Toxic Metals Lurk in Lubumbashi’s Vegetables as Consumers Keep Buying Them

In the sprawling mining city of Lubumbashi, in the Democratic Republic of the Congo, the vegetables that fill market stalls and family pots may carry a hidden burden. A new interdisciplinary study published in Discover Sustainability has quantified just how heavy that burden is, measuring concentrations of cadmium, copper, lead and zinc in the six vegetables most commonly consumed by the city’s residents and finding that many samples exceed the maximum permissible limits set by the Food and Agriculture Organization and the World Health Organization. The research, led by Salifu Adam of the University of Lubumbashi together with colleagues Jonas Lwalaba Wa Lwalaba and Arsene Mushagalusa Balasha, goes beyond chemistry alone. By pairing laboratory measurements with consumer surveys and statistical modeling, the team has exposed a troubling gap between what people know about contamination and what they actually put on their plates.

The analytical backbone of the study is inductively coupled plasma optical emission spectrometry, or ICP-OES, a technique that excites atoms in a sample with a plasma torch and reads the characteristic wavelengths of light they emit to determine elemental concentrations with high precision. Using this method, the researchers measured heavy metal levels in spinach (Spinacia oleracea), Chinese cabbage (Brassica chinensis), amaranth (Amaranthus vulgaris), cassava (Manihot esculenta), onion (Allium cepa) and tomato (Solanum lycopersicum). Leafy vegetables emerged as the most contaminated group, a pattern consistent with the way leafy crops accumulate metals from both soil and airborne deposition. Spinach recorded a mean cadmium concentration of 4.02 milligrams per kilogram, lead at 1.44, copper at 25.27 and zinc at 136.21, all above the FAO and WHO thresholds that define safe levels for human consumption.

Cadmium deserves particular attention because of its toxicological profile. The metal has no known biological function in humans, accumulates primarily in the kidneys, and has a biological half-life measured in decades. Chronic exposure damages renal tubular function, weakens bones, and is classified as a human carcinogen. In Lubumbashi, decades of intensive mining and smelting of copper and cobalt ores have loaded surrounding soils and dust with cadmium and other metals, which then enter the food chain through crops grown in contaminated ground or irrigated with tainted water. The study’s findings confirm that this pathway is not hypothetical but measurable in the everyday food supply of an urban population that depends heavily on locally grown and locally sold produce.

To translate chemical concentrations into health outcomes, the team applied standard risk assessment metrics. The hazard quotient, or HQ, compares an estimated daily intake of a metal with its reference dose, the level below which adverse effects are not expected over a lifetime. When hazard quotients for multiple metals are summed, the result is the hazard index, or HI. Values above 1 signal a potential non-carcinogenic health risk. In this study, both HQ and HI values exceeded 1 for consumers of the contaminated vegetables, indicating that routine dietary exposure could plausibly produce harmful effects over time. The authors also calculated cancer risk, expressed as the incremental probability of developing cancer over a lifetime of exposure, and compared it against the regulatory acceptable range of 10 to the power of minus 6 to 10 to the power of minus 4.

The cancer risk results were stark. For cadmium, the computed cancer risk exceeded the acceptable range in three of the six vegetables studied: spinach at 6.22 times 10 to the power of minus 4, cassava at 5.05 times 10 to the power of minus 4, and amaranth at 3.49 times 10 to the power of minus 4. In practical terms, these figures represent probabilities of additional cancer cases on the order of several per ten thousand exposed individuals, well above the upper bound of what regulators typically tolerate. Because cassava is a dietary staple across the region and leafy greens are eaten daily in large quantities, the population-level implications are considerable. The metals are not distributed evenly across crops, however; onions and tomatoes generally accumulated less, suggesting that crop choice could become part of a practical risk reduction strategy.

What makes the study unusual is its second half, which turns from spectrometers to human minds. The researchers surveyed consumers in Lubumbashi about their awareness of food-chain contamination, their perception of the risks, and their purchasing behavior. The results revealed a striking paradox: even among respondents who knew that vegetables could be contaminated, preference for the highest-risk foods remained strong, with cassava in particular continuing to command loyalty. This disconnect between knowledge and behavior is a well-recognized challenge in environmental health, where awareness alone rarely changes practices when cultural attachment, taste, affordability and habit all pull in the opposite direction.

To probe the relationships statistically, the team used logistic regression, a modeling technique that estimates how predictor variables influence the odds of a binary outcome. The analysis showed that awareness significantly predicted knowledge, risk perception, and the adoption of safer practices. In other words, people who were better informed were more likely to understand the danger, to perceive themselves as exposed, and to take protective measures. That finding carries a hopeful message: information campaigns could shift behavior, provided they are designed with local realities in mind rather than simply broadcasting warnings that compete against economic necessity and culinary tradition.

The survey also uncovered a market signal with real policy potential. More than half of the respondents said they would be willing to pay a premium for safer food options, including vegetables produced hydroponically, a soil-free growing method that sidesteps contaminated ground entirely. In a city where mining has degraded urban and peri-urban soils so thoroughly that remediation may be impractical on the required scale, hydroponics offers a technologically credible alternative: crops grown in controlled nutrient solutions cannot inherit the metal burden of the soil beneath them. A consumer base willing to pay extra for such produce could give entrepreneurs and policymakers the economic justification to invest in clean production systems, turning public concern into a self-sustaining market for food safety.

The authors frame their findings as a call for integrated food safety policy interventions in mining-impacted urban settings, and the study’s structure shows why integration matters. Chemistry without behavioral science would have documented a hazard but missed the reasons consumers keep buying contaminated food; surveys without laboratory data would have captured perceptions without revealing how far reality departs from them. By combining ICP-OES measurements, quantitative risk assessment and regression-based analysis of consumer attitudes, the research delivers a complete picture of a food system under stress. The work was supported by the COCREATE-Africa project funded by the European Union under the Africa Academic Mobility Scheme, and was approved by the Research Ethics Committee of the Faculty of Agricultural Sciences at the University of Lubumbashi.

For Lubumbashi’s residents, the study confirms that the risk is real, measurable and concentrated in the foods they love most. For cities across the mining belts of Central Africa and beyond, it offers a template: measure the contamination, quantify the exposure, understand the behavior, and then design interventions that meet people where they are. The willingness of more than half of surveyed consumers to pay more for safer vegetables suggests the demand for clean food already exists. What remains is the supply, and the political will to build it.

Subject of Research: Heavy metal contamination of vegetables and associated health risks and consumer perceptions in the mining city of Lubumbashi

Article Title: Heavy metal human health risk assessment and consumer perception of vegetables in Lubumbashi, Democratic Republic of the Congo

Article References: Adam, S., Lwalaba, J. L. W., & Balasha, A. M. (2026). Heavy metal human health risk assessment and consumer perception of vegetables in Lubumbashi, Democratic Republic of the Congo. Discover Sustainability. https://doi.org/10.1007/s43621-026-04887-y

Image Credits: AI Generated

DOI: 10.1007/s43621-026-04887-y

Keywords: heavy metals, cadmium, food safety, mining contamination, vegetables, health risk assessment, consumer perception, Lubumbashi, Democratic Republic of the Congo, hydroponics, cancer risk, public health