Heavy Metals Contamination Assessment in Soils of Different Land Uses in Central District of Zanjan Province Using Contamination Factor

The study area is about 2000 km2 which is important in terms of agriculture, industry and residential complexes. For the purpose of evaluation, 241 samples of surface soil were taken based on systematic nested method from the land soils in the depth of 0 to 10 cm that were under agriculture, pasture and urban uses. The total concentrations of heavy metals of the samples were determined by an atomic absorption spectrometer following the extraction with 5N nitric acid. The results showed that the total amounts of lead, zinc, cadmium and copper in the soil of the studied area were 1.6, 2.0, 4.0, and 1.5 times higher than those in the soil of the natural background respectively. The total concentrations of iron, manganese, chromium, cobalt and nickel in samples were less than those in the background soil. Based on the contamination factor, in the most of samples, concentration of the iron, manganese, chromium, cobalt, nickel and copper were in low to moderate and Pb concentration in 10% of the samples was in high contaminated classes. More than 40 percent of the area was highly polluted with Cd. High levels of contamination factor for lead, zinc, cadmium and copper (Group I) were found in urban land area and contaminated soils with iron, manganese, chromium, cobalt, and nickel (Group II) were observed in agricultural and pasture lands. Overlaying the maps of contamination factors with those of land uses showed that the first group of heavy metals were mostly affected by human activities and the second group by parent materials.