Identification of fipronil metabolites by time-of-flight mass spectrometry for application in a human exposure study

Transfer and risk assessment of fipronil in laying hen tissues and eggs

Fipronil is a persistent insecticide known to transfer into hen eggs from exposure from animal drinking water and feed, but some questions remain regarding its transfer behavior and distribution characteristics. Therefore, the dynamic metabolism, residue distribution and transfer factor (TF) of fipronil were investigated in 11 edible tissues of laying hens and eggs over 21 days. After a continuous low-dose drinking water exposure scenario, the sum of fipronil and all its metabolites (defined as fipronilT) quickly transferred to each edible tissue and gradually increased with exposure time. FipronilT residue in eggs first appeared at 3 days and then gradually increased. After a single high-dose feed exposure scenario, fipronilT residue in edible tissues first appeared after 2 h, quickly peaked at 1 day, and then gradually decreased. In eggs, fipronilT residue first appeared at 2 days, peaked 6-7 days and then gradually decreased. The TF values followed the order of the skin (0.30-0.73) > egg yolk (0.30-0.71) > bottom (0.21-0.59) after drinking water exposure, and the order of the skin (1.01-1.59) > bottom (0.75-1.1) > egg yolk (0.58-1.10) for feed exposure. Fipronil sulfone, a more toxic compound, was the predominant metabolite with higher levels distributed in the skin and bottom for both exposure pathways. FipronilT was distributed in egg yolks rather than in albumen owing to its lipophilicity, and the ratio of egg yolk to albumen may potentially reflect the time of exposure. The distinction is that the residues after feed exposure were much higher than that after drinking water exposure in edible tissues and eggs. The study highlights the residual characteristics of two exposure pathways, which would contribute to the tracing of contamination sources and risk assessment.

Immunoassays and Emerging Analytical Techniques of Fipronil and its Metabolites for Food Safety: A Review

Fipronil, classified as a phenylpyrazole insecticide, is utilized to control agricultural, public health, and veterinary pests. Notably, its unique ecological fate involves degradation to toxic metabolites, which poses the risk of contamination in water and foodstuffs and potential human exposure through the food chain. In response to these concerns, there is a pressing need to develop analytical methodologies for detecting fipronil and its metabolites. This review provides a concise overview of the mode of action, metabolism, and toxicology of fipronil. Additionally, various detection strategies, encompassing antibody-based immunoassays and emerging analytical techniques, such as fluorescence assays based on aptamer/molecularly imprinted polymer/fluorescent probes, electrochemical sensors, and Raman spectroscopy, are thoroughly reviewed and discussed. The focus extends to detecting fipronil and its metabolites in crops, fruits, vegetables, animal-derived foods, water, and bodily fluids. This comprehensive exploration contributes valuable insights into the field, aiming to foster the development and innovation of more sensitive, rapid, and applicable analytical methods.

Effects of sublethal fipronil exposure on cross-generational functional responses and gene expression in Binodoxys communis

The effective systemic insecticide fipronil is widely used on a variety of crops and in public spaces to control insect pests. Binodoxys communis (Gahan) (Hymenoptera: Braconidae) is the dominant natural enemy of Aphis gossypii Glover (Homoptera: Aphididae), an important cotton pest, and has good efficiency in inhibiting aphid populations. The direct effects of environmental residues of sublethal fipronil doses on adult B. communis have not previously been reported. This study therefore aimed to evaluate the side effects and transcriptomic impacts of sublethal fipronil doses on B. communis. The results showed that exposure to the LC10 dose of fipronil significantly reduced the survival rate and parasitism rate of the F0 generation, but did not affect these indicators in the F1 generation. The LC25 dose did not affect the survival or parasitic rates of the F0 generation, but did significantly reduce the survival rate of F1 generation parasitoids. These results indicated that sublethal doses of fipronil affected B. communis population growth. Transcriptome analysis showed that differentially expressed genes (DEGs) in B. communis at 1 h after treatment were primarily enriched in pathways associated with fatty acid elongation, biosynthesis of fatty acids, and fatty acid metabolism. DEGs at 3 days after treatment were mainly enriched in ribosomal functions, glycolysis/gluconeogenesis, and tyrosine metabolism. Six DEGs (PY, ELOVL, VLCOAR, MRJP1, ELOVL AAEL008004-like, and RPL13) were selected for validation with real-time fluorescent quantitative PCR. This is the first report of sublethal, trans-generational, and transcriptomic side effects of fipronil on the dominant parasitoid of A. gossypii. The results of this study show that adaptation of parasitoids to high concentrations of pesticides may be at the expense of their offspring. These findings broaden our overall understanding of the intergenerational adjustments used by insects to respond to pesticide stress and call for risk assessments of the long-term impacts and intergenerational effects of other pesticides.

