Sorption-desorption of two "aged" sulfonylaminocarbonyltriazolinone herbicide metabolites in soil.

Aging (herbicide-soil contact time) has been shown to significantly affect the sorption-desorption characteristics of many herbicides, which in turn can affect the availability of the herbicide for transport, plant uptake, and microbial degradation. In contrast, very little work in this area has been done on herbicide metabolites in soil. The objective of this study was to characterize the sorption-desorption of sulfonylaminocarbonyltriazolinone herbicide metabolites incubated in soils at different soil moisture potentials. A benzenesulfonamide metabolite and a triazolinone metabolite from sulfonylaminocarbonyltriazolinone herbicides were incubated in clay loam and loamy sand soils for up to 12 weeks at -33 kPa and at water contents equivalent to 50 and 75% of that at -33 kPa. Chemicals were extracted sequentially with 0.01 N CaCl(2) and aqueous acetonitrile (solution and sorbed phase concentrations, respectively), and apparent sorption coefficients (K(d,app)) were calculated. Sufficient metabolite remained during the incubation (>55% of applied) to allow determination of the coefficients. The initial aging period (2 weeks after application) significantly increased sorption as indicated by increased K(d,app) values for the chemical remaining, after which they remained relatively constant. After 12 weeks of incubation at -33 kPa, K(d,app) values for benzenesulfonamide and triazolinone increased by a factor of 3.5 in the clay loam soil and by a factor of 5.9 in the loamy sand as compared to freshly treated soils. There was no effect of moisture potential on aged apparent K(d,app) values. These data show the importance of characterization of sorption-desorption in aged herbicide residues, including metabolites, in soil, particularly in the case of prediction of herbicide residue transport in soil. In this case, potential transport of sulfonylaminocarbonyltriazolinone herbicide metabolites would be overpredicted if freshly treated soil K(d) values were used to predict transport.