rice paddies
© AP Photo/ Anupam Nath
Researchers claim that as much as 15 mg of silver can be extracted from a kilogram of the Garib-sal variety of rice which accumulates an unusual quantity of the noble metal in its aleurone layer.

Indian scientists have rediscovered a rice variety that accumulates an unusually high quantity of silver in the grains. The test conducted by researchers from the Indian Institute of Technology (IIT) could become a novel method of bio-extraction of silver metal.

"Our study of 505 native rice landraces showed that nine of them accumulate silver at a high concentration when grown in the same soil. Among these, a medicinal rice landrace from West Bengal, Garib-sal was found to accumulate silver at an especially high concentration in the grains. Cultivation of Garib-sal rice in three successive years in Basudha farm in the rice growing period of June-October confirmed that for the same concentration of silver in the soil (∼0.15 mg/kg), Garib-sal accumulates it in the grains to the extent of ∼15 mg/kg," reads the report published in science journal - ACS Sustainable Chemistry & Engineering.

"The rice variety has the ability to accumulate silver about 100 times more than any other rice. It is possible to extract 14.60 mg per kg of silver from the rice using a cheap and simple chemical method. This is a unique way of extracting silver through agriculture. With further research, it may be possible to find better ways of enhancing the bioaccumulation of silver," Prof. T. Pradeep told The Hindu.

To detect the location of deposition of silver in the grains, scientists had performed secondary ion mass spectrometry where it is revealed that silver is concentrated in the aleuronic layer of the rice bran. Its concentration decreases in the sub-aleurone and becomes negligible in the endosperm. "Accumulation of silver does not alter the grain morphology and chemical characteristics. The metal may be extracted from the bran after milling of the rice, thereby causing no loss of the foodstuff," the research paper claims.

Garib-Sal was once grown in West Bengal and was recommended as a diet for patients with gastrointestinal infections and the presence of silver in rice might have had a therapeutic effect by killing pathogenic microbes in the human gut.