Arsenic Mobilization Process in Shallow Aquifer of Bengal Delta Plain: A Field Scale Study to Identify the Role of Coliform Bacteria

Abstract

In Bengal Delta Plain (BDP), shallow aquifer (<50 m) is often contaminated with Arsenic (As). The phenomenon is wide spread in nature thought the BDP notable in Nadia district of west Bengal. The present study highlights a primary screening of As, Fe, MPN and FC in monitored shallow wells. The study designed for two different sites (site-A, High As and site-B Low As area). The water quality monitoring results suggest that high As concentration (Range- 103-171 μgL-1) has been noticed in site A when compared with site B (range-53-99 μgL-1). In sites A, the Fe concentration is high and low in site B. The correlation study (r2) between arsenic and iron are also determined. The value of r2is 0.94 for site A and 0.73 for site B. The water quality results suggest that the nature of the monitor aquifer is anoxic in nature with low Eh, DO absent and low NO3- and SO4+. Major anion is HCO3- (376 mgL-1) followed by Cl- (28 mgL-1). However chloride concentration is largely varying in the monitored tube well. Microbial study (MPN & FC count) also indicates some relationship among MPN (r2-0.32) and Fe (r2 -0.24). However the relationship is scatter when As concentration is low. The linear trended has also obtained when both As, MPN and FC are high. The physical observation of plate count (Color reaction in Chromo colt Agar) has also been observed. This is a clear indicator of fecal coli form contamination. The study indicates that the microbial mobilization of As is the key factor for enrichment of As in ground water. The possible sources of the microbes are local land-use pattern (notable pit-latrine). Finally, the study highlights the role of coli forms bacteria (Both facultative and non-facultative) are wide spread in shallow rural aquifer of Bengal. Thus microbial process possibly enriches arsenic in shallow ground water.