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Adsorption of Isoxaflutole Degradates to Aluminum and Iron Hydrous Oxides
Si-Hyun
1
1
Wu ,
1
Goyne ,
Keith W.
Chung-Ho
3
Lin ,
and Stephen H.
1
Anderson
Department of Soil, Environmental and Atmospheric Sciences, University of Missouri, 302 ABNR Bldg., Columbia, MO 65211
2 USDA-ARS, Cropping Systems and Water Quality Research Unit, 265 Ag. Eng. Bldg., Columbia, MO 65211
3 Department of Forestry and the Center for Agroforestry, University of Missouri, 203 ABNR Bldg., Columbia, MO 65211
Structure of IXF and its degradates
HAO-DKN Adsorption
• Isoxaflutole (IXF) is a relatively new herbicide which rapidly hydrolyzes to
a diketonitrile (DKN) degradate after field application 1,2.
HAO-DKN Desorption
F
C
F
O
F
N
F
F
6,7,8.
9, 10.
F
Sorption envelope experiments will be performed (pH 3 – 8) to elucidate
DKN sorption as a function of pH.
•
Sorption envelope experiments will be at a higher ionic strength
(I =0.09 M) in a similar manner.
•
Mineral surface charge will be measured using ion adsorption
techniques to determine p.z.n.c. values.
•
ATR-FTIR experiments will be conducted to elucidate the mechanism(s)
of surface binding to HAO and HFO.
)
N
+ H3 O+
Enolic DKN
IXF
HAO-BA Desorption
-1
C
C
•
HAO-BA Adsorption
O
SO2MeO
H
USEPA4,5.
• Further, the exact mechanism of BA formation in soils is still unclear
H2O
SO2MeO
• Subsequently, DKN is transformed to a benzoic acid (BA) derivative and
other inactive degradates (Fig. 1)3.
• DKN is more soluble than IXF and it has a longer half-life than IXF
Future Experiments
100
 ads or  des ( m mol kg
Introduction
• DKN and BA are classified as human carcinogens by the
Robert N.
2
Lerch ,
10
• Our previous research indicated:
(1) DKN was adsorbed to hydrous aluminum oxide (HAO) and hydrous
iron oxide (HFO).
SO2MeO
SO2MeO
O
1
(a)
OH
(2) DKN was adsorbed to HFO to a greater extent.
F
C
(3) Slight hysteresis exists between DKN adsorption and desorption
isotherms when the degradate is reacted with HAO.
F
F
C
F
F
0.01
C
0.1
1
10
-1
Equilibrium Conc. of degradates (mmol L )
N
F
Ketonic DKN
BA derivative
Conclusions
100
HFO-DKN Adsorption
• The data collected confirms that DKN and BA adsorb to variable-charged
soil minerals, such as HAO and HFO.
HFO-DKN Desorption
HFO-BA Adsorption
)
HFO-BA Desorption
 ads or  des ( m mol kg
-1
Fig. 1. Degradation of isoxaflutole (IXF) to form enolate ion, diketonitrile (DKN)
and benzoic acid (BA) derivative (Lin et al., 2003).
Objectives
(1) To examine the influence of soil mineral chemical composition (HAO and HFO) on
DKN and BA adsorption and retention.
(2) To quantify the sorption-desorption hysteresis for DKN and BA to the metal
oxides.
• Based on observations to date, soil pH is an important factor governing
BA sorption to soil and it is likely to be important for DKN sorption as
well.
10
• Collectively, these data indicate that iron and aluminum oxides in acidic
subsoils may influence the fate and transport of isoxaflutole degradates
in the environment.
• Additionally, more research is needed to elucidate the mechanism(s) of
BA and DKN sorption to variable-charged soil minerals using
spectroscopic analysis.
1
(b)
100
(3) To investigate the influence of pH on DKN and BA adsorption to HAO and HFO.
HFO-DKN Adsorption
0.01
0.1
1
10
HFO-BA Adsorption
-1
Equilibrium Conc. of degradates (mmol L )
HAO-DKN Adsorption
 ads ( m mol kg
-1
)
HAO-BA Adsorption
Methods
Fig. 4. Diketonitrile (DKN) and benzoic acid (BA) derivative sorbed on (a) HAO
and (b) HFO after adsorption (ads) or desorption (des) reaction at pH 5.5.
Error bars, where observed, represent the 95% confidence interval.
10
References
1. Pallett, K.E., J.P. Little, M. Sheekey, and P. Veerasekaran. 1998. The mode of action of
Preparation amorphous minerals
Table 1. Freundlich parameters for HAO and HFO adsorption/desorption isotherms.
• The minerals HFO and HAO were prepared in the laboratory by forced hydrolysis
reaction and repetitively washed to remove salts.
1
• X-ray diffraction analysis was used to confirm that HFO and HAO were
amorphous in nature.
0.1
1
Adsorbent
10
• 0.500 g of mineral was added to PPCO centrifuge tubes containing 0.01 M CaCl2,
and 0.03 M HCl or 0.01 M Ca(OH)2 was added to achieve pH 5.5 after 24 h of
reaction
2. Luscombe, B.M., and K.E. Pallett. 1996. Isoxaflutole for weed control in maize. Pestic.
Outlook 7: 29-32.
Degradate
Reaction
Phase
log Kf ± 95% CI
N ± 95% CI
r2 (n)
DKN
adsorption
1.02 ± 0.10
1.03 ± 0.20
0.91 (15)
desorption
1.31 ± 0.09
0.85 ± 0.10
0.96 (15)
-1
Equilibrium Conc. of Degradates (mmol L )
Isotherm Studies (adsorption and desorption)
HAO
Fig. 2. Diketonitrile (DKN) and benzoic acid (BA) derivative adsorbed
(ads) on HAO and HFO as a function of initial concentration at pH 5.5.
