Evaluation of high levels of fluoride, arsenic species and other physicochemical parameters in underground water of two sub districts of Tharparkar, Pakistan: A multivariate study

Abstract

In present study total arsenic, inorganic arsenic species and fluoride ion contaminations in underground water of Diplo and Chachro sub district of Tharparkar, Pakistan were investigated. The concentrations of total As, inorganic As species, F− and others physicochemical parameters were reported in terms of basic statistical parameters, principal component analysis, cluster analysis, sodium absorption ratio and saturation indices. The As3+ was determined by cloud point extraction using ammonium pyrrolidinedithiocarbamate (APDC) as complexing reagent, and complex was extracted by surfactant-rich phases in the non-ionic surfactant Triton X-114; after centrifugation the surfactant-rich phase was diluted with 0.1 mol/L HNO3 in methanol. While total inorganic arsenic (iAs) was determined by solid phase extraction using titanium dioxide (TiO2) as an adsorbent, after centrifugation, the solid phase was prepared to be slurry for determination. The extracted As species were determined by electrothermal atomic absorption spectrometry. The concentration of As5+ in the water samples was calculated by the difference of the total iAs and As3+, while F− and other anions were determined by ion chromatography. The positive correlation of F− and As species with Na+ and HCO3− showed that the water with high salinity and alkalinity stabilized the As species and F− in the groundwater. The positive correlation (r = 0.640, p = 0.671) was observed between total As and it species with F−. Results showed that underground water samples of these two areas of Tharparkar were severely contaminated with arsenic and fluoride ion, which are exceeded the World Health Organization (WHO) provisional guideline value, and United States Environmental Protection Agency, maximum contaminant level of 0.01 mg/L and 1.5 mg/L, respectively.