GROUNDWATER ARSENIC: RESEARCH ACHIEVEMENTS AND PROSPECTS FOR REDUCING ARSENIC EXPOSURES THOUGH DRINKING WATER AND FOOD CHAIN

Arsenic (As) is a ubiquitous element in the Earth’s crust and one of the very few heavy metalloids and oxyanion forming elements. Elevated levels of geogenic As are encountered in groundwater globally, and the extent of contamination vary from a local scale to more regional and/or continental scale. The processes related to the mobilization and retention of As operate in a wide variety of hydrologic environments and groundwater pH ranges (6.5 to 8.5), under natural conditions in both oxidizing and reducing environments. An important outcome of present research reveals that the occurrence of As in each geographic location is related to geology, geomorphology, hydrology and land use pattern and needs site-specific attention to assess its controls and challenges for mitigation. The earliest example of groundwater arsenic poisoning groundwater from the high prolific shallow, Holocene sedimentary aquifers has undermined the success for achieving safe drinking water and food security in the Bengal Delta region in West Bengal, India and Bangladesh. As is mobilised in reducing environments through reductive dissolution of Fe(III)-oxyhydroxides. There has been a significant progress in characterization of source, understanding the mobilization process as a function of sediment-water interactions and the overall scenario of As distributions in the aqueous and the solid phases in the sedimentary sequences. Excepting the installations of tubewells within the targeted safe aquifers, no other mitigation option has been successfully implemented on a larger scale. Alternatively, increased demand for irrigation water resulted in shift from policy of predominant surface water to groundwater exploitation and the use of contaminated groundwater for irrigation has led to an increased bioaccumulation in the crops and emerges as an important pathway of As exposure to the population in the areas with arsenic contaminated groundwater. This warrants a further holistic approach for mitigation of the exposure risks from As in affected regions.