title: Sorption of isoxaflutole diketonitrile degradate (DKN) and dicamba in unsaturated soil.
abstract: When analyzing the sorption characteristics of weakly sorbing or labile pesticides, batch methods tend to yield a high margin of error attributable to errors in concentration measurement and to degradation, respectively. This study employs a recently developed unsaturated transient flow method to determine the sorption of isoxaflutole's herbicidally active diketonitrile degradate (DKN) and dicamba. A 20-cm acrylic column was packed with soils with varied texture that had been uniformly treated with 14C-labeled chemical. The antecedent solution herbicide in equilibrium with sorbed phase herbicide was displaced by herbicide-free water, which was infiltrated into the column. Sorption coefficients, Kd, were obtained from a plot of total herbicide concentration in the soil versus water content in the region where the antecedent solution accumulated. DKN Kd values were approximately 2-3 times (average Kd = 0.71 L kg-1) greater using the unsaturated transient flow method as compared to the batch equilibration method in clay loam (Kd = 0.33 L kg-1), but similar for the two methods in sand (0.12 vs 0.09 L kg-1) soils. Dicamba Kd values were 3 times greater using the unsaturated transient flow method as compared to the batch equilibration method in the clay loam soil (0.38 vs 0.13 L kg-1), however, the Kd values were the same for the two methods in the sand (approximately 0.06 L kg-1). This demonstrates that to determine sorption coefficients for labile hydrophilic pesticides, an unsaturated transient flow method may be a suitable alternative to the batch method. In fact, it may be better in cases where transport models have overpredicted herbicide leaching when batch sorption coefficients have been used.
authors.affiliation: US Department of Agriculture, Agriculture Research Service, St Paul, MN 55108, USA. koskinen@umn.edu
authors.forename: William C
authors.initials: WC
authors.lastname: Koskinen
authors.forename: Tyson E
authors.initials: TE
authors.lastname: Ochsner
authors.forename: Brandon M
authors.initials: BM
authors.lastname: Stephens
authors.forename: Rai S
authors.initials: RS
authors.lastname: Kookana
mesh_terms: D000327:Adsorption; D002250:Carbon Radioisotopes; D003996:Dicamba / Q000737:chemistry*; D004784:Environmental Monitoring / Q000379:methods*; D006540:Herbicides / Q000032:analysis / Q000737:chemistry*; D007555:Isoxazoles / Q000737:chemistry*; D009570:Nitriles / Q000737:chemistry; D015203:Reproducibility of Results; D012989:Soil Pollutants / Q000032:analysis*; D013450:Sulfones / Q000737:chemistry
chemical_list: D002250:Carbon Radioisotopes; D006540:Herbicides; D007555:Isoxazoles; D009570:Nitriles; D012989:Soil Pollutants; D013450:Sulfones; C486641:diketonitrile; C415327:isoxaflutole; D003996:Dicamba