SOURCE AND ORIGIN OF ARSENIC CONTAMINATION IN MIDDLE GANGETIC PLAIN OF UTTAR PRADESH AND BIHAR, INDIA

Holocene alluvial aquifers of Ballia, Ghazipur and Bhagalpur districts in the middle Gangetic Plain of India are characterized by groundwaters wiith elevated concentrations of geogenic arsenic (As) in a regional scale. Climatic conditions, weathering of carbonate and silicate minerals, surface water interactions, ion exchange, and anthropogenic activities were found controlling the high concentrations of cations, anions and As in the groundwater. The spatial and temporal variations were observed. As concentration are greater in the pre-monsoon (6.4-259.5 μg/l) when compared to the post-monsoon period (5.1-205.5 μg/l). The enriched As concentration was observed close to meandering zones of the Ganges River in these districts. The depth profile of As revealed that low concentrations of HCO₃^- and NO₃^- , which are associated with high concentration of As . The As depletion was observed with the increasing depth in almost all the sites. The poor correlations observed between As and Fe indicate the As release in the groundwater is controlled by weathering process, O₂ consumption, and NO₃^- reduction. Statistical analysis identifies various factors influencing the As enrichment in the middle Gangetic Plain. The present study is vital considering of the fact that groundwater is exclusive source of drinking water in the these region through the year for the rural population of this region