Confounding factors and tertiary-phase control by a surfactive agent on smectite sorption of atrazine

Atrazine is a widely used commercial pesticide applied to soil for the control broadleaf weeds in agriculture. Frequent detection of atrazine in surface and subsurface waters and the potential for adverse effects on toxicity to aquatic and terrestrial life have generated numerous investigations into the mechanisms governing atrazine sorption by soils. This dissertation seeks to add to that body of knowledge by elucidating basic mechanisms and processes that influence sorption of atrazine on clays in the presence and absence of surfactants commonly used in commercial formulations. Sorption studies showed that air-dried (AD), resuspended K+-saturated PC (KPC) exhibited a significantly enhanced sorption affinity for atrazine over KPC that was never-dried (ND). X-ray diffraction (XRD) analysis revealed that air-drying had irreversibly collapsed the basal spacing of KPC. It was hypothesized that the atrazine sorption was enhanced in the collapsed KPC because it provided a less hydrated environment where atrazine's alkylamino sidechains could simultaneously interact with hydrophobic nanosites on both of the opposing basal surfaces. Furthermore, this work explored the potential of a nonionic surfactant, Brij 35, which is similar to the surfactant used in commercial atrazine formulations, to modify the sorption chemistry of atrazine. Experiments revealed that lower concentrations of Brij 35 inhibited atrazine sorption while higher concentrations enhanced sorption; an opposite trend from what was expected. At low Brij 35 concentrations, XRD evidence indicated that Brij 35 was intercalated and progressively filled the clay interlayer. At high concentration, interlayer sites were completely filled with Brij 35 and excess surfactant formed micelles on the external surfaces of the smectite quasicrystals. Atrazine sorption was enhanced by partitioning to these surface micelles. Effects of co-solvents on surface micelle formation are discussed.