Studies On Behaviors, Bioactivities And Toxicity Of Chiral Fungicide Of Propiconazole Stereoisomers In Paddy Field Environments

The pure stereoisomers of the same chiral pesticide may differ dramatically in bioactivity to pathogens, toxicity to non-target organisms, and degradation in plants and environment. In conventional risk evaluations, the chiral pesticides were often treated as one compound, and the data obtained were incomplete and nonspecific, bringing potential risks posed by these pesticides to environment and public health. Propiconazole, a broad spectrum systemic chiral triazole fungicide, was extensively used in paddy field. However, little work was made to date about bioactivity, toxicity, and stereoselectivity degradation of propiconazole isomers in paddy environments.Firstly, enantioseparation of four propiconazole isomers was studied. Baseline separation of four propiconazole stereoisomers was successfully obtained using OD-H or AD-H chiral column with optimal conditions by HPLC; Under UPC2-MS/MS determination system, baseline separation of the four isomers was also achieved within short time using Chiralpak(?) IA-3,3μm chiral column with optimization of MS/MS and ultra performance convergence chromatography(UPC2) conditions.Next, stereoselective analysis method for propiconazole in five matrices (i.e., rice grain, rice husk, rice straw, paddy soil and paddy water) by UPC2-MS/MS was successfully developed for the first report, and the validated method with high accuracy, precision, sensitivity was found to meet the test requirements.Based on above method, enantioselective degradation of propiconazole stereoisomers in rice plants, paddy soils and paddy water was studied. The results indicated that the dissipation rates of the four isomers in rice plants followed the order of in tender rice plants> in old rice straw>in rice grains, as the same order as degradation enantioselectivity in rice stems and leaves. The preferential dissipation of (+)-propiconazole-B and (-)-propiconazole-A in rice plants was also determined. No obvious enantioselective degradation was observed in paddy soil and water under field condition.Secondly, enantioselective degradation of propiconazole stereoisomers in three paddy soils under laboratory-controlled conditions were investigated. Under aerobic conditions,(-)-propiconazole-B and (-)-propiconazole-A were degraded preferentially, that could be observed obviously in Hainan paddy soil. But in anaerobic incubation, not obvious or only weak enantioselective degradation was observed with preferential dissipation of (+)-propiconazole-B and (+)-propiconazole-A. No enantioselective degradation was found in three paddy soils under sterile conditions. Results also showed that the four stereoisomers of propiconazole were configurationally stable in three incubation mode, and no interconversion occurred among them.Thirdly, photolysis of propiconazole four isomers in seven solvents was studied. Results indicated that there were no interconversion among propiconazole stereoisomers under photolysis condition. The photo-degradation of the four isomers complied with the first-order kinetics. Among six organic solvents, the photolysis rates were the fastest in methanol, followed by which in ethanol, and the slowest in2-propanol. Eliminating the interference of photolysis products, the photolysis rates of them had little differences.Finally, stereoselective bioactivity towards five rice pathogens (including Pyricularia oryzae Cav., Fusarium moniliforme Sheld., Thanatephorus cucumeris (Frank) Donk., Rhizoctonia solani kuhn, Ustilaginoidea oryzae (Patou.) Bref) and acute toxicity towards S. obliquus and D. magna of propiconazole stereoisomers were determined. The results showed that bioactivities of the stereoisomers against Fusarium moniliforme Sheld had the maximum difference, EC50value of the isomer with the lowest activity was about23.47times of that with the highest activity; while the difference of bioactivities towards Ustilaginoidea oryzae (Patou.) Bref was minimum, with only2.43fold differences in bioactivity. The biological activities orders of the four stereoisomers varied with pathogens. Small differences of acute toxicity among the four stereoisomers towards S. obliquus and D. magna were observed. As for S. obliquus, EC50value of (+)-propiconazole-B was2.25times (72h) and2.13times (96h) of that of (-)-propiconazole-B; for D. magna, ratio of the highest48h-EC50to the lowest48h-EC50was only1.48.Thus, development and use of individual stereoisomers of triazole fungicide propiconazole were not recommended.