Distribution Characteristics Of Myclobutanil In The Paddy Field And Evaluation Of Its Biological Activity

Rice sheath blight and rice false smut are two main diseases in the rice,seriously damage rice growth,and reduce rice yield and quality.Myclobutanil is a triazole fungieide with high eiffeieney,low toxicity and broad-spectrum,which is currently used mainly for controlling the diseases of fruit,vegetables and other dryland crop.An analytical method was established for determination of myclobutanil residues in the paddy field,and the distribution characteristics of myclobutanil in the soil,water and rice plants of the paddy field were determined,and the adsorption behavior of myclobutanil in the paddy soils and its photodegradation in the paddy water were also investigated based on the test of its effects on rice sheath blight and rice false smut,which could provide data for the scientific application and future environmental risk assessments of myclobutanil in the paddy field.The results are as follows:1.The efficacy of myclobutanil 25% EC against rice sheath blight and rice false smut was tested in paddy field by method of foliar spray.The results indicated that the efficacy of myclobutanil 25% EC with the dosages of 54-72 g?ha-1 against rice sheath blight was over 57% 20 d after treatment by spraying one time during peak stage of early rice tillering,over 60% 12 d after the second treatment by spraying two times during peak stage of late rice tillering and booting stage,there was no significantly difference to compare with the efficacy of thifluzamide 240 g/L SC with the dosages of 72 g?ha-1,and its efficacy of disease index against rice false smut was over 73% simultaneously.Myclobutanil is suitable for controlling rice sheath blight and false smut.2.An analytical method using high performance liquid chromatography?HPLC?was developed for determination of myclobutanil residues in the paddy soil,water and rice plants,and the distribution characteristics of myclobutanil in the paddy soil,water and rice plants were also investigated in a field experiment.The average recovery rates of myclobutanil at the fortifying concentration of 0.05-2 mg kg-1 in the soil,water,rice plants,rice and rice husk samples reached 87.72%-92.17%,96.26%-101.31%,82.56%-103.79%,83.31%-90.19% and 85.05%-88.17% with relative standard deviations of 2.44%-5.60%,0.47%-2.39%,1.75%-4.73%,2.60%-8.90% and 4.29%-7.81%,respectively.The result indicated that the method satisfied the requirements for detection of myclobutanil residue in the paddy soil,water,rice plants,rice and rice husk in accuracy,precision and sensitivity.The field experiment showed that degradation dynamics of myclobutanil in the paddy soil,water and rice plants accorded with the first-order kinetics equation with the half-lives of 7.62,1.20 and 2.26 d,respectively,and which belonged to the easily degradable pesticide.Myclobutanil residues in the paddy soil,rice plants and rice samples during the rice harvest period were not detected,and its residue in the rice husk samplewas detected in the range of 0.15-0.22 mg kg-1.The results indecated that the myclobutanil residue in rice was mainly exposed,which was not easily transferred from rice plants and rice husk to rice.3.Photodegradation of myclobutanil in water and influence factors were investigated under the UV lamp.The results showed that the photodegradation rates of myclobutanil in different types of water were in sequence of pond water>paddy water>tap water>pure water with the half-lives of 42.5,59.8,150.7 and 247.6 d,respectively.Low-molecular-weight organic acid,include to tartaric acid,citric acid and malic acid,had photosensitizing effect on the photodegradation of myclobutanil in water.Among them,tartaric acid had the strongest effect on the degradation of myclobutanil in water.The H₂O₂ had a significant promoting effect on the degradation of myclobutanil in water.In the treatment with 10,20,50 and 100 mmol L-1,the half-lives of myclobutanil were 13.6,11.8,9.1,and 8.5 h,respectively.The NO2-had a promoting effect on the degradation of myclobutanil in water,and the photochemical degradation increased as NO^2-concentration increased.The NO3-had an inhabiting effect on the degradation of myclobutanil in water at10,20 mg L-1,and a promoting effect at 50 mg L-1.The presence of Fe3+ and surfactant of sodium dodecyl sulfate?SDS?showed the photosensitizing effect on the photodegradation of myclobutanil in water.The photodegradation of myclobutanil increased as the concentration of Fe3+ and SDS increased.The effect of Fe²⁺ on the photodegradation of myclobutanil in water was firstly enhanced and then weakened as the concentration of Fe²⁺increased.4.The adsorption-desorption behavior of myclobutanil was investigated in three types of soil using batch equilibration experiments.And the effect of pH,temperature and surfactant on the adsorption of myclobutanil in the soil was also investgated.The results showed that the adsorption-desorption isotherms of myclobutanil in three types of soil fitted the Freundlich equation well.The adsorption Kf values indicated adsorption of myclobutanil in the three soils was in the sequence of Dongbei' black soil >Jiangxi' red soil >Nanjing' yellow brown soil,while the desorption was contrary to the adsorption.The maximum adsorption capacity was observed in Jiangxi' red soil and Dongbei' black soil at pH 5,and the adsorption capacity in Nanjing'yellow brown soil was the highest at pH 2.The adsorption Kf was decreased as temperature increased from 298 K to 318 K.In addition,the effects of surfactants on the adsorption of different types of soil were different.