Research On The Photochenmical Degradation Of Paclobutrazol In Aqueous Solution

Paclobutrazol {(+/-R^*, R^*)-B-[(4-Chlorophenyl) methyl]-alpha-(1, 1-dimethylethyl)-1H-1, 2,4-thiazol-1-ethanol}is one kind of Plant Growth Regulator, which is popularized to use all overthe world today, but little information is available about its degradation behavior in the paddy andchenmical behavior in aqueous solution. In order to comprehensively evaluate environmentalsecurity of Paclobutrazol and for its reasonab application and ecological environmental restoration,and to provide referrence for production wastewater processing craft of Paclobutrazol, this paperaims to study the degradation of Pachlobutrazol in the paddy and photolysis of Paclobutrazol inaquatic environment, including the determination of Paclobutrazol, the degradation ofPaclobutrazol in the paddy and photolysis of Paclobutrazol in in aquatic environment, theinfluence as factors and disposed of pesticide wasterwater. The main results obtained were asfollows.Chapter one was introduction, in which the basic concepts, theories and current advances athome and abroad were reviewed briefly on residue degradation in the paddy enviroment,photolysis and the disposed of pesticide wasterwater with Fenton reagent. In addition, researchadvance of Paclobutrazol was summarized concisely. The contents and significances of thisresearch was also included in this chapter.In the chapter two,it studies and builds up the method of residual detemination of PlantGrowth Regulator 15ï¼…Paclobutrazol WP in the water, soil and paddy, and the degradation ofPaclobutrazol in the paddy. The results showed:(1)A new analytical method for deteminingresidues of Paclobutrazol in water, soil and paddy by GC was developed. The soil samples wereextracted with acetone water solution(1/1,v/v), and the paddy sample extracted withdichoromethane, then the extract re-extracted three times with dichoromethane, choose petroleumplus acetone(4/1,v/v) for pour solution. The quantification of the Paclobutrazol residue wasestablishied by GC. The results showed that the average recoveries of the method was from91.40％—106.90ï¼…at the fortified levels of 0.05～1.0mg/kg ( water sample mg/L) for the samples,and coefficient of variation was in range of 2.52％—5.78ï¼…. The minimun detectable limits inwater, soil and paddy were 0.001mg/L,0.025mg/kg,0.05mg/kg, respectively. The parameterssuch as accuracy, sensitivity, precision for the method were good to satisfy the essential rules ofpesticide residue determination. (2) At the application rate of 6000g/hm², the half-life ofPaclobutrazol in the water, soil and paddy were 5.5d, 15.75d, 2.93d(Hunan), 8.88d, 15.13d, 2.36d(Tianjin), respectively. (3) At the application rate of 3000g/hm², during the rice harvest, itdidn't detected Paclobutrazol among the rice and rice busk in Hunan and Tianjin. At theapplication rate of 6000g/hm², during the rice harvest, the final residual was 0.034mg/kg and0.025mg/kg, respectively, in Hunan and Tianjin.Chapter three was Studies on the photochenmical degradation of Paclobutrazol in aqueoussolution. The results showed that: (1) In natural water, the photolysis rate of Paclobutrazol hasgreat disparity under high-pressured mercury lamp, ultraviolet lamp and sunlight. Its order is thehigh-pressured mercury lamp＞ultraviolet lamp＞sunlight. (2) Under the high-pressured mercurylamp, the photolysis rate decreased with the increasing of initial concentration of Paclobutrazol.Under the identical initial concentration, photolysis rate of Paclobutrazol gradually tended to begentle with the extended time. Under the high-pressured mercury lamp, the differentconcentrations of dissolved oxygen in the pure water showed different orders of photolysis rate ofPaclobutrazol in the solutions. Its order was ventilate O₂＞not ventilate O₂ and N₂＞ventilateN₂. The dissolved oxygen had an important effect on photooxidation of Paclobutrazol. (4) Thephotolytic rates of Paclobutrazol in different aquatic solutions showed the followingsequences: pure water＞well water＞river water＞pond water＞paddy water. The main reason to causethe difference of photolysis of Paclobutrazol was the differences of dissolved organic, inorganicmatrix and conductivity in different natural water systems, pH value played an important role inthe photolysis rate of Paclobutrazol in the pH buffer solution. It showed that the photolysis ratewas quicker in pH6 and pH7 than in other buffer solutions. Photolysis of Paclobutrazol was stablein acid water and alkalinity water. (6)in metallic ion solution, Fe3 made the half-life ofPaclobutrazol reduce, and the effect increases along with the ion concentration increases. Cu²⁺ andCa²⁺ showed photo-quenching effects on photolysis of Paclobutrazol and the photolytic half-lifewas posotively correlated to the concentration of Cu²⁺ and Ca²⁺. (7) From the experiments of fourfertilizers towards photolysis rates of Paclobutrazol under the high-pressured mercury lamp, itshowed that KH2PO4 had photosensitizing effects on Paclobutrazol. Its photolytic half-life wasnegatively correlated to the concentration of KH₂PO₄. When the concentration of KH₂PO₄ reached10mg/L, the photolysis effect of Paclobutrazol is the largest.However, NH₄HCO₃, urea and KClall showed photo-quenching effects on photolysis of Paclobutrazol. (8) under the high -pressuredmercury lamp, the higher concentration of HA and FA could reduce the photolysis rates, and haveremarkable photo-quenching effects on photolysis of Paclobutrazol. (9) under the high-pressuredmercury lamp, the photolysis rate of Paclobutrazol will be accelerated by the concentration ofH₂O₂. the higher the concentration of Paclobutrazol is the quicker the potolysis rate ofPaclobutrazol is. When the concentration of Paclobutrazol reached 20mg/L, photolysis rate didn't increase again.In the chapter four, it studied the four effect factors to the treatment wasterwater ofsimulation Paclobutrazol with orthogonal experiment. This paper compared with the treatmenteffects of wastewater containing Paclobutrazol with UV/Fenton(Fe²⁺), UW/ Fenton(Fe³⁺) andUV/H₂O₂. The result showed that (1)On the Basis of reasearch on herbicide simulationwastewater, determination the condition of the experiments by charging the amount of initialH₂O₂, Fe²⁺, pH and reaction time were made: [H₂O₂]=0.1mol·L^-1, [Fe²⁺]=7mmol·L^-1, pH=4,reaction time=80min. (2) On the Basis of reasearch on herbicide simulation wastewater, carrieson the optimization to Paclobutrazol simulation wastewater in four kind of influences factor. Withthe increase of H₂O₂ and Fe²⁺ doses, pH value and reaction time, the photolysis rate ofPaclobutrazol increased, then the chemical oxygen demand removal rate increased also. But whenthe doses of H₂O₂ reached 0.2mol/L, the doses of Fe²⁺ reached 7mmol/L, pH value reached 4and the time surpassed 80min, the photolysis rate of Paclobutrazol up to largest, the chemicaloxygen demand removal rate was the largest and it reached 85ï¼…. Then the chemical oxygendemand removal rate maintained stable. (3) This paper compared with the treatment effects ofwastewater containing Paclobutrazol using Fenton reagent, UV/Fenton(Fe²⁺), UV/ Fenton(Fe³⁺)and UV/H₂O₂. Under the same illumination condition, after 150min, the chemical oxygen demandremoval rate of UV/Fenton(Fe²⁺), UV/ Fenton(Fe³⁺) and Fenton reagent reached above 85ï¼….In the last chapter, a summary was done on the research results, and meanwhile theinnovation of the research and the projects that need to be further studied were suggested.