Cancer rates attributable to arsenic in rice vary globally
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rice. However, says Smith, “There milligrams per kilogram (mg/kg), Exposure to inorganic arsenic in are also many uncertainties in but inorganic arsenic varied only rice is associated with various insuch estimates, including those between 0.05 and 0.15 mg/kg. In ternal cancerssliver, bladder, kidderiving from the fact that, in my Chinese rice, the median total arney, and lungsas well as other opinion, the EPA potency estisenic was lower, 0.14 mg/kg, but health problems, including skin mate underestimates cancer risks inorganic arsenic showed greater cancer and diabetes. But how by a factor of at least 2.” variation, reaching higher levels, much does rice in the diet conAccording to Smith, although between 0.07 and 0.38 mg/kg. tribute to human exposure, when high levels of arsenic in compared with arsenic in drinking water in some drinking water? Research parts of the world are the in ES&T (DOI 10.1021/ number one source of exes802612a) shows that rice posure, “for those with may be an important adlittle arsenic in their water, dition to arsenic dose, esinorganic arsenic in food pecially for people with a becomes a source of expohigher than usual rice sure to consider. This paintake. per shows that rice can be Andrew Meharg at the an important addition to University of Aberdeen dose, especially for those (U.K.) and coauthors comwith a higher than typical piled an extensive data set intake of rice. of arsenic levelss901 “However, millions of samples of white rice New research shows that rice may be an important addition people in the world are originating on four to arsenic dose, especially for those with a higher than exposed to high concencontinentssand modeled usual rice intake. trations of arsenic in the global distribution of Using their data, the authors drinking water, and concerns arsenic “by weighting each counmodeled cancer ratessthe preabout arsenic in rice only apply to try’s arsenic distribution by that dicted excess arsenic-caused canpeople whose drinking water concountry’s contribution to global cer rate relative to the baseline tains less than 10 micrograms per production,” says Meharg. cancer ratesby multiplying proliter of arsenic,” Smith “Rice is the largest source of jected daily intake of inorganic emphasizes. inorganic arsenic in the human arsenic in rice by a risk factor Geochemist David Polya, at the diet. Perhaps 100-200 million proposed by the U.S. EPA. Using University of Manchester (U.K.), people have elevated inorganic this model, the authors calculated agrees with the paper’s findings arsenic in their water, while half the median excess internal cancer that “relatively high arsenic in the world consumes rice as a dirates to be 1 per 10,000 people in rice constitutes a significant risk etary staple,” Meharg says. But Italy and the U.S., 7 per 10,000 in to health to many people around not all scientists agree about the India, 15 per 10,000 in China, and the world.” A probabilistic risk relative health impact of arsenic 22 per 10,000 in Bangladesh. assessment conducted by Polya’s in rice. group broke down median arUniversity of California Berkeley For this study, the researchers senic-attributable risk of a range epidemiologist Allan Smith, direcdetermined the levels of inorganic of cancers in a highly impacted tor of the Arsenic Health Effects and organic arsenicscalled ararea of West Bengal into 48% of Research Program, explains that senic speciationsin a subset of 63 risk from drinking water, 44% from “in 10,000 people you would exrice samples, originating from rice, and 8% from cooking of rice. pect roughly 2000 to eventually Bangladesh, China, India, Italy, The risk assessment is published in die from cancer. If, due to some and the U.S. Previous studies Applied Geochemistry (2008, DOI exposure, there are more cancer showed that these countries have 10.1016/j.apgeochem.2008.06.025). deaths and 2030 die due to cancer both elevated arsenic levels in Two limitations apply to many among 10,000 exposed people, rice and populations (or subpoparsenic risk assessments, Polya then the excess cancer risk is 30 ulations in the U.S.) who eat large says. Although many assume a per 10,000 people.” Thus, this paamounts of rice, Meharg says. linear relationship between expoper suggests that in Bangladesh Grain speciation differed among sure and lifetime cancer risk, the median excess risk would be countries. In U.S. rice samples, there is substantial discussion 22 per 10,000 due to arsenic in the median total arsenic was 0.25 10.1021/es900020m
2009 American Chemical Society
Published on Web 01/21/2009
March 1, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 1243
about whether dose-response relationships for arsenic really are linear. In addition, certain factors are not considered in many risk assessments, including age, nutritional status of the population, and genetic factors. Indeed, notes Polya, Ashok Giri at the Indian Institute of Chemical Biology has found a number of genetic poly-
morphisms related to susceptibility to arsenic-attributable diseases. “In many countries, we have the choice to eat other forms of carbohydrate or to at least have a mixed diet-this is not currently an option for hundreds of millions of people in India, Bangladesh, or China. So, it is
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important for researchers to focus on ways of reducing arsenic in rice, perhaps through genetic modification, or identification of low-arsenic varieties, or looking at cooking methods, all of which the Aberdeen group are currently pursuing,” says Polya. —BARBARA BOOTH
