title: Degradation of bromoxynil and trifluralin in natural water by direct photolysis and UV plus H(2)O(2) advanced oxidation process.
abstract: The degradation of two pesticides, bromoxynil and trifluralin, was investigated in ultrapure and natural water solutions under ultraviolet (UV) light and a combination of UV and hydrogen peroxide (H(2)O(2)). The effect of pH on the photooxidation of the pesticides was also studied. The results indicated that under direct photolysis with monochromatic light at 253.7 nm and different conditions, the photochemical rates followed first-order kinetics, with fluence-based rate constants ranging from 9.15 x 10(-4) to 6.37 x 10(-3) cm(2) mJ(-1) and 7.63 x 10(-3) to 1.47 x 10(-2) cm(2) mJ(-1) for bromoxynil and trifluralin, respectively. Quantum yields, in the range of 0.08-0.25 for bromoxynil and 0.12-0.72 for trifluralin, were observed in experiments using ultrapure water. The study also found that the UV/H(2)O(2) process enhanced the oxidation rate in comparison to direct photolysis. A 90% degradation with UV dose of 333 and 188 mJ cm(-2) was achieved for bromoxynil and trifluralin, respectively, in natural water, in presence of 8.8 x 10(-4) M H(2)O(2). To assess the aquatic toxicity, the Microtox 81.9% screening test protocol was used before and after treatment. The test results indicated a decrease in the acute toxicity of the samples after treatment for both pesticides.
authors.affiliation: Department of Civil and Environmental Engineering, 3-141 Markin/CNRL Natural Resources Engineering Facility, University of Alberta, Edmonton, Alberta, Canada T6G 2W2.
authors.forename: Pamela
authors.initials: P
authors.lastname: Chelme-Ayala
authors.forename: Mohamed Gamal
authors.initials: MG
authors.lastname: El-Din
authors.forename: Daniel W
authors.initials: DW
authors.lastname: Smith
mesh_terms: D048908:Aliivibrio fischeri / Q000187:drug effects / Q000528:radiation effects; D006861:Hydrogen Peroxide / Q000494:pharmacology* / Q000633:toxicity; D007700:Kinetics; D009570:Nitriles / Q000737:chemistry* / Q000633:toxicity; D010084:Oxidation-Reduction / Q000528:radiation effects; D010573:Pesticide Residues / Q000737:chemistry; D010782:Photolysis; D018675:Toxicity Tests; D014274:Trifluralin / Q000737:chemistry* / Q000633:toxicity; D014466:Ultraviolet Rays; D014874:Water Pollutants, Chemical / Q000737:chemistry* / Q000633:toxicity; D018508:Water Purification / Q000379:methods
chemical_list: D009570:Nitriles; D010573:Pesticide Residues; D014874:Water Pollutants, Chemical; D006861:Hydrogen Peroxide; D014274:Trifluralin; C006826:bromoxynil