INVESTIGATING THE OCCURRENCE OF ARSENIC AND MANGANESE IN URBAN AQUIFERS OF CHITTAGONG, BANGLADESH

While serious health effects due to extensive consumption of groundwater elevated in arsenic (As) have been documented in several countries, the source and mechanisms responsible for As mobilization in aquifers remain poorly understood. This happens particularly, in coastal city Chittagong, Bangladesh where flood plain and coastal aquifer systems occurred in the sediments of Quaternary age. The study area has the complex groundwater system; the northern part of the city is a part of Anticline associated with Tertiary aquifer system and the southern part of the city is more or less plain land. The unique geological settings of Chittagong provides opportunities to understand the hydro-geochemical processes that fuel arsenic concentrations in both Quaternary and Tertiary aquifer systems. This is a growing globally significant environmental and public concern because similar type of groundwater aquifers are the principle sources of drinking water and irrigation water for billions of people worldwide. Field studies conducted by researchers earlier had reported the elevated arsenic and manganese in groundwater of plain land and coastal aquifers of Chittagong. However, as to date, no hydro-geochemical study has been conducted to understand the hydro-geochemical processes that control the arsenic distribution in water and sediments. In light of this suggestion, aquifer sediments were collected from two sites of coastal city Chittagong, Bangladesh. Total 30 core samples at 1.5 meter intervals were collected from subsurface sediments of each site. The samples were run by the optimized handheld XRF for elemental abundance particularly heavy metals including Pb, Cd, Cu, Zn, As, Fe, Mn. Acid leachable arsenic was determined in all core samples by modifying the existing Econo-Quick testing arsenic field kit method. The results obtained from the depth profile for sedimentary arsenic showed consistency with the groundwater arsenic profile, measured on site by ETS test kits in existing private wells at different depths. An improved understanding of these processes has broad implications to assess the risks posed by the As-&Mn-enriched sites and to design the mitigation strategies.