Triallate adsorption onto humic acids of different origin and nature

Abstract

Humic acids (HAs) isolated from two different soils sampled at two different depths and from a pig slurry used as soil amendment, and their interaction products with the herbicide triallate were characterized by elemental and functional group analyses and Fourier transform infrared (FT-IR), electron spin resonance (ESR) and fluorescence spectroscopy in the emission, excitation and synchronous scan modes. The pig slurry HA exhibited a greater aliphatic character, higher presence of proteinaceous and polysaccharide constituents, lower acidic functional group content, and lower aromatic polycondensation and humification degrees than soil HAs. Only small differences occurred between HAs from the two soil types and the two sampling depths of each soil. Adsorption of triallate onto HAs, measured using a slurry-type method combined with high-pressure liquid chromatography (HPLC), could be described in all cases by linear isotherms. The extent of adsorption of triallate onto pig slurry HA was between two and four orders of magnitude higher than that onto soil HAs. The types of binding mechanisms appeared to be related to the compositional, structural and functional properties of the HA. Hydrophobic bonds possibly prevailed in the interaction of triallate with pig slurry HA, whereas adsorption of triallate onto soil HAs possibly involved charge-transfer and ionic bonds, with the participation of fluorophore groups of the HA macromolecules.