Arsenic speciation: Sources of salinity and its impact on mobilization of arsenic and fluoride in groundwater of Rachna Doab

Abstract

The current research was based on studying the sources of groundwater salinity in Rachna Doab, Pakistan and its possible impact on the enrichment of arsenic and fluOlide levels. Por this purpose blanket sampling was conducted throughout Rachna Doab to test the occurrence of salinity, As and P-. The groundwater was found to have varied TDS concentrations i.e., 233.6 to 4556.8mgll. Based on the results of blanket sampling representative groundwater samples from all villages were selected. The samples were classified into three groups based on their TDS levels and analyzed for As, P- and other physicochemical parameters. As and P- concentrations in the study area ranged from below detection limits to 183.42)lgll and 3.9mgll respectively with the prevalence of both arsenate and arsenite in the area. Graphical biplots, stable isotopic analysis (8 18 0 and 8 2H relative to VSMOW), Gibbs plot and hydrogeochemical modeling of the groundwater samples revealed mineral dissolution, ion exchange processes and partial input of evaporation towards groundwater salinity in the region. The results were in accordance with the conceptual model developed based on secondary data. Na+ and CI- were the major cation and anion identified in the area with reference to elevated TDS levels. Piper plot reflected NaCI as the dominant water type in moderately saline samples whereas CaHC03 mainly prevailed in non-saline water samples. The moderately saline samples were found to have high fluoride levels (greater than WHO level) with the exception of one sample suggesting a positive influence of groundwater salinization on groundwater P- levels. Groundwater As levels showed an overall decreasing trend with increasing salinity identifying a negative effect of salinization on enrichment of arsenic in ground water.