# The legacy of mining revealed by environmental DNA: long-term ecological structuring of marine benthic communities after the Fundão dam collapse

## TL;DR

This study uses environmental DNA to show how a 2015 mining disaster in Brazil continues to affect marine life more than three years later.

## Contribution

The study reveals long-term ecological impacts of the Fundão dam collapse using eDNA metabarcoding to track benthic community changes.

## Key findings

- The Front region near the river mouth showed a community dominated by metal-tolerant species like diatoms and protists.
- The North and South regions had higher biodiversity and included benthic invertebrates like nematodes and sea cucumbers.
- Species richness and diversity varied significantly across regions, indicating persistent ecological disruption from mining waste.

## Abstract

Coastal marine ecosystems are key components of biodiversity and ecosystem functioning but have been increasingly degraded by human activities. One of the most severe environmental disasters in Brazil occurred in November 2015, when the Fundão tailings dam collapsed in Mariana (Minas Gerais), releasing approximately 40 million m3 of iron ore waste into the Rio Doce basin and adjacent coastal environments. To evaluate the long-term biological consequences of this event, we analyzed the taxonomic composition and diversity of marine communities using environmental DNA (eDNA) metabarcoding from sediment cores collected in 2018 across three coastal sectors—Front (mouth of the Doce River), North, and South. A total of 761,517 reads generated 11,061 unique amplicon sequence variants (ASVs) assigned to 148 taxa revealing significant spatial variation in taxonomic (species-level) composition and diversity indices (PERMANOVA, pseudo-F = 16.55; p = 0.047). The South region exhibited the highest species richness (q₀ = 103 taxa), followed by the North (97) and Front (70). Cluster and SIMPER analyses indicated two distinct biological assemblages: (1) the Front region, dominated by diatoms (Mediophyceae, Bacillariophyceae) and protists tolerant to metal enrichment, and (2) the North–South regions, characterized by higher evenness and presence of benthic invertebrates such as Holothuroidea and nematodes (Desmodorida). Species abundance distribution (SAD) models differed among areas, reflecting ecological gradients associated with the dispersal and chronic accumulation of mining residues. These results demonstrate a persistent imbalance in marine communities near the Doce River mouth, suggesting that the legacy of historical contamination and the Fundão dam failure continues to shape benthic biodiversity patterns more than three years after the disaster.

The online version contains supplementary material available at 10.1007/s10661-026-15092-9.