Chiral conazole fungicides - (Enantioselective) terrestrial bioaccumulation and aquatic toxicity

Enantiomer-specific burden of metalaxyl and myclobutanil in non-occupationally exposed population with evidence from dietary intake and urinary excretion

Metalaxyl (MET) and myclobutanil (MYC) are two widely used chiral fungicides that may pose health risks to non-occupationally exposed populations. Here, the two fungicides were enantiomer-specific quantified in the dietary food and urine of residents in an Eastern China city, to determine the exposure and excretion of these contaminants in different populations. Results indicate that residues of MET and MYC varied with different food items at 0.42-0.86 ng/g fresh weight (FW) and 0.18-0.33 ng/g FW, respectively. In urine samples, the residual levels after creatinine adjusting (CR) ranged from 10.2 to 1715.4 ng/g CR for MET and were below the detection limit up to 320.7 ng/g CR for MYC. Significant age- and gender-related differences were separately found in urinary MET and MYC of different populations. Monte-Carlo simulations suggested that children had higher daily dietary intake (DDI) but lower urinary excretion (DUE) rates than youths, and thus may suffer higher body burdens. The residues of antifungally ineffective enantiomers (S-MET and R-MYC) were slightly higher than their antipodes in foods. Moreover, the enantiomer-selective urinary excretion resulted in higher retention of S-MET and R-MYC in the human body. Our results suggest that both dietary intake and urinary excretion should be enantiomer-specifically considered when assessing the exposure risk and body burden of chiral fungicides in the non-occupationally exposed population. Furthermore, substitutive application of enantiomer-enriched fungicide formulations can not only benefit the antifungal efficacy but also be safer for human health.

Study on the enantioselective bioaccumulation and dissipation of uniconazole enantiomers in earthworm-soil microcosm through supercritical fluid chromatography-tandem mass spectrometry (SFC-MS/MS)

In this work, the enantioselective bioaccumulation and dissipation of uniconazole enantiomers in earthworm-soil microcosm were studied. A fast enantioseparation method of uniconazole through supercritical fluid chromatography-tandem mass spectrometry (SFC-MS/MS) was established. The CHIRALCEL OZ-3 column and a mixture of CO₂ and methanol (80:20, v/v) were used within 1.0 min to separate uniconazole enantiomers. The recoveries of uniconazole enantiomers in earthworm and soil samples ranged from 83.3 to 113%, and the intra-day and inter-day relative standard deviation values were lower than 11%. In earthworms, the bioaccumulation concentrations of uniconazole enantiomers increased with time and reached the maximum on the 7th day and then decreased. The elimination of uniconazole enantiomers in earthworms followed the first-order kinetics equation, and the elimination half-lives were approximately 7 days. In artificial soil, the dissipation of uniconazole enantiomers was slow, and the dissipation half-lives were both 25.7 days. No enantioselectivity occurred in the earthworm-soil microcosm. These results may reduce the uncertainty of environmental risk assessment for uniconazole.

Effects of triazole plant growth regulators on molting mechanism in Chinese mitten crab (Eriocheir sinensis)

Rice crab co-culture is a new integrated farming model in China. The application of triazole plant growth regulators (PRGs) is often used as an advantageous option to combat rice lodging. However, there is still a gap regarding the toxicity of these PRGs on the growth and development of the Chinese mitten crab (Eriocheir sinensis, E. sinensis). Here the effect of triazoles (paclobutrazol and uniconazole) on the molting mechanism of E. sinensis was investigated. Monitoring of regulatory genes associated with molting showed that the two PRGs were found to inhibit the expression of ecdysteroid hormone (EH), ecdysteroid receptors gene (EcR), and retinoid X receptors gene (RXR) and induce secretion of molt-inhibiting hormone (MIH) gene. In addition, the activities of chitinase (CHIA) and N-acetyl-β-d-aminoglucosidase (β-NAGase) were also inhibited by exposure to PRGs. Exposure to PRGs also elevated the mRNA expression of the growth-related myostatin gene (MSTN). These results revealed that there is a long-term risk of exposure to triazoles PRGs that may inhibit molting and affect normal development and immune system of E. sinensis.

