Potential risk assessment and hydrogeochemical characteristics of Chromium in Golbou water resources, Norf Torbat Heydarieh, Khorasan Razavi

The study area, located in north Torbat Heydarieh, contains ophiolitic units comprised by chromium-bearing minerals such as Spinel. The results obtained from water samples analysis using XRF indicate high chromium concentrations in ophiolite complex as major source. Serpentinite, the dominant lithology in the area, comprises excess chromium concentration, being responsible for chromium-polluted water resources. As well as average chromium concentration severely decreases from serpentinite to other lithological units. Hydrogeochemical investigation of water resources that major cations and anions are in the order of Na>Mg2>Ca2>K and Cl->HCO3->HSO42-, respectively. Regarding piper diagrams, water samples indicate a variety of facies (water type) including Na-HCO3 (3 samples), Na-Cl (3 samples), Ca-HCO3 (3 samples), Mg-Cl (3 samples) and Mg-HCO3 (2 samples). Comparing with WHO (2011) permissible chromium limit, water resources of the study area indicate excess chromium concentration. Due to limited chromite mining in the area, the anthropogenic activity
could not be responsible for the elevated chromium level in the water resources, suggesting the dominant geogenic source of chromium. The abundance of Fe-Mn oxy-hydroxides in most sites of the area leads to chromium oxidation from Cr3 to Cr6. Average values of pH> 7.6 and DO> 7.67 mg/l of the water resources also reflect that Cr chiefly occurs as Cr6 and Cr2O72- and CrO4- deposits.