title: Variation in concentrations of the fungicides tebuconazole and dichlofluanid following successive applications to greenhouse-grown lettuces.
abstract: Residual levels and degradation rates of tebuconazole and dichlofluanid in lettuce plants grown in a greenhouse under agricultural conditions typical of northwestern Spain were studied. Lettuce plants were sprayed four times with a homogeneous 0.2% aqueous solution of Folicur Combi (wettable powder containing 40% dichlofluanid and 10% tebuconazole) at a rate of 2500 g/ha. Samples were collected 1, 5, and 9 days after the first two applications and at times ranging from 1 to 27 days after the last two applications. All samples were stored in a refrigerator at 4 degrees C. Fungicide levels were determined by solid-liquid extraction (SLE) followed by gas chromatography and mass spectrometry detection (GC-MSD). Recovery was good for tebuconazole (98%) but low for dichlofluanid (29%); precision was good (<10% for both analytes), and quantification limits were low (<1.5 mg/kg). Seven days after the last application, dichlofluanid levels were below the maximum allowed limit established in Spain (10 mg/kg), but tebuconazole levels were above the corresponding limit (5 mg/kg). Tebuconazole concentration dynamics was accurately fitted by zeroth- or combined first- and zeroth-order models (depending on variety), but modeling of the behavior of dichlofluanid was less satisfactory, probably due to its instability.
authors.affiliation: Nutrition and Bromatology Group, Analytical and Food Chemistry Department, Faculty of Food Science and Technology, University of Vigo, Ourense Campus, 32004 Ourense, Spain.
authors.forename: Raquel
authors.initials: R
authors.lastname: Rial-Otero
authors.forename: Manuel
authors.initials: M
authors.lastname: Arias-Estévez
authors.forename: Eugenio
authors.initials: E
authors.lastname: López-Periago
authors.forename: Beatriz
authors.initials: B
authors.lastname: Cancho-Grande
authors.forename: Jesús
authors.initials: J
authors.lastname: Simal-Gándara
mesh_terms: D000383:Agriculture / Q000379:methods; D000814:Aniline Compounds / Q000008:administration & dosage / Q000032:analysis*; D005659:Fungicides, Industrial / Q000008:administration & dosage / Q000032:analysis*; D018545:Lactuca / Q000737:chemistry* / Q000254:growth & development; D014230:Triazoles / Q000008:administration & dosage / Q000032:analysis*
chemical_list: D000814:Aniline Compounds; D005659:Fungicides, Industrial; D014230:Triazoles; C087114:tebuconazole; C016370:dichlofluanid