Sorption of Imidazolinone Herbicides by Humic Acid Preparations

Abstract

Isotherms were obtained and analysed for the sorption and desorption of a selection of imidazolinone xenobiotic organic chemicals by H+-and Ca2+-exchanged humic acid (HA) preparations isolated in a sodium hydroxide solution from a sapric histosol. The data show that the extents and the reversibilities of the sorption processes are governed by the compositions and the structures of the sorptive (sorbing) species, and by the exchangeable cation (H+ or Ca2+) satisfying the charges on the HA sorbent. To a considerable extent the sorption processes are influenced by the pKa values of the sorptives, by their extents of ionization at the pH of the medium, and also by the different influences the cations (H+and Ca2+) have on aspects of the structures (conformations) of the HAs. Sorption of the Ca2+- exchanged HAs was small, and that would suggest that the compounds could have considerable biological activities in soils with high organic matter contents when the exchangeable inorganic cations are divalent or polyvalent.