Adsorption of Isoxaflutole Degradates to Aluminum and Iron Hydrous Oxides
- Si Hyun Wuab,
- Keith W. Goyne *a,
- Robert N. Lerchc and
- Chung-Ho Lind
- a Goyne, Dep. of Soil, Environmental and Atmospheric Sciences, Univ. of Missouri, 302 ABNR Bldg., Columbia, MO 65211
b current address: Dep. of Agro-Food Safety, National Academy of Agricultural Science, 249 Suin-Ro Kweonseonku, Suwon, Republic of Korea 441-857
c USDA–ARS, Cropping Systems and Water Quality Research Unit, 269 Agric. Eng. Bldg., Columbia, MO 65211
d Center for Agroforestry, Univ. of Missouri, 203 ABNR Bldg., Columbia, MO 65211. Assigned to Associate Editor K.G. Karthikeyan
Isoxaflutole is a preemergence herbicide that has been marketed as a substitute for atrazine. It is rapidly transformed to a more stable and soluble diketonitrile degradate (DKN) after field application and can further degrade to a benzoic acid degradate (BA) within soil. However, no previous research has been conducted to investigate DKN and BA sorption to metal oxide minerals. The primary objective of this research was to elucidate the interactions of DKN and BA with synthetic hydrous aluminum and iron oxides (HAO and HFO, respectively) to understand how variably charged minerals may influence adsorption of these compounds in soil. The herbicide degradates did adsorb to HAO and HFO, and the data were well described by the Freundlich model (R 2 > 0.91), with N values ranging from 0.89 to 1.2. Adsorption isotherms and K d values demonstrate that BA is adsorbed to HFO to a greater extent than other degradate–mineral combinations that were studied. The degree of hysteresis between adsorption/desorption isotherms was characterized as slight (hysteresis index values <1.7), suggesting weak DKN and BA retention to HFO and HAO oxide surfaces. Degradate adsorption was observed to greatly diminish as suspension pH increased. Attenuated total reflectance–Fourier transform infrared spectra show no evidence that DKN or BA adsorb to mineral surfaces as inner-sphere complexes under hydrated conditions. Instead, DKN and BA adsorb to positively charged metal oxide surfaces as outer-sphere or diffuse ion swarm complexes via electrostatic attraction. This research indicates that metal oxides may serve as important retardants for DKN and BA migration through acidic soils enriched with aluminum and iron oxides.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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