The research team, led by Samkelisiwe Khanyile, combined post-classification change detection in a geographic information system with chi-square statistical testing and a spatial clustering index. Their raw material was the South African National Land Cover dataset, built from Landsat 5 Thematic Mapper imagery for 1990 and Landsat 8 Operational Land Imager imagery for 2020, both at a 30-meter resolution. The original 73 and 72 land cover classes were collapsed into 12 comparable categories, allowing every one of nearly 2.9 million pixels to be traced from its 1990 state to its 2020 state. The resulting transition matrix, a 12-by-12 table of conversions, became the evidentiary backbone for asking whether landscape change in a post-mining region follows logic, chance, or policy failure.

The statistical verdict was unambiguous. The chi-square test returned a value of 11,319,251.69 with 121 degrees of freedom and a p-value below 0.001, and 141 of the 144 possible transitions proved significant. Cramér’s V, a measure of effect size, reached 0.60, indicating that the transitions substantially reshaped the composition of the landscape rather than nudging it at the margins. In plain terms, the land did not drift randomly into new uses. Institutional, economic, and planning forces drove the conversions, which means the inequities embedded in those conversions are also the product of decisions, not accidents.

The headline numbers tell a story of paradox. On one hand, 54.53 square kilometers of former mining land, 37.8 percent of the mining footprint recorded in 1990, successfully transitioned to natural vegetation, a conversion that occurred far more often than chance would predict and that points to genuine revegetation efforts. On the other hand, the wider landscape degraded. Natural vegetation shrank by 150.33 square kilometers, planted vegetation plummeted by 47.6 percent, waterbodies and wetlands declined by more than 12 percent, and barren land surged by 376.4 percent. Site-level rehabilitation, in other words, could not counteract landscape-scale ecological loss, a finding that echoes international evidence that point-source restoration rarely offsets cumulative regional damage.

Urbanization compounded the pressure. Built-up formal areas grew by 60.74 square kilometers, commercial areas nearly doubled with a 37.41 square kilometer expansion, and informal settlements exploded by 42.91 square kilometers, an astonishing 847.89 percent increase. Informal settlements also showed a persistence rate of only 45.42 percent, meaning they are constantly forming, dissolving, and reforming. Crucially, the spatial clustering index derived from the chi-square residuals reached 99,240.66, far above the 1,000-to-5,000 range expected from random distributions. The changes concentrated in Soweto, Tsakane, Simunye, Daveyton, and Mohlakeng, townships historically designated for Black residents under apartheid and deliberately sited near mining operations.

That geographic concentration is where the study’s environmental justice argument becomes sharpest. Environmental justice scholarship has long held that hazards are disproportionately placed near marginalized populations, but demonstrating this with quantitative landscape evidence has been rare in mineralized urban contexts of the Global South. Here, three lines of evidence converge: the transitions are systematic, they cluster in previously disadvantaged areas, and they include residential development on contaminated land. The belt hosts more than 270 tailings storage facilities covering roughly 400 square kilometers, some of them radioactive because of uranium co-occurring with gold. Provincial authorities identified 157 of 374 mine residue sites as radioactive, spanning 220 square kilometers.

Perhaps the most damning finding concerns the buffer zones that were supposed to keep people away from that contamination. In 2003, the Gauteng Department of Agriculture and Rural Development established pollution buffers around mine residue sites, later codified at distances of 500 to 1,500 meters under the 2012 Gauteng Pollution Buffers Policy, amended in 2017. Yet the analysis found that 0.80 square kilometers of mining land was converted to formal and informal built-up areas, placing residents directly adjacent to potentially contaminated ground despite explicit regulatory protection. The study also documents the reverse flow: 41.55 square kilometers of natural vegetation was converted to mining-related land use, showing that extraction continued consuming green space even as the sector contracted overall, with mining land declining only marginally from 144.25 to 143.28 square kilometers.

The authors frame this as a policy-implementation gap with two possible readings, both unjust. Either mining companies successfully defended their land holdings through regulatory power, monopolizing urban land while housing-poor populations are pushed onto the highest-risk zones, or mining actors strategically permitted settlement in buffer zones to monetize their land assets. Either way, the injustice is both spatial and temporal: apartheid-era mining footprints continue to structure environmental exposure and development opportunity three decades after the regulatory regime that produced them was formally dismantled. South Africa’s post-apartheid legal architecture, including the Constitution’s environmental rights clause, the National Environmental Management Act, the Mineral and Petroleum Resources Development Act with its mandatory rehabilitation provisions, and the Spatial Planning and Land Use Management Act, has not translated into protection on the ground.

