The Photolysis, Hydrolysis And Adsorption Properties Study Of Topramezone

Topramezone was a new uptake and broad-spectrum post emergence herbicide used in cornfield which was developed by BASF. Topramezone had broad spectrum herbicides and longduration which was expected to become the future mainstream varieties of corn field herbicidesmarket. However there was few researches of the environmental behavior of topramezone. Thisexpermient was based for laboratory simulation method. We researched photolysis, hydrolysisand adsorption of topramezone under different conditions.The study was to evaluate theenvironmental behavior of topramezone. The results could provide scientific basis for guidingthe reasonable use of topramezone and evaluating environmental risk in ordor to reduceenvironmental pollution.500W mercury lamp as a light source was researched the photolysis characteristics.Thispaper studied the impact of different buffer solutions, organic solvents such as methanol,acetonitrile and acetone, various concentrations of nitrate, different concentrations of humic acidand various concentrations of the oxide to the photolysis topramezone. We researched thephotolysis of topramezone under500W mercury lamp, the buffer solution of pH5,7,9as media.The results show that half-life of topramezone under that three kinds of buffer solution was64.7,24.1,33.6h. And the photolysis of topramezone was fast on neutral than on alkaline conditions.However, the photolysis was slowest in acidic conditions of the three. Photolysis of organicsolvents showed photolysis of topramezone was fastest on acetonitrile conditions, photolysiswas slowest on methanol conditions. Different concentrations of nitrate could effect thephotolysis of topramezone, Low concentrations of nitrate could promote the photolysis oftopramezone, might decrease with increasing concentration of nitrate, in contrast enhancedinhibition, photolysis rate reduced twice under200mg/L of nitrate. Humic acid had a stronginhibition to the photolysis of topramezone, the photolysis rate of topramezone loweredSevenfold under5mg/L of humic and lowered eightfold under50mg/L of humic. Differentoxides as TiO2, SiO2could promote the photolysis of topramezone, but not significant.The slowly degradation rates of topramezone due to its chemical structure. This paperstudied the impact of different buffer solutions, different temperatures and differentconcentrations of humic acid to the hydrolysis of topramezone. The test results showed that thedegradation rates of topramezone had a good correlation with pH. The hydrolysis rate oftopramezone on acidic conditions was slower than neutral and alkaline conditions. Buffer solution of pH5with the half-lives as807.0d, buffer solution of pH7with the half-lives as366.5d and buffer solution of pH9with the half-lives as354.1d. Hydrolysis of topramezone withdifferent initial concentrations showed that the lower concentration the shorter degradation time.Under the conditions of50℃topramezone hydrolysis rate was higher than room temperatureabout10times. The impact of humic acid to the hydrolysis of topramezone was as the same asphotolysis of topramezone its hydrolysis rate was below the topramezone solution which therewas no humic acid. So humic acid would affect the rates of degradation of topramezone.Adsorption was one of the major degradation pathway of pesticides in soil, This paperstudied the adsorption of topramezone in five kinds soil. Set ratios of water and soil as20：1,10：1,5：1, study the effects of different proportions of water and soil to adsorption oftopramezone. Experimental results showed that the adsorption of topramezone was highestwhen the proportions of water and soil was5：1. With this condition, the adsorption oftopramezone in five kinds soil at different times were detected. The result showed that theadsorption of topramezone can reach equilibrium within1-3h, but in order to ensure completeadsorption we controlled adsorption time to24h. Different concentrations and soils todetermination the adsorption of topramezone were setted.The sorption constants of soil to topramezone were increased with the initial concentration,but when concentration reaches a certain limit the option constants might rises slowly,eventually reached adsorption equilibrium. The order to the adsorption of topramezone in fivekinds soil was Gray brown soil>black soil> Calcium soil> White pulp soil> Sodic soil.Topramezone shows medium absorption was in the gray brown soil, while more difficultadsorption in the remaining four soil. The effect of soil properties to the adsorption oftopramezone was researched, the results showed that the organic matter content affect thesorption constants of soil to topramezone. The sorption constants of soil to topramezone werenegatively related to the contents of soil pH. We can see low adsorption under alkalineconditions but under acidic conditions showed a better adsorption. The sorption constants of soilwere positively related to the contents of CEC, but the correlation was not significant. Weresearched the influence of humic acid to the adsorption, found when there was humic acid thesorption constants might significantly increased.as humic acid was an important factor in soiladsorption Adsorption with changes of free energy was less than40·kJ/mol which was a type ofphysical adsorption.