ABSTRACT The diversity of methods for heavy metal extraction from soils complicates comparison of results used by environmental agencies to establish quality reference values. The aim of this study was to evaluate three soil digestion methods regarding the solubilizing capacity of Ba, Cr, Cu, Fe, Mn, Ni, Pb and Zn, and to propose a standard method to establish Quality Reference Values (QRVs) for Brazilian Histosols. Twenty soil samples were selected to evaluate the USEPA 3051, USEPA 3051A and Aqua Regia methods in a closed system. The methods tested were statistically similar regarding Cu, Fe and Mn extraction from soils. However, the methods can not be considered similar for Ba, Cr, Ni, Pb and Zn; Aqua Regia recorded the highest levels, except for Ba. The Aqua Regia method proved suitable for metal extraction from soils with organic characteristics and can be used to establish QRVs.

Com o objetivo de avaliar a possível solubilização do sulfato de bário em solos sob condições redutoras e aumento da biodisponibilidade do bário, instalou-se ensaio em vasos com Oryza sativa. Avaliaram-se doses de bário e duas condições de potencial redox. Os resultados do fracionamento geoquímico demonstraram que a condição de redução favoreceu o aumento nos teores de bário nas formas de maior labilidade e diminuição nas formas de maior estabilidade. A produção de grãos foi influenciada, de forma negativa, pela aplicação da maior dose de bário. Os teores mais elevados e acúmulo de bário nas folhas, raízes, e grãos foram encontrados na maior dose e na condição de redução. Esses resultados evidenciaram que a condição de redução proporcionou maior biodisponibilidade desse elemento.

To evaluate the possible solubilization of barium sulfate in soils under reducing conditions and its effects on barium bioavailability, an Oryza sativa pot trial was established. Increasing barium doses and two redox potential conditions were evaluated. The geochemical fractionation data demonstrated that reducing conditions led to an increase in the levels of more labile forms of barium and a reduction in more stable forms. Furthermore, higher doses of barium were found to have a negative impact on grain production. The highest levels of barium accumulation in the leaves, roots, and grains were observed with the highest barium dose under reducing conditions. These results demonstrate that reducing conditions increased barium bioavailability and absorption by rice plants.