Abstract
A groundwater arsenic (As) distribution in Faizabad, Gonda, and Basti districts of Uttar Pradesh is shown in the entrenched channels and floodplains of the Ghaghara River. Tubewell water samples were analysed for As through flow injection hydride generation atomic absorption spectrometry (FI-HG-AAS) system. About 38, 61, and 42 % of tubewells in Faizabad, Gonda, and Basti districts, respectively, have As >10 µg/l (WHO guideline). Moreover, 15, 45, and 26 % of tubewells in Faizabad, Gonda, and Basti districts, respectively, have As above 50 µg/l. About 86, 69, and 35 % of tubewells in Faizabad, Gonda, and Basti districts, respectively, are from shallow depth (21–45 m), and it is worth noticing that 47 % As-contaminated (As >10 µg/l) tubewells in these three districts are located within the depth of 10–35 m in Holocene Newer Alluvium aquifers. The high content of As (7.11 mg/kg) is measured in suspended river sediments of the Ghaghara River. Most of the As-contaminated villages in the Ghaghara Basin are located close to abandoned or present meander channels and floodplains of the Ghaghara River. In contrast, tubewells in Faizabad, Ayodhya, and Nawabganj towns are As-safe because of their positions on the Pleistocene Older Alluvium upland surfaces. Quaternary geomorphology plays an important role in groundwater arsenic contamination in the Ghaghara Basin. The sources of groundwater arsenic are geogenic and perennial mountainous rivers in the Ghaghara Basin supplied high sediment loads. The arsenic in groundwater of Ghaghara Basin is getting released from associated sediments which were likely deposited from the Himalayas. The process of release of groundwater arsenic is reductive dissolution of iron hydroxides.
Highlights
Arsenic (As) is found in soil and groundwater by natural and anthropogenic sources
Groundwater As distributions in entrenched channels and floodplains of the Ghaghara River are divided into three parts viz., (1) Pleistocene Older
I.e. Varanasi Older Alluvium with oxidized to yellow–brown coloured sediments, and aquifers are As-safe in groundwater, (2) narrow belts of older floodplains covered with Holocene sediments on top, and aquifers are locally As-contaminated, and (3) Holocene to recent entrenched channels and floodplains of the Ghaghara River and tubewells are highly As-contaminated in groundwater (Fig. 2)
Summary
High concentrations of As is one of the most hazardous chemical elements in drinking water in several parts of the world. The major switch from polluted surface water to groundwater in early 1970s helped people to avoid waterborne diseases, but naturally occurring high concentration of dissolved As in groundwater of alluvial aquifers has been causing serious health problems in millions of people for the last three decades. The mode of occurrence, origin, and mobility of As in sedimentary aquifers in the Bengal Delta and other fluvial-deltaic setting in different parts of the world are mainly influenced by local geology, geomorphology, hydrogeology, and geochemistry of sediments and water, as well as anthropogenic activities (Nickson et al 1998; Acharyya et al 2000; Kinnibugh and Smedley 2001). The worst As-affected regions in Asia are mainly Bangladesh and West Bengal in India
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