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TECHNICAL REPORT

Organic Compounds in the Environment

Degradation and Sorption of Metribuzin and Primary Metabolites in a Sandy Soil

^a Geological Survey of Denmark and Greenland (GEUS), Øster Voldgade 10, DK-1350 Copenhagen, Denmark
^b Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen, Denmark

^* Corresponding author (the{at}geus.dk).

Received for publication May 8, 2003. Leaching to the ground water of metabolites from the herbicide metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5-one] has been measured in a Danish field experiment in concentrations exceeding the European Union threshold limit for pesticides at 0.1 µg/L. In the present work, degradation and sorption of metribuzin and the metabolites desamino-metribuzin (DA), diketo-metribuzin (DK), and desamino-diketo-metribuzin (DADK) were studied in a Danish sandy loam topsoil and subsoil from the field in question, using accelerated solvent extraction and liquid chromatography–tandem mass spectrometry (LC–MS/MS) analysis. Fast dissipation of metribuzin and the metabolites was observed in the topsoil, with 50% disappearance within 30 to 40 d. A two-compartment model described degradation of metribuzin and DA, whereas that of DADK could be described using first-order kinetics. Part of the dissipation was probably due to incorporation into soil organic matter. Degradation in subsoil occurred very slowly, with extrapolated half-lives of more than one year. Sorption in the topsoil followed the order DA > metribuzin > DK > DADK. Subsoil sorption was considerably lower, and was hardly measurable for metribuzin and DK. Abiotic degradation was considerably higher in the topsoil than the subsoil, especially concerning the de-amination step, indicating that organic matter may be related to the degradation process. The present results confirm observations of metribuzin and transformation product leaching made in the field experiment and demonstrate the need for knowledge on primary metabolites when assessing the risk for pesticide leaching.

Abbreviations: DA, desamino-metribuzin • DADK, desamino-diketo-metribuzin • DK, diketo-metribuzin • DT₅₀, dissipation time for 50% of a pesticide added • DT₉₀, dissipation time for 90% of a pesticide added • K_d, ratio of sorbed pesticide to pesticide in the aqueous phase • LC–MS/MS, liquid chromatography–tandem mass spectrometry

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JEQ 2004 33: 413-418. [Full Text]  

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