Error bars, where observed, represent the 95% confidence interval.
BA
DKN
• Initial DKN and BA concentrations ranged from 0 – 5.25 mM, and samples were
reacted in the dark for 24 h at 25oC.
HFO
BA
• Desorption experiments were initiated immediately following adsorption
experiments.
adsorption
0.97 ± 0.11
1.17 ± 0.24
0.90 (15)
desorption
1.02 ± 0.25
0.50 ± 0.34
0.51 (12)
adsorption
1.06 ± 0.12
1.15 ± 0.25
0.88 (15)
desorption
1.12 ± 0.15
0.86 ± 0.20
0.87 (15)
adsorption
1.35 ± 0.04
0.85 ± 0.07
0.98 (15)
desorption
1.29 ± 0.10
0.60 ± 0.13
0.89 (15)
• DKN and BA concentrations in supernatant solutions were measured using HPLC.
• Degradate adsorbed and desorbed from the mineral surface (mmol kg-1) was
calculated based on mass of loss from solution.
500
• Data were fit to the Freundlich equation:
400
I = 0.03 M CaCl2
HFO-BA Adsorption
Summary of Results
)
-1
Adsorption Envelope Studies
 ads ( m mol kg
ads  K f C
300
• Tubes were spiked with DKN or BA solution to achieve a final concentration of
5.25 µM), and samples were reacted in the dark for 24 h at 25oC.
DKN and BA were adsorbed to HAO and HFO at pH 5.5 (Fig. 2).
•
HFO adsorbed more of the BA degradate than HAO over a wide range of initial
concentrations (Fig. 2 and Table 1) at pH 5.5.
•
BA adsorption to HAO and HFO decreases as pH increases (Fig. 3).
•
Hysteresis was observed between the HAO-DKN adsorption/desorption
isotherms (Fig. 4a) but hysteresis was not observed the HFO-DKN
adsorption/desorption isotherms (Fig. 4b).
•
No hysteresis was observed between the isotherms when BA was reacted with
either mineral (Fig. 4a and Fig. 4b).
0
3
4
5
6
7
8
9
pH
• Samples and controls (no mineral) were reacted in duplicate.
• DKN and BA adsorption as a function of pH was determined based on mass lost
from solution.
•
200
100
• 0.300 g of mineral was added to PPCO centrifuge tubes containing 0.01 M CaCl2
and 0.03 M HCl or 0.01 M Ca(OH)2 was added to achieve pH 3 – 8 after 24 h of
reaction.
3. Lin, C.H., R.N. Lerch, H.E. Garrett, W.G. Johnson, D. Jordan, and M.F. George. 2003.
The effect of five forage species on transport and transformation of atrazine and
balance (isoxaflutole) in lysimeter leachate. Journal of Environmental Quality 32.
1992-2000.
4. United States Environmental Protection Agency (USEPA). 1998. Pesticide fact sheet:
Isoxaflutole. USEPA Office of Pesticide Programs, Washington, D.C.
5. Nelson, E.A., and D. Penner. 2005. Sensitivity of selected crops to isoxaflutole in soil
and irrigation water. Weed Technol. 19: 659-663.
6. Taylor-Lovell, S., G. K. Sims, and L. M. Wax. 2002. Effects of moisture, temperature,
and biological activity on the degradation of isoxaflutole in soil. J. Agric. Food Chem.
50: 5626-5633.
7. Rice, P.J., W.C. Koskinen, and M.J. Carrizosa. 2004. Effect of soil properties on the
degradation of isoxaflutole and the sorption-desorption of isoxaflutole and its
diketonitrile degradate. J. Agric. Food Chem. 52: 7621-7627.
8.
BA = 5.25 mM
HAO-BA Adsorption
N
eq
isoxaflutole: I. Physiological effects, metabolism, and selectivity. Pestic. Biochem.
Physiol. 62: 113-124.
Fig. 3. Benzoic acid (BA) derivative adsorbed (ads) on HAO and HFO
as a function of pH. Error bars, where observed, represent the 95%
confidence interval.
•
DKN may interact with surface functional groups on HFO via weak electrostatic
interaction and interact with HAO via a stronger ligand exchange interaction.
•
Additionally, BA may sorb to surface functional groups on HAO and HFO via
weak electrostatic interaction.
Lazo M., F. Lopez de Medina, J.L. Sardina and J. Gomez-Arnau. 1997 Isoxaflutole, a
new corn herbicide from Rhone-Poulenc. Proceedings of the Sixth Congress of the
Spanish Weed Science Society, pp.383-387. Departmento de Horticultura, Botanica
yjardinera, Lleida, Spain.
9. Rouchaud, J., O. Neus, H. Eelen, and R. Bulcke. 2002. Soil Metabolism of Isoxaflutole
in Corn. Arch. Environ. Contam. Toxicol. 42: 280-285.
10. Mougin, C., F.D. Boyer, E. Caminade, and R. Rama. 2000. Cleavage of the diketonitrile
derivative of the hernicide isoxaflutole by extracellular fungal oxidases. J. Agric. Food
Chem. 48: 4529-4534.
Acknowledgments
Financial support was provided by a grant from the Missouri Water
Resources Research Institute Program funded through the United States
Geological Survey (USGS), the University of Missouri Agricultural
Experiment Station, the University of Missouri Office of Research, and the
USDA– Agricultural Research Service.