Terrestrial and aquatic ecotoxicity of iron ore tailings after the failure of VALE S.A mining dam in Brumadinho (Brazil)

Abstract

This study consists of an ecotoxicological assessment related to one the most important environmental Brazilian disasters: the failure of an iron mining dam of the Vale S.A. in Brumadinho (Minas Gerais State, Brazil). Tailing samples (mixed with many other materials) were collected in three areas: (i) Zona Quente (n = 9) – close to the dam collapse; (ii) Parque das Cachoeiras (n = 3) – downstream of the Zona Quente; and (iii) Alberto Flores (n = 3), closer to Paraopeba river (an important tributary of one of the most important Brazilian watersheds). Acute ecotoxicological tests with Eisenia andrei and Daphnia similis and chronic reproduction tests with Folsomia candida and Chlorella vulgaris were performed. The bioassays with aquatic organisms were carried out with elutriates of the samples. Metal concentrations and physical, chemical and mineralogical properties of the samples were determined to support the interpretation of the ecotoxicological data. The increase of the particle density values (significantly correlated to an anomalous iron-enrichment and positive ΔpH values) seem to play a relevant role in the toxicity. As a result of iron-enrichment, the reduction of organic matter contents and water holding capacity were also crucial in the toxicity. Metal-enrichment factors showed abnormally high values, especially for Fe, Mn and Ni, while toxic metals concentrations exceeded the limits established by Brazilian law. Reproduction chronic effects were more intense than the acute ones, for both aquatic and soil organisms. Such extremely low reproduction levels of F. candida and C. vulgaris should be highlighted, since such organisms have a key ecological relevance. The samples collected in the Zona Quente were significantly different from the samples collected in downstream areas — fact that might be related to a high energy and turbulent flux of tailings in zones closer to dam, and the reduction of its energy in downstream areas.