Status of groundwater arsenic pollution of Mirzapur district in Holocene aquifers from parts of the Middle Ganga Plain, India

A groundwater arsenic (As) distribution in Mirzapur district of Uttar Pradesh is shown in the entrenched channels and floodplains of the Ganga River. A total of 45 tubewell water samples were analysed for As through flow injection hydride generation atomic absorption spectrometry (FI-HG-AAS) system. Iron in tubewell water was analysed by 1,10-phenanthroline method by the use of UV spectrophotometer. About 37.7 % of tubewells in this district have As >10 µg/l (WHO guideline) and 15.5 % of tubewells have As above 50 µg/l. About 84.4 % of tubewells have higher concentrations of iron (Fe) beyond its permissible limit 1 mg/l (BIS guideline). The iron (Fe) content in tubewell water samples varies from 0.1 to 7.6 mg/l. About 75.5 % of tubewells in Mirzapur district are from shallow depth (20–40 m), and it is worth noticing that 37.7 % of As-contaminated (As >10 µg/l) tubewells are located within the depth of 25–40 m in the Holocene Newer Alluvium aquifers. Most of the As-contaminated villages in Mirzapur district are located close to abandoned or present meander channels and floodplains of the Ganga River. In contrast, tubewells in Mirzapur and Chunar towns have low concentrations of As in groundwater (As <10 µg/l) because of their positions on the Pleistocene Older Alluvium upland surfaces. In As-contaminated areas, deeper tubewells (>50 m) in the Pleistocene Older Alluvium aquifers would be better option for As-safe groundwater. The potential sources of As are mainly from the Himalayas and the Himalayas rivers have high content of As in suspended river sediments.