Published in the peer-reviewed journal Environmental Science and Technology, the study follows a series of work on the presence of the carcinogen in rice and rice products.
But the latest study reveals that of all widely available commercial rice products, rice bran was found to contain the highest arsenic content.
Initial industry response to the new study suggests that the science is “flawed”.
Originally a by-product of rice processing that is usually discarded or used for animal feed, rice bran has emerged in recent years as a functional ingredient for use in foods and dietary supplements. It is also used in food aid programs especially targeting malnourished children in developing countries.
The product is marketed as a rich source of vitamins, minerals, antioxidants and fiber.
However, concerns have been raised in the past about levels of arsenic in rice and rice products. Rice is particularly susceptible to taking up arsenic present in the soil due to the way it is cultivated in paddies.
Arsenic is a nonthreshold class one carcinogen, which means that there are no ‘safe’ levels of exposure. “Every concentration of arsenic you take in will have an associated cancer risk,” explained Professor Meharg.
In the new study, Meharg and colleagues purchased whole grain rice samples from arsenic-elevated regions in China and Bangladesh, and milled them as in commercial processing. The bran, the whole grain and the endosperm (polished white rice) were then ground into fine powders and oven dried.
The researchers also purchased a variety of rice bran products commercially available in the US, the UK and Japan.
Rice flour was used as the certified reference material, and all samples were analyzed in duplicate.
The findings revealed that rice bran and rice bran solubles contain inorganic arsenic levels of around 1mg/kg dry weight, which is around 10-20 times the concentration found in bulk grain.
Currently, China is the only country to have modern levels of how much arsenic is permitted in food, and has set the limit at 0.15mg of inorganic arsenic per kg of food.
The US and EU have no standards for arsenic levels in food, but the US has a 0.01mg/liter limit in drinking water. The World Health Organization (WHO) has also placed a provisional level of 0.01mg/l in drinking water. The UK has standards that date back to 1959, and that set the limit of 1mg/kg total arsenic in foodstuffs.
According to the recent findings, none of the rice bran samples tested would pass the more stringent and modern Chinese limits, and only two out of the nine samples would pass the 50 year-old UK standards.
The tests were conducted on four bran solubles, one defatted bran, one riceo-ex and three bran products.
Out of the bran solubles, testing found the highest inorganic arsenic level of 0.86mg/kg in a sample from Holistic Enterprises, Santa Ana, USA. A sample from NutraCea, USA was found to contain 0.82mg/kg. A sample from Pure Planet Products, Long Beach, CA, USA, contained 0.71mg/kg and one from Integris, RiSO Triene, USA, contained 0.61mg/kg.
The rice bran products tested were from: General Dietary, UK & Eire; The Barry Farm, Ohio, USA; and Tsuno Rice Fine Chemicals Co, Japan. They contained levels of 0.48, 0.64 and 1.65mg/kg respectively.
The defatted bran and the riceo-ex products were again sourced from Japan’s Tsuno Rice, and contained 1.16 and 1.88mg/kg respectively.
Rice bran in food?
“With respect to the threat that rice bran products pose to dietary exposure, dosage needs to be considered,” write the researchers.
“The manufacturers recommended daily serving of rice bran solubles is around 20g per day, based on either direct weights given on packaging, or using the provided scoops. A 20g serving equates to 0.014-0.017mg of inorganic arsenic for the 4 products specifically described as rice bran solubles.”
“It’s a novel product that has a problem,” Professor Meharg told NutraIngredients-USA.com, adding that he did not think it is “a wise way to proceed” to use these products in food items, given their high levels of inorganic arsenic.
He stressed that: “I am not concerned about one company in particular. What I’m concerned about is the product in general. We’ve raised problems in the past with rice grain, baby rice and rice milk. Rice bran is just another product that needs to be seriously thought about.”
NutraCea, which is the market leader for stabilized rice bran supply, was unable to respond to calls for comment in time for publication this morning, but suggested that it held the position that the new study is flawed.
However, in a letter to customers sent last year, NutraCea addressed similar concerns about arsenic levels in rice products.
“Recent articles in the media have called into question the safety of US rice,” wrote Leo Gingras, NutraCea chief operating officer in September 2007.
“Assertions that arsenic levels in US rice may be harmful to health are not new. It is truly unfortunate that these assertions, unsupported by scientific data and analysis, continue to confuse the public. Our message to you is simple, US rice and NutraCea products derived from it are safe.”
NutraCea markets its rice bran as a functional ingredient high in vitamins and antioxidants. It also specifically targets health condition markets including diabetes, arthritis and immunity.
Source:‘Inorganic arsenic levels in rice bran and its products are an order of magnitude higher than in bulk grain’, Environmental Science & TechnologyPublished online: August 21 2008DOI: 10.1021/es801238pAuthors: Guo-Xin Sun, Paul N Williams, Anne-Marie Carey, Yong-Guan Zhu, Claire Deacon, Andrea Raab, Joerg Feldmann, Rafiqul Islam, Andrew Meharg.