Triallate adsorption onto humic acids of different origin and nature

Humic acids (HAs) isolated from two different soils sampled at two differen t depths and from a pig slurry used as soil amendment, and their interactio n 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, excita tion and synchronous scan modes. The pig slurry HA exhibited a greater alip hatic character, higher presence of proteinaceous and polysaccharide consti tuents, lower acidic functional group content, and lower aromatic polyconde nsation and humification degrees than soil HAs. Only small differences occu rred between HAs from the two soil types and the two sampling depths of eac h soil. Adsorption of triallate onto HAs, measured using a slurry-type meth od combined with high-pressure liquid chromatography (HPLC), could be descr ibed in all cases by linear isotherms. The extent of adsorption of triallat e onto pig slurry HA was between two and four orders of magnitude higher th an that onto soil HAs. The types of binding mechanisms appeared to be relat ed to the compositional, structural and functional properties of the HA. Hy drophobic 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 gro ups of the HA macromolecules. (C) 1999 Elsevier Science Ltd. All rights res erved.