The sustainability implications reach beyond South Africa. The findings show direct misalignment with Sustainable Development Goal 11 on sustainable cities, since urban growth in the mining belt has been predominantly informal and hazard-adjacent rather than planned, and with SDG 15 on terrestrial ecosystems, given the vegetation losses and barren land expansion. Gauteng’s position on a watershed divide between the Crocodile, Olifants, and Vaal river systems makes the wetland losses particularly troubling, as the landscape loses its capacity to retain and filter water precisely when demand is escalating. Acid mine drainage, soil contamination, and radioactive dust remain persistent threats that satellite imagery cannot capture, which the authors acknowledge as a limitation alongside their reliance on two time points and pre-classified 30-meter data with 88 to 96 percent accuracy.

What distinguishes this study is its replicable methodological template: transition matrices validated by chi-square testing, effect sizes, and clustering indices, all benchmarked against regulatory buffer zones. Because the changes are systematic, the authors argue, they can be deliberately reversed through targeted intervention. Their prescriptions include stronger regulatory enforcement with meaningful penalties, affordable housing provision to relieve pressure on contaminated land, participatory rehabilitation planning that centers community voices, and accountability mechanisms grounded in independently verifiable landscape-scale evidence rather than self-reported site compliance. A periodic land cover monitoring framework benchmarked against the provincial buffer policy could, they suggest, turn satellite pixels into enforceable metrics. The Witwatersrand’s golden scar will not heal on its own, but for the first time its growth, its healing patches, and its human costs have been measured with a precision that regulators can no longer ignore.

Subject of Research: Mining-driven land use and land cover change and environmental justice along the Witwatersrand mining belt, Gauteng, South Africa, 1990–2020

Article Title: Mining Legacies and Environmental Injustice: Systematic Mining-Led LULC Change in the Witwatersrand Mining Belt, Gauteng, South Africa (1990–2020)

Article References: Khanyile, S., Tsoriyo, W., & Mahamuza, P. (2026). Mining Legacies and Environmental Injustice: Systematic Mining-Led LULC Change in the Witwatersrand Mining Belt, Gauteng, South Africa (1990–2020). Environmental Management, 76(10), Article 336. https://doi.org/10.1007/s00267-026-02543-9

Image Credits: AI Generated

DOI: 10.1007/s00267-026-02543-9

Keywords: land use land cover change, mining, environmental justice, Witwatersrand, Gauteng, remote sensing, GIS, chi-square analysis, informal settlements, mine rehabilitation, tailings storage facilities, sustainable development goals

The research team, led by Rinae Makhadi of the University of the Free State and the University of Johannesburg, together with Robert Hansen, Kim Dowling and Hassina Mouri, collected sixteen soil samples from eleven locations around four abandoned tailings dams, a tailings footprint, informal residential areas and farming and grazing lands near Welkom and the neighbouring mining towns of Odendaalsrus and Virginia. A control sample was taken from open land in Riebeeckstad, where the underlying geology is similar but mining disturbance is minimal. Nine water samples were also gathered, spanning four groundwater boreholes, two wetlands and three surface water sites near tailings dams. Soils were analysed for both total and leachable element concentrations using inductively coupled plasma mass spectrometry, while water chemistry was resolved with ICP optical emission spectrometry and a suite of standard physicochemical measurements.

The results are stark. Mean soil concentrations were highest for iron at 18,425 milligrams per kilogram, manganese at 273 milligrams per kilogram and chromium at 200 milligrams per kilogram, and these values were frequently highest close to the tailings themselves. Arsenic ranged from 3 to 304 milligrams per kilogram, with the highest reading recorded at a grazing site near Virginia, far exceeding both the Dutch target value of 29 milligrams per kilogram and South Africa’s soil screening value of 5.8 milligrams per kilogram for the most sensitive land uses. Chromium breached regulatory limits at every single sampling site, a finding the authors describe as evidence of the severity of contamination across the study area. Uranium, detected for the first time in Welkom soils, reached 49 milligrams per kilogram at the Virginia site.

That uranium detection carries particular weight. The Witwatersrand gold ores are famously associated with uraninite, and the tailings left after gold extraction remain rich in radioactive and nephrotoxic uranium. Yet South Africa’s national soil screening standards contain no limit for uranium, a regulatory gap the researchers flag as concerning given the country’s substantial uranium reserves and the documented health risks of exposure, which include carcinogenic and renal effects. The team argues that uranium must be added to the national screening framework if compliance monitoring around goldfields is to be meaningful.

To quantify contamination, the researchers deployed a battery of established indices. Geoaccumulation index values showed that aluminium, barium, manganese, iron, cobalt, copper, nickel, titanium and vanadium remained at background levels, but arsenic, chromium, lead and uranium registered clear anthropogenic pollution at several sites. The Virginia grazing land stood out dramatically, with a geoaccumulation index of 12 for arsenic, indicating extreme enrichment, and contamination factors of 63 for arsenic, 17 for lead and 18 for uranium. Pollution load index values ranged from uncontaminated to moderately contaminated, with the tailings footprint and the Virginia site again ranking highest. Spatial distribution maps reinforced the pattern: sites close to tailings dams consistently recorded the highest concentrations, while more distant locations, including the Riebeeckstad control, were comparatively clean, strong evidence that the tailings themselves are the source.

