Studies On The Metabolism,Transmission In Cucumber And The Environmental Behaviors Of Pyrametostrobin

Pyrametostrobin is a novel strobilurin fungicide developed by Shenyang Research Institute of Chemical Industry with broad fungicidal spectrum and high fungicidal activity.In 2011, 95% pyrametostrobin TC and 20% pyrametostrobin SC have been registered in China for the control of cucumber powdery mildew. In this paper, we established the analytical method for determining pyrametostrobin and its two metabolites in cucumber and soil at trace levels, studied the metabolism and the transmission of pyrametostrobin in cucumber as well as the leaching, adsorption and degradation in soil and water-sediment system of pyrametostrobin. In addition, we tested the fish acute toxicity and did bioconcentration experiment for pyrametostrobin. Also, a dissipation experiment for 20%pyrametostrobin SC in soil and cucumber was performed.An easy, fast and accurate QuEChERS method was established for the determination of pyrametostrobin and its metabolites pyrametostrobin-Ml and pyrametostrobin-M2 based on HPLC-MS/MS. Cucumber samples were extracted by acetonitrile, cleaned up by PSA and GCB sorbents, and analyzed by HPLC-MS/MS, while soil samples were extracted by acetonitrile, cleaned up by PSA sorbent, and analyzed by HPLC MS/MS. MS/MS appliedthe MRM modle while ESI source was the positive ion mode. The quantitive ion pairs for pyrametostrobin and its metabolites were respectively 382.1/164.2.368.1/164.1 ?352.2/189.1. The three analytes were separated at 3.2 min ? 3.9 min. The linearity was good for pyrametostrobin in the range of 0.05?10.0 ?g/L (and for its metabolites in the range of 0.5?100.0 ?g/L) with R values all above 0.9988. The mean fortified recoveries were 78.8%?93.8% for soil and cucumber samples with RSD values all below 6.9%, which is in accordance of the requirments for pesticide residue detection.The metabolism, degradation and transmission of pyrametostrobin were studied using High Performance Liquid Chromotographt Tandem Mass Spectrometry (HPLC-MS/MS).The results showed that the degradation of in cucumber plant was fast with a 2.4?2.2 d.Pyrametostrobin had good systemic and transmit properties, which can be absorbed by roots and leaves, and transmitted from roots to leaves, from leaves to leaves, or from leaves to roots. Thus, pyrametostrobin showed good protective and curative activities. By comparing the cucumber plant samples treated with or with not pyrametostrobin, two possible metabolites of pyrametostrobin were found, whose molecular weight were respectively 367.2 (pyrametostrobin-M 1) and 351.2 (pyrametostrobin-M2). The possible chemical structures of the two metabolites were identified through the analysis of the mass spectrums of pyrametostrobin and the two metabolites. The two metabolites were finally obtained by synthesis.The leaching characteristics of pyrametostrobin in three types of soil were evaluated based on soil layer chromatography and soil column leaching method. The results showed that pyrametostrobin were not to move and leach in all three types of soil, and is not easy to go into underground water through raining or soil capillarity and to contaminate the underground water.The adsorption characteristics of pyrametostrobin in black soil,red soil and paddy soil were studied. The adsorption rate of pyrametostrobin was the highest in black soil and lowest in red soil. The adsorption of pyrametostrobin was in accordance of Freundlich isothermal adsorption model.The Kf values of pyrametostrobin in black soil, red soil andpaddy soil were respectively 127.8, 49.8 and 85.2, while the Koc values of which were respectively7473.7, 4742.9 and 14947.4. The adsorption grade of pyrametostrobin in black soil and paddy soil were grade ?, easy soil adsorption, and that in red soil was grade ?,medium soil adsorption. The Gibbs free energy changes of pyrametostrobin in the three types of soil were all below 40KJ/mol, which indicates a physical adsorption. The organic content and the cation exchande capacity were the main factors that affect the soil adsorption.The degradation half-lives of pyrametostrobin at aerobic conditions were 67.3 d in black soil with degradation characteristics of ? grade (moderate degradation), and respectively 96.3 d and 110.0 d in red soil and paddy soil with degradation characteristics of? grade (difficult degradation). The degradation half-lives were distinctly shortened with degradation characteristics of easy degradation in all the three types of soil. The degradation half-lives of pyrametostrobin in soil is negatively correlated with soil organic content.The dissipation experiment for 20% pyrametostrobin SC was performed in field trials in one year at three places in Shenyang of Liaoning Province, Shouguang of Shandong Province and Hangzhou of Zhejiang Province. The dissipation half-lives of 20%pyrametostrobin SC in these places were 12.9-14.9 d which is distinctly faster than its degradation under laboratory conditions. This is probably due to the sunlightintensity and raining difference.The degradation half-lives of pyrametostrobin were 5.0-6.5 d in water-sediment systems at high-carbon-aerobiotic, high-carbon-anaerobic, low-carbon-aerobiotic and low-carbon-anaerobic conditions, which indicates pyrametostrobin is easy to degradate in water-sediment systems. The content changing of pyrametostrobin in the four water-sediment systems was similar to the general trend of the syatemic degradation, which was a clear dissipation downtrend. The degradation of pyrametostrobin in water-sediment systems was mainly affected by its concentration in water, while the sediment did not have notable impact on pyrametostrobin degradation in water-sediment systems.The acute toxicity and bioconcentration tests were performed using zebra fish. The 96h-LC50 was 0.20 mg/L,with a 95% confidence limit of 0.17?0.23 mg/L,which indicated a high toxicity to zebrafish. The fish bioconcentration test was based on fluence method which changes the water every 4.8 h. The treatment concentrations were setted as the 1/10 and 1/100 of 96h-LC50, i. e. 0.02 mg/L and 0.002 mg/L. The assimilation phase was 12 d, while the elimination phase was 4 d. For treatment concentration of 0.002 mg/L, the assimilation rate constant was 69.3 d-1, the elimination constant was 0.9945 d-1, the dynamic bioconcentration constant was 69.7. For treatment concentration of 0.02 mg/L, the assimilation rate constant was 45.0 d'1, the elimination constant was 0.8036 d-1, the dynamic bioconcentration constant was 56.0, which indicated a medium bioconcentration.