Submitted to: Clay International Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 4/7/1997
Publication Date: N/A
Technical Abstract: Soil clay (mineral and organic components) has been shown to be responsible for sorption of many pesticides. Sorption of pesticides by soil colloidal particles affects their transport in runoff, surface waters, and to ground water. This study assessed the influence of different components of the clay fraction of five soils and model sorbents (montmorillonite, iron oxide eand humic acid) and their binary and ternary associations on sorption of the insecticide imidacloprid. Sorption coefficients on soil clay fractions did not correlate with any single component, but when organic matter was reduced by H2O2 treatment, sorption decreased although Koc increased, indicating a contribution of the surfaces of mineral components of the soil clay in sorption of imidacloprid. This increase was greater on clays whose surface areas substantially increased after H2O2 treatment. Imidacloprid sorbed on SWy-montmorillonite and humic acid, whereas sorption was very low won iron oxide. Sorption coefficient Kd for SWy-Fe montmorillonite was higher than for SWy-Ca, and increased from 15 to 180 when pH was decreased from 3.5 to 1.0, suggesting protonation of the -NH group of the imidazol ring. Sorption on binary and ternary associations of these model adsorbents indicated that organic matter is the most important single component affecting sorption of imidacloprid, but that there is also a contribution to sorption by the mineral surfaces.