9. Understanding Hydrogeochemical Processes Governing Arsenic Contamination and Seasonal Variation in the Groundwater of Buxar District, Bihar, India

The presence of high concentrations of arsenic (As) in groundwater is a worldwide well known environmental problem in recent years (Nriagu et al. Arsenic in soil and groundwater: an introduction. In: Bhattacharya P, Mukherjee AB, Bundschuh J, Zevenhoven R, Loeppert RH (eds), Arsenic in soil and groundwater environment: biogeochemical interactions, health effects and remediation, trace metals and other contaminants in the environment, vol 9, (Ser ed Nriagu JO). Elsevier, Amsterdam, 2007). Most estimates of As pollution have focused on the predominance of As poisoning in the groundwater of West Bengal (India) and Bangladesh and thought to be limited to the Ganges delta (the lower Ganga plain) (Bhattacharya et al. Int J Water Res Dev 13:79–92, 1997; Bhattacharya et al. Arsenic in the environment: a global perspective. In: Sarkar B (ed) Handbook of heavy metals in the environment. Marcell Dekker, New York, 2002a; Ahmed et al. Appl Geochem 19(2):181–200, 2004; Ben et al. Appl Geochem 18:1417–1434, 2003). High As in the groundwater of the Lower Gangetic plain of Bangladesh and West Bengal was reported by Bhattacharya et al. (Int J Water Res Dev 13:79–92, 1997). Several authors suggested that the reductive dissolution of Fe (III)-oxyhydroxides in strongly reducing conditions of the young alluvial sediments is the cause for groundwater As mobilization (Ahmed et al. Appl Geochem 19(2):181–200, 2004; Bhattacharya et al. Int J Water Res Dev 13:79–92, 1997; Bhattacharya et al. Bull Environ Contam Toxicol 69:538–545, 2002b; Harvey et al. Science 298:1602-1606, 2002; McArthur et al. Water Resour Res 37:109–117, 2001; Nickson et al. Nature 395:338–349, 1998; Nickson et al. Appl Geochem 15:403–413, 2000). The reduction is driven by microbial degradation of sedimentary organic matter, which is a redox-dependent process consuming dissolved O₂ and NO₃ ⁻ (Stumm and Morgan. Aquatic chemistry: an introduction emphasizing chemical equilibria in natural waters. Wiley, New York, 1981; Bhattacharya et al. Int J Water Res Dev 13:79–92, 1997; Bhattacharya et al. Arsenic in the environment: a global perspective. In: Sarkar B (ed) Handbook of heavy metals in the environment. Marcell Dekker, New York, 2002a; Bhattacharya et al. Bull Environ Contam Toxicol 69:538–545, 2002b; Nickson et al. Appl Geochem 15:403–413, 2000). Overall, the quality of groundwater depends on the composition of recharging water, the mineralogy and reactivity of the geological formations in aquifers, the impact of human activities and the environmental parameters that may control the geochemical mobility of redox sensitive elements in the groundwater environment (Kumar et al. Environ Geol 50:1025–1039, 2006, 2007; Bhattacharya et al. Environ Geochem Health 31:23–44, 2009; Hasan et al. Environ Geol 57:499–511, 2009).