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National project of Important Heavy Metals Identification of Iran (IHMI), following the UNDP and supported by Department of Environment of Iran (DOE), has been completed by Modares Environmental Research Center (MERC). Due to this project the pollution potential sources was investigated by overall distribution maps of any parameters that may cause the lead pollution. Then the sampling points was determined by some geo-statistical analysis and the sampling process was done according to standard methods of sampling, preserving, transferring to lab, measuring and analyzing etc through the 3 months in three phases of materials (effluent and discharges, solid waste, water, soil and sediment samples from natural sources like river etc.). After gathering the final results, overlaying the potential sources and polluted positions (according to violation of national and international standards of sampled points) by Geographic Information Systems (GIS) led the research to closing to the pollutant sources in north west provinces (Eastern Azerbaijan, Western Azerbaijan, Ardabil and Zanjan). The synthetic and natural pollution sources observed were 17 and 20 respectively. Abir River, Niroo Gostar Taban Industrial Complex and Copper Industries were the most important pollution sources in material phases of Natural, effluent and solid waste respectively. This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 7Article available at

Abstract. Heavy metals are stable and persistent pollutants of the environment, and can cause both natural and anthropogenic pollution in the environment. Therefore, they are regarded as a serious risk for survival of living organisms. In order to reduce environmental problems of these metals, we need to identify natural and anthropogenic resources of them. Indeed, identifying the risk factors and awareness of the amount and effects of pollutants on the one hand, and accurate ranking of the polluting units on the other are essential steps for proper evaluation and timely and appropriate response to these risks, resulting in reduced damage due to them. The purpose of this study is to identify potential pollution sources of heavy metals of mercury, arsenic, lead, cadmium and chromium in Zanjan Province of Iran and their sampling, in order to present an index for ranking polluting units using appropriate scientific approaches like multi criteria decision making for a more accurate and quantitative assessment of risks and planning response to them in due time. The results of this study indicate that among 26 sites sampled, Mineral Processing Corporation of Iran is the most critical place of environmental risk in Zanjan province.