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[SANET-MG] rice in asia iron and arsenic
August 7, 2004
Prof. Joe Cummins
“Rice in Asia: Too little iron, too much Arsenic”
The main food in Asia is facing two catastrophes the first is that the
food contributes too little iron to the human diet and the second is
that the food is gathering to much arsenic from soil and water. The
following discussion describes the problems and the independent remedies
proposed for their alleviation. However, there is evidence that the two
problems may be linked and the remedy for one problem may increase the
impact of the other. The two problems should be considered together and
a remedy that takes care of both problems should be sought.
The Iron Problem
It has been estimated that 40% of the world’s women suffer some degree
of iron deficiency. Anemia is associated with reduced learning in
children, increased susceptibility to disease and reduced work
capacity(1). Pre-menopausal women are most severally affected by iron
deficiency , while men tend to retain iron(as indicated below an iron
overload diet may lead to cancer in males). Increasing iron in the diet
is a desirable global goal and rice is the preferred crop for genetic
modification (GM) to increase iron in the diet. Researchers from the
Japanese Electrical Power research Institute increased the iron content
of rice threefold by adding a seed specific ferritin ( an iron storage
protein) from soybean under the control of a rice seed storage protein
promoter (2).Even though the iron content of the rice grain was
increased significantly there has been concern that the ferritin bound
iron may not be readily available in the digestive tract of mammals. A
Swiss research group transformed rice with a ferritin gene from snap
beans under the control of a rice storage protein promoter accompanied
by a fungal phytase gene also under control of the storage protein
promoter. The phytase gene produces an enzyme that increased iron
availability during digestion. An endogenous rice metallothionein was
overexpressed in the transgenic rice to further aid in iron digestion An
antibiotic resistance marker gene for the antibiotic hygromycin was
added during the transformations of the rice.The iron content of the
rice was doubled but the iron was more readily available during
digestion (3). The Swiss study was supported by the Rockefeller
foundation (4).
Iron overload is a significant problem in males, it may lead to a
condition called hemochromatosis in which the liver and other organs may
be damaged and cause cancer of the liver or colorectal cancer . As much
as one person in a hundred may bear a mutation (hereditary
hemochromatosis ) that makes them sensitive to iron overload at
relatively modest iron intake levels (5). There is an association
between increasing iron stores and risk if cancer (6). In areas of the
world where iron deficiency is commonplace iron enriched rice may prove
beneficial , but the same iron enriched rice could prove to be a
liability in areas where iron intake is at as high level. Iron overload
should be discussed in presentations on the distribution of iron
enhanced rice. The need for labeling of iron rich rice products is evident,
The Arsenic Problem
Asia is facing a growing disaster in the use of arsenic contaminated
ground water for drinking and in irrigation of rice paddies. Arsenic
pollution is a severe problem over Bangladesh/West Bengal (7) and in the
Red River Delta of Vietnam (8) but it is also a chronic problem in
Taiwan, China and Thailand (7). Most arsenic pollution is of natural
origin , amplified by drawing water from contaminated deep aquifers but
China has experienced arsenic pollution from burning high arsenic
containing coal (9). Arsenic has been shown (from studies in Taiwan) to
cause cancer and circulatory problems at very low levels, the cancers
observed include cancers of liver, lung, bladder and kidney (10). It has
been estimated that average arsenic pollution of drinking water in the
United States causes 3000 cancer cases per year (10).
In Asia the arsenic is problem amplified by the pollution of rice, the
prime food source ( (7,8,11,12). Arsenic has been accumulating in paddy
soil leading to contamination of the grain (11). Rice contributes to ,an
estimated, 30 to 60% of the dietary intake of arsenic in polluted
regions (11).
There is hope that rice strains can be selected that take in less
arsenic than do the varieties of rice currently in use. It has been
found that arsenic is sequestered on iron plaque on the roots of rice
varieties that accumulate reduced levels of arsenic in grain (11,12).
Rice paddies will continue to be polluted with arsenic in the soil
because there is no practical method known to remediate the vast
expanses of polluted soil. Breeding rice to reduce grain pollution seems
to be an effective first step towards improving the diet in polluted
areas and varieties with reduced grain input of arsenic are known.
Iron and arsenic interact in rice
There is a potential conflict in governmental and foundation programs to
develop and disseminate high iron grain to alleviate iron deficiency
among rice consumers. The high iron rice varieties currently under
development include amplifying ferritin in grain and solubilizing iron
using a phytase gene from a fungus (3).In the iron plaque rice varieties
arsenic reduced iron in shoots and roots while the varieties lacking
arsenic sequestering plaque did not have reduced iron in the presence of
arsenic(11,12). The iron enhanced grain designed to combat iron
deficiency are bound to contain high arsenic levels in the arsenic
polluted areas of Asia. It seems a devilish mistake to make high iron
rice available at the cost of elevated arsenic or to make low arsenic
rice available without providing an alternate source of dietary iron. A
solution to the problems of iron deficiency and arsenic poisoning should
be sought that deals with both problems together and not separately.
References
1. Information systems for biotechnology Biotechnology Used to
Fortify Rice With Iron pp1-2
http://www.nbiap.vt.edu/articles/dec9702.htm
2. Goto,F, Yoshihara,T, Shigemoto,N, Toki,S. and Takaiwa,F Iron
fortification of rice seed by the soybean ferritin gene 1999
Nature Biotechnology 17,282-7
3. Lucca,P, Hurrell,R. and Potrykus,I. Fighting Iron Deficiency
Anemia with Iron-Rich Rice 2002 Journal of the American College of
Nutrition 21, 184S–190S
4. Conway,G. Crop Biotechnology: Benefits, Risks and Ownership 2004
http://www.rockfound.org/display.asp?context=1&Collection=4&DocID=141&Preview=0&ARCurrent=1
5.Haung,X. Iron overload and its association with cancer risk in
humans:evidence for iron as a carcinogenic metal 2003 Mutation Research
533,153-71.
6.Toyokuni,S. Iron induced carcinogenesis :the role of redox regulation
1996
Free Radical Biology & Medicine 20,553-66
7.Meharg,A. and Rahman,M. Arsenic contamination of Bangladesh paddy
field soils: implication for rice contribution to arsenic consumption
2003 Environ Sci Technol 17,229-34
8.Berg,M,Tran,H,Nguyen,T,Pham,H,Schertenleib,R. and Giger,W. Arsenic
contamination of groundwater and drinking water in Vietnam: a health
threat 2001 Environ Sci Technol 35,2621-7
9. Liu,J Zheng,B, H. Aposhian,H,Zhou,Y,Chen,M,Zhang,A. and Waalkes,M.
Chronic Arsenic Poisoning from Burning high-Arsenic-Containing Coal in
Guizhou, China 2002 Environmental Health Perspectives 110, 119-22
10Morris,R. Environmental Health Issues 1995 Environmental Health
Perspectives 103 (suppl 8) 1-14
11..Meharg,A. Arsenic in rice-understanding a new disaster for
south-east asia 2004 trends in plant sciences in press
12. Lui,W,Zhu,Y,Smith,E. and Smith,S. Do phosphorous nutrition and iron
plaque alter arsenate (As) uptake by rice seedlings in hydroponic
culture 2004 New Phytologist 162,481-8
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