Yuele Lu

Vortex-assisted surfactant-enhanced-emulsification liquid–liquid microextraction

A novel sample pre-treatment technique, based on vortex-assisted surfactant-enhanced-emulsification liquid-liquid microextraction (VSLLME), followed by gas chromatography-flame photometric detection (GC-FPD) has been developed for the determination of seven organophosphorus pesticides (OPPs) in wine and honey samples. In the VSLLME method, the extraction solvent was dispersed into the aqueous samples by the assistance of vortex agitator. Meanwhile, the addition of a surfactant, which was used as an emulsifier, could enhance the speed of the mass-transfer from aqueous samples to the extraction solvent. The main parameters relevant to this method were investigated and the optimum conditions were established: 15 μL chlorobenzene was used as extraction solvent, 0.2 mmol L(-1) Triton X-114 was selected as the surfactant, the extraction time was fixed at 30s, 3% sodium chloride was added and the extraction process was performed under the room temperature. Under the optimum conditions, limits of detections (LODs) were varied between 0.01 and 0.05 μg L(-1). The relative standard deviation (RSD, n=6) ranged from 2.3% and 8.9%. The linearity was obtained by five points in the concentration range of 0.1-50.0 μg L(-1). Correlation coefficients (r) varied from 0.9969 to 0.9991. The enrichment factors (EFs) were in a range of 282-309. Finally, the proposed method has been successfully applied to the determination of target analytes in real samples. The recoveries of the target analytes in wine and honey samples were between 81.2% and 108.0%.

Environmental behavior of the chiral aryloxyphenoxypropionate herbicide diclofop-methyl and diclofop: enantiomerization and enantioselective degradation in soil.

In this study, the degradation of diclofop-methyl (DM) and its main metabolite, diclofop (DC), in two soils under aerobic and anaerobic conditions were investigated using enantioselective HPLC. Under aerobic or anaerobic conditions, rapid hydrolysis to the corresponding acid diclofop (DC)was observed. The results from this study revealed that the degradation of DM in the two soils is not enantioselective, and the calculated half-lives (t(1/2)) for the two soils were both less than 1 day. However, the degradation of DC in the two soils is enantioselective both under aerobic and anaerobic conditions, and the S-(-)-DC was preferentially degraded, resulting in relative enrichment of the R-(+)-form. The calculated t(1/2) values of the enantiomers of DC ranged between 8.7 and 43.3 days for aerobic incubation experiments and between 14.7 and 77.0 days for anaerobic incubation experiments, respectively. The enantiopure S-(-)- and R-(+)-DC were incubated under aerobic conditions, and it revealed significant enantiomerization with inversion of the S-(-)-enantiomer into R-(+)-enantiomer, and vice versa, and the S-(-)-DC showed a significantly higher inversion tendency than the R-(+)-DC.

Enantioselective Degradation in Sediment and Aquatic Toxicity to Daphnia magna of the Herbicide Lactofen Enantiomers

Many pesticides in use are chiral compounds containing stereoisomers. However, the environmental behavior and fate of such compounds with respect to enantioselectivity so far has received little attention. In this study, the degradation of lactofen and its main metabolites (acifluorfen, an achiral compound; desethyl lactofen, a chiral compound) in sediment were investigated under laboratory conditions using enantioselective HPLC, and the enantioselectivities of individual enantiomers of lactofen and desethyl lactofen in acute toxicity to Daphnia magna were studied. The calculated LC(50) values of S-(+)-, rac-, and R-(-)-lactofen were 17.689, 4.308, and 0.378 microg/mL, respectively, and the calculated LC(50) values of S-(+)-, rac-, and R-(-)-desethyl lactofen were 21.327, 13.684, and 2.568 mug/mL, respectively. Therefore, the acute toxicities of lactofen and desethyl lactofen enantiomers were enantioselective. In sediments, S-(+)-lactofen or S-(+)-desethyl lactofen was preferentially degraded, resulting in relative enrichment of the R-(-)-form. Lactofen and desethyl lactofen were both configurationally stable in sediment, showing no interconversion of S- to R-enantiomers or vice versa. Furthermore, the conversion of lactofen to desethyl lactofen proceeded with retention of configuration. These results for major differences in acute toxicity and degradation of the enantiomers may have some implications for better environmental and ecological risk assessment for chiral pesticides.

