Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2006
Publication Date: 1/9/2007
Citation: Locke, M.A., Zablotowicz, R.M., Steinriede Jr, R.W., Kingery, W.L. 2007. Degradation and sorption of fluometuron and metabolites in conservation tillage soils. Journal of Agricultural and Food Chemistry. 55:844-851. Interpretive Summary: Conservation management practices are being promoted to improve and sustain soil production and an increasing number of farmers are using conservation management practices in cotton production systems. A series of laboratory studies were conducted to provide information concerning the effects of conservation management on the fate of pesticide metabolites in soil. These studies showed an increased affinity of fluometuron and metabolites in reduced tillage soils, suggesting that in these tillage systems where there is an accumulation of organic matter, mobility of these compounds will be inhibited. These results are of interest to regulatory and other agencies and the pesticide industry as part of overall assessments of contributions of management, soil characteristics, and pesticide characteristics on the fate and behavior of herbicides and metabolites in the environment.
Technical Abstract: Laboratory assessment of pesticide metabolite dissipation is a component of pesticide fate assessments. This paper describes two studies that addressed factors influencing the dissipation of the herbicide fluometuron (FLM) and three primary metabolites, desmethyl fluometuron (DMF), trifluoromethyl phenyl urea (TFMPU), and trifluoromethyl aniline (TFMA). In Study I, surface (0-5 cm) Dundee silt loam soil from no-tillage (NT) and reduced tillage (RT) was treated with 14C ring-labeled FLM or TFMA or unlabeled DMF, incubated for 34 to 42 d, extracted with MeOH, and analyzed by HPLC or TLC. Mineralization and volatilization of 14C FLM and TFMA were monitored using NaOH and polyurethane foam traps, respectively. In Study II, soils from reduced- (RT) and conventional-tillage (CT) areas were selected for batch sorption studies to determine the relative affinity of fluometuron and metabolites in soils with differing characteristics (Dundee silt loam, Tunica clay, Weswood silt loam, and Norfolk loamy sand). Soils were treated with fluometuron or metabolite concentrations ranging from 2-50 umol L-1 (2:1 solution:soil), equilibrated 18 h, and samples were centrifuged and supernatant analyzed by scintillation counting (14C fluometuron) or HPLC (DMF, TFMA, TFMPU). In Study I, mineralization of 14C FLM (3%, d 42) or TFMA (4%, d 34) and FLM volatilization (ca. 2%) was low for both soils. However, TFMA volatilization was a significant mechanism of loss (> 16%) for both soils. FLM and DMF dissipated more rapidly in CT soil than NT soil. In FLM-treated CT soil, there was a more rapid accumulation of both DMF and TFMPU as FLM degraded. TFMA dissipated rapidly, primarily attributed to volatilization (~ 15%) and formation of non-extractable residues (d 42, ~ 70%). Greater affinity for fluometuron and metabolites in NT soil help explain their greater persistence. For all respective soils in Study II, sorption Kd values of all four compounds were higher for RT soils than the CT soils, indicating a strong relationship between organic C and sorption of fluometuron and these metabolites since organic carbon was higher in RT for all soils. Overall, sorption Kd values were greater for metabolites (e.g., Tunica CT: TFMPU 1.61-2.18, DMF 1.71-2.34, TFMA 3.33-5.24) than for FLM (Tunica: CT 1.34 – RT 1.60). Presence of non-substituted amino groups likely facilitated sorption to organic carbon, with non-substituted aniline in TFMA having the greatest affinity.