Enantiomer-Specific Study of Fenpropathrin in Soil-Earthworm Microcosms: Enantioselective Bioactivity, Bioaccumulation, and Toxicity

In this study, the enantiomer-specific bioactivity, bioaccumulation, and toxicity of fenpropathrin (FEN) enantiomers were investigated in soil-earthworm microcosms. The bioactivity order was S-FEN > rac-FEN > R-FEN for Spodoptera litura and Conogethes punctiferalis. Moreover, S-FEN was 12.0 and 32.2 times more toxic than rac-FEN and R-FEN to earthworms, respectively. S-FEN degraded faster than R-FEN with the enrichment of R-FEN in the soil environment. Furthermore, the peak-shaped accumulation curves for FEN enantiomers were observed, and R-FEN was preferentially bioaccumulated by earthworms. As compared to R-FEN, S-FEN induced greater changes in the activities of detoxification enzymes, antioxidant enzymes, and malondialdehyde content, which suggested that earthworms exhibited enantioselective defense responses to S-FEN and R-FEN. Integrated biomarker response results indicated that S-FEN exhibited higher toxic effects on earthworms than R-FEN. Finally, molecular simulation revealed that the greater interaction forces between S-FEN and sodium channel protein could be the primary reason for the enantioselective bioactivity and toxicity of FEN enantiomers. This study comprehensively highlights the enantiomer-specific bioactivity, bioaccumulation, toxicity, and mechanism of FEN in soil-earthworm microcosms at the enantiomer level. Our findings will contribute to a better risk assessment of FEN in the soil ecosystem.

Evaluation of Chiral Fungicide Penflufen in Legume Vegetables: Enantioseparation and Its Mechanism, Enantioselective Behaviors, and Risk Assessment

Illustrating the enantioselective behaviors of the novel chiral fungicide penflufen was extremely important for ecological safety and human health. For penflufen enantiomers, an excellent separation method including a short analysis time (4 min), a high sensitivity (2 ng/g), and lesser consumption of an organic solvent was first established through supercritical fluid chromatography-tandem mass spectrometry. The enantioseparation mechanism was explained by computational chemistry, and the stronger binding ability of S-(+)-penflufen with cellulose tris-(3-chloro-4-methylphenylcarbamate) (the chiral stationary phase OZ-3 column) contributed to the posterior elution. In legume vegetables, penflufen dissipation was the fastest in Pisum sativum Linn plants (half-life, 1 day) and the slowest in Glycine max plants (half-lives, 11.3-12.9 days). After 30, 50, and 40 days, the rac-penflufen residues were lower than the maximum residue level value in the Electronic Code of Federal Regulations (10 ng/g) in G. max, P. sativum Linn, and Vigna unguiculata, respectively. Abundant S-(+)-penflufen was found in these plants with stereoisomeric excess (se) changes being >10% in the initial stage, so the risk assessment might be driven by S-(+)-penflufen. However, the se changes were <10% in V. unguiculata plants, and the risk assessment might be calculated based on rac-penflufen. Moreover, penflufen enantiomers could be transferred from legume vegetables to soils, and the concentrations increased with time. The high persistence and medium mobility of penflufen in soils might lead to potential groundwater contamination, which was noteworthy. These results could contribute to a more accurate risk assessment of penflufen in legume vegetables.