Enantioselective bioaccumulation of soil-associated fipronil enantiomers in Tubifex tubifex

Enantioselective behavior of chiral pesticides in the aquatic environment has been a subject of growing interest. In this study, the enantioselective bioaccumulation of fipronil enantiomers in Tubifex tubifex (Oligochaeta, Tubificida) was detected in both spike-water and spike-soil systems, respectively. For the spike-water treatment, a 9-day exposure experiment was employed and the enantiomer fraction in tubifex tissue was maintained approximately at 0.58 during the experiment. In addition, a 14-day bioaccumulation period was chosen for the spike-soil treatment and a more significant deviation of enantiomer fraction from 0.5 in tubifex tissue was detected, with concentrations of the R-form higher than that of the S-form. Therefore, the bioaccumulation of fipronil was enantioselective in tubifex tissue for the two treatments and the magnitude of enantioselectivity may be influenced by different exposure conditions. For the spike-soil treatment, the concentrations of fipronil in verlying water and soil were also determined. With the presence of tubifex worms, higher concentrations of fipronil in overlying water and lower concentrations in soil were detected than that in the absence of tubifex treatment during the whole 14-day exposure period. This means that tubifex has positive functions in fipronils diffusion from soil to overlying water and in the degradation of the soil-associated fipronil.

Enantioselective Bioaccumulation and Dissipation of Soil‐Associated Metalaxyl Enantiomers in Tubifex

Many pesticides are chiral compounds and stereochemistry is an important factor for any reaction of chiral structures in biological systems. In this study, experiment about bioaccumulation of the two metalaxyl enantiomers in Tubifex (Oligochaeta, Tubificida) was conducted in laboratory aquatic ecosystems. Terrestrial soil spiked with two dose levels of metalaxyl was employed as the artificial bottom substrate. A method of determination of metalaxyl enantiomers in tubifex tissue, soil and overlying water were developed by HPLC. During a 14-day exposure, concentrations of metalaxyl in tubifex increased with the of soil concentration, however, the enantioselective bioaccumulation was only detected at high-dose exposure group, with the preferential accumulation of (-)-(R)-metalaxyl. The bioturbation activity of tubifex decreased water clarity and released soil-associated metalaxyl to overlying water. In those experiments where tubifex was exposed to metalaxyl from soil, pore water and overlying water, each route contributed to the total body burden, and our results indicated the pore water and soil are the primary exposure routes for high-dose exposure concentration treatment.

Stereoselective degradation of Diclofop-methyl during alcohol fermentation process.

Stereoselective degradation of Diclofop-methyl (DM) has been found in alcohol fermentation of grape must and sucrose solution with dry yeast. A method was developed for separation and determination the two enantiomers of DM during the fermentation process by high-performance liquid chromatography based on cellulose tri-(3,5-dimethylphenyl-carbamate) chiral stationary phase. The results showed that the enantiomers of DM degraded following the first-order kinetics in the sucrose solution and the degradation of DM enantiomers in grape must were biphasic (slow-fast-slow process). In the sucrose solution, half lives of (+)-(R)-DM and (-)-(S)-DM were calculated to be 8.5 h and 3.1 h, respectively. In the grape must, half life of (+)-(R)-DM was calculated to be 41.7 h while (-)-(S)-DM was 16.0 h. The result was that (-)-(S)-enantiomer degraded faster than the (+)-(R)-enantiomer in both alcohol fermentation. The results also showed that the differences of the enantioselective degradation of DM depended on the fermentation matrix. DM was configurationally stable in fermentation, showing no interconversion of (-)-(S)- to (+)-(R)- enantiomer, and vice-versa.

Dissipation behavior of organophosphorus pesticides during the cabbage pickling process: residue changes with salt and vinegar content of pickling solution.

In this experiment, the behavior of 10 pesticides in three different cabbage pickling treatments has been studied. The brine used for pickling was made up with different salt and vinegar contents to determine the influence of different pickling solutions on pesticide dissipation and distribution. A modified QuECHERS and SPE method was established for the analysis of the pesticides in the cabbage and brine. It was found that different pesticides showed different dissipation patterns and finally represented dissimilar residue levels in the cabbage and brine. Statistical analysis was performed to compare the distinctions of these pesticides between each treatment and proved that salt content and pH value had certain influence on the dissipation and distribution of these pesticides during the pickling process. The data from this experiment would help to control pesticide residues in pickled cabbage and prevent potential risk to human health and environmental safety.