Chiral pesticides levels in peri-urban area near Yangtze River and their correlations with water quality and microbial communities

From degradation to detection: Assessing enantioselective behavior of chiral triazole fungicides in horticultural stream waters

Chiral pesticides constitute nearly 40 % of active ingredients used in agriculture, yet their enantioselective environmental behavior is often overlooked in risk assessments. This study examined the enantioselective degradation of three widely used triazole fungicides-cyproconazole, epoxiconazole, and tebuconazole-in surface water from horticultural streams, and assessed their enantiomeric distribution in environmental samples. Laboratory degradation experiments were conducted under light and dark conditions using racemic standards. Enantiomers were separated and quantified via LC-MS/MS using a Lux Cellulose-2 chiral column. Under light conditions, degradation followed simple first-order (SFO) kinetics, showing faster dissipation of the (+)-enantiomers compared to the (-)-enantiomers. For cyproconazole, DT50 values ranged from 2.64 to 2.74 days for (+)-enantiomers and 2.78-2.90 days for (-)-enantiomers; epoxiconazole and tebuconazole followed the same trend. The enantiomeric fraction (EF) increased over time in degradation assays, reaching values of up to 0.62 for cyproconazole and 0.73 for tebuconazole, confirming progressive enrichment of the (-)-enantiomers. In real surface water samples, EF values were >0.5 in 86 % (EFA) and 90 % (EFB) of detections for cyproconazole, 100 % for epoxiconazole, and 98 % for tebuconazole. These results represent the first EF data reported for cyproconazole in environmental waters and confirm the occurrence of enantioselective pollution. The consistent enrichment observed in both experimental and field data highlights the role of stereoselective degradation processes in shaping environmental profiles. Given the differential toxicity and persistence of individual enantiomers, these findings support the need for enantiomer-specific monitoring and risk assessment of chiral pesticides.

Fourier Transform Ion Trap Mass Analysis by Deciphering Ion Ejection Signals in the Frequency Domain

Mass analysis in an ion trap is conventionally realized through time domain analysis of the ejected ion current collected from an electron multiplier (EM), in which the ion ejection time is found to have a correlation with the mass-to-charge (m/z) ratio of the ion. In this study, we investigated a new method for mass analysis by examining ion ejection signals in the frequency domain. Theoretical analysis and ion trajectory simulations show that ions of the same m/z ratio are ejected from an ion trap at regular intervals, producing a periodic pulsed signal on the EM. The period of this pulsed ejection signal is directly linked to the m/z values of the ions. To realize this method experimentally, a broadband preamplifier was built and integrated on a miniature ion trap mass spectrometer (the "Brick" series from Nier Inc.) to capture this pulsed ion ejection signal collected from the EM. Experimental results were in good agreement with theoretical and simulation analyses. This method has the potential to improve the mass resolution of an ion trap mass analyzer. As a proof-of-concept demonstration, a peak width of 0.1 Da at a m/z value of 281 was achieved in experiments.

Characterization of two novel hydrolases from Sphingopyxis sp. DBS4 for enantioselective degradation of chiral herbicide diclofop-methyl

Diclofop-methyl, an aryloxyphenoxypropionate (AOPP) herbicide, is a chiral compound with two enantiomers. Microbial detoxification and degradation of various enantiomers is garnering immense research attention. However, enantioselective catabolism of diclofop-methyl has been rarely explored, especially at the molecular level. This study cloned two novel hydrolase genes (dcmA and dcmH) in Sphingopyxis sp. DBS4, and characterized them for diclofop-methyl degradation. DcmA, a member of the amidase superfamily, exhibits 26.1-45.9% identity with functional amidases. Conversely, DcmH corresponded to the DUF3089 domain-containing protein family (a family with unknown function), sharing no significant similarity with other biochemically characterized proteins. DcmA exhibited a broad spectrum of substrates, with preferential hydrolyzation of (R)-(+)-diclofop-methyl, (R)-(+)-quizalofop-ethyl, and (R)-(+)-haloxyfop-methyl. DcmH also preferred (R)-(+)-quizalofop-ethyl and (R)-(+)-haloxyfop-methyl degradation while displaying no apparent enantioselective activity towards diclofop-methyl. Using site-directed mutagenesis and molecular docking, it was determined that Ser175 was the fundamental residue influencing DcmA's activity against the two enantiomers of diclofop-methyl. For the degradation of AOPP herbicides, DcmA is an enantioselective amidase that has never been reported in research. This study provided novel hydrolyzing enzyme resources for the remediation of diclofop-methyl in the environment and deepened the understanding of enantioselective degradation of chiral AOPP herbicides mediated by microbes.

Enantioselective effect of chiral prothioconazole on the conformation of bovine serum albumin

As a typical chiral triazole fungicide, the enantioselective toxicity of prothioconazole to environmental organisms is of increasing concern. Herein, the binding mechanism of chiral PTCs to BSA was investigated by multi-spectral technique and molecular docking. Fluorescence titration and fluorescence lifetime experiments fully established that quenching BSA fluorescence by chiral PTCs is static quenching and could spontaneously bind to BSA. Hydrophobic interactions dominate the binding process of chiral PTCs to BSA. Differently, although both chiral PTCs and BSA have a primary binding site, the difference in chiral isomerism leads to a stronger binding ability of S-PTC than R-PTC. Both configurations of PTC can change the conformation of BSA and induce changes in the microenvironment around its amino acid residues, and the effect of S-PTC is more significant. Overall, S-PTC exhibited a more substantial effect on BSA structure relative to R-PTC. That is, S-PTC may lead to more potent potential toxicological effects on environmental organisms. This study provides a comprehensive assessment of the environmental behavior of chiral pesticides and their potential toxicity to environmental organisms at the molecular level and provides a theoretical basis for the screening of highly effective and biologically less toxic enantiomers of chiral pesticides.