The review, led by Temitayo Olamide Ale of Adekunle Ajasin University in Nigeria together with colleagues in Nigeria and Malaysia, screened an initial pool of 321 publications and retained 172 peer-reviewed studies published between 2013 and 2025. The team set out with four goals: to classify the techniques used to investigate soil and water contamination around dumpsites, to evaluate how well stabilizing agents immobilize potentially toxic elements, to examine the role of artificial intelligence in contamination assessment, and to review remediation strategies for polluted soils and groundwater. Groundwater supplies nearly half of all drinking water worldwide and supports the daily needs of more than 2.5 billion people, so the stakes of the exercise could hardly be higher.

The problem begins with the dumpsites themselves. Unlike engineered sanitary landfills, open dumps are typically unregulated, unlined, and poorly managed, allowing waste to interact directly with surface water, soil, and groundwater. Rainwater percolating through heterogeneous mixtures of food waste, plastics, metals, batteries, electronics, and even hospital refuse generates leachate—a concentrated liquid cocktail of dissolved salts, organic matter, and potentially toxic elements such as lead, chromium, arsenic, cadmium, mercury, and nickel. Several major Nigerian dumpsites, including Olusosun in Lagos and Awotan in Ibadan, have operated continuously for more than four decades and now cover roughly 42 and 20 hectares respectively, making them long-term contamination engines rather than temporary nuisances.

One of the review’s most striking technical findings concerns how leachate moves underground. Geophysical imaging combined with hydrogeochemical analyses consistently reveals that migration is not a simple downward seepage. Instead, subsurface structure—weathered zones, fracture networks, and lithological boundaries—acts as a network of preferential highways, driving both vertical and lateral transport. Electrical resistivity tomography and vertical electrical sounding, the workhorses of dumpsite investigation, detect leachate-saturated zones as low-resistivity anomalies, with many studies adopting thresholds below 40 ohm-meters as indicators of possible contamination. Depth estimates show leachate commonly penetrating 10 to 15 meters into shallow aquifers, and in fractured basement terrains the plumes can follow faults and lineaments far deeper than soil properties alone would predict.

But resistivity anomalies are notoriously non-unique: saline intrusion, clay-rich sediments, and shale layers can all mimic leachate signatures. That is why the review argues forcefully for integrated, multi-method frameworks. Induced polarization adds chargeability information that helps distinguish leachate from clay; self-potential surveys track the electrochemical signals of active fluid flow; electromagnetic methods provide rapid reconnaissance over large sites; and seismic refraction, ground-penetrating radar, magnetic, and gravity surveys constrain stratigraphy, buried waste, and structural pathways. When these geophysical images are cross-validated against borehole logs, geotechnical tests, and water chemistry, interpretational ambiguity drops sharply and the true geometry of a contamination plume comes into focus.

The hydrogeochemical evidence assembled in the review is sobering. Mean concentrations of lead, cadmium, nickel, arsenic, manganese, and iron frequently exceed guideline values set by the World Health Organization, the US Environmental Protection Agency, and national standards in groundwater surrounding dumpsites. At the Abule-Egba dumpsite in Lagos, elevated total dissolved solids, sodium, potassium, chloride, and nitrate appeared in both shallow wells and deeper boreholes, signaling migration into multiple aquifers. Around Olusosun, hardness, lead, nickel, manganese, iron, and chromium rose highest during the wet season, when enhanced recharge and runoff flush contaminants downward. Temporal studies show the problem is cumulative: concentrations of arsenic, zinc, lead, and copper increased over time at long-operating sites, and roughly 80 percent of polluted water in some developing regions is used for irrigation, carrying toxins into the food chain.

The human health risk calculations are where the review becomes genuinely alarming. Using standard exposure models—average daily dose, hazard quotient, hazard index, and cancer risk—the authors synthesized results across dozens of sites and found that hand-to-mouth ingestion of contaminated soil and drinking of polluted groundwater dominate the risk profile. Hazard indices for soil ingestion reached values orders of magnitude above the safety threshold of one, with manganese and arsenic the dominant contributors, and children bearing the heaviest burden because of their lower body weight and higher soil ingestion rates. Total carcinogenic risk from groundwater ingestion exceeded the acceptable range of one in a million to one in ten thousand by several orders of magnitude at the worst sites. By contrast, dermal exposure during bathing and inhalation of airborne dust remained largely within acceptable limits—a finding that sharply narrows where intervention money should be spent.

On the solutions side, the review documents a rapidly evolving toolkit. Biological remediation exploits fungi such as Aspergillus niger and Phanerochaete chrysosporium, whose ligninolytic enzymes and organic acids can cut cadmium levels by up to 90 percent in various environments. Stabilization and solidification using cement, lime, fly ash, and phosphate binders lock contaminants into insoluble matrices, and studies show that agricultural and industrial wastes—sugarcane straw, sawdust ash, hydrated lime—incorporated at 5 to 30 percent can significantly reduce contaminant mobility. More futuristic are nanotechnology approaches: nanoscale zero-valent iron and magnetite nanoparticles stabilize toxic elements and polycyclic aromatic hydrocarbons in soil, while green-synthesized composites such as bentonite–green tea extract–nZVI have immobilized chromium. The authors caution, however, that most nanoremediation remains at laboratory scale, with open questions about nanoparticle transport, toxicity to soil microbiota, and long-term stability.

Perhaps the most forward-looking section concerns artificial intelligence. Machine learning frameworks—Random Forest, Naive Bayes, and Bivariate Local Moran’s I among them—are proving remarkably good at predicting the distribution of potentially toxic elements and delineating high-risk zones from environmental covariates such as soil pH, organic matter, elevation, and population density. One cited study achieved R-squared scores of 0.76 to 0.86 predicting eight different metals. The review is careful to note the caveats: model reliability depends on data quality, feature selection, and physical interpretability, and predictions must be constrained by geological and hydrogeological knowledge to remain meaningful. Embedded within integrated, process-informed frameworks, however, these data-driven tools promise faster, cheaper, and more transferable contamination assessment than conventional methods alone.

The review closes with a clear-eyed prescription. Site-specific assessment, regular monitoring at bi-monthly or seasonal intervals, informed urban planning, and integrated remediation frameworks are essential to mitigate the long-term impacts of dumpsite leachate. Engineered sanitary landfills—with compacted clay and geomembrane liners, leachate collection systems, and low-permeability caps—must be sited away from flood zones and fracture-prone bedrock, and targeted financial support is needed to build them in developing countries. The authors also call for stronger public education, protective equipment for the informal scavengers who work the dumps without gloves or masks, and honest communication of research findings to the communities whose hand-dug wells sit downstream of decades of unmanaged waste. As urban populations grow and waste volumes climb, the review makes clear that the invisible plumes beneath the world’s dumpsites will only deepen unless science, governance, and investment converge on the problem now.

Subject of Research: Soil and groundwater contamination from dumpsite leachate and its assessment and remediation

Article Title: A systematic review of soil and water contamination in dumpsite leachate impacted environments

Article References: Ale, T. O., Ololade, I. A., Akingboye, A. S., Ogunribido, T. H. T., Ajidahun, J., & Faseki, O. E. (2026). A systematic review of soil and water contamination in dumpsite leachate impacted environments. Discover Soil, 3(1), Article 112. https://doi.org/10.1007/s44378-026-00265-2

Image Credits: AI Generated

DOI: 10.1007/s44378-026-00265-2

Keywords: dumpsite leachate, groundwater contamination, soil pollution, potentially toxic elements, geophysical methods, electrical resistivity tomography, health risk assessment, machine learning, nanoremediation, bioremediation, sanitary landfill design, developing countries