Studies On Final Residues, Degradation Of Tebuconazole And Chlorothalonil In Wheat, And Their Behaviors In Soil

At present, tebuconazole and chlorothalonil are widely used on wheat to controlpowdery mildews, rust, blight disease and so on. Pesticide residue level on wheat isan important factor to evaluate the quality of the wheat. In the designed fieldexperiment, degradations of chlorothalonil and tebuconazole in wheat and soil wereinvestigated. Also, the influences of dosage and spraying times on the residual levelwere studied. With the tebuconazole of chiral pesticides, degradations of tebuconazoleenantiomers in wheat and soil were also investigated. These results may provide valueto promote wheat pollution-free production safety and reduce environmentalpollution.The tebuconazole and chlorothalonil in soil and grain were extracted withacetonitrile through ultrasonic extraction, while the analytes in straw were extractedwith acetonitrile containing1%acetic acid through ultrasonic extraction. After salting,the supernatant were transferred and concentrated by rotary evaporation. The extractswere redissolved in acetonitrile, then cleaned by dispersive-solid phase extraction,determined tebuconazole and chlorothalonil by gas chromatography-massspectrometry and determined tebuconazole enantiomers by liquid chromatography-tan-dem mass spectrometry. In the three kind of samples, the recoveries ofchlorothalonil ranged from75%to108%, RSD≤8.1%; the recoveries oftebuconazole ranged from74%to108%, RSD≤7.8%; the recoveries of tebuconazoleenantiomers ranged from73.4%~112%, RSD≤14.0%. This method is accuracysimple, rapid, economic, consistent with requirements of pesticide residue testing.In the Field trials of Beijing, Zhejiang and Hunan, the half-life of chlorothalonilin the soil was6.60-7.79d, in the straw was1.94-5.41d. The half-life of tebuconazole in the soil was18.73-30.13d, in the straw was3.05-4.25d. It suggested that the speedof degradation of chlorothalonil and tebuconazole in the staw were faster than in thesoil.The results of field trials in Beijing and Zhejiang, indicated that the degradationof tebuconazole enantiomers followed first-order kinetics in straw and soil. In straw,the half-lives of ()-tebuconazole were3.88-4.02d;(+)-tebuconazole were4.03-4.93d.In soil, The half-lives of ()-tebuconazole were40.76-43.86d;(+)-tebuconazole were41.50-43.58d. The degradation of ()-tebuconazole was faster in the both region straw.Preferential degradation of (+)-tebuconazole was observed in Zhejiang soil, whereasin the Beijing soil, the degradation of tebuconazole enantiomers was contrary toZhejiang soil. The terminal residues of ()-tebuconazole were higher than its antipodein most grains, indicating significant enantioselective residues.After being respectively sprayed75%tebuconazole· chlorothalonil WP on wheatand soil with two or three times at two dosages(600g ai/ha,900g ai/ha). The samplesof grain, straw and soil were randomly collected from the harvest at intervals of7,14,and21days after the last spraying. These results show that the final residuesdecreased with haverst time in most samples. The final residues had not effects onspraying dosage and the spraying times in most samples.