| Summary: | Introduction<br>
Heavy metals are the most toxic pollutants in aquatic ecosystems. This contamination can result from the release of heavy metal elements during alteration and weathering of ultramafic and mafic rocks (ophiolite zones). Among the important metals and pollutants in the ophiolite; chromium, cobalt, nickel, iron, magnesium, manganese, zinc and copper could be noted. Basically, a mass of serpentine consists of serpentine, amphibole, talc, chlorite, magnetite, and the remainder of olivine, pyroxene and spinel (Kil et al., 2010). In such areas, the prevailing cold climate, during the serpentinization, chloritization and epidotiization, the activity of the solvent, such as chloride, fluoride, carbonates, sulfide, sulfosalt would be able to import the elements such as magnesium and iron, copper and zinc into the soil and groundwater. The study area is located in northwestern Iran. This area is located in the northwest of the city of Khoy. <br>
Because of the proximity to the north and northwest Khoy plains with ophiolite rocks, the soil of this region could possibly show the potential of contamination with heavy metals. Due to the toxicity and disease of unauthorized grades of these elements in groundwater in the study area, this study is focused on the more contaminated groundwater of the areas. <br><br>
Materials and methods<br>
In this study, over a period of 5 days, sampling from 42 water sources, including fountains, aqueducts, wells, piezometers and wells in operation, was performed. The container was washed with acid and then rinsed 3 times with the water sample. The pH and temperature of the water in the samples was measured in the field. Then to each of the samples was taken from 2 to 5 ml of concentrated nitric acid (This causes that the metal elements would not adsorbed or precipitated by these particles) and pH of the samples was measured with litmus paper to reach level 2. This was done to ensure the consolidation of the water samples. Analysis of samples carried out in the chemistry laboratory of the University of Urmia. All water sampling procedures were performed based on standard protocols (SMEWW, 2010). The maximum concentration of heavy metal contamination of drinking water with EPA, WHO and national standards were compared. In this study, the chemical analysis of heavy metals, were used by graphite furnace atomic absorption spectrometry (at ppb) for the elements Cu, Mg, Fe and Zn. Concentration of the heavy metals in acidified water samples (pH value of 2), using a flame atomic absorption spectrophotometer were analyzed. <br><br>
Discussion<br>
There are enormous amounts of Fe and magnesium in groundwater from the north and northwest Khoy plain, and the amount of Cu and zinc are in the normal range in water resources. The source of iron and magnesium in the groundwater of the study area is ultramafic and mafic rocks of the Khoy ophiolite complex. Weathering of ultramafic and mafic igneous rocks such as peridotite, olivine basalt, gabbro and pillow lava and then soil formation, high concentrations of the elements Mg and Fe were transferred to soil. Ferromagnesian olivine is formed Mg2+ and Fe2+ ions and tetrahedral silicon. If sufficient amount of Mg2+ and Fe3+ ions combine with silicon and oxygen, silicon into the soil, forms silicic acid (H4SiO4), or magnesium or iron smectite (clay minerals) (Alexander et al., 2007). Several types of pyroxene are more stable than olivine. Orthopyroxene during weathering decompose into talc and smectite. Magnesite (MgCO3) is present in some serpentine soils. <br>
With respect to the empirical relationship (Kierczak et al., 2007) and based on temperature and rainfall, the study area with a drought index of 12.48 places in the category of semi-arid-cold climate between 10 and 19.9. Temperature changes in the condition cause weathering and leaching of serpentine soils, and subsequently can remove large amounts of magnesium. Weathering and leaching serpentine soils, releases immediately magnesium and its concentration in soil decreases. As a result, the concentration of the element in the water increases. <br><br>
Results<br><br>
Based on the charts and maps of iron, magnesium, zinc and copper contaminations, it is found that the concentrations of Fe and Mg in the north and northwest Khoy plain are higher than the permissible limit for drinking water. In some parts of the sample, the concentrations of Cu and Zn are exceeded WHO. However, based on EPA standard, the amount of copper is less than the limit. On the basis of three criteria: EPA, WHO and national standards, except for the village Ghez Ghaleh, zinc concentration is below the standard. According to the geological map of Khoy, the Khoy ophiolite complex containing mafic rocks and ultramafic is a source of iron and magnesium in groundwater. <br><br>
Acknowledgements<br>
Editor of the Journal of Economic Geology, Professor Mohammad Hassan Karimpour and reviewers of this article are acknowledged for their unwavering assistance. Also, the authors thank Deputy of Research of the University of Urmia for the support required for this study. <br><br>
References<br>
Alexander, E.B., Coleman, R.G., Keeler-Wolf, T. and Harrison, S., 2007. Serpentine Geoecology of Western North America, Geology, Soils, and Vegetation. Oxford University Press, London, United Kingdom, 512 pp. <br>
Kierczak, J., Neel, C., Bril, H. and Puziewicz, J., 2007. Effect of mineralogy and pedoclimatic variations on Ni and Cr distribution in serpentine soils under temperate climate. Geoderma, 142(2): 165–177. <br>
Kil, Y., Lee, S.H., Park, M.H. and Wendlandt, R.F., 2010. Nature of serpentinization of ultramafic rocks from Hero Fracture Zone, Antarctic: Constraints from stable isotopes. Marine Geology, 274(1): 43–49. <br>
SMEWW, 2010. Standard Methods for the Examination of Water and Wastewater (SMEWW). American Public Health Association (20th Edition), New York, 2671 pp. <br>
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