Studies On The Analysis, Environmental Behaviors, And Toxicity Of Typical Chiral Triazole Fungicide Enantiomers

Triazole fungicides is one of the most widely used in the agricultural crops, and most of themhave stereogenic centers and they consist of one or two pairs of enantiomers. Once introduced inthe ecological environmet, chiral pesticide enantiomers often show different bioactivity to thetarget organisms and toxicity non-target organisms; however, this property is usually ignoredwhen evaluating their environmental and public health risks in the traditional studies. Thus, whentraditional risk assessment are unreliable if the enantioselective behaviors occur. The establisheddata indicated that the enantiomers of chiral triazol fungicides often different bioactivity, however,most triazole pesticides still sold and widely used in the racemic form.In this study, a series of novel and sensitive single or multi-residue methods for enantiomericanalysis of triazole fungicides and their chiral metabolites (tebuconazole, tetraconazole,epoxiconazole, diniconazole, hexaconazole, paclobutrazol, myclobutanil, triadimefon andtriadimenol, fenbuconazole and its chiral metabolites) in plants and (or) environmental samplesusing chiral liquid chromatography coupled with tandem mass spectrometry combined withreversed chiral columns. Validation of the methods included precisions, linearity and limit ofdetection (LOD). The results indicated that the developed methods were effective enough fordetecting the residual enantiomers in the matrix and could be used for studying theenantioselective environmental behaviors.Based on the established chiral analytical methods, Stereoselective environmental behaviors ofthe some triazole fungicides enantiomers were investigated. Firstly, the proposed method wassuccessfully applied to investigate the possible enantioselective environmental behaviors ofrac-hexaconazole and rac-triadimefon in plants (tomato and cucumber) and soil under greenhouseconditions. The results shows that:(1) The degradation of the two enantiomers of hexaconazoleproved to be enantioselective and dependent on the media: The (+)-enantiomer showed a fasterdegradation in plants, while the (-)-enantiomer dissipated faster than the (+)-form in field soil,resulting in relative enrichment of the opposite enantiomer.(2) Under foliage application or soilirrigation application, the S-(+)-triadimefon was preferentially degraded, resulting in relativeenrichment of the more toxic R-(-)-enantiomer in two vegetables and soil. Further enantioselectiveanalysis of converted triadimenol showed that the composition of four product stereoisomers weredifferent from each other and closely depend on environmental conditions as well as applicationmodes: the most toxic RS-(+)-triadimenol was the most preferentially produced isomer in tomatounder foliage treatment, while the RR-(+)-triadimenol was proved to be the highest amount ofmetabolite isomer in cucumber and soil under both treatment modes and in tomato under soiltreatment.Secondly, the enantioselective degradation of fenbuconazole and its chiral metabolites,RH-9129and RH-9130, in two soils under aerobic and anaerobic conditions were investigated.Under aerobic or anaerobic conditions, the results showed the occurrence of enantioselectivity with (-)-fenbuconazole preferentially degraded in both soils. Further enantioselective analysis ofconverted products showed that the concentrations of four RH-9129and RH-9130stereoisomerswere different from each other under both aerobic and anaerobic conditions. The four stereoisomerconcentrations followed the order (-)-RH-9129>(+)-RH-9129>(-)-RH-9130>(+)-RH-9130inLangfang alkaline soil. However, in the case of Changsha acidic soil, different RH-9129and RH-9130stereoisomer patterns were produced in the order (-)-RH-9129>(+)-RH-9129>(+)-RH-9130>(-)-RH-9130. The degradation of RH-9129and RH-9130in the two soils is alsostereoselective under both aerobic and anaerobic conditions, the results indicating that the(+)-RH-9130enantiomer degraded faster than the (-)-RH-9130enantiomer and the (+)-RH-9129enantiomer degraded faster than the (-)-RH-9129enantiomer.Lastly, in present study, triadimefon, triadimenol, tebuconazole, and myclobutanil as well astheir enantiomers in acute toxicity to three aquatic organisms (S. obliquus, D. magna and Daniorerio) were studied. The results indicated there were significant differences between (among)stereoisomers of the same compound: as for the S. obliquus, the SR-(-)-triadimenol was about8.2times more toxic than the SS-(+)-form, the R-(-)-tebuconazole was about5.9times more toxicthan the S-(+)-form, and the rac-myclobutanil about7.3and6.1times more toxic than the(+)-myclobutanil and (-)-myclobutanil, respectively; for the D. magna, the RS-(-)-triadimenol wasabout3.2times more toxic than the SS-(+)-form, the R-(-)-tebuconazole was about1.6times moretoxic than the S-(+)-form, and the rac-myclobutanil about2.5and2.1times more toxic than the(+)-myclobutanil and (-)-myclobutanil, respectively. However, in the case of Danio rerio, thedifferences between the enantiomers were slightly: the R-(-)-tebuconazole was about1.4timesmore toxic than the S-(+)-form, and the rac-myclobutanil about1.4and1.3times more toxic thanthe (+)-myclobutanil and (-)-myclobutanil, respectively. The results show that the distancebetween (among) the stereoisomers of chiral fungicides to aquatic organism gets shorter at highernutrition level.