Natural and anthropogenic gamma-ray emitters and iron-bearing compounds distribution in peatlands of the southern Espinhaço mountain chain, Brazil

Abstract

To help understand the dynamics of peatlands forming on the Southern Serra do Espinhaço, Brazil, the occurring natural (226Ra, 232Th, 40K) and anthropogenic (137Cs) activity of gamma-ray emitters located at three sites, namely the localities of São João da Chapada (CH), Pinheiro (PIN) and Pau de Fruta (PDF), was studied. The iron compounds were characterized by 57Fe Mössbauer spectroscopy. Differences on natural radionuclide levels and distributions were found among the peatland sites, indicating differences on mineral composition, hydric regimes and living. Significant correlation was found only for 232Th–226Ra activity values (Pearson correlation coefficient of − 0.5), which is different from other South American soils, where significant positive correlations among all radionuclides were determined. In PDF and CH, the dose rate results are lower than the worldwide mean value, but in PIN, they are higher because of the relatively high 226Ra concentration. The only anthropogenic radionuclide is 137Cs. The convection–diffusion model fits the CH and PDF activity profiles, although the PIN profile is likely affected by other soil mechanisms as well. Mössbauer spectra reveal Fe3+ in two different local environments and the occurrence of hematite in the upper samples of the CH site. The iron concentration decreases with depth. Contrary to soils of other regions, no significant correlation was found between iron species and the natural radioactivity. The studied peatlands exhibit clear differences between their natural and anthropogenic radionuclide distributions to those of mineral soils.