Evaluation of Spatial Distribution of Heavy Metal pollution Using Pollution Factor and Geo - Accumulation Index in the Surface Soil of Gorgan Hazarpich Landfill

Landfills are one of the sources of heavy metal pollution worldwide. The increasing expansion of urban life and the excessive increase of the urban population have caused an increase in the production of all kinds of waste materials. One of the problems of rapid population growth and industrialization in third world countries, especially Iran, is the improper disposal of waste and and pollution caused by it. One of the issues that should be paid special attention to is the burial of these wastes and urban solid wastes, water and gases produced from the decomposition of wastes containing organic compounds. The purpose of this study was to investigate the impact of Gorgan urban waste disposal landfill with a burial history of more than 37 years, in the Hazara Pitch area, on the spatial distribution of heavy metals including nickel, cadmium, lead and copper in the soil of the area. The amount of pollution was investigated using the environmental indicators of spatial distribution of heavy metals, pollution factor, Geo-accumulation and Pollution Load. By conducting preliminary studies and taking into account the existing basic maps, 110 samples were prepared from zero to 30 cm depth with regular intervals and finally, the amounts of heavy metals were measured using an atomic absorption spectrophotometer. The obtained results showed that the concentration of heavy metals in the collected samples was the highest in zinc, lead, copper and cadmium, respectively. The average concentration of heavy metals cadmium, lead, copper and zinc respectively increased by 2.25%, 1.01%, 0.99% and 0.63% compared to the background, which indicates the presence of a source of point pollution in the study area.Spatial distribution according to the extracted maps showed that the high level of concentration of heavy metals in the central and northwestern parts of the studied area was indicated by the location of the landfill. The humid climate and the presence of topography in the area have caused the release of waste leachate by runoff, but with increasing distance from the landfill site, the downward trend of the concentration of pollutants is evident. The pollution factor in the target area indicated moderate contamination for lead, copper and zinc heavy metals and Severe contamination for cadmium metal. The results related to the Geo-accumulation index also showed that the average value of this index in cadmium is in the " slightly contaminated " Contamination class and in copper, zinc and lead it is in the " Uncontaminated to slightly contaminated " Contamination class. Also, according to the average value of the pollution load index, the surface soil has a Moderate contamination load, and the results of the pollution load confirm the contamination of the soil with heavy metals.The highest concentration of heavy metals can be seen in the vicinity of the landfill, and there was a decreasing trend as the distance increased based on the available slope and topography. It seems that the source of heavy metal pollution was the landfill, and the main factor of spreading the resulting leachate was spreading the pollution to the surrounding areas based on the topography of the area and in the direction of the slope.