Impact of solid waste disposal on heavy metals concentration and distribution in a naturally remediated landfill site

Abstract South Africa produces approximately 122 million tons of solid waste annually, which poses a significant environmental concern. The decomposition of solid waste in landfill sites results in the release of toxic heavy metals into the soil, posing a threat to human health and biodiversity. This study evaluated the impact of solid waste disposal in the distribution of heavy metals, that is, lead (Pb), zinc (Zn), cadmium (Cd), and arsenic (As), in landfill site soils. Soil samples collected (0-20 cm depth) from five dumping cells, two non-dumping zones, and a wetland were analyzed for soil chemical properties (exchangeable bases, extractable phosphorus (P), and micronutrients) and heavy metal concentrations. The results showed clear spatial variation in nutrient concentration across the landfill, with boundaries exhibiting lower fertility than dumping cells. The results indicated that cell 5 had higher organic matter concentration compared to all the treatments, except for cell 4. Heavy metal concentration results showed that Cd was below detection (< 1 mg kg −1 ) in the boundaries, wetlands, and cell 5 but exceeded the permissible levels (17.5-32.8 mg kg −1 ) in cells 1 to 4. Pb exceeded the permissible limit (50 mg kg −1 ) across all zones, with cell 5 showing concentrations almost double the ones in boundaries and wetland. Zinc concentrations were extremely high in cell 5 (1795 mg kg −1 ), > 100% higher than other treatments, while As remained relatively uniform across the treatments. These findings demonstrate the importance of natural remediation in reducing contaminant mobility and provide landfill sites management insights.