Environmental and public health outcomes following the Fundão dam collapse (Mariana, Brazil): a retrospective ecological study of drinking water quality and cancer mortality

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Background: The Fundão dam collapse, which occurred in 2015 in Minas Gerais, Brazil, was the largest tailings dam failure in history, releasing 60 million tons of mining waste onto 3.5 million people and contaminating 660 km of rivers and water sources. Methods: This study analyzed data from the Brazilian Water Quality Information System (SISAGUA, 2014-2023) for water-quality records and SIM/DATASUS (2011-2023) for mortality, focusing on municipalities affected by the 2015 Fundão dam collapse in the Doce River Basin, Minas Gerais, Brazil. The dataset included records of micropollutants that exceeded Brazilian Maximum Residual Limits (MRLs) across 203 cities. Contamination levels were compared with those in unaffected municipalities in the Grande and Jequitinhonha River Basins. Micropollutant profiles, cancer risk indexes, estimated cancer cases, and global and cancer mortality data were evaluated. Findings: We found extensive contamination in the Doce River Basin, particularly by metals such as cadmium, arsenic, lead, and antimony. A total of 300 cancer cases were estimated. All-cause mortality in the Doce River Basin increased between the pre-disaster period (2011-2014) and the post-disaster period (2015-2023; +0.005 deaths per population, 95% CI 0.0022 to 0.0078, p = 0.028). A formal difference-in-differences (DID) test against comparison basins yielded a positive but non-significant estimate. Cancer-specific mortality rates for ovarian, rectal, oropharyngeal, and central nervous system were higher in affected municipalities than in comparison basins. Interpretation: The study highlights the need for improved water treatment and health monitoring in the region, as well as further research into the long-term health impacts of mining-related contamination. Funding: Brazilian National Council for Scientific and Technological Development (CNPq; Grants 402364/2021-0 and 303076/2025-9).

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