Silver in rice

The Hindu
A rice variety originally from West Bengal is able to accumulate the
metal in its grain, IIT researchers find

It is a rice variety with a silver touch, literally. Garib-sal, one of
505 types of rice plants tested by scientists, is capable of absorbing
silver found naturally in soil and accumulating it in the grain to
unusually high levels of 15 mg per kg.

The rice was able to accumulate high quantities of silver even when the
soil contained only about 0.15 mg per kg.

The unusual accumulation of silver in the grain and other parts of the
plant, researchers say, throws open the possibility of commercial
extraction of the metal through farming.

The maximum concentration of silver in the plant is in the grains.
Silver accumulation is largely in the bran of the rice grain, and once
polished, the silver in the grain is reduced significantly.

Polishing grain is crucial

It is not, however, for consumption as food. "We do not advocate
consumption of the unpolished rice as staple food. If the rice is
polished very well then it may not lead to silver toxicity," says Prof.
T. Pradeep from the Department of Chemistry, Indian Institute of
Technology Madras, who authored the research.

Silver is not known to accumulate in the reproductive tissues of any
cereal, and in agricultural crops the amount of silver that gets
accumulated is less than 1 mg per kg of dry weight of the plant.

Researchers at IIT Madras stumbled upon the rice variety while screening
for different metal ions in the 505 rice varieties. Only nine showed
high silver accumulation, with Garib-sal the highest.

The rice varieties are maintained by Dr. Debal Deb, head, Centre of
Interdisciplinary Studies, Kolkata, as part of rice variety conservation
efforts. Garib-sal used to be grown by farmers in Purulia, West Bengal.
The researchers tested Garib-sal's ability to accumulate silver even
when grown in soils with very low silver concentration. Even when the
soil contains only about 0.01 mg of silver per kg, the rice plant was
able to concentrate 0.20 mg of silver per kg in the grains.

"The rice variety has the ability to accumulate silver about 100 times
more than any other rice," says Prof. T. Pradeep. The variety was
cultivated in the farm for three successive years in soil containing
about 0.15 mg per kg and the uptake and accumulation of the noble metal
was nearly the same.

Garib-sal accumulated 50 times more silver than another type in control
tests.