SORPTION OF IMIDACLOPRID ON SOIL CLAY MINERAL AND ORGANIC-COMPONENTS

Soil clay mineral and organic components have been shown to be respons ible for sorption of many pesticides. This study assessed the influenc e of the different components of the clay fraction of five soils and m odel sorbents (montmorillonite, Fe oxide, and humic acid) and their bi nary and ternary associations on sorption of the insecticide imidaclop rid (1-[(6 3-pyridinyl)-methyl]-N-nitro-2-imidazolidinimine), Sorption was very high on a clay fraction containing a high content of low-lam inar-charge montmorillonite and relatively high organic C content. Whe n organic matter of the soil clays was reduced by H2O2, sorption decre ased; however, the sorption coefficient based on organic C (K-oc) incr eased. The increase in K-oc was greater on clays whose surface areas s ubstantially increased after H2O2 treatment. This indicates a contribu tion of the surfaces of mineral components of the soil clay to sorptio n of imidacloprid. Imidacloprid sorbed on both montmorillonite and hum ic acid, whereas sorption on Fe oxide was very low. The sorption distr ibution coefficient, K-d, on montmorillonite 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 associat ions of these model sorbents indicated that organic matter is the sing le most important component affecting sorption of imidacloprid, althou gh there is some contribution of the mineral surfaces.