Researchers in soil science, environmental engineering, and public health from the University of São Paulo (USP), the Federal University of Espírito Santo (UFES) in Brazil, and the University of Santiago de Compostela in Spain investigated whether crops grown near the Doce River estuary are safe to eat. The area in Linhares, Espírito Santo, has been exposed to iron mining waste since the Fundão tailings dam collapsed in Minas Gerais in November 2015.
The team focused on bananas, cassava, and cocoa pulp cultivated in soil affected by the disaster. They examined levels of cadmium, chromium, copper, nickel, and lead, metals linked to iron oxides, which are the primary component of the tailings. Their findings suggest that eating bananas grown in contaminated soil may present a potential health risk for children six years old and younger.
“Our group has been studying the impacts of the dam collapse for years. We obtained the first samples seven days after the accident and immediately understood that there was an imminent risk of contamination of plants, soil, water, and fish. But the question remained: Does this contamination pose a risk to human health?” recalls Tiago Osório, an agronomist and professor in the Department of Soil Science at the Luiz de Queiroz College of Agriculture at the University of São Paulo (ESALQ-USP).
The study, published in Environmental Geochemistry and Health, explains how plants absorb potentially toxic elements (PTEs) from mining waste and store them in edible tissues. It also outlines how these substances can move into the human food supply. The research forms part of Amanda Duim’s doctoral work at ESALQ. Her thesis has produced seven international publications and earned two major awards in 2025: the USP Thesis Award in Sustainability and the Capes Thesis Award, granted by the Brazilian Ministry of Education’s Coordination for the Improvement of Higher Education Personnel (CAPES). Duim received support from FAPESP through a doctoral scholarship.
How Contaminated Soil Transfers Metals Into Plants
Duim, the study’s lead author, says the research stands out because it directly links human health risk to the movement of PTEs from soil into crops. “The iron oxide content in the soil, which is the main constituent of the tailings, correlates with its content in the plant. We studied the passage of constituents from the tailings in the soil to the water, and then from the water to the plant, including its leaves and fruits.”
“First, we need to know which elements are there and in what quantities in order to understand the biochemical dynamics of their release,” Osório explains.
Duim began her doctoral research in 2019 by exploring whether plants from flood-prone areas could help restore contaminated environments. She evaluated both cultivated crops and native species. “We evaluated cultivated and native species. In the case of the latter, we wanted to know how they affect the dissolution of iron oxide and, in this process, understand if and how the PTEs associated with this waste enter the plant, since different species accumulate PTEs differently,” she says. “The idea was to find the best native species for cleaning up contaminated environments, and we found more than one species that can fulfill this function, with results already published. In the case of cultivated species, we wanted to know if PTEs would be transferred to the fruits and edible parts of the plants.”
To measure contamination, the researchers carefully collected soil and plant samples. They washed and weighed the fresh plants, then dried them and weighed them again. Roots, stems, leaves, and peeled fruits were ground separately for analysis. “We dissolved the ‘plant powder,’ transforming it into a solution using various acids, and determined the concentration in the solution. We converted the calculation of the concentration of material in the solution and compared it with the weight of the diluted material, thus obtaining the PTE concentration in milligrams per kilogram of dry biomass,” Duim describes.
In bananas and cassava, nearly all PTEs except chromium were found in higher amounts below ground, in roots and tubers. Cocoa behaved differently, with elevated levels in stems, leaves, and fruits. In cocoa pulp, copper and lead concentrations exceeded limits set by the Food and Agriculture Organization of the United Nations (FAO).
When the team discovered that some edible portions contained PTE levels above recommended standards, they conducted a formal health risk assessment.
Health Risk Assessment for Children and Adults
The scientists calculated the risk quotient (RQ), risk index (RI), and total risk index (TRI) for people consuming bananas, cassava rhizomes, and cocoa pulp. They evaluated children (under six years of age) and adults (over 18 years of age) separately. The RQ compares a person’s estimated daily intake of a substance to a reference dose considered safe. The TRI helps determine potential non-carcinogenic health risk from exposure to PTEs. A TRI below 1 indicates low risk.
“These elements exist naturally in the environment. We’re exposed to them in lower concentrations. But in the case of a disaster like the one in Mariana, when exposure is expected to increase, we need to exercise extra caution,” says Tamires Cherubin, a health sciences Ph.D. and co-author of the study. Standard methods evaluate how bioavailable these elements are, since certain concentrations can lead to kidney and heart problems, gastrointestinal discomfort, and lung damage if inhaled. Short-term effects may also include skin irritation and eye problems.
The researchers factored in how much locally grown food residents consume, using data from the Brazilian Institute of Geography and Statistics (IBGE). They also considered how long individuals might be exposed, differences in body weight between children and adults, and the time required for harmful effects to develop.
“According to the reference daily intake doses for contaminants covered by the literature, we consider the limits of 0.05 mg/kg-1 for the presence of cadmium in fruits and 0.1 mg/kg-1 in tubers, 0.5-1.0 mg/kg-1 for the presence of chromium, 20.0 mg/kg-1 for copper, 0.5-1.0 mg/kg-1 for nickel, 0.8-2.3 mg/kg-1 for lead, and 50.0 mg/kg-1 for zinc,” Cherubin explains.
For most metals, TRI values were below 1, indicating no significant non-carcinogenic risk for adults consuming these foods from the Doce River estuary. However, the TRI for bananas exceeded 1 for children, signaling possible health concerns. Elevated lead levels were the primary driver, and cadmium concentrations in bananas also surpassed FAO recommendations. The researchers note that long-term exposure to lead, even at low levels, can permanently affect brain development, potentially lowering IQ and contributing to attention and behavioral problems.
Long-Term Cancer Concerns and Ongoing Exposure
The team cautions that eating food grown in contaminated soil over many years could lead to cumulative effects. “Over time, considering the life expectancy in Brazil of around 75 years, there may be a carcinogenic risk since there’s a possibility of direct and indirect DNA damage,” says Cherubin. Such genetic damage may increase the likelihood of cancers affecting the central nervous system, digestive tract, and blood-forming tissues. “It all depends on the human body’s ability to absorb and metabolize these elements that are available in the environment,” she adds.