Isoxaflutole is relatively new herbicide which is rapidly hydrolyzes to a diketonitrile (DKN) degradate after field application. Subsequently, DKN is degraded to form a benzoic acid (BA) derivative and other inactive degradates. However, our understanding of soil solid phases influencing or governing the fate of DKN and BA in soils is still poor. Due to the anionic nature of DKN and BA in natural waters, we hypothesize that variable-charged minerals may be important adsorbents for isoxaflutole degrades. Our previous research indicated (1) that DKN is adsorbed to hydrous aluminum and iron oxides (HAO and HFO, respectively), (2) DKN is adsorbed to HFO to a greater extent, and (3) slight hysteresis exists between DKN adsorption and desorption isotherms when the degradate is reacted with HAO. 

The objective of our current study is to (1) examine the influence of soil mineral chemical composition (HAO and HFO) on BA adsorption and retention, (2) investigate the influence of pH on DKN and BA adsorption to HFO and HAO, and (3) elucidate the mechanism(s) of DKN and BA binding to metal hydrous oxide surfaces using FTIR spectroscopic investigations. Results from ongoing work will be presented, and comparisons/contrasts between DKN and BA interactions with HAO and HFO will be discussed.

Fig. 1. Degradates adsorbed or desorbed (Γ_ads or Γ_des) on HFO as a function of initial concentration at pH 5.5.  Error bars, where observed, represent the 95% confidence interval.

Fig. 2. Degradates adsorbed or desorbed (Γ_ads or Γ_des) on HAO as a function of initial concentration at pH 5.5.  Error bars, where observed, represent the 95% confidence interval.

Table 1. Freundlich parameters for degradates – HAO and HFO adsorption isotherms.