Fundão Dam Collapse: Brazilian Bananas and Toxic Metals

Key points

• Researchers have identified increased concentrations of toxic metals, including cadmium and lead, in bananas, cassava and cocoa cultivated near the site of the 2015 Fundão dam collapse.
• The study concluded that children could face health risks from eating bananas grown around the Doce River estuary, while cassava and cocoa also contained troubling metal levels.
• Although the majority of bananas imported into the US come from Central America, the findings show how industrial pollution can taint crops and endanger food safety long after an environmental catastrophe.

In 2015, the Fundão tailings dam - an embankment used to hold waste products from iron mining - failed in Minas Gerais, Brazil. The disaster, widely described as the “worst environmental disaster” in the country’s history, may now be particularly unwelcome news for anyone fond of Brazilian bananas.

When the dam collapsed, it unleashed a wave of mud that engulfed and buried a nearby town. It killed 19 people, forced hundreds from their homes and ultimately flowed to the coast, damaging coral reefs, mangroves and beaches before also affecting farmland. Researchers in soil science, environmental engineering and public health at the University of São Paulo, Brazil’s Federal University of Espírito Santo, and Spain’s University of Santiago de Compostela are now examining its lasting effects.

In late 2025, the researchers published a study in Environmental Geochemistry and Health assessing whether crops grown near the disaster site, particularly in the Doce River estuary, remain safe to eat.

Fundão dam collapse and contaminated crops

The team examined bananas, cassava and cocoa pulp grown in soil impacted by the disaster. To establish whether the crops had been harmed, it measured cadmium, chromium, copper, nickel and lead - metals associated with iron oxides, which the researchers said “are the primary components of the tailings.” Their findings indicate that eating a banana from the area could create health risks, particularly for children.

“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,” 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, said. “But the question remained: Does this contamination pose a risk to human health?”

The researchers described how plants take up these “potentially toxic elements”, or PTEs, from mining waste and then retain them in edible tissues that can eventually reach supermarket shelves.

“The iron oxide content in the soil, which is the main constituent of the tailings, correlates with its content in the plant,” PhD researcher Amanda Duim Ferreira explained. “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.”

To establish precise contamination levels, the group gathered soil and plant samples, then put them through washing and weighing procedures. The edible sections were separated from the remaining plant material and dried into powder.

“We dissolved the ‘plant powder,’ transforming it into a solution using various acids, and determined the concentration in the solution,” Duim Ferreira said. “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.”

Metal levels in bananas, cassava and cocoa

The analysis showed that, in bananas and cassava, almost every PTE apart from chromium appeared at greater concentrations in the roots and tubers. Cocoa followed a different pattern, with elevated levels found in its stems, leaves and fruits. The researchers noted, “In cocoa pulp, copper and lead concentrations exceeded limits set by the Food and Agriculture Organization of the United Nations (FAO).”

“These elements exist naturally in the environment,” Tamires Cherubin, a health sciences Ph.D. and co-author of the study, said. “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.” At higher concentrations, the metals can cause numerous health problems, including kidney and heart issues, gastrointestinal discomfort and, when inhaled, lung damage.

Taking this “extra” caution into account, the researchers calculated the risk quotient (RQ), risk index (RI) and total risk index (TRI) for people who eat bananas, cassava rhizomes and cocoa pulp. They separately assessed children under six and adults. Once they accounted for residents’ consumption of locally cultivated food, prolonged exposure and weight differences between children and adults, they found that the TRI for most metals was below 1, suggesting no substantial risk for adults. For children, however, the TRI for bananas was above 1 for cadmium, “signaling possible health concerns.”

“Over time, considering the life expectancy of around 75 years, there may be a carcinogenic risk since there’s a possibility of direct and indirect DNA damage,” Cherubin said. The researchers said such damage could raise the risk of certain cancers involving the central nervous system, digestive tract and blood-forming tissues. However, “It all depends on the human body’s ability to absorb and metabolize these elements that are available in the environment.”

Should you be worried?

For most US shoppers, the study is unlikely to change what goes into the fruit bowl. The researchers investigated crops grown around Brazil’s Doce River estuary, an area directly affected by the 2015 dam collapse, rather than the country’s agricultural production as a whole.

Nor does the research point to widespread contamination among Brazilian banana exports. Most bananas sold in the United States are imported from Guatemala, Ecuador and Costa Rica, rather than Brazil.

The heightened risk found by the study was chiefly associated with young children eating locally grown bananas over extended periods. Overall risk levels for adults remained below the thresholds regarded as significant.

The broader lesson is that contamination in the environment can remain in soil for years, with communities nearest the source experiencing the greatest effects.

There is marginally less cause for concern among US consumers. American Farm Bureau data shows that, although most bananas eaten in the United States are grown in Central and South America, Guatemala provides 40% of US banana imports. Ecuador and Costa Rica follow, each supplying 16%. Brazil is nevertheless among the world’s top 10 banana-producing nations, so frequent travellers may still come across Brazilian bananas.

The study also adds to evidence that soil pollutants can contaminate fruit and vegetables. In October, Food & Wine reported on separate research finding that microplastics can pass through plants’ natural root barriers and build up in edible vegetables such as radishes, further underlining why healthy soil matters for human health.