Transfer of Arsenic from Groundwater and Paddy Soil toRice Plant {Oryza sativa L.): A Micro Level Study in West Bengal, India

摘要

Rice (Oryza sativa L.) is one of the major food crops in many countries. As the cultivation of rice requires huge volume of water, long term use of arsenic contaminated groundwater for irrigation may result in the increase of arsenic concentration inthe agricultural soil and eventually accumulation in rice plants. Thus a micro level study was conducted to investigate the transfer of arsenic from irrigation water and soil to rice plants in the arsenic affected 17 villages of Chakdaha block, Nadia district, West Bengal, India. Results showed that the level of arsenic in irrigation water (0.11±0.012 and 0.76±0.014 mg l~(-1)) was very much above the WHO permissible limit of 0.01 mg l~(-1) for drinking water and was also above the FAO permissible limit of 0.10 mg l~(-1) for irrigation water. The paddy soil gets contaminated by the irrigation water and thus enhances more probable condition for bioaccumulation of arsenic in rice plants. The total soil arsenic concentrations ranged from 1.38±0.108 to12.27±0.094 mg kg~(-1) dry weight of arsenic, which was below the maximum acceptable limit for agricultural soil of 20.0 mg kg~(-1) as recommended by the European Community. In the rice plant, the highest accumulation of arsenic was noticed in the root(7.19±0.166 to 18.63±0.155 mg kg~(-1)) and the lowest in the grain (0.25±0.014 to 0.73±0.009 mg kg~(-1)). Regardless of the sampling locations the arsenic accumulation follows the order of root > straw > husk > grain. Consumption of rice straw containing considerable amount of arsenic (1.17±0.014 to 4.15±0.033) by cattle could potentially lead to increased arsenic levels in meat or milk. As because the total amount of arsenic in raw rice is not taken in human body due to its distribution in root,straw, husk and grain parts and also because in any rice sample from the study area concentration of arsenic in the grain part did not exceed 1.0 mg kg~(-1) dry weight of arsenic (the permissible limit of arsenic in rice according to WHO recommendation),thus atleast for now rice has remained harmless for consumption in the study area. But the results clearly showed that the arsenic content in rice plant is correlated to the degree of arsenic contamination of irrigation water and soil.