RESUMO
The organic soils (Histosols) are important as filters for organic and inorganic pollutants, mainly because they are usually located on the banks of rivers and lakes. The aim of this study was to evaluate which functional groups of soil organic matter (SOM) most contribute for the Pb2+ and H2AsO4- adsorption in Histosols. This study used 20 samples (160 ~ 290 g kg-1 of organic carbon (OC) collected at 0-5 cm in five areas of Histosols from Curitiba, Southern of Brazil. Hydrofluoric acid (10%) was used to solubilize minerals to concentrate organic matter (391 to 510 g kg-1 of OC) in the samples. Samples having been submitted to pyrolysis in combination with gas chromatography (Py-GC/MS) that identified 186 organic compounds grouped based on their chemical similarity. The samples were saturated separately with Pb2+ and H2AsO4- under acid conditions (pH 4.0). The exchangeable (electrostatic interactions with SOM charges) and nonexchangeable (complexed to SOM) Pb2+ and H2AsO4- were determined for sequential methods (Ca(NO3)2 and EPA 3051A, respectively. Positive correlations occurred between exchangeable Pb2+ and phenolic compounds (r = 0.6, p < 0.05), lignin phenols (r = 0.5, p < 0.05), and sterols (r = 0.6, p < 0.05). For nonexchangeable Pb2+, there was a significant correlation with alkenes (r = 0.8, p < 0.01), alkanes (r = 0.8, p < 0.01), and methyl ketones (r = 0.7 p < 0.01). The exchangeable H2AsO4- is related to alkanes, alkenes, and methyl ketones. Therefore, in acid Histosols constituted of aliphatic organic matter tend to have less environmental fragility, due to the lesser transportation of these contaminants to other compartments like surface and subsurface waters.