In many parts of India, groundwater is contaminated with arsenic. So, public attention is focussed on arsenic in drinking water. However, using arsenic contaminated water for irrigation and cooking can also lead to arsenic poisoning.
Recently, researchers from the Kalyani University, Kolkata and the CSIR-NEERI, Kolkata in collaboration with the University of Michigan, USA investigated the effect of cooking method, rice variety, and arsenic concentration in raw rice and cooking water on arsenic concentration in cooked rice.
The team selected Chaku Danga, a village in a highly arsenic affected part of West Bengal. Rice is the main crop there. The team administered a brief questionnaire about cooking practices, sources of rice and water used, and amount of rice consumed daily. On the basis of rice variety consumed, income level, and ease of access for research staff, they selected 100 households for further exploration.
“Rice is traditionally cooked by washing rice 3-4 times, soaking for about 15-20 minutes, cooking with excess water and taking away the excess starch. We analyzed samples at each stage using Atomic Absorption Spectroscopy,” says Payal Singh, NEERI, Kolkata.
Out of the six varieties grown in the region, Swarna had the highest grain arsenic content. This brown, short, bold grained rice is preferred by villagers since it is cheap.
“Approximately 93% of arsenic in rice grain is inorganic – the most toxic form,” says Ujjal Mandal, Kalyani University, Nadia.
The researchers found that washing, before cooking, removed up to eight micrograms from a kilogram of rice. However, the water used for cooking had about 90 to 230 micrograms per litre of arsenic. Thus, the arsenic level in cooked rice rose by more than 50 percent.
“The starch water from the rice gruel, which the villagers drink, had nearly 150 micrograms per kilogram,” says Debashis Chatterjee, Kalyani University, Nadia.
“We found a significant correlation between arsenic concentration in cooked rice, raw rice and cooking water,” adds Subhamoy Bhowmik, NEERI, Kolkata,
The team stresses the need for arsenic-free water not only for drinking but also for cooking. They recommend raising awareness in arsenic affected areas.
Sci. Total Environ., 648: 720-727 (Jan 15, 2019); DOI: 10.1016/j.scitotenv.2018.08.172
Kavita Pal, Translational Research Laboratory, ACTREC, Navi Mumbai