The aim of this study was to evaluate the effects of soil organic matter on the sorption and desorption of glyphosate in three soils with different mineralogical attributes. The experiments were carried out at the Laboratório de Ecotoxicologia of the Centro de Energia Nuclear na Agricultura (CENA/USP), Piracicaba, SP (Brazil). The soils were classified as: Rhodic Kandiudalf (NVef), Anionic Acrudox (LAw) and Typic Humaquept (G). In order to evaluate the influence of organic matter on the ghyphosate sorption, the soils were oxidized with H2O2 (30%). The design was completely randomized with a 2 x 3 factorial experiment. For the sorption experiment, five gliphosate solutions were employed with concentrations of 0.42, 0.84, 1.68, 3.36 and 6.72 mg L-1 and radioactivity of 0.233 kBq mL-1. The desorption experiments were performed at concentration of 0.84 mg L-1. The results showed that glyphosate was extremely sorbed to all soils, regardless of the presence of organic matter. The glyphosate sorption was related mainly to the mineral fraction of the soils, i.e., to the Fe and Al oxides. However, the organic fraction only played a secondary role. It was not observed glyphosate desorption, mostly forming soil bound residues.
sorption; desorption; bound residue; herbicide; oxides; dissipations