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Although some radioecological studies have been accomplished in Brazilian soils supplying useful information to optimization of emergency planning actions in rural areas and to the management of soils contaminated by 137Cs, 60Co and 90Sr, few studies were made with transuranic elements in tropical agricultural areas. The different scenarios found in Brazilian agricultural environments enhance the importance of studying the biogeochemical behavior of radionuclides in representative soils. The objective of this work was to determine the mobility of 241Am in 3 different Brazilian agricultural soils evaluating migration with depth and Kd values for 241Am and the effect of organic amendments on this behavior. A strong effect of organic amendments on mobility of americium could be observed. The values of Kd obtained in all studied tropical soils were however smaller than those found in European soils and from those recommended by IAEA to be used as default values in the absence of regional data. This result reinforces the vulnerability of some tropical soils to a contamination, emphasizing the need to use of regional values. Made available in DSpace on 2016-10-03T22:36:48Z (GMT). No. of bitstreams: 1 radioproicrer46955.pdf: 300175 bytes, checksum: 4cadb82fee031a00d08ba0c9d65ab713 (MD5) Previous issue date: 2012-03-12

Sewage sludge has predominantly organic composition and can improve soil characteristics, such as fertility and erosion resistance. Therefore, its application as an amendment for agriculture is an adequate alternative for its final disposal. However, there is a lack of information concerning soil enrichment with radionuclides in long-term experiments in tropical areas. Thus, the objective of this study was to determine the impact of soil biosolid amendment on the concentration of 210 Pb, 226 Ra, 228 Ra, U, Th, and other elements in maize grown in a Brazilian Ferralsol. The results obtained showed that radionuclide concentrations in maize grains were not significantly influenced by either the applied biosolid doses, or biosolid origin, or the interaction of these two factors.

In this work, soil to plant transfer factor of 226 Ra and 228 Ra obtained in areas of traditional agricultural practices varied as a function of the considered cultivated species, but little variation was observed as a function of the soil type. Beans and soybeans presented a more important absorption than cereals (com, rice and wheat). Values of transfer factor of the legumes (beans and soybeans) were about an order of magnitude greater than the average obtained in areas of high natural radioactivity, while the results for the cereals did not presented such clear differences. Cultural inputs of 226 Ra and 228 Ra are occurring in agricultural areas, but few species can demonstrate it. Soil to plant transfer factor values for 226 Ra and 228 Ra, obtained in agricultural areas seem more applicable in models of risk evaluation.

Results of a sequential chemical extraction procedure for 137 Cs in an acidic Oxisol showed that 3 years after the contamination, 40 % of total concentration was considered readily bio-available, 20 % bound to organic matter and 40 % bound to Fe and Mn oxides. Four years after, the 137 Cs distribution in this soil have been changed as a consequence of changes in soil properties : 8 % bio-available, 16 % bound to organic matter, 43 % bound to Fe and Mn oxides and 33% strongly bound to soil compounds. Changes in the 137 Cs distribution in this soil were followed by reductions in soil to plant transfer factor (TF) : TFOxisol1996 = 2,21 ± 1,30 (n=3) and TFOxisol2000 = 1,63 ± 0,38 (n=6). During the same period, the soil properties of a basic Oxisol remained almost the same, consequently the geochemical distribution and soil to plant transfer factor for 137 Cs did not change in this soil. The geochemical distribution in an acidic Alfisol showed that Mn oxides are the main sink for this element and no 60 Co was detected in the readily bio-available phase. In this soil, four years after contamination with 60 Co, it was not detected in plants.