Características estruturais de ácidos húmicos isolados de solos com adição de resíduos orgânicos de origem urbana: composição elementar, análise de RMN 13C e Pi-CG/EM

Abstract

SUMMARYThe structural features of humic acids (HA) after addition of organic matter from urban residues were evaluated. The HAs were extracted from the surface (0-20 cm) of an ultisol (Seropédica, RJ) and oxisol (Piraí, RJ) which had been treated with the equivalent of 80 t ha -1 (dry material) of compost from urban waste and also sewage sludge. The incubation time in the laboratory was 24 weeks under room temperature and humidity at field capacity. Tha HAs were characterized by elemental analysis, 13 C NMR spectroscopy and pyrolysis coupled to gas chromatography/mass spectrometry (Py-GC/MS). NMR spectroscopy allowed the clear observation of alterations in the molecular composition of the HAs, mainly through the increase in the content of mono and dioxygenated carbon atoms (δ δ δ δ δ 50-100) and decrease in the content of CH 2 and CH 3 groups (δ δ δ δ δ 0-40). The increase in the amount of carbohydrates suggests the presence of more labile structures in the HAs with organic residues amendment. In addition, Py-GC/MS led to the observation of significant qualitative differences between the compounds which arose from the thermal fragmentation of HAs, mainly lipids and carbohydrate derivatives (such as furan), for soil samples treated with either organic residues. The coupling of 13 C NMR spectroscopy and Py-GC/MS has proven useful in evaluating physical changes in HAs isolated from soils treated with urban organic residues.Index terms: humic substances, soil quality, spectroscopic methods, urban compost, sewage sludge.(