Early pedogenesis of anthropogenic soils produced by the world’s largest mining disaster, the “Fundão” dam collapse, in southeast Brazil

The overwhelming production of waste represents a complex environmental challenge for mining companies worldwide. Efforts are currently being made to develop methods for storing or reusing such potentially hazardous waste. Among innovative environmentally-friendly solutions, constructing Technosols from mining waste may be a feasible solution for revalorizing this type of waste. However, there is a knowledge gap regarding the pedogenic processes that govern the functioning of these soils. The Fundão Dam collapse (2015) offers a unique opportunity to evaluate the early pedogenesis of a Technosol unintentionally formed from Fe-rich tailings deposited in the Doce River estuary. This study aimed to assess the pathways of Technosol pedogenesis, four years after the world’s largest mining disaster. Based on a multi-technique approach (including macro-and micromorphological analysis, mineralogical analysis, physicochemical parameters and geochemical analysis of Fe partitioning), bare tailings and different Technosol profiles were analyzed to unravel the action of early pedogenesis in a hydromorphic environment. Within four years, rapid colonization by plants favored fine particle accumulation and triggered a process of cumulization, as evidenced by a 6-fold increase in the clay content. The vegetation also promoted input of organic carbon (from 0.4 to 2.1 %), which altered the geochemical environment and Fe dynamics. These changes promoted melanization, incipient paludization and gleization. The Fe partitioning revealed that the bare tailings, primarily comprising crystalline Fe oxides, transitioned to soil matrices dominated by poorly crystalline Fe oxyhydroxides (41 ± 3 %). Examination of thin sections revealed rapid Fe translocation through Technosol profiles associated with the formation of Fe coatings and hypocoating pedofeatures. This study provides valuable insights into the action of both time and organisms as factors for Technosol formation and functioning.