Abstract
The purpose of the present study is to assess the environmental impacts of municipal solid waste disposal on Babolsar beach, Mazandaran Province, and its effects on the adjacent soils. For this purpose, 15 surface soil samples and 10 leachate samples were collected and analyzed using standard methods. The concentrations of major and trace elements in soil and leachate samples were measured by ICP-OES and ICP-MS instruments, respectively. The obtained results indicate that the concentrations of Ag and Cu in all studied soil samples, and those of Mn and Ni in most samples, were higher than the world soil average composition. The average values of the elements' enrichment factors followed this trend: Ag (12.6) > Ni (6.3) > Mo (6.2) > Cu (5) > Cd (4.7) > As (4.5) > Cr (3.5) > Pb (3.2) > Co (2.6) > Mn (2) > Fe (1.9) > Zn (1.5). The concentrations of Cd, Co, Cr, Fe, and Ni in leachate samples were higher than the permissible values for leachate disposal into surface and groundwater resources. The obtained results in the present study show that waste disposal management in the study area is a necessity according to environmental guidelines, which may prevent the pollution of soil, plants, and water resources in adjacent areas.


1. INTRODUCTION
During the last decades, the excessive growth of the population and the development of urbanization have caused the emergence of various environmental problems. The disposal of produced municipal solid wastes in urban areas is a significant challenge that needs proper environmental management (Wang et al., 2009; Aydi et al., 2013). Site selection for waste disposal is considered the most important step in waste management (Uyan, 2014), since improper disposal of waste will eventually result in soil and water resource pollution, which is mainly due to the production of extremely polluted leachates in disposal sites (Gottschall et al., 2009). The leachate composition is highly complex and contains numerous dissolved and suspended organic/inorganic pollutants such as NH₄⁺, Ca²⁺, Mg²⁺, Na⁺, K⁺, Fe, SO₄²⁻, Cl⁻, NO₃⁻, PO₄³⁻, and potentially toxic elements (e.g., Cd, Cr, Cu, Pb, Ni, and Zn) as well as pathogenic agents (Ogundiran and Afolabi, 2008; Kassasi et al., 2008). Due to the presence of toxic organic and inorganic pollutants in waste leachate, waste disposal sites in urban areas can be a major threat to soil and water resources (Christensen et al., 1992; Chofqi, 2004; Claudio et al., 2006).
In Babolsar city, a high amount of municipal waste is produced daily and is disposed of near the beach without environmental considerations. The humid weather of the area leads to the production of a large amount of waste leachate, which can infiltrate into the Caspian Sea and groundwater resources and may cause severe pollution of the coastal area and marine ecosystem. On the other hand, soil pollution in the area is worrying due to the expansion of agricultural lands around the landfill site. The objective of the present study is to assess the level of soil pollution in this area and to investigate the chemical composition of solid waste leachate.
2. MATERIALS AND METHODS
Fifteen topsoil samples (0–15 cm depth) were collected using a stainless steel shovel. The soil samples were dried at room temperature for 48 hours. Then, the samples were passed through a 10-mesh sieve and pulverized using an agate mortar until the particle size reached up to 75 microns. The concentrations of major and trace elements in powdered soil samples were measured by an ICP-MS instrument (Perkin 9000 DRCE model) after strong acid digestion (HF+HCl+HNO₃+HClO₄). To evaluate the accuracy of the data, blank samples and reference materials were analyzed, and to check the precision of the analytical results, triplicate analyses of target elements in each sample were carried out. In order to quantitatively evaluate the level of soil pollution around the Babolsar waste disposal site, some geochemical indices including Enrichment Factor (EF), Pollution Index (PI), and Pollution Load Index (PLI) were calculated. The pH and EC values of the leachate samples were recorded in the field using a portable pH-EC meter. Ten leachate samples were collected in 1.5-litre polyethylene bottles. In each sampling site, two subsamples were collected: one for measuring the concentration of potentially toxic elements and the other for determining the physicochemical parameters. Before sampling, the bottles were rinsed with leachate. The first subsamples were filtered through a 0.45-micron filter paper, and the pH was reduced to less than 2 by adding a few drops of dilute HNO₃. The concentration of potentially toxic elements was measured by an ICP-MS device immediately after sample preparation. The second subsamples were used without any preparation to measure total dissolved solids (TDS) and total suspended solids (TSS) using the gravimetric method.
3. RESULTS AND DISCUSSION
The concentrations of Ag and Cu in all studied soil samples and the concentration of Mn and Ni in most samples were higher than the world soil average composition. The concentrations of Co, Cr, Fe, Mo, Pb, Cd, and As in some soil samples were higher than their values in the world soil average composition. The Zn concentration in all samples was lower than its average value in world soils. On the basis of enrichment factor values, the studied soils were highly enriched in Ag, Ni, and Mo, and moderately enriched in Cu, Cd, As, Cr, Pb, and Co. There was a low enrichment of soils in Mn, Fe, and Zn. The pollution index values of Ag, Cu, Mn, and Mo were higher than 1, indicating a probable anthropogenic source of these elements in the soil. The calculated pollution load index values also showed average soil pollution in the study area. Based on the obtained results, in most leachate samples, the EC value was higher than the maximum allowable limit (1500 µs/cm). The amounts of TDS and TSS in all samples were higher than the standard values. The concentrations of Al, As, Ba, Cu, Pb, Mn, Se, and Zn in all leachate samples were within the permitted range provided by the World Health Organization for the discharge of landfill leachate into surface waters, while the concentrations of Cd, Co, Cr, Fe, and Ni in some samples were higher than their respective values in the WHO standard. According to the degree of pollution (Cd), the studied leachate samples were highly polluted.
4. CONCLUSION
The results of the present study show that improper disposal of municipal wastes on Babolsar beach may cause serious environmental issues for the surrounding environment and local residents. The infiltration of municipal leachate may reduce the quality of water resources and soils. Therefore, the reduction of leachate production before waste disposal is deemed necessary. In general, it is of crucial importance to select a suitable site for sanitary waste disposal to prevent leachate leakage and the release of pollutants into water resources and soil.