ABSTRACT Failures of mining tailings dams can cause severe environmental impacts, as sadly illustrated by the Fundão dam collapse in Mariana-Minas Gerais State, Brazil, in 2015. This event induced significant physical and chemical changes in the affected landscape, including variations in soil pH, texture, and key edaphic properties. Soils formed from post-industrial anthropogenic activities, known as Technosols, exhibit high biological, chemical, and physical heterogeneity. In the affected area, Technosols comprise a mixture of tailings, iron mining sediments, natural soils, and debris, with high concentrations of iron oxides, silt, and fine sand. This study aimed to deepen the understanding of Technosols on floodplains and riverbanks impacted by the dam rupture by characterizing their physical and chemical properties in detail. Seventy soil profiles were analyzed — 50 Technosols and 20 unaffected soils — using a slice-wise algorithm to generate standard profile sketches for comparison. Tailings-containing layers exhibit distinct chemical characteristics, including higher pH, phosphorus content, base saturation, and silt content than unaffected layers. These horizons exhibited low cation exchange capacity, indicating low fertility. Tailings deposition was controlled by the basin geomorphological gradient, showing greater heterogeneity upstream and more uniformity downstream. Physically, Technosols displayed higher fine particle content in surface layers, associated with the tailings, while deeper layers showed increased coarse sand and clay, reflecting truncated unaffected horizons of the alluvial environment. Chemically, impacted soils exhibited elevated pH and slight increases in phosphorus, sodium, and potassium at the surface, contrasting with more acidic and less fertile unaffected soils downwards, despite local variability, most profiles showed homogeneous responses, with impacts confined to surface layers.
Almeida et al. (Thu,) studied this question.