A research team led by Rosa Zárate-Quiñones of the National University of Central Peru sampled leaves of chamomile (Matricaria chamomilla), lemon verbena (Aloysia citrodora), eucalyptus (Eucalyptus globulus), Peruvian pepper tree (Schinus molle), and muña mint (Minthostachys mollis) in the agricultural districts of Chupuro and Pucará, at elevations between roughly 3,270 and 3,350 meters. During the 2023 dry season, the researchers collected 90 samples across six georeferenced sites, using non-metallic tools and nitrile gloves to avoid contamination. The material was authenticated at the university herbarium, washed, dried at 80 degrees Celsius, ground, and sieved before acid digestion with high-purity nitric and hydrochloric acids.

Quantification was performed with an Agilent 7700x inductively coupled plasma mass spectrometer, an instrument prized for its ability to detect trace and ultra-trace elements in complex biological matrices. The analyses were carried out by a laboratory accredited under ISO/IEC 17025 by Peru’s National Institute of Quality, and validated through spiked-sample recovery assays yielding recoveries between 80 and 100 percent. Detection limits ranged from 0.0141 milligrams per kilogram for lead to 0.0456 milligrams per kilogram for zinc, giving the team a sensitive baseline for elements that occur at very low concentrations in plant tissue.

The results revealed a consistent hierarchy of accumulation across all five species: zinc, copper, chromium, cobalt, arsenic, and then lead, in decreasing order. Eucalyptus globulus proved the most prolific accumulator, recording the highest mean concentrations of zinc (11.99 milligrams per kilogram) and copper (5.27 milligrams per kilogram) in Pucará, and the highest chromium level (0.98 milligrams per kilogram) in Chupuro. Minthostachys mollis, by contrast, carried the greatest arsenic burden (0.30 milligrams per kilogram in Pucará) and the highest lead concentrations (0.49 milligrams per kilogram in Chupuro). Crucially, every measured value remained well below international maximum permissible limits, including the World Health Organization thresholds of 1.00 milligram per kilogram for arsenic and 10.00 milligrams per kilogram for lead in raw medicinal plant material.

Statistical testing showed significant differences among species within each district but striking spatial homogeneity between Chupuro and Pucará, suggesting that both areas share a common environmental legacy of mining and metallurgy. Principal component analysis explained 75.21 percent of the total variance in just two axes, with zinc and copper loadings of 0.422 and 0.419 dominating the first component. Eucalyptus samples clustered firmly at the positive extreme of this axis, pointing to an especially efficient translocation mechanism for these essential micronutrients. Hierarchical clustering reinforced the picture, splitting samples into two groups defined primarily by zinc and copper levels, while arsenic, lead, and cobalt stayed uniformly low across the heatmap.

The team then translated tissue concentrations into human exposure estimates using a deliberately conservative model. They assumed a daily consumption of 500 milliliters of infusion, equivalent to about two cups, taken on 350 days per year for 30 years, with a body weight of 60 kilograms. Because metals are not fully extracted into hot water, they applied literature-based transfer factors, ranging from 24 percent for copper to 50 percent for lead, to estimate how much of each element actually reaches the drinker. Non-carcinogenic risk was expressed as a hazard quotient for each element and a cumulative hazard index, benchmarked against reference doses from the United States Environmental Protection Agency.

By these measures, the non-cancer risk was negligible. Every hazard quotient fell below unity, and the cumulative hazard index peaked at just 4.07 times ten to the minus three in Pucará’s muña mint, several orders of magnitude below the safety threshold. Arsenic and chromium dominated the risk profile relative to the other elements, reflecting their high intrinsic toxicity and low reference doses, but the actual mass transferred into the infusions remained too small to trigger systemic effects. The authors note that this finding echoes earlier regional work in which eucalyptus and muña infusions yielded hazard indices well below one even when dry-tissue lead concentrations were far higher than those measured here, underscoring how the low extraction kinetics of household infusion preparation fundamentally limits exposure.

The carcinogenic assessment told a more nuanced story. Using lifetime average daily doses averaged over 70 years and oral slope factors for arsenic, chromium, and lead, the team calculated total cancer risks ranging from 5.49 times ten to the minus seven to 1.14 times ten to the minus six in the four highest-risk scenarios. The United States Environmental Protection Agency considers risks below one in a million ideal and those between one in a million and one in ten thousand acceptable. Only one scenario, eucalyptus infusions from Chupuro, marginally exceeded the ideal baseline, representing what the authors describe as a low but non-negligible concern rather than a trigger for regulatory action. Chromium and arsenic were the dominant drivers, contributing up to 6.86 times ten to the minus seven and 5.96 times ten to the minus seven respectively, while lead’s contribution was consistently insignificant.

The study is candid about its limitations. The deterministic screening model applies uniform consumption assumptions that may overestimate real intake for many consumers, and it relies on fixed transfer coefficients rather than measuring metals directly in brewed infusions, so variables such as steeping time, water temperature, and leaf-to-water ratio are not captured. Without direct soil, irrigation water, or geochemical background data, the precise source of the detected elements, whether legacy mining or natural mineralization of the region’s Mesozoic volcanic rocks, cannot be definitively established. Standard risk indices also cannot capture synergistic effects or the well-documented neurotoxicity of lead, which chronic screening thresholds may understate in vulnerable populations.

Even so, the findings carry practical weight for a region where herbal infusions are a near-daily cultural fixture. The authors recommend targeted quality control screening along the collection and distribution chain, the establishment of maximum permissible limits specific to medicinal plants rather than borrowed from other food categories, and biomonitoring programs in mining-impacted areas. Future work, they suggest, should incorporate probabilistic dietary surveys and Monte Carlo simulations, extend analysis to roots and bark, and combine plant testing with direct measurement of soils and irrigation water. For now, Andean tea drinkers can take comfort in the numbers: the metals are there, but the cup delivers very little of them.

Subject of Research: Heavy metal contamination and toxicological risk assessment of medicinal herbal infusions in the Mantaro River basin, central Peru

Article Title: Screening-level assessment of potential toxicological risks from heavy metals in medicinal herbal infusions from central Peru

Article References: Zárate-Quiñones, R., Custodio, M., Damian-Alvarado, R., Cuadrado, W., Basaldúa-Galarza, A., Zúñiga-López, D., & Avila-Chirinos, A. (2026). Screening-level assessment of potential toxicological risks from heavy metals in medicinal herbal infusions from central Peru. Heliyon, 12(15), Article e45523. https://doi.org/10.1016/j.heliyon.2026.e45523

Image Credits: AI Generated

DOI: 10.1016/j.heliyon.2026.e45523

Keywords: heavy metals, medicinal plants, herbal infusions, Peru, Mantaro River basin, arsenic, chromium, risk assessment, ICP-MS, public health, Andes, mining contamination

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