Toxic Legacy: How Brazil's Mining Disaster Contaminates Food Crops
A decade after Brazil's catastrophic Fundão dam collapse, a new study reveals that toxic metals from mining waste are migrating into common food crops. Researchers found that bananas, cassava, and cocoa grown in contaminated soil absorb dangerous elements like lead and cadmium. While adults face lower immediate risks, the study identifies significant health concerns for young children, particularly from banana consumption, highlighting the long-term environmental and public health consequences of industrial disasters.
More than a decade after one of Brazil's worst environmental disasters, a sobering reality is emerging from the soil. The 2015 collapse of the Fundão tailings dam in Minas Gerais unleashed a torrent of iron mining waste that contaminated vast areas along the Doce River. Now, scientific research published in Environmental Geochemistry and Health reveals that this toxic legacy is not confined to the environment—it's making its way into the food supply. This article examines how potentially toxic elements (PTEs) from mining waste are being absorbed by edible crops and what this means for human health, particularly for vulnerable populations.
The Pathway from Soil to Food
The research, conducted by scientists from the University of São Paulo (USP), the Federal University of Espírito Santo (UFES), and the University of Santiago de Compostela in Spain, focused on understanding how mining contaminants move through agricultural systems. The team investigated crops grown in the Linhares region of Espírito Santo, an area affected by the Doce River estuary contamination. According to lead researcher Amanda Duim, whose doctoral work formed the basis of the study, "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."
The researchers employed meticulous sampling and analysis methods, collecting soil and plant specimens, processing them into solutions, and measuring concentrations of cadmium, chromium, copper, nickel, and lead—metals commonly associated with iron mining waste. Their findings revealed distinct patterns of metal accumulation across different crops, with implications for food safety and public health.
Crop-Specific Contamination Patterns
The study examined three staple crops: bananas, cassava, and cocoa. Each showed different patterns of metal accumulation. In bananas and cassava, nearly all PTEs except chromium were found in higher concentrations below ground—in roots and tubers. This distribution pattern suggests that while the edible fruits of bananas might be contaminated, the primary storage occurs in non-edible plant parts. However, the research found that banana fruits still contained concerning levels of certain metals.
Cocoa presented a different scenario, with elevated metal levels appearing in stems, leaves, and—most alarmingly—in the cocoa pulp itself. The study found that copper and lead concentrations in cocoa pulp exceeded limits established by the Food and Agriculture Organization of the United Nations (FAO). This finding is particularly significant given cocoa's economic importance in Brazil and its widespread consumption globally.
Health Risk Assessment for Vulnerable Populations
When researchers discovered that edible portions contained PTE levels above recommended standards, they conducted a formal health risk assessment. The team calculated risk quotients (RQ), risk indices (RI), and total risk indices (TRI) for people consuming bananas, cassava rhizomes, and cocoa pulp. They evaluated children under six years old separately from adults over 18, recognizing the different vulnerabilities between these groups.
The results revealed a concerning disparity. For most metals and for adult consumers, TRI values remained below 1—the threshold indicating no significant non-carcinogenic risk. However, the TRI for bananas exceeded 1 for children, signaling potential health concerns. Elevated lead levels were the primary driver of this increased risk, with cadmium concentrations in bananas also surpassing FAO recommendations. As co-author Tamires Cherubin explains, "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."
Long-Term Health Implications
The research team emphasizes that while immediate risks for adults appear lower, long-term exposure presents significant concerns. Cherubin notes that "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." Such genetic damage could increase the likelihood of cancers affecting the central nervous system, digestive tract, and blood-forming tissues.
For children, the risks are more immediate and potentially more severe. The study highlights 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. The researchers factored in consumption patterns using data from the Brazilian Institute of Geography and Statistics (IBGE), along with considerations of body weight differences, exposure duration, and the time required for harmful effects to develop.
Environmental and Policy Implications
This research represents more than just an academic exercise—it has direct implications for environmental policy, agricultural practices, and public health interventions in affected regions. The findings underscore the persistent nature of industrial contamination and challenge assumptions about how quickly ecosystems can recover from such disasters. As Tiago Osório, an agronomist and professor at ESALQ-USP, recalls, "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?"
The study provides a clear answer to that question and suggests the need for ongoing monitoring of agricultural products from contaminated regions, targeted public health interventions for vulnerable populations, and potentially revised agricultural practices in affected areas. It also highlights the importance of considering cumulative exposure risks when evaluating the long-term consequences of environmental disasters.
The research conducted by Duim and her colleagues represents a significant contribution to understanding the complex relationship between industrial accidents, environmental contamination, and food safety. Their work, which earned the USP Thesis Award in Sustainability and the Capes Thesis Award in 2025, demonstrates how scientific investigation can illuminate hidden risks in our food systems and inform policies to protect public health in the aftermath of environmental disasters.