The ecological risk assessment sharpened the picture further. Individual ecological risk values for arsenic reached 630 at the Virginia site and 100 at the tailings footprint, while lead scored 85 at Virginia, both figures signalling considerable potential harm to ecosystems. The comprehensive potential ecological risk index ranged from a very low 14 to a high of 765, with Virginia and the tailings footprint topping the scale. Although the two informal residential sites near the tailings footprint showed low ecological risk in their own soils, their proximity to contaminated ground raises concern, particularly for children, whose ingestion of soil and dust is recognised as a primary exposure pathway to contaminants.

Water told an equally troubling story. Groundwater pH values sat within World Health Organization guidelines, but electrical conductivity and total dissolved solids frequently exceeded permissible limits, with one urban borehole recording a conductivity of 295 millisiemens per metre and dissolved solids of 2,092 milligrams per litre. Manganese in one farm borehole surpassed the WHO limit, and lithium exceeded its guideline value in the urban borehole. The wetlands fared worse still: one showed extreme salinity with total dissolved solids approaching 8,900 milligrams per litre and concentrations of arsenic, fluoride and nickel above drinking water standards. Most striking were the mine waters themselves, where pH dropped as low as 2.5 and sulphate concentrations reached nearly 3,700 milligrams per litre, accompanied by arsenic, iron, manganese, nickel and uranium at levels far beyond South Africa’s discharge limits under the National Water Act.

The chemistry behind these numbers is classic acid mine drainage. Welkom’s tailings are dominated by quartz and mica but contain pyrite, an iron sulphide that oxidises when exposed to air and water, generating sulphuric acid. The resulting acidity dissolves metals from the tailings and mobilises them into soil moisture, groundwater and surface runoff. Piper trilinear diagrams classified the mine waters and three groundwater samples as calcium-magnesium-sulphate type, a signature the authors identify as a key indicator of sulphide oxidation in acid mine environments. Gibbs diagrams pointed to rock weathering and evaporation as the dominant geochemical processes, with the high dissolved solids of the mine waters reflecting long residence times and intense evaporation. The interconnectedness of groundwater, wetlands and surface water means contamination from the tailings does not stay put; it migrates through the whole hydrological system.

Water quality index calculations, which compress physical and chemical parameters into a single score from 0 to 100, delivered a sobering verdict: three of the four groundwater samples were rated poor and unsuitable for drinking, and one of the two wetlands was rated very poor. Only the borehole farthest from the tailings, on an Odendaalsrus farm, returned good quality, and it was also the only groundwater sample plotting in the sodium-bicarbonate facies associated with fresher, less mining-affected water. Because small farming communities in the region depend on groundwater for domestic supply, and wetlands are used for household purposes, these ratings translate directly into potential human exposure.

The authors are careful to note what the study does not cover. Airborne dust and food crops were not analysed, leaving open questions about inhalation and dietary exposure pathways, and they recommend detailed follow-up work on dust, crops, grazing grass and community health through questionnaire-based investigations. In the meantime, they offer practical guidance for residents: avoid growing food in contaminated soils or add clean topsoil, limit children’s play near tailings, encourage hand washing after outdoor play, and consider dust masks during windy seasons. Farmers grazing livestock on the Virginia land should be informed of the risks to both animals and families. The broader message is unambiguous: abandoned tailings dams are not inert relics of a finished industry but active chemical reactors, still acidifying, still leaching and still dispersing toxic elements into the soils and waters on which Welkom’s communities depend. Without systematic monitoring, regulatory closure of the uranium gap and a comprehensive strategy to contain seepage, the gold that built this region will keep exacting a heavy environmental price.

Subject of Research: Geochemical contamination of soil and water around abandoned gold mine tailings dams in the Welkom Goldfield, South Africa

Article Title: Geochemical assessment of soil and water around abandoned gold mine tailings dams: evidence from the Welkom Goldfield, South Africa

Article References: Makhadi, R., Hansen, R., Dowling, K., & Mouri, H. (2026). Geochemical assessment of soil and water around abandoned gold mine tailings dams: evidence from the Welkom Goldfield, South Africa. Environmental Geochemistry and Health, 48(15), Article 618. https://doi.org/10.1007/s10653-026-03513-0

Image Credits: AI Generated

DOI: 10.1007/s10653-026-03513-0

Keywords: gold mining, mine tailings, soil contamination, water quality, arsenic, uranium, acid mine drainage, South Africa, Witwatersrand, ecological risk, heavy metals, geochemistry