CONCENTRATION AND SPATIAL DISTRIBUTION OF TOTAL AND BIOAVAILABLE HEAVY METALS IN TOP SOILS IN TAHAM DISTRICT OF ZANJAN PROVINCE-IRAN

Toxic elements like heavy metals are natural constituents of the earth's crust and a number of these elements are biologically essential at trace levels and play an important role in human health. Heavy metal contamination of soil is a widespread problem in Zanjan province located in North West Iran due to natural pedogeochemical background and anthropogenic sources. Taham district was selected for detail study and the objectives of the study were set to evaluate the total as well as bioavailable fraction of heavy metals in surficial soils within the studied area. 57 surficial soil samples were collected and analyzed for heavy metal contamination by Atomic Absorption Spectrometry (AAS). The obtained results when compared with WHO and EPA standards show a very high concentration of some toxic metals notably As, Pb and Cd. Bioavilable fraction of studied metals was also measured with formation of metal complex with Diethylene Tri Amine Penta Acid (DTPA) agent. To find the share of the anthropogenic sources in the contamination of soils, the Enrichment factor (Ef) and Geological accumulation index were measured and the distribution maps were drawn using Arc GIS (9.3). High concentrations of some toxic metals like As, Pb and Cd were found in isolated patches in North West, East and South West of the studied area originating both from pedogenic as well as anthropogenic sources. Soil contamination by metals was very high around industrial town and agricultural lands within the studied area. The most effective factors responsible for high concentrations of other elements like Cu, Co, Ni and Fe in soil were found to be pedogenic in nature.

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