MAGNITUDE OF INORGANIC ARSENIC CONTAMINATION INGROUNDWATERS OF MIDDLE GANGETIC BASIN OF UTTAR PRADESH AND BIHAR, INDIA

An attempt has been made to summarize the solute chemistry of the middle Gangetic plain of Uttar Pradesh and Bihar, India with the special reference to naturally occurring Arsenic (As) contamination of the aquifers. Uttar Pradesh (area: 238000 km2; population: 166 million) and Bihar (area: ~ 94000 km2; population: 104 million), are situated in the middle Gangetic basin is a peneplain and highly fertile area. The needs of drinking as well as irrigation water mainly dependent on shallow aquifers <50 m below ground level in the middle Gangetic plain. Groundwater shows neutral to alkaline nature with a pH range of 7 to 8.31. Bicarbonate and TDS shows a wide range all over the middle Gangetic plain. There is a disproportion in the concentration of As in this area which varies from 5.8 ±13.6 in Varanasi to 331±156 in Ballia, Uttar Pradesh, most of the tubewells exceed the WHO limit 10µg/L. Arsenite found as a dominant species in Ballia while Arsenate found as dominant species in Ghazipur, Uttar Pradesh and Bhagalpur, Bihar. The concentration of As is found to be depth dependent: shallow aquifers has a higher concentration than the deeper. Reductive dissolution of Fe(III) oxy–hydroxide driven by microbial degradation of younger alluvium containing active organic carbon is the widely accepted mechanism for mobilization of As in groundwater in the middle Gangetic plain. To access actual status of the groundwater quality, other elements should be considered in further studies.