The hydrochemistry of the water resources in Pangi area (Kadkan, NW Torbat Hydarieh), has revealed high concentrations of Cr and heavy metals (Cd, Ni, As) exceeding maximum permissible limit. The result of measurement by GFAAS showed that the highest Cr concentrations were found in waters in the vicinity of chromite mines. The high levels of Mg2+, Na+, Cl-, SO42-, HCO3- and Cr in the stream sediments often exceed the thresholds of the WHO standards. The water samples of the study area display pH with a mean 8.5, TDS with a mean of 1259 mg/l and EC showed 1978 μs/cm. Hydrochemical facies using Piper trilinear plot delineated two water samples as Na-Cl facies with Ca-SO4, Mg-Cl, Na-HCO3 and Mg-HCO3 facies as minor types. Local ophiolitic rocks, especially serpentinites and ultramafic units, are Cr-rich and represent a Cr source for groundwaters. Hydrogeological investigations confirmed high total Cr contents in soils and waters related to ultramafic rocks from northern ophiolitic zone. Cr(III) concentrations in resulting soils and sediments are magnified by weathering reactions, as a consequence of selective alteration of silicate minerals relative to chromite. The high concentrations of Cl-, Mg2+, Ca2+ and HCO3- well as high values of EC, pH and TDS in studied samples are related to weathering reactions of ferromagnesian rocks of ophiolitic complex. The abundance of Mn and Fe oxy-hydroxide (as electron acceptor) with Cr rich spinels in the study area, creates a chemical systems potentially able to increase the Cr(III) to Cr(VI) oxidation. Cr(III) is highly concentrated in areas where the dissolved oxygen content of less than 1 mg/l and pH is in the neutral range. The rate and amount of Cr(VI) in environment increases with increasing chromium concentrations and decreasing pH. As in the ophiolitic zone, pH is greater than neutral range (pH> 7.9) and DO>7.67 mg/l, Therefore, given the values of DO, Eh and alkaline pH of the water sample in the area, chromium in water resources area must contain significant amounts of Cr(VI) and is in the form of chromate (CrO42-). The hydrochemical data demonstrate that serpentinites and serpentine soils are main potential source of non-anthropogenic Cr(VI).The enrichment and variability of Cr in serpentinites and serpentine soils is directly related to the abundance and weathering of multicomponent spinel system.

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