Post burial modifications of humic acids in a paleosol sequence from the south of Spain

Humic acids (HA) were extracted from four Chromic Luvic paleosols belonging to the Pinos Genil formation (Granada, SPAIN). Comparison of HA extracted from the surface soil to those of paleosols showed substantial structural alterations, mainly decarboxylation and progressive degradation of aromatic structures. Changes observed in FT-IR spectra of HA after heating pellets at 105 °C suggested an increasing presence of strong metal-humate complexes with soil age. Chromatographic profiles obtained by HPLC-SEC were modified in presence of EDTA, confirming extensive formation of inter-molecular cationic bridges. Electrofocusing carried out with and without EDTA confirmed the hypothesis of metal-humate complexes formed in paleosols.