Urbanization in developing countries has caused extensive soil and environmental contamination with heavy metals. Determination of pollution indices and fractionation of heavy metals in soil is pivotal for assessment and prediction of their mobility and hazard potentials in the environment. Therefore, in this investigation pollution factor as single (PF) and comprehensive (Pn), pollution load index (PLI) and sequential extraction technique were used for Ni, Pb, Cd, Zn, and Cu in soils affected by municipal wastewater in some large cities of Hamedan province, western Iran. According to results, PF factors for heavy metals in Hamedan, Malayer, Razan and Kabudarahang were respectively 2.47-27.40, 2.44-28.80, 2.46-27.20, and 2.50-27.10. PF results indicated that pollution intensity were 21.6-26.56 (very high) for Ni, 4.52-4.81(High) for Pb, 21.90-28.80 (very high) for Cd and 2.44-2.74 (medium) for Zn and 11.85-13.92 (very high) for Cu in the studied sites. Pn and PLI were 20.89-24.88 and 9.44-10.16 in the studied area, respectively. According to results, the OM fraction was the most abundant pool for Ni, Pb, and Cd. The mobility of metals in calcareous soils acquired for Ni (22.81%), Pb (15.32%), Cd (17.88%), and Cu (18.18%) was a representative of potential risk for groundwater contamination through deep percolation or runoff. The bioavailability factor related to each metal was estimated for Ni (26.51-35.72 %), Pb (27.67-35.55 %), Cd (30.22-39.51 %), Zn (22.06-26.71 %), and Cu (22.88-27.34 %). Such high bioavailability of heavy metals especially for Cd can severely impose adverse effects on the environment, groundwaters and accordingly human health
