Soil is regarded as one of the natural slow biodegradable source which plays an important role in the cycle of mineral and organic elements. As a dynamic ecosystem, it provides the life for big and small creatures, so removing its pollution is of considerable attention. The pollution of heavy metals not only affects directly the physical and chemical features of soil and reduces biological activities and access to nutrition materials in soil, but also is considered as a serious danger for human health. In fact, they can enter food chain or penetrate underground water sources.Iran is one of the oil-rich countries in the world in which high amount of oil is extracted in southern regions and refined in other places yearly. Once oil is extracted, transmitted and refined, its release in the soil causes pollution. A group of soil pollutant sources is related to oil discoveries, production, saving, transmission, distribution and final burial of wastes. If these industries are pollutants, they will cause dangers. The increase of soil pollution by heavy metals has led to a lot of research.
2-Materials and methods:Kermanshah province is located to the west of Iran sharing borders with Lorestan, Kurdistan, Ilam and Hamedan and an international border with Iraq. Its geographical coordinate is between (33˚37̕to 35˚17̕) northern longitude and (45˚20̕ to 48˚01̕) eastern longitude. Since Kermanshah Refinery is built on alluvial terraces, fans of new low foothills and Inceptisols and Vertisols,15 samples of surrounded soil were collected by an iron shovel from the depth of 15 to 25 cm. ICP-MS method, were used to analyze and determine the density of heavy elements in of the samples. Grinded to the sizes less than 4 mm by crusher, the samples were become powder to the size of 75 microns (200 mesh) by disc mill. Weighing the samples by Teflon pipes in digest 4 acid, hydrochloric, perchloric, nitric and choloridric acid were added to the samples equally. All samples were kept in Hot Box case. After complete digest operations, the samples were cold in the environment temperature and achieved volume by distilled water.
3-Results and discussion:The findings from geo-accumulation index shows that the intensity of Refinery soil is classified in the range of no pollution to average regarding chromium and nickel. Besides, enrichment index indicates average enrichment for cadmium (station 14), copper (stations 13, 11, 2 and 14), lead (stations 6 and 13), zinc (stations 11, 6, 2, and 13) and chromium (the stations from 6 to 15). In addition, pollution bar index of chromium, copper, nickel, zinc and lead is more than 1 proving the inappropriate soil quality and soil pollution of the region. However, chromium has the most considerable value, 2/75. Average value of EF is less than 2 for arsenic, cobalt and vanadium proving that the region does not show enrichment for the aforesaid elements. Enrichment index values for cadmium, chromium, copper, nickel, lead and zinc are between 2 to 5 indicating average enrichment of these samples than other metals. Since enrichment element for these sample are higher than 2, they have anthropogenic source.
According to Pearson correlation coefficient, there is a high correlation between nickel and chromium, scandium and cobalt, vanadium and chromium, and zinc and copper and lead indicating the equal source or similar geochemical behavior of the elements toward each other. Since vanadium is considered as one the oil pollution indices, it can be concluded that high pollution of this element and chromium around the region comes from petroleum.
4- Conclusion:The findings from the present study shows that soil surrounded Kermanshah Refinery are polluted to some elements. According to the values of geoaccumulation in the studying area, elements nickel and chromium have pollution. The finding from enrichment factor indicates the average enrichment of the region soil by chromium and lead. Besides, enrichment factor higher than 2 for lead and copper proves anthropogenic interference factors in the region pollution to them. The results from pollution bar for chromium, nickel, zinc, copper and lead is more than 1 indicating soil pollution to these metals. Pearson correlation coefficient reveals that there is a high correlation among vanadium, cobalt, chromium, and nickel proving same origin. Making zoning map of heavy metal density in the region soil demonstrates that high density of the elements in some stations is related to petroleum producing installations and storage tank. Cluster analysis shows the division of the elements into 7 clusters. Besides, the elements with structural relationship are related in next subcategories. Clusters 6 and 7 together indicate the same origin for these elements. Since vanadium is derived from oil compound, it can be concluded that chromium and nickel pollution have the same pollution origin with oil compounds. Factor analysis introduces 3 main factors in which the first factor with total 40/1% of total variance is the most effective factor in density of the soil elements. This factor has a high positive correlation with Sc, V, Ni, Cr, and Co proving the same density origin with petroleum compound.