Pollution Assessment of Soils in Ophiolitic Robat Sefid Area (Khorasan-e-Razavi)

The serpentinite soils in ophiolitic zone of Robat Sefid in 60km south of Mashhad (Khorasan-e-Razavi) were examined to evaluate the pollution potential of heavy elements in the area soils. Main parameters of soil texture, EC, pH, organic matter (OM%) and calcium carbonate equivalent (CCE%) were determined in geochemical lab of geology department in the Ferdowsi University of Mashhad. Total concentration of Cr, Ni, Co, Mn and Zn in soil samples were measured by using AAS analysis method. Selective sequential extraction (SSE) was conducted to determine those heavy metals concentration in 5 different soil phases based on Tessier method. Correlation coefficient of geochemical parameters, and also geo-accumulation index (Igeo) and enrichment factor (EF) were computed to assess the pollution level in the soil samples. Those calculated indices represented different levels of heavy metals enrichment and soil pollution in studied area. According to potential ecological risk index (RI), the risk was high. Also, pollution load index (PLI) value was more than 1, which indicates polluted soils. The correlation was significant between Cr, Ni and Co to sand (%), which indicate sand-size heavy metals bearing minerals such as chromites are abundant in the soils. Concerning the mobility factor (Mf) and risk assessment code (RAC), Co, Ni and Mn categorized in low to moderate levels. The Mn and Ni element with high activity and bio-accessibility could be considered as pollutant elements in the area.