Investigating the Effect of Long-term Municipal Waste and Manure Application on Soil Heavy Metal Availability in Soil

Municipal waste is a cost-effective and valuable source of organic matter for agricultural soils. In recent years, MSW compost has been widely used in agriculture as a soil conditioner and fertilizer. However, the excessive use of organic and mineral fertilizers in the production of greenhouse crops leads to the accumulation of heavy metals in the soil and health risks for humans. Therefore, this study investigated the effect of the municipal waste and manure application on heavy metals in the soil. Also, the health risks for humans were evaluated through the consumption of cucumber cultivated in these soil. In this study, the concentration of heavy metals Cd, Cu, Ni, Pb and Zn in soil, mobility of metals, bioavailability, fractionation of metals, effects of pollution in the greenhouse soil and uptake of these metals by cucumber plant following 3 cultivation years of application of municipal waste compost and manure were studied in a randomized complete block design with three replicates in a greenhouse located in the south of Theran province. Also, environmental pollution risks were evaluated. The results showed that the application of municipal waste compost and manure increased both the total and available concentration of heavy metals in the soil. However, the concentration of the measured metals was at the permissible limit of the concentrations of heavy metals in Iranian soils. Copper and Zn were detected as the most mobile metals in control and treated soils with municipal waste compost and manure, respectively. The amount of Pb (2.26 mg kg-1) and Cd (0.06 mg kg-1) in cucumber in treated soil with municipal waste exceeded the limit value for edible vegetables. Based on the results obtained from the health risk index, Pb and Cu represented a high potential risk for the health of adults and children by consuming cucumbers in compost-treated soils. The results of this study showed that despite the three-year application of municipal waste compost and manure, the concentration of heavy metals measured was not higher than the allowed guideline level. However, considering the high bioavailability of heavy metals, repeated application of municipal waste compost would carry a risk of gradual accumulation in the soil over time. Therefore, measuring the total and extractable concentration of heavy metals and metal mobility when assessing likely effects on plant yields and metal uptakes and setting soil quality criteria is important.