Arsenic in Rice Unrelated to Organics
Numerous studies have been published over the past decade documenting arsenic content in rice grown from around the world. Dr. Andrew Meharg, a professor of biogeochemistry at the University of Aberdeen, has led or been part of the team of researchers on many of these studies.
In 2007, Dr. Meharg led a study that measured arsenic levels among rice grown throughout the U.S. He and his team analyzed 107 samples of rice grown in Louisiana, Mississippi, Texas, Missouri, and Florida, and 27 samples of rice grown in California.
Meharg and his team found that the 107 southern US and central US rice samples averaged .30 micrograms/gram of arsenic, and the California rice samples averaged 0.17 micrograms/gram (ppm). Organic brown rice grown in California had the lowest levels of all 134 samples, with 0.10 micrograms/gram. This indicates that organic rice is not necessarily higher in arsenic, and is most likely lower in arsenic.
The reason is found in the soil. Rice crops with more arsenic content are grown in fields that have been previously sprayed with arsenic-based chemical pesticides. Those arsenic residues will contaminate the soils for many years after the chemicals were sprayed (another reason to be buying organic foods). Cotton crops have historically been sprayed with arsenic-based pesticides to control boll weevils.
Accordingly, Louisiana rice – where a fair amount of rice is grown on land previously farmed in cotton – had the highest levels of arsenic in Dr. Meharg’s research. Louisiana rice had 0.66 micrograms/gram of arsenic. This means that the arsenic levels of the organic rice were 15% of the arsenic levels of the Louisiana conventional (non-organic) rice.
Dr. Meharg’s team calculated that using the arsenic content from the research, one would have to consume over 115 grams of rice to exceed the EPA’s standard of 10 micrograms/liter, equivalent to 10 parts per billion (ppb). The average American consumes only about 12 grams of rice per day. Asian Americans, however, average more than 115 grams of rice in a day.
A recent Meharg study from Spain showed that most the rice-based infant formulas – which used conventionally-grown rice grown around the world – tested with high arsenic content.
Other research by Dr. Meharg found that arsenic levels in rice milk often exceed the US as well as EU arsenic drinking water limits. Dr. Meharg and his team found that 80% of the rice milk samples they tested from supermarkets in 2008 exceeded 10 microgram/liter limit. Rice cakes and crackers also contained higher levels of arsenic according to another study.
Other Meharg research found that cooking rice in good water lowered the inorganic arsenic content.
Dr. John Duxbury of Cornell University also studied U.S. rice, and discovered that the total arsenic content found in his samples were only 22% inorganic, while Dr. Meharg’s research showed that the inorganic arsenic content of the total arsenic content averaged nearly double these levels, at 42%.
This definition of organic/inorganic has nothing to do with organic farming or organic foods. This relates to the molecule type. Yet even in this respect, organic arsenic is better than inorganic in terms of toxicity.
The reason the molecule type is important is because organic unoxidized arsenic is a trace element found in nature, that is not necessarily harmful to the body in trace amounts. The body utilizes and metabolizes this form. It is the inorganic form – the oxidized versions called arsenic oxides or arsenic trioxide, typically used in industrial manufacturing of synthetic chemicals – that have been shown to be the most carcinogenic (although high quantities of organic arsenic can also be harmful and even carcinogenic).
In addition to cotton, fruit trees were sprayed with lead hydrogen arsenate for many decades. Now, conventional fruit trees are often sprayed with disodium methyl arsenate (DSMA) or monosodium methyl arsenates. These yield oxidized arsenic, but without the lead. Oxidized arsenic is also used in wood preservatives, antifungals and many other chemicals.
Research has illustrated that rice from Bangladesh has some of the highest arsenic levels in the world. This is not surprising, since Bangladesh has been faced with an arsenic catastrophe stemming from contaminated groundwater sources.
Dr. Duxbury holds that using less water to grow rice will dramatically reduce its arsenic content.
Dr. Meharg and his associates also studied arsenic levels in China’s rice. They found that most of the varieties contained less than .15 micrograms/gram, but rice grown in regions that were near or on previous mining sites had as much as .64 micrograms/gram.
Dr. Meharg’s research also discovered that some of the lowest arsenic levels among foreign rice are found in basmati rice from India and Pakistan and jasmine rice from Thailand.
Carbonell-Barrachina AA, Wu X, Ramírez-Gandolfo A, Norton GJ, Burló F, Deacon C, Meharg AA. Inorganic arsenic contents in rice-based infant foods from Spain, UK, China and USA. Environ Pollut. 2012 Apr;163:77-83.
Carey AM, Lombi E, Donner E, de Jonge MD, Punshon T, Jackson BP, Guerinot ML, Price AH, Meharg AA. A review of recent developments in the speciation and location of arsenic and selenium in rice grain. Anal Bioanal Chem. 2011 Dec 8.
Abedin MJ, Cresser MS, Meharg AA, Feldmann J, Cotter-Howells J. Arsenic accumulation and metabolism in rice (Oryza sativa L.). Environ Sci Technol. 2002 Mar 1;36(5):962-8.
Meharg AA, Rahman MM. Arsenic contamination of Bangladesh paddy field soils: implications for rice contribution to arsenic consumption. Environ Sci Technol. 2003 Jan 15;37(2):229-34.
Williams PN, Price AH, Raab A, Hossain SA, Feldmann J, Meharg AA. Variation in arsenic speciation and concentration in paddy rice related to dietary exposure. Environ Sci Technol. 2005 Aug 1;39(15):5531
Williams PN, Islam MR, Adomako EE, Raab A, Hossain SA, Zhu YG, Feldmann J, Meharg AA. Increase in rice grain arsenic for regions of Bangladesh irrigating paddies with elevated arsenic in groundwaters. Environ Sci Technol. 2006 Aug 15;40(16):4903-8.
Williams PN, Raab A, Feldmann J, Meharg AA. Market basket survey shows elevated levels of As in South Central U.S. processed rice compared to California: consequences for human dietary exposure. Environ Sci Technol. 2007 Apr 1;41(7):2178-83.
Meharg AA, Deacon C, Campbell RC, Carey AM, Williams PN, Feldmann J, Raab A. Inorganic arsenic levels in rice milk exceed EU and US drinking water standards. J Environ Monit. 2008 Apr;10(4):428-31.
Zhu YG, Sun GX, Lei M, Teng M, Liu YX, Chen NC, Wang LH, Carey AM, Deacon C, Raab A, Meharg AA, Williams PN. High percentage inorganic arsenic content of mining impacted and nonimpacted Chinese rice. Environ Sci Technol. 2008 Jul 1;42(13):5008-13.
Sun GX, Williams PN, Zhu YG, Deacon C, Carey AM, Raab A, Feldmann J, Meharg AA. Survey of arsenic and its speciation in rice products such as breakfast cereals, rice crackers and Japanese rice condiments. Environ Int. 2009 Apr;35(3):473-5.
Raab A, Baskaran C, Feldmann J, Meharg AA. Cooking rice in a high water to rice ratio reduces inorganic arsenic content. J Environ Monit. 2009 Jan;11(1):41-4. Epub 2008 Nov 20.