GROUNDWATER IRRIGATION AND INTENSIFICATION OF ARSENIC CONCENTRATION IN MONSOON RICE GRAINS

Amon rice cultivation depends mainly on monsoonal rainfall. But due to scarcity of rainfall in growing season, farmers use shallow ground water for irrigation often used for winter cultivation. The change of traditional monsoon rice cultivation pattern in the arsenic contaminated region leads to higher integration of arsenic in the rice. The presence of arsenic in rice grain through the water-soil crop routes has raised a worldwide concern in terms of food safety. The present work aims to investigate the trend of arsenic in rice field and its accumulation in different parts of the paddy plants during monsoon cultivation. The monsoon fed rice field irrigated with highly arsenic contaminated (94.02μg/l) shallow ground water showed a higher concentration of arsenic in rice grains well as in upper soil layer and decreased with increasing soil depth, which are quite similar with boro cultivation in that region. At the initiation of plantation of paddy some amount of rainfall occurred which allowed infiltration of soil soluable arsenic to deeper soil layer and increased the concentration of arsenic over soil depths. Onward most of field were irrigated with shallow ground water till harvest, which enhanced arsenic concentration at upper layer of soil. The mean concentration (mg/kg) of As, Mn, Ni, Cr and Fe were 48.5, 402.6, 153.4, 71.8, 43,200 in the experimental soils whereas, 11.0, 326.3, 41.3, 67.9 and 41,163 in the control field soils. The concentrations (mg/kg) of As in different parts of the rice plants in contaminated fields were 50.8 in roots 21.9 in straw, 0.78 in husk and 1.6 in grains. From this present study it was obvious that even though it was a monsoon cultivation, the arsenic in rice grain was above the permissible limit (1 mg/kg) given by WHO. This triggers a possible dietary risk to human health and also risk of environmental hazards.