Arsenic eyes rice nutrients

The heavy metal can disrupt amino acid synthesis in the grain

By Biplab Das
Published: Wednesday 15 August 2012

CIATARSENIC accumulation in rice is something that is largely unexplored. A study has now found that the heavy metal can disrupt amino acid synthesis in the grain, a staple diet for many. This can reduce the levels of essential and non-essential amino acids found mainly in rice which are essential for a healthy life.

Essential amino acids like lysine, phenylealanine, histidine and methionine not only improve digestion, stimulate hormonal release and enhance memory, they are also the building blocks of all proteins. Deficiency of glutamic acid, a non-essential amino acid, has been linked to Parkinson’s disease.

For the study, researchers from India and the UK analysed arsenic and amino acid contents in 16 rice genotypes grown in arsenic-contaminated soils in West Bengal. They chose three regions—Chinsurah in Hooghly district, Purbosthali in Bardhaman district and Birnagar in Nadia district. They found that the levels of arsenic in groundwater of the three sites were 17, 27 and 53 microgramme/litre (mg/l) respectively. The concentrations of arsenic in soil varied from 10.4 mg/l in Chinsurah to 12.6 mg/l in Purbosthali and 15.5 mg/l in Birnagar. The acceptable limit for arsenic in groundwater, according to WHO, is 50 mg/l and the permissible limit of soil arsenic as set by the European Union is 20 mg/kg soil.

The rice genotypes were then divided into two categories based on the arsenic accumulation behaviour—low arsenic accumulating rice genotypes (LAARGs) and high arsenic accumulating rice genotypes (HAARGs).

The researchers found that the levels of essential and non-essential amino acid differed significantly in HAARGs and LAARGs. In most of the genotypes the levels of amino acids reduced significantly as the arsenic concentration rose. The researchers say this is due to the heavy metal altering the degradation of the proteins and subsequently leading to inhibition of amino acid synthesis. The levels of essential and non-essential amino acids in rice were the highest in Chinsurah.

They also found rice varieties that resisted arsenic accumulation in areas with high levels of the heavy metal in soil and vice-versa. The study will be published in the October 1 issue of Environment International.

The findings can act as a guide to identifying rice varieties suitable for growing so that the grain has minimum arsenic concentration and highest levels of required amino acids, says Rudro Deo Tripathi, scientist at National Botanical Research Institute.

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