Scannotation: A Suspect Screening Tool for the Rapid Pre-Annotation of the Human LC-HRMS-Based Chemical Exposome

In an increasingly chemically polluted environment, rapidly characterizing the human chemical exposome (i.e., chemical mixtures accumulating in humans) at the population scale is critical to understand its impact on health. High-resolution mass spectrometry (HRMS) profiling of complex biological matrices can theoretically provide a comprehensive picture of chemical exposures. However, annotating the detected chemical features, particularly low-abundant ones, remains a significant obstacle to implementing such approaches at a large scale. We present Scannotation (https://github.com/scannotation/Scannotation_software), an automated and user-friendly suspect screening tool for the rapid pre-annotation of HRMS preprocessed data sets. This software tool combines several MS1 chemical predictors, i.e., m/z, experimental and predicted retention times, isotopic patterns, and neutral loss patterns, to score the proximity between features and suspects, thus efficiently prioritizing tentative annotations to verify. Scannotation and MS-DIAL4 were used to annotate blood serum samples of 75 Breton adolescents. Scannotation's combination of MS1-based chemical predictors allowed us to annotate 89 chemically diverse environmental compounds with high confidence (confirmed by MS2 when available). These compounds included 62% of emerging molecules, for which no toxicological or human biomonitoring data are reported in the literature. The complementarity observed with MS-DIAL4 results demonstrates the relevance of Scannotation for the efficient pre-annotation of large-scale exposomics data sets.

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.

Metabolism of an insecticide fipronil by soil fungus Cunninghamella elegans ATCC36112

In this study, the metabolic pathway of the phenylpyrazole insecticide fipronil in Cunninghamella elegans (C. elegans) was investigated. Approximately 92% of fipronil was removed within 5 days, and seven metabolites were accumulated simultaneously. The structures of the metabolites were completely or tentatively identified by GC-MS and ¹H, ¹³C NMR. To determine the oxidative enzymes involved in metabolism, piperonyl butoxide (PB) and methimazole (MZ) were used, and the kinetic responses of fipronil and its metabolites were determined. PB strongly inhibited fipronil metabolism, while MZ weakly inhibited its metabolism. The results suggest that cytochrome P450 (CYP) and flavin-dependent monooxygenase (FMO) may participate in fipronil metabolism. Integrated metabolic pathways can be inferred from the control and inhibitor experiments. Several novel products from the fungal transformation of fipronil were identified, and similarities between C. elegans transformation and mammalian metabolism of fipronil were compared. Therefore, these results will help to gain insight into the fungal degradation of fipronil and potential applications in fipronil bioremediation. At present, microbial degradation of fipronil is the most promising approach and maintains environmental sustainability. In addition, the ability of C. elegans to mimic mammalian metabolism will assist in illustrating the metabolic fate of fipronil in mammalian hepatocytes and assess its toxicity and potential adverse effects.

