West Bengal || Bangladesh
Middle Ganga Plain, Bihar ||
AN UNIQUE WAY TO REMOVE EXCESS ARSENIC FROM THE COOKED RICE
Arsenic concentration of rice by irrigation with contaminated groundwater and secondarily increased soil arsenic compounds the arsenic burden of population dependent on subsistence rice diet. The arsenic concentration of cooked rice is known to increase with the arsenic concentration of the cooking water but the effects of cooking methods have not been defined. Worldwide, there are three common methods cooking rice: (A) The traditional method still used by more than 90% of the villagers in Bengal delta; raw rice is washed till the washing become clear (5 – 6 times), washings are discarded and then the rice is boiled in excess water (5 – 6 times the weight of raw rice) till cooked, finally discarding the remaining water (discard water) by tilting the pan against the lid before serving the rice. (B) The rice is washed as in A and boiled with water of a volume 1.5 – 2 times the weight of rice until no water is left to discard. (C) Unwashed rice is boiled with water 1.5 – 2 times the weight of rice; the wash and discard steps are both omitted. This is the contemporary method.
Using low arsenic water (<3 ppb), the traditional method of Indian subcontinent removed up to 57% of the arsenic from rice containing arsenic 203 – 540 μg/ kg. Approximately half of the arsenic was lost in the wash water, half in the discard water. Despite the use of low arsenic water, the contemporary method of cooking unwashed rice at rice:water :: 1:1.5-2.0 until no discard water remains did not modify the arsenic content. Preliminary washing until clear did remove 28% of the rice arsenic. The results were not influenced by water source (tubewell, dugwell, pond water or rain water); cooking vessel (aluminium, steel, glass or earthenware); or the absolute weight of rice or volume of water. The use of low arsenic water in the traditional preparation of arsenic contaminated rice can reduce the ingested burden of arsenic.
The maximum tolerable daily intake of As (III) is 2 μg/kg body mass (WHO, 1993). In an earlier study from arsenic affected areas of West Bengal we observed, 95% of arsenic in rice was in inorganic form and for an adult male (average weight 60 kg), rice consumption rate was 0.75 kg/ day and water consumption 4L/day. Generally the weight of cooked rice is around four times the weight of raw rice when method A was followed, for method B and C it is around three times. At raw rice As concentration 540 μg/kg (the maximum among all the rice varieties we collected) the amount of arsenic ingestion is 3.004, 4.721 and 7.339 μg/kg body mass if cooking method A, B and C used respectively. This is equivalent to consumption of 4L water per day with arsenic concentration 45.1, 70.8 and 110.1 μg/L.
Table 1:-Ingestion of arsenic through cooked rice per kg body weighta and equivalent contaminated water consumptionb
a Considering average weight of an adult male is 60 kg.
We also devised an apparatus, which performs all the steps needed in method A in a user friendly and faster way. This pot fitted with a central colander takes care of washing the rice and easy removal of the ‘discard water’ after cooking.
Arsenic speciation in rice, straw, soil, hair and nails samples from the arsenic affected areas of Lower and Middle Ganga Plain. E. Sanz, R. Munoz Olivas, C. Camara, M.K. Sengupta, S. Ahamed. Journal of Environmental Science & Health Part A. Vol.42; Issue 12; pp. 1695 – 1705.
Arsenic in the breast milk of lactating women in arsenic affected areas of West Bengal, India and its effect on infants. G.Samanta, D. Das, B.K. Mondal, T. Roychowdhury, D.Chakraboti, A. Pal, S. Ahamed. Journal of Environmental Science & Health Part A. Vol.42; Issue 12; pp. 1815 – 1825.