In India and other Southeast Asian countries, large areas of the bedrock naturally contain arsenic (As), which leaches into the groundwater. The FAO estimates that up to 500 million people are at risk of being exposed to dangerous levels of arsenic in both drinking water and in the crops that were irrigated with the groundwater. The problem was investigated by the FAO in Bangladesh in 2006. They found that:
[A]rsenic levels in the grain of different varieties of rice in Bangladesh were as high as 1.8 parts per million, compared to levels of just 0.05 parts per million in Europe and the US. Contamination was even greater in leafy vegetables – in amaranthus and spinach, arsenic content can be double or triple the levels found in rice. For drinking water, WHO recommends a maximum arsenic level of 0.01 parts per million, which indicates that for some people, staple food crops such as rice may be an important source of exposure to arsenic.
Until now, the farmers essentially have three options: leave the fields fallow, plant rice and hope it doesn’t have too much arsenic, or attempt to plant a crop that doesn’t need as much water.
Om Parkash (photo and story from Newswise) of the University of Massachusetts Amherst primarily works on bioremediation, which aims to remove pollutants from the soil by binding it up in plants. His recent work branches into the opposite direction, using genetic engineering to produce rice plants that take up less As. The work is in the process of patenting, so technical details are scarce. For now, I’ll have to be content with the following:
“By increasing the activity of certain genes, we can create strains of rice that are highly resistant to arsenic and other toxic metals,” says Parkash, a professor of plant, soil and insect sciences. “Rice plants modified in this way accumulate several-fold less arsenic in their above-ground tissues, and produce six to seven times more biomass, making the rice safer to eat and more productive.” This could help alleviate the current world-wide rice shortage.
I’m really looking forward to learning more about the genetics, and hope that Dr. Parkash is able to move forward with this exciting crop improvement.
While As is actually a necessary mineral in small amounts and only becomes dangerous to health when consumed in high levels (as in Bangladesh), decreasing As in the food supply is definitely a worthy cause. Dr. Parkash says that As can accumulate in all parts of the rice plant, including grain and straw. High As levels in rice not only affect people, but can sicken animals who eat the straw and contaminate their meat (think bioaccumulation). See GreenFacts for a good summary of arsenic as it relates to human health and the environment (incidentally, they also have some of the most levelheaded information on GM crops that I’ve ever seen).
Other recently published work on arsenic levels in rice by Yamily Zavala and John Duxbury of Cornell was reported in the 2 May 2008 ISAAA Crop Biotech Update. For a summary of the articles, see the press release from the American Chemical Society. Disclosure: I wasn’t able to access these two articles themselves as ISU’s library site is down while I write this.
In Arsenic in Rice: I. Estimating Normal Levels of Total Arsenic in Rice Grain, they showed that mean As concentrations in samples of commercial rice in Europe and the US (0.198 mg/kg) were higher than in samples from Asia (0.07 mg/kg). The concentrations varied greatly by region, but not by farming method. Their data confirmed that irrigation with As contaminated groundwater in Bangladesh is correlated with higher As concentrations in grain. In the US, where groundwater is not contaminated with As, the authors suggest that historical contamination of soil is a likely cause. Note: mg/kg and ppm are equivalent units.
In Arsenic in Rice: II. Arsenic Speciation in USA Grain and Implications for Human Health, they showed that the As in some rice varieties accumulates in a less toxic form than inorganic As (inorganic = molecules do not contain carbon). Arsenic in rice grown in the US is bound into mostly into dimethyl arsinic acid (DMA), which . This data is in agreement with previous studies done by Andrew Meharg of the University of Aberdeen in the UK. There is evidence that DMA is safer than inorganic As, which means that US rice may be safer than European or Asian rice. The authors hypothesize that 30 years of breeding in the US for straighthead disorder resistant rice could have caused US varieties to acquire this As metabolic pathway.
Huge phenotypic variance is present in rice grains across varieties. It’s easy to imagine that metabolic pathways vary widely from variety to variety as well.