorganic arsenic from rice: A global health issue ?, Environ. Pollut., 154/2 (2008) 169-171. doi:10.1016/j.envpol.2008.03.015

E. Smith, A.L. Juhasz, J. Weber, R. Naidu, Arsenic uptake and speciation in rice plants grown under greenhouse conditions with arsenic contaminated irrigation water, Sci. Total Environ., 392/2-3 (2008) 277-283.

Andrew A. Meharg, Enzo Lombi, Paul N. Williams, Kirk G. Scheckel, Jörg Feldmann, Andrea Raab, Yongguan Zhu, Rafiql Islam, Speciation and Localization of Arsenic in White and Brown Rice Grains, Environ. Sci. Technol., 42/4 (2008) 1051-1057. doi: 10.1021/es702212p


Related News

EVISA News, March 15, 2008: Arsenic in rice milk exceeds EU and US drinking water standards
EVISA News, February 15, 2008:
Arsenic speciation in rice: a question of the rice plant species
EVISA News, January 31, 2008: New arsenic species detected in carrot samples
EVISA News, March 7, 2007: Elevated Arsenic Levels Found In Rice Grown In South Central States of the USA
EVISA News, September 7, 2006: Toxic inorganic arsenic species found in Japanese seaweed food
EVISA News, August 3, 2005: Surprisingly high concentrations of toxic arsenic species found in U.S. rice
 EVISA News, May 15, 2005: Use of organoarsenicals as pesticides may lead to contamination of soils and groundwater with toxic arsenic species


last time modified: July 18, 2008









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