Heavy Metal Pollution in Soils at Various Landfills Vicinity: A Review Study

Landfill soils are often heavily contaminated with heavy metals (HMs), posing a significant risk of environmental pollution in surrounding areas. Historically, many landfills have been unregulated, poorly constructed, or have exceeded their design lifespans, contributing to their status as major pollution sources. Leachate generation, driven by waste degradation, microbial activity, rainfall infiltration, and groundwater intrusion, exacerbates this issue but is frequently untreated. Anthropogenic activities produce vast quantities of waste, ranging from biodegradable to hazardous materials. In rapidly urbanizing municipalities, particularly in developing countries, the challenges of solid waste management are pressing. Household waste is commonly discarded in unregulated dumpsites, waterways, and public spaces, exacerbating pollution. In contrast, developed nations typically manage municipal solid waste (MSW) more effectively due to advanced waste management infrastructure. This study investigates the classification of landfills based on waste type and evaluates the associated heavy metal (HM) contamination in soils. Representative landfill sites from various countries, including Ghana, Iran, Malaysia, China, South Africa, the Czech Republic, and Tunisia, were analyzed to determine the average concentrations of HMs in surrounding soils. Heavy metals such as arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), cobalt (Co), lead (Pb), zinc (Zn), manganese (Mn), iron (Fe), nickel (Ni), aluminum (Al), mercury (Hg), and vanadium (V) were detected in soils adjacent to these landfills. Soil pollution was assessed using several indices. The Ecological Risk Index (Eⁱ_r) and the summation of the Ecological Risk Index (ERI) quantified individual and total ecological risks, respectively. Anthropogenic pollution was evaluated through the geo-accumulation index (Igeo), pollution index (PI), and integrated pollution index (IPI), providing insights into pollution levels relative to natural elemental content in soils. Factors influencing heavy metals contamination included the proximity of the soil to the landfill, the depth of soil infiltrated by leachate, seasonal variations, and site topography. To address soil contamination, remediation strategies were proposed, including the application of biochar (BC), humic substances (HS), and iron oxide (FO) amendments to immobilize HMs effectively and other remediation techniques to remove heavy metals. These findings contribute to developing sustainable approaches for mitigating heavy metal pollution in landfill-adjacent soils.