Heavy Metals in Andean Herbal Teas Pose Little Risk, Study Finds

In the high-altitude valleys of central Peru, a steaming cup of chamomile or eucalyptus tea is more than a comfort; it is a pillar of primary health care. But the Mantaro River basin, which waters these medicinal plants, carries a century-old burden of mining waste and naturally occurring metal contamination. A new screening-level study published in Heliyon has now measured six toxic elements in five of the region’s most popular medicinal herbs and calculated what decades of daily tea drinking might mean for human health. The verdict is broadly reassuring, though with a cautionary footnote about arsenic and chromium.

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