Abstract:
Soluble inorganic arsenic found in ground water is poisonous. It pollutes water, land and crops, ultimately affecting human health. The most dangerous aspect for human is, when arsenic releases into ground water from sediments through natural, chemical and biochemical processes like oxidation of arsenic rich sulphide compounds and the reduction of arsenic containing iron oxides. Irrigation with arsenical ground water leads to elevated level of arsenic in soils, which may lead to increased concentration of arsenic in plants. Irrigated wetland rice is most vulnerable to arsenic in the irrigation water-soil system in India as it grows under anaerobic soil condition, which makes arsenic mobile and bio-available.
Over the last three decades, huge numbers of tube wells have been installed throughout the state of West Bengal, India, Due to heavy ground water withdrawal, underground aquifer becomes aerated and oxygen causes degradation of arsenic rich sources mainly, in eastern part of Bhagirathi River in the state. To date, only limited attention has been paid to the risks of using arsenical ground water for irrigation. Ground water under eighty one numbers of blocks in eight numbers of districts in West Bengal is declared as arsenic infested by the State Water Investigation Directorate (SWID),Govemment of West Bengal. Murshidabad is one of these eight districts in West Bengal, where ground water in shallow aquifers of eighteen numbers of blocks covered with younger alluvium got affected byarsenic. It has been brought into notice during post-monsoon'09 and pre-monsoon' 10 that ground water in deeper aquifers is affected with arsenic having maximum concentration of 0.005 to 1.50 mg/l. In Murshidabad district, 1, 91,768 ha (91% of total actual area irrigated) is irrigated by using ground water only (Third Minor Irrigation Census in West Bengal 2000-2001). Summer paddy (Boro) cultivations, which depend heavily on irrigation with ground water, have been practiced in 91% Boro cultivation area in the district, which led declining of water table rapidly because of over-extraction. Long-term use of arsenical irrigation water could result in food chain contamination in Murshidabad district.
Several water-soil-crop management techniques like reduction of quantum of irrigation water without any yield losses, summer paddy cultivation on raised beds, shifting to dry-land crops like wheat, maize etc. and rotational crop cultivation may be experimented to reduce the arsenic load on the soils, crops as well as the food chain in younger alluvial plains of Murshidabad district.
