Abstract
Landfills are major sources of environmental pollution. This study evaluated heavy metal concentrations in soils and plants around the closed Lumberstewart landfill in Bulawayo, Zimbabwe, to determine the pollution potential of a closed landfill and the risks they present to plants growing in this environment and surrounding communities. Soil samples were collected at depths of 0–30 cm, 30–60 cm, and 60–90 cm around the landfill and at a control site and characterized for various properties and concentrations of Cd, Cu, Cr, Fe, Ni, and Zn. Samples of Datura stramonium, collected from the same sites where soil samples were collected, were also analyzed for the same heavy metals. The soils were sandy, mostly acidic (5.01 < pH < 7.65) with low organic matter content (<2%) and cation exchange capacity (<15 meq/100 g). These properties varied with depth around the landfill. Heavy metals concentrations in the soils and Datura stramonium followed the order Fe > Zn > Cu > Cr > Ni > Cd with samples from around the landfill having higher concentrations than samples from the control site. Soil heavy metal enrichment was highest at a depth of 30–60 cm. Pollution load index (PLI) values indicated that all sites around the landfill were polluted (PLI > 1). Heavy metal transfer coefficient in Datura stramonium ranged between 0.0 and 209 with <60% of the variation observed in heavy metal transfer coefficient in Datura stramonium explained by the extent of heavy metal enrichment in the soils. More than 20 years after closure of the landfill, there are indications that leachate migration may still be going on around the landfill. Monitoring of environments around closed landfills needs to be ongoing to mitigate negative impacts on humans and the environment.
Highlights
Municipalities, commercial centers, and industries worldwide generate tons of waste annually which end up in landfills
Results from this study indicate that some transfer of heavy metals from soils to plants at the Lumberstewart landfill is going on. ough heavy metals TF values for Datura stramonium may be low, this may not be the case with other plants
Results from this study indicate that, several years after the closure of the Lumberstewart landfill, elevated concentrations of Fe, Cu, Ni, and Zn are still found in the soils especially at a depth of 30–60 cm. ese metals show no correlation with the properties of the soils, which indicates nongeogenic origins. e contamination factor values indicated moderate to significant contamination at a depth of 30–60 cm and moderate contamination at depths of 0–30 cm and 60–90 cm
Summary
Municipalities, commercial centers, and industries worldwide generate tons of waste annually which end up in landfills. Landfills remain the best option for solid waste disposal because they can accommodate huge volumes of waste and are cheaper to run compared to other solid waste disposal options such as incineration. Despite these advantages, landfills remain major point sources of pollutants such as heavy metals and organic compounds to the environment. According to Aziz et al [1], Kamaruddin et al [2], Kjeldsen et al [3], and Ngole and Ekosse [4], landfill leachate usually contains dissolved organic matter, inorganic macrocomponents, heavy metals, and xenobiotic compounds derived from decomposing waste. Heavy metals and xenobiotic compounds have received global attention because they cause several negative health and environmental impacts
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