Physical, chemical and microbiological characterization of the soils contaminated by iron ore tailing mud after Fundão Dam disaster in Brazil

Abstract

The collapse of the Fundão dam in Mariana – Minas Gerais, in the Iron Quadrilateral, considerably modified the Carmo riverbank. This study aimed to perform a physical, chemical, and biological characterization of the soils contaminated by iron ore tailing mud after the dam disaster. From the riverbank to uncontaminated soil, three sites were sampled: site I (sandy sediment), site II (iron ore tailing mud) and site III (pasture soil). Analysis were performed to characterize soil physical features and soil fertility, fumigation-extraction method was applied to measure soil microbial biomass C, and to evaluate the photobiotic organisms' diversity by a growth experiment in a controlled chamber, for the samples collected in three sites. The results showed that site I presented quartz as the main mineral; site II presented both quartz and hematite; and site III presented greater diversity in the mineralogical composition. Site III showed greater fertility, except for the phosphorus and iron content that was higher in site II. The sites I and II have higher values of metabolic quotient and lower microbial carbon/organic carbon ratio, unlike site III. The results indicated that after one year of the dam failure the microbial activity was disturbed, as the nutrients and carbon concentration from the sites were decreased due to the presence of iron ore tailing mud in comparison to unaffected soil from the same area. However, a community of phototrophic microorganisms has been observed with a predominance of cyanobacteria, which may be important to enhance the development of this initial stage of succession.