ABSTRACT

This paper reports the extended study from a previously-described study on As and F contaminated groundwater from a small village, Kalalanwala, in east Punjab, Pakistan (Farooqi et al., 2007). Of the 147 groundwater samples investigated, 91% exceeded the WHO standard (10 μg/L) for As and 75% exceeded the WHO standard (1.5 mg/L) for F^-. The highly contaminated As (max. 2400 μg/L) and F^- (max. 22.8 mg/L) groundwaters were found from shallow depths down to 30 m from the surface. The contaminated groundwaters are characterized by high pH (max. 8.8), alkalinity (HCO₃^- up to 1281 mg/L), SO₄^2- (max. 960 mg/L), Na⁺ (max. 1058 mg/L) and maximum electric conductivity >4.6 mS/cm. Fluoride concentrations showed positive correlations with those of Na⁺ and HCO₃^- and negative ones with Ca²⁺ and Mg²⁺. The alkaline waters were saturated with calcite in spite of the low Ca²⁺ concentrations. Fluoride concentration is governed by fluorite solubility. Speciation analysis showed As is mostly in the form of As^V. There was a positive correlation between As and pH, while there is no relationship between As vs. Fe and F^-. Thus, the fluoride and As contamination occurred in the oxidizing and alkaline conditions of the groundwater. However, F^- and As are derived from two or more sources. Suspected contaminant sources in the study area contained considerable amounts of F^- and As; fertilizers (DAP, n = 5) contained leachable F^- ranging from 53-255 mg/kg, and As 5-10 mg/kg, and coals (n = 8) contained F^- ranging from 5-20 mg/kg. Sulfur isotopic ratios indicated that the high SO₄^2- in groundwater (3.2-7.0‰, CDT) is mainly derived from coal combusted atmospheric pollutants, fertilizers and household wastes. Nitrogen isotope data (8-30‰, Air) showed that NO₃^--N is attributed to animal waste distributed in the study area. The major chemical characteristics of the groundwaters are related with anthropogenic activities on the ground surface. The resultant major chemistry, especially highly alkaline and low Ca²⁺ and Mg²⁺ concentrations, must promote the high concentrations of F^- and As in the studied groundwaters.