Study of distribution of soil pollution by heavy metals with geostatistics and fuzzy clustering in Dizajabad area, Zanjan Province

This study was conducted to know the intensity and spatial pattern of soil heavy metals pollution around the national Iranian lead and zinc complex factories in Dizajabad area, Zanjan province. A sum of 272 surface samples (0-10 cm) were collected based on a grid methods with nodes of 250 and 500 meters and the samples were extracted with HNO3 and the concentrations of Pb, Zn and Cd were determined. Average concentrations of Pb, Zn, and Cd in soil were 181.3, 182.28 and 1.48 mgkg-1, respectively. To study spatial pattern of variables, experimental variograms were calculated and best model was fitted in each case, which was exponential for all. Influence ranges for variograms of Pb, Zn, and Cd were 1131, 1073 and 1026 m, respectively. Using ordinary kriging method, interpolation was carried out, which performed well. To classify the data in taxonomic space, a fuzzy c-means with extragrades clustering algorithm was run on the data using several fuzziness exponents (Φ). Plausible fuzzy clusters were obtained at Φ=1.2. To find 7 as the optimal number of classes from a 2-10 assemblage, fuzziness validation functions F, H and S were used. Most polluted classes A, B, E and G are located at center and around the factory, while C, D and F are covered northern, northeast and southeast parts of the study area. Major parts of extragrade class was the location of factory and landfill compliance.