Fipronil and its transformation products in the Yangtze River: Assessment for ecological risk and human exposure

Fipronil (FP), a phenylpyrazole insecticide, is widely used in agricultural, residential, and veterinary settings. It is toxic to ecosystems and humans; moreover, some of its transformation products are more toxic than FP. A comprehensive profile of the contamination of the Yangtze River by FP and its transformation products (FPs) is not yet available. This study aims to fill this data gap. A total of 144 water samples were collected from 72 sampling locations along the river during the wet (June 2021) and dry (December 2020) seasons. High detection rates (85.4-91.7%) of FPs were found, with ΣFPs' median concentration of 0.49 ng/L. The parent compound FP was the most abundant (median: 0.13 ng/L), followed by FP-desulfinyl (0.08), FP-sulfone (0.07), FP-detrifluoromethylsulfinyl (DTF, 0.07), FP-sulfide (0.06) and FP-amide (0.06). Their concentrations increased significantly from the upper to the lower reaches; for approximately every 100 km toward the lower reaches, the level of FPs increased by 13-15%. The urban region and wet season had the higher FPs contamination. Through water ingestion, the human exposure risk posed by FPs in the river was acceptable; however, the ecological risk assessment showed a moderate to high risk posed by FPs. Follow-up studies are warranted to establish integrated ecological risk assessment models and conduct epidemiological risk assessments among population groups with high exposure levels of FPs. Given the high ecological risk of FPs, regular monitoring of them in the Yangtze River is necessary. FP-DTF was reported in surface water for the first time.

Pet dogs transfer veterinary medicines to the environment

Worldwide, the number of pet dogs increases yearly, and as a result so does the use of veterinary medicines for flea and tick control. We investigated the potential transfer of veterinary flea products from dogs to the environment in a 'proof of principle' experiment. For this purpose, samples of hair, urine, and water after swimming were investigated. Nine dogs were recruited for this study, eight of which had been recently treated with an ectoparasiticide product. Hair and urine samples were tested for afoxalaner, fluralaner, fipronil and imidacloprid. Interestingly, contamination with ectoparasiticides was frequently demonstrated in samples from dogs untreated with these particular substances, suggesting widespread secondary transfer. In addition, hair retrieved from a bird's nest contained fipronil, fluralaner and imidacloprid, indicating a potential pathway for the exposure of juvenile birds. Three of the dogs also participated in a swimming experiment. One had been treated with oral fluralaner, whilst the remaining two had received other compounds not included in our study. However, in all three dogs, both fluralaner and imidacloprid were detected in hair samples. Fluralaner concentrations in the swimming water exceeded Dutch water quality standards, indicating a potential risk to the aquatic environment. Imidacloprid levels increased after each swimming dog, but did not breach Dutch water quality standard levels. These findings all call for improvements in the current risk assessment and management for veterinary medicines, by including companion animals and their exposure pathways into ecosystems.

Fipronil and its metabolites in chicken feather: residue analysis, depletion study, and application analysis of pollution sources in laying hens

A method based on a multi-mechanism impurity adsorption and ultra-performance liquid chromatography-tandem mass spectrometry was established to detect fipronil and four of its metabolites in chicken feathers. This method was successfully applied to the depletion study of fipronil in feathers of laying hens. Fipronil and two metabolites were found in feathers during treatment. Fipronil concentrations in feathers increased during medication and then regularly decreased during withdrawal, and they were still detected on the 14th day after withdrawal. High residue concentrations were also present in feathers on day 23 of the experimental period. Pollution sources of fipronil can be inferred on the basis of the residue ratio of fipronil metabolites from different pollution modes. Result shows that feathers were an effective matrix for residue monitoring and risk analysis of fipronil in animals and the environment.

