Degradation of Fenoxaprop-p-Ethyl and Its Metabolite in Soil and Wheat Crops.

The dissipation kinetics of fenoxaprop-p-ethyl and its metabolite (fenoxaprop acid) at two application rates under wheat field conditions for two seasons was investigated. Herbicides were extracted by solid liquid extraction, cleaned up, and analyzed by a liquid chromatography-UV detector. Dissipation followed first-order kinetics; in soil, fenoxaprop-p-ethyl dissipated rapidly with an average half-life of 1.45 to 2.30 days, while fenoxaprop acid persisted for more than 30 days. The method was validated in terms of accuracy, linearity, specificity, and precision. Linearity was in the range of 5 to 5,000 ng, with a limit of detection (LOD) of 2 and 1 ng for fenoxaprop-p-ethyl and fenoxaprop acid, respectively. The quantitation limits in soil, grain, and straw were 5, 8, and 10 ng g-1 for fenoxaprop-p-ethyl and 5, 10, and 10 ng g-1 for fenoxaprop acid, respectively. Recovery in soil, grains, and straw ranged from 85.1 to 91.25%, 72.5 to 84.66%, and 77.64 to 82.24% for fenoxaprop-p-ethyl and 80.56 to 86.5%, 78 to 81.88%, and 75.2 to 79.68% for fenoxaprop acid, respectively. At harvest, no detectable residues of fenoxaprop-p-ethyl or acid were observed in soil, wheat grain, and straw samples. Owing to the short persistence under field conditions, fenoxaprop-p-ethyl is safe for use because parent and metabolite residues were below the European Union maximum residue limit and would not pose an adverse effect on the environment and human or animal foods.