Environmental Radioactivity and Fe Phases in Peatlands of the Serra Do Espinhaço Meridional, Brazil

MONTES M.L.; MERCADER, R.C.; MORAIS BARRAL U; A.C.SILVA; FABRIS J.D.; M.A. TAYLOR

Santiago de Chile

Congreso; XVI Latin American Conference on the Applications of the Mössbauer Effect; 2018

Universidad de Santiago de Chile

Peatlands are important wetlands that have a high capacity to stock fresh water and sequester and fix carbon from the atmosphere. There are several peatlands currently in formation of great interest for their environmental and economical meaning across the Serra do Espinhaço Meridional, Minas Gerais, Brazil. To help understand the properties and genesis of the peatlands we have studied the activity of natural (226Ra, 232Th and 40K) and anthropogenic (137Cs) gamma-ray emitters. In addition, for the three peatlands studied: São João da Chapada, Pinheiro and Pau de Fruta, we have characterized the Fe compounds by Mössbauer spectroscopy. For the Pinheiro and Chapada sampling sites, the 232Th activity increases with depth but it remains constant for Pau de Fruta. In Pinheiro, the 226Ra activity values are significantly higher than for the other peatlands. Like in Pau de Fruta, activity shows a Gauss-type distribution with depth. In Chapada, the 226Ra activity mainly decreases with depth. The 40K activity in Pau de Fruta is relatively higher and, like in Chapada, decreases with depth. In Pinheiro, the 40K activity fluctuates. The natural radioactivity reported here exhibits values and behaviors different from other South American soils. They yield a significant correlation only for 232Th-226Ra, with a Pearson correlation coefficient of -0.5, also different from other soil types. The only anthropogenic radionuclide is 137Cs. The convection-diffusion model fits its activity profiles, although the Pinheiro profile seems to be affected by other soil mechanisms as well. Mössbauer spectra reveal Fe3+ in two environments and the occurrence of hematite in the surface samples of Chapada. The Fe concentration decreases with depth. Significant correlations were obtained between Fe phases and natural radioactivity, like in other soil types. These results call for a soil formation model that must also consider the current findings under investigation at UFVJM.