ARSENIC CONTAMINATION FACTORS ASSESMENT IN THE MIDDLE GANGETIC PLAIN USING WATER QUALITY AND SEDIMENT SPECIATION ANALYSIS

Natural occurrence of Arsenic (As) in groundwater of Ganga alluvial plains has assumed serious proportion and its source and mechanism of release into the groundwater is still under debate. The present study was undertaken in the Semria Ojhapatti block of Bhojpur district, Bihar which falls under the middle Gangetic plains. In total 30 groundwater samples and one sediment core (cutting sample collected at intervals) of length110 ft (approx. 34 m) was collected from the studyarea to study the aquifer sediment dynamics using metal speciation study. Of the 30 groundwater samples 76% were above WHO limit (10µg/L). The depth of handpumps and borewells showing As more than 10µg/L were <35m in depth. The aquifer sediment study undertaken shows that As was associated in the order residual > reducible > acid-soluble > oxidizable for different fractions of the sediments. A considerable % (0.5%) of As is present in the acid-soluble fraction (47 to 373µg/L) which can be easily exchangeable during the sediment–water interaction, thus, posing a threat for severe groundwater contamination with changing redox conditions in the aquifer sediments. The enrichment factor for As in the sediments shows moderate to very high enrichment for the core sediments