Study On The Environment Behaviors Of Three Imidazolinone Herbicides In Two Types Of Typical Microcosm

It is important to investaged the behaviours and mechanism of pesticides in the environmental,which can provide an scientific basis for environmental risk assessment and rational use of pesticides.Imidazolinone herbicides are a group of chiral herbicides that are widely used to control weeds in peanuts,soybeans,cereal crops,and potatoes fields worldwide.However,a main characteristic of these herbicides is their high environment persistence.Residues in environment can significantly affect the growth of subsequent crops.Furthermore,few studies have investigated the fate and environmental behaviors of imidazolinone herbicide in terrestrial and aquatic systems.In this study,three imidazolinone herbicides was selected as the target chiral pesticide.The environmental behavior of three imidazolinone herbicides were systemically evaluated in aquatic and terrestrial environmental at enantiomeric level.These could provide scientific basis for safety use and risk assessment of these herbicides in field.The main results were shown as follows:1:An effective and rapid stereoselective analysis method for the determination of three imidazolinone herbicides residues in water,sediment,soil and earthworm was developed by ultra-performance liquid chromatography-tandem mass spectrometry(UPLC-MS/MS)using the modified quick,easy,cheap,effective,rugged,and safe(Qu ECh ERS)extraction concept.Average recoveries ranged from 80.4%-102%with intra-day RSDr(n=5)of 1.6%-8.9%,and the limit of detection(LOD)and limit of quantification(LOQ)were 0.25?g/kg-0.55?g/kg and0.74?g/kg-1.88?g/kg in four matrices for three herbicides enantiomers.The validated method with high accuracy,precision,sensitivity was found to meet the test requirements.2:The bioaccumulation and dissipation behaviors of enantiomers of three imidazolinone herbicides in earthworm-soil microcosms were examined.Significant stereoselective dissipation in soil occurred in earthworm-soil microcosms for imazapic,with the half-lives of the two enantiomers of imazapic ranged from 21 d-63 d and 23.9 d-49.5 d,the half-lives of S-(+)-imazethapyr and R-(-)-imazethapyr were 25.7 d-31.5 d and 33 d,respectively.However,imazamox and imazethapyr showed no significant stereoselectivity in their dissipation in HN,HLJ and CQ soil,with the half-lives of imazamox and imazethapyr were ranged from 31.5d?53.3 d and 25.7 d?27.5 d,respectively in HN,HLJ and CQ soil.Significant stereoselective dissipation in GX soil occurred in earthworm-soil microcosms for imazamox and imazethapyr,with the half-lives of S-(+)-imazethapyr and R-(-)-imazethapyr were 31.5 d and 33 d in GX soil,and the half-lives of S-(+)-imazamox and R-(-)-imazamox were 33 d and 31.5 d in GX soil.The three imidazolinone herbicides did not show enantioselective bioaccumulation in earthworms in the earthworm-soil microcosms.All three herbicides were absorbed by earthworm mainly via the skin.The results also indicated that the BSAFs values were negatively correlated with the log K_ow values of herbicides,but were positively correlated with organic matter content of soil.3:The adsorption behavior of three herbicides on sediment and microplastics were investigated in this study.The adsorption kinetics of three imidazolinone herbicides on sediment and microplastics were accurately described by the pseudo-second-order kinetic model(R²>0.99).The adsorption kinetics study revealed that herbicide adsorption on the sediment and microplastics all mainly relies on chemical processes.And the intraparticle diffusion model further suggested that the whole adsorption process of the three imidazolinone herbicides is controlled by external mass transfer,intraparticle diffusion,and dynamic equilibrium processes.The results of adsorption isotherms experiment showed that imidazolinone herbicide adsorption fits well with the Freundlich model.Furthermore,the yield n values were over 1,indicating that the adsorption isotherms are in class L-type curves and showed a relatively high herbicide-sediment affinity at low concentrations.And the herbicides were mostly absorbed by the amorphous materials in the sediment.The results of FTIR analysis indicated that suggest that the adsorption of imidazolinone herbicides to the sediment was influenced not only by physics but also by chemisorption.In fact,molecular structural changes that occurred could account for the formation of a hydrogen bond,leading to increased polarity after sorption and?-?interactions between herbicides and sediment.4:The stereoselective dissipation,distribution,and transformation behaviors in water-sediment microcosms and the stereoselective dissipation behavior in water and sediment phase for three imidazolinone herbicides were investigated.The first-order kinetics model was well fitted to the degradation data for the enantiomers of the three herbicides in sediment and water.The half-lives of the enantiomers of the three herbicides in water and sediment were ranged from 86.6 d to 231 d and from 63 d to 99 d,respectively.The EF values of the three herbicides in the water and sediment samples did not deviate much from the racemic value(0.5)(p>0.05),indirectly suggesting that no stereoselective dissipation occurred during the incubation period.The half-lives of the enantiomers of the three herbicides in water and sediment were 346.5 d-990 d and 99 d-138.6 d in the presence of microplastics.These results indicated that the presence of microplastics markedly inhibited dissipation of the enantiomers of all three herbicides(p<0.05).The results of the effects of microplastics on the stereoselective dissipation of three imidazolinone herbicides in sediment and water,indicated that the presence of microplastics markedly reduce dissipation of the enantiomers of all three herbicides and made the herbicides more persistent in water and sediment.And stereoselective processes did affect imazapic in the presence of microplastics in sediment and water.The EF values for imazamox and imazethapyr in sediment and water in the presence of microplastics were little different from 0.5,suggesting that the microplastics little affected stereoselective processes affecting imazamox and imazethapyr in water and sediment.The water–sediment microcosms experiment results indicated sediments are a major sink for herbicides in aquatic systems and microbial degradation would have been an important pathway for imidazolinone herbicide degradation in sediment.And no stereoselective dissipation or distribution of the three herbicides occurred in the water–sediment microcosms.The water-sediment microcosms experiment also imply that microplastics can affect the residues,and distribution of herbicides in water–sediment microcosms through adsorption and desorption.Microplastics had a significant effect on the stereoselectivity of imazapic in the water–sediment microcosms(p<0.05);however,no significant stereoselectivity was observed in the presence microplastics of water–sediment microcosms for imazamox and imazethapyr.