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 ( 226 Ra, 232 Th, 40 K) and anthropogenic ( 137 Cs) 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 57 Fe 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 232 Th-226 Ra 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 226 Ra concentration. The only anthropogenic radionuclide is 137 Cs. 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 Fe 3+ 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.

Use of nuclear techniques in soil science: A literature review of the Brazilian contribution

“…These limits were established by analyzing soil profiles from latitudes varying from 00° 49' N (Handl et al, 2008) to 52° 12' S (Minella et al, 2014). The influence of the latitude on 137 Cs stocks has been pointed out as a relevant factor in the deposition of the fallout in soil profiles in Brazil (Schuch et al, 1994;Fraga and Salcedo, 2004;Handl et al, 2008;Andrello et al, 2009;Antunes et al, 2010;Montes et al, 2019).…”