title: Key environmental processes affecting the fate of the insecticide chloropyrifos applied to leaves.
abstract: Chlorpyrifos (CP) is still a commonly employed organophosphorus insecticide worldwide. In semi-arid and Mediterranean climates, applied CP is expected to remain on leaves surfaces for relatively long time due to the lack of summer rains and common use of drip irrigation. The present work examines the loss rate of CP from leaves via different surface processes: evaporation, direct photolysis and reactions with ozone and OH radicals. Laboratory experiments showed that evaporation rate constant of CP increased from 0.109 to 0.492 h-1with the increase in wind speed up to 4 m/s. First-order rate constant of direct photolysis, measured using a solar simulator, was k'UV= 1.15 (±0.01) x 10-20cm2photon-1. Second-order rate constants for the reaction of CP with ozone and OH were measured as 6 × 10-20and 6 × 10-12cm3molecule-1s-1, respectively. The above rate constants were applied successfully in an outdoor experiment to predict the disappearance of chloropyrifos under specific environmental conditions. Further modeling showed that the insecticide half-life time on exposed surfaces under typical Mediterranean environment will be in the range of 0.9-6.9 h. Evaporation is expected to be the dominant removal path under most environmental conditions, followed by direct photolysis and reaction with OH.
authors.affiliation: The Water Research Center, Tel Aviv University, 69978, Tel Aviv, Israel. Electronic address: yaallest@tauex.tau.ac.il.
authors.forename: Yaal
authors.initials: Y
authors.lastname: Lester
authors.affiliation: Faculty of Civil and Environmental Engineering, Technion-Israel Institute of Technology, Haifa, Israel.
authors.forename: Sara
authors.initials: S
authors.lastname: Sabach
authors.affiliation: Faculty of Civil and Environmental Engineering, Technion-Israel Institute of Technology, Haifa, Israel.
authors.forename: Ohad
authors.initials: O
authors.lastname: Zivan
authors.affiliation: Faculty of Civil and Environmental Engineering, Technion-Israel Institute of Technology, Haifa, Israel.
authors.forename: Yael
authors.initials: Y
authors.lastname: Dubowski
mesh_terms: D001272:Atmosphere; D004390:Chlorpyrifos / Q000032:analysis / Q000494:pharmacology*; D031743:Cymbopogon / Q000737:chemistry; D029788:Diospyros / Q000737:chemistry; D004777:Environment; D006207:Half-Life; D017665:Hydroxyl Radical / Q000737:chemistry; D007306:Insecticides / Q000032:analysis / Q000494:pharmacology*; D027845:Malus / Q000737:chemistry; D010126:Ozone; D010782:Photolysis; D018515:Plant Leaves / Q000737:chemistry* / Q000187:drug effects; D013472:Sunlight
chemical_list: D007306:Insecticides; D017665:Hydroxyl Radical; D010126:Ozone; D004390:Chlorpyrifos
keywords: Chloropyrifos; Evaporation; Indirect photolysis; Leaves; Photolysis