Arsenic in rice and food grains !!! Is it true? Is it harmful? How do you avoid it?
The use of arsenic-contaminated groundwater for irrigation purpose in crop fields elevates arsenic concentration in surface soil and in the plants grown in arsenic contaminated areas. The arsenic concentrations in the edible parts of a plant depend on the availability of the soil arsenic and the accumulation and translocation ability of a plant.
In many arsenic-affected countries, including Bangladesh and India, rice is reported to be one of the major sources of arsenic contamination.
Cooking tip: The concentration of arsenic in cooked rice is reduced by cooking rice in arsenic free water and straining out the rice water.
Rice is much more efficient at accumulating arsenic into the grains than other staple cereal crops. Rice is generally grown in submerged flooded condition, where arsenic bioavailability is high in soil. As arsenic species are phytotoxic, they can also affect the overall production of rice, and can reduce the economic growth of a country. Arsenic accumulation in soil irrigated by arsenic contaminated water and its transfer into rice may vary depending on the soil types, cropping pattern, arsenic concentration in irrigation water, distance from the water source, depth of water source and duration of the monsoon flood.
It has been reported that the concentration of arsenic in cooked rice was higher than that of raw rice. The concentration of arsenic in rice is increased when it was cooked with arsenic contaminated groundwater and the gruel was not discarded after cooking. Arsenic is absorbed in the cooked rice from water, thus increased the concentration. Its concentration in boro rice is much higher than in aman variety, because much higher amount of water is needed for boro cultivation compared to aman cultivation.
Rice straw is often used as a cattle feed in South Asia. This represents another entry route of arsenic into the food chain, as rice straw typically contains much higher amount of arsenic than grains. Cattle population also used to drink water contaminated with arsenic in those areas, which, in turn, can further increase the toxicity level. Cattle manure is often used as fuel in household purposes, which can also increase the contamination risk. Besides, the dry straw often been used by people as fuel, which can release arsenic in air as oxides, and can cause pollution and health hazards. Large-scale use of rainwater in irrigation systems, bioremediation by arsenic-resistant organisms and hyper accumulating plants, and the aerobic cultivation of rice are some possible ways to reduce the extent of arsenic bioaccumulation in rice and other edible plants. Intensive investigation on a complete food chain is urgently needed in the arsenic contaminated zones, which should be our priority in future researches.
Written by: Dr. Sayan Bhattacharya, Assistant Professor, School of Ecology and Environment Studies, Nalanda University, Rajgir, Bihar, India. Email: sbhattacharya@nalandauniv.edu.in
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