Radiological characterization of the area impacted by the Mariana dam disaster, in Mariana City-MG-Brazil

This study was developed with the aim of determining the activity concentration of ²²⁶Ra, ²²⁸Ra, ²¹⁰Pb and ⁴⁰K in samples of technosols (soils formed by the deposition of tailings from the dam rupture on the banks of rivers and in riverside regions) and in natural soils from the Mariana region in Minas Gerais, after the Mariana tragedy, which is considered the biggest accident in terms of volume of material dumped. The soil samples were analyzed by gamma spectrometry in a hyperpure germanium detector system. The concentrations of all studied radionuclides were higher in the natural soils of Mariana (²²⁶Ra 471–1204 Bq kg⁻¹, for ²²⁸Ra 415–789 Bq kg⁻¹, for ²¹⁰Pb 327–641 Bq kg⁻¹ and for ⁴⁰K 707–2080 Bq kg⁻¹) than in the technosols formed after the accident (²²⁶Ra of 179–384 Bq kg⁻¹, for ²²⁸Ra of 60–269 Bq kg⁻¹, for ²¹⁰Pb of 463–818 Bq kg⁻¹ and for ⁴⁰K of 105–204 Bq kg⁻¹), indicating that the region may present some type of radioactive anomaly or that the use of fertilizers in agricultural soils may have promoted some increase in these elements. On the other hand, the concentrations in the technosols were high when compared with tailings from iron mining in other countries (42 Bq kg⁻¹ for ²²⁶Ra and 16 Bq kg⁻¹ for ²¹⁰Pb), as well as tailings from phosphorus mining in Brazil and in the world. It is admitted that these high values are the result of the mixture of pure tailings with the natural soil of the region, that presented radioactive anomaly, and also result of the peculiar geology of Mina Alegria.