Enantioselective acute toxicity, oxidative stress effects, neurotoxicity, and thyroid disruption of uniconazole in zebrafish (Danio rerio)

Uniconazole is a widely used plant growth retardant in the agricultural field. However, toxicological effects of uniconazole in aquatic ecosystem at chiral level are still unclear. Herein, acute toxicity, oxidative stress effects, neurotoxicity, and thyroid disruption of uniconazole enantiomers were investigated through using zebrafish as a model. (R)-Uniconazole possessed 1.16-fold greater acute toxicity to zebrafish than (S)-enantiomer. Then, integrated biomarker response values of oxidative stress parameters in zebrafish exposed to (R)-uniconazole were about 1.27~1.53 times greater than those treated by (S)-uniconazole, revealing that (R)-uniconazole could result in more significant adverse effects than (S)-uniconazole. Subsequently, the results of acetylcholinesterase activity of experimental fish demonstrated a state of inhibition-activation-inhibition after 14-day exposure to uniconazole, and a significant enantioselective neurotoxicity of uniconazole was observed in zebrafish after exposure for 4 and 7 days (p < 0.05). Moreover, thyroxine and triiodothyronine contents in (R)-uniconazole-exposed zebrafish were 0.89-fold (p=0.007) and 0.80-fold (p=0.007) than those in (S)-enantiomer-treated group, respectively. Furthermore, molecular docking results between uniconazole enantiomers and thyroid hormone receptors revealed that (R)-uniconazole was more tightly bound than (S)-uniconazole to the receptors. Briefly, our findings provide favorable information for ecological risk assessments of chiral agrochemicals in the environment and health of aquatic organisms.

Accumulation of epoxiconazole from soil via oleic acid-embedded cellulose acetate membranes and bioavailability evaluation in earthworms (Eisenia fetida)

A passive sampler in the soil environment is a relatively novel technique and has had quite limited applications, especially for pesticides. Oleic acid-embedded cellulose acetate membranes (OECAMs) were developed to evaluate the bioavailability of epoxiconazole (EPO) to earthworms (Eisenia fetida). The uptake of EPO by OECAMs (R² = 0.975) and earthworms (R² = 0.938) was compared and found to follow a two-compartment kinetic model. EPO sampling by OECAMs reached equilibrium (94%) within 2 d. OECAM could be used to determine the concentration of EPO in soil porewater. Furthermore, a significant linear relationship (R² = 0.990) was observed between the EPO concentrations in earthworms and the OECAMs. The EPO concentrations in the porewater and OECAMs were lower in soils with a higher organic matter (OM) content. The EPO concentrations in the porewater, earthworms, and OECAMs decreased by 64.4, 49.0, and 56.1%, respectively, in the presence of 0.5% biochar, compared with the control. Furthermore, the use of OECAMs versus earthworms for soil testing also allows you to avoid factors that increase variance in organisms, such as avoidance behaviors or feeding. Therefore, OECAMs show good potential for use as a passive sampler to evaluate the bioavailability of EPO.

Stereochemistry of chiral pesticide uniconazole and enantioselective metabolism in rat liver microsomes

In this work, stereochemistry of uniconazole enantiomers and their metabolism behaviors in rat liver microsomes have been researched. Significance analysis has been applied in data processing. Absolute configurations of uniconazole enantiomers were identified through vibrational circular dichroism spectroscopy. According to their elution order from the chiral column using the CO₂-methanol (80:20, v/v) mixture, two eluted fractions were determined to be (R)-uniconazole and (S)-uniconazole, respectively. A high-efficient and sensitive LC-MS/MS chiral analysis method was established for investigating the metabolism of uniconazole enantiomers in rat liver microsomes. The metabolic half-life of (R)-uniconazole (38.7 min) in rat liver microsomes was half that of (S)-enantiomer (74.5 min), and maximum velocity of metabolism, Michaelis constant of metabolism as well as the intrinsic metabolic clearance of (R)-uniconazole were significantly higher than (S)-enantiomer (p < 0.05), which indicated that (R)-uniconazole was preferentially metabolized in rat liver microsomes. By the virtue of molecular docking, (R)-uniconazole exhibited a higher binding affinity to cytochrome CYP2D2 than (S)-enantiomer, which corroborated well with the metabolism results. This work will shed light on the risk assessment of uniconazole toward human health and the ecological environment.