Arsenic in groundwater of matured bengal delta plain a case study in nadia

Abstract

The ground waters enriched with natural arsenic in different chemical forms are now newlinesignificantly noticed from BDP and elsewhere. In BDP, shallow aquifers (lt50 m) are newlinelargely affected with arsenic. The groundwater is frequently contaminated with arsenic newlinewhere levels are often exceeding WHO guideline value (As T lt 10 µgL-1). The large scale newlinenatural arsenic groundwater contamination has been usually associated with strong newlineto moderate reducing aquifers of young BDP, for example, arsenic affected areas of newlineNadia district, West Bengal, India. In Nadia, the arsenic contaminated groundwater is newlineoften found in young sediments (Holocene), low-lying areas of flood basin and flood newlineterrain, where groundwater flow are slow and sluggish with poor aquifer flushing. newlineHistorically, these are deltaic environment. The delta building process and sediment newlineenvironment are the major platform to host he sediments. The geomorphological newlinefeatures are important and also found throughout the district. Nadia is grouped into newlinetwo major land-forms such as UDP (Upper Deltaic Plain) and LDP (Lower Deltaic newlinePlain). Both land-forms are adorned with several surficial features. The arsenic newlinecontent of the aquifer materials is not regularly high (up to 18 mg.Kg-1). However, newlinegroundwater arsenic content is often exceptionally high (up to 1186 µgL-1). The newlinechemical composition of the groundwater is also varying in between the blocks as well newlineas locally and regionally. The most notable features of the groundwater is their newlinepredominantly reducing conditions at near neutral pH with high redox sensitive newlinespecies (Fe, Mn and As). Arsenic is released to groundwater majorly by desorption newlinefrom iron bearing minerals which is often coated on sand and/or mica under local newlinereducing conditions. Often observed arsenic distribution pattern (spatial variability newlineand depth variability) is largely heterogeneous. newline