Urban and agricultural environmental geochemistry and identification of heavy metals in the soil of Sari City (Mazandaran Province, Iran)

Urban geochemistry is the knowledge of applying the principles of geochemistry to find out the cause of the distribution of chemical elements in the ecosystem and to discover its impact on the health of living organisms. There are over 3000 years that cities have been built around the world and home to large numbers of people. It is predicated that the growing trend of population and urbanization reach to 60% until 2030. In general, urbanization means the spatial and economic concentration of people. Rapid-scale changes such as earthquakes, subsidence, and flooding in the natural environment concern people today, but the consequences of overexposure to chemical elements, organic material, and heavy metals such as mercury, lead, or dioxins causing permanent handicap are not known for people. Organisms are always in exchange of elements with the environment and human health requires receiving essential and nonessential elements in certain concentrations, and more or fewer elements in the human body will cause disease. Due to the importance of determining the concentration of heavy and toxic elements in urban soil sources, this study was conducted to identify geochemical contaminants in the soil of the Sari City area. The concentration of heavy metals with special importance of environmental aspect was sampled using the soil sampling standard in 196 stations from both topsoil and deep soil. Then, preparing and using the ICP-OES (Germany-G mbh) instrument was chemically analyzed. After processing the data and preparing environmental geochemical maps, metals affecting the pollution of urban and suburban soils of Sari City, which is used for agriculture and paddy, were identified. The results show that the lead concentration in the topsoil and deep soil does not have the same correlation and there is a possibility of differences in the origin of lead in the soil at these two depths. The concentration of arsenic and chromium at these two depths has the same correlation, and this probably confirms the same origin of these elements in the soil. In topsoil, the maximum correlation is seen between iron, vanadium, and aluminum. While in deep soil, the maximum correlation is related to arsenic, cadmium, copper, zinc, and potassium. Calculation of the index of geoaccumulation of elements shows that cadmium, potassium, and magnesium are in the class of non-contaminated to moderate contamination. Aluminum, arsenic, calcium, iron, manganese, and phosphorus are in the class of moderate contamination and in the class of moderate to high contamination. Also, chromium, copper, nickel, vanadium, and zinc are in the high contamination class and barium is in the high contamination to extreme contamination class. The results of calculating the pollution index also show that in three sampling sites in the southwest of the region, the area of Barik Absar and Sorkh Kala villages in the southeast of Nudeh region and Khan Abasi village, the pollution index is in the moderate risk class probably due to its proximity to wood and paper industries.