assessment of heavy metal contamination in surface sediment of the darreh-morad beyg river

background and purpose: the heavy metal pollution and its fractionations in the surface sediments of darreh-morad beyg river, hamedan city were monitored for cd, cr, cu, fe, ni, pb, and zn in 2014.   materials and methods: totally 30 surface sediment samples were taken from 10 stations with three replicates. the samples subjected to bulk digestion and chemical partitioning. the concentrations of heavy metals in sediment were determined by icp-oes. i-geo, ef, cf, and pli were also used to assess the sediment contamination. results: the results of the present study showed that the proportions of residual fraction for cu, ni, pb, cd and especially cr (93.61%) were relatively high, which implied their lower pollution risks due to low mobility characterization, while zn was mainly associated with the anthropogenic portion of the existing pollution which meant an increase in mobility for this element. also, on the basis of the mean, the i-geo values of metals were found in the following order: cr>cu>zn>ni>pb>fe>cd. at the same time, the average ef of metals in the sediment samples was in the order of cr>cu>zn>ni>pb>fe>cd. according to the calculated pli, the pollution class of heavy metals in sediments from the darreh-morad beyg river was between 1 and 2, indicating a moderately polluted degree. conclusion: regarding the high zn concentrations in sediments, it is likely that this element is a major hazard for the aquatic environment since it is mainly found in the anthropogenic portion. also, cu, ni, pb, cd, and cr are present in the greatest percentages in the residual fraction, which implies that these metals are strongly linked to the sediments.