Novel fast pesticides extraction (FaPEx) strategy coupled with UHPLC-MS/MS for rapid monitoring of emerging pollutant fipronil and its metabolite in food and environmental samples

In this work, we demonstrated a new, environmental-friendly and effective sample preparation strategy named 'in-syringe-assisted fast pesticides extraction (FaPEx)' technique coupled with LC-MS/MS for the rapid identification and monitoring of emerging pollutant fipronil and its metabolite fipronil sulfone in chicken egg and environmental soil samples. FaPEx strategy comprising of two simple steps. Firstly, the sample was placed in the syringe and extracted using low-volume acetonitrile with NaCl and anhydrous MgSO₄ salts. Secondly, the extractant was passed through in-syringe-based solid-phase extraction (SPE) kit containing cleanup sorbents and salt combinations (C18, primary secondary amine, and anhydrous MgSO₄) for the cleanup process. Then, the obtained clean extractant was injected into LC-MS/MS for the quantification of target analytes. Various important parameters influencing the FaPEx performances, such as solvent type, salt type, salt amount, sorbent type, and amount, were examined and optimized. The method validation results showed excellent linearity with high correlation coefficients were ≥ 0.99. The estimated LODs were between 0.05-0.07 μg/kg, and LOQs ranged between 0.1-0.25 μg/kg for target analytes in both egg and soil sample matrices, and precision values were ≤7.90%. The developed method was applied to commercial chicken egg samples and environmental soil samples analysis. Spiked recoveries ranged between 88.75-110.91% for egg samples with RSDs ≤7.42% and 82.47-107.46% for soil samples with RSDs <7.37%. These results proved that the developed sample preparation method is a simple, fast, green, low-cost, and efficient method for the analysis of fipronil and its metabolites in food and environmental samples. Thus, this method can be applied as an alternative analytical methodology in routine and standard food and environmental testing laboratories.

Comparative in vitro biotransformation of fipronil in domestic poultry using liver microsome

Domestic poultry are among the non-target species of exposure to fipronil, but limited information is available on the metabolic effects of fipronil exposure in avian. We investigated the comparative capacity of in vitro biotransformation of fipronil among chicken, duck, quail, goose, and rat. Interspecies differences in kinetic parameters were observed; the clearance rate calculations (Vmax/Km) indicated that chicken and duck are more efficient in the cytochrome P450-mediated metabolism of fipronil to sulfone than quail, goose and rat. The lower hepatic clearance of fipronil in quail, goose and rat, suggested that fipronil sulfone may serve as a biomarker to indicate fipronil exposure in these species.

Diverse positional 14C labeling-assisted metabolic analysis of pesticides in rats: The case of vanisulfane, a novel vanillin-derived pesticide

Information on pesticide metabolites is crucial for accurate environmental risk assessment. However, identifying the various metabolites of a novel pesticide is challenging since the potential metabolic pathways are unknown. In this study, we coupled diverse positional ¹⁴C labeling with high-resolution mass spectrometry to quantitatively and qualitatively study pesticide metabolism in rats. With the unique M/(M + 2) ratios derived from ¹⁴C, precursor compounds of metabolites could be better distinguished from impurity ions. Additionally, the use of diverse ¹⁴C labeling positions is a powerful tool to elucidate the complete metabolic fate of novel contaminants. Vanisulfane is a novel vanillin-derived antiviral agent with encouraging prospects for the efficient control of cucumber mosaic virus in China, but its metabolic pathways in mammals are still poorly understood. Thus, the metabolism of vanisulfane was studied in rats of both sexes by this strategy. The results showed that phase I and phase II metabolism occurred in both sexes. The former included mainly oxidation reactions, and the latter involved binding reactions that formed glucuronide, sulfate and amino acid conjugates. Sex-related differences were observed in the experiment, with earlier appearance of downstream metabolites and a preference for sulfate conjugate formation in males compared to females. This research facilitates the risk evaluation of vanisulfane, and offers an effective framework for screening unknown pesticide metabolic pathways, which could be applied to establish the metabolic profiles of other novel contaminants with limited information.

Determination of fipronil and its metabolites in environmental water samples by meltblown nonwoven fabric based solid-phase extraction combined with gas chromatography-electron capture detection

In this study, a new method for determination of fipronil and its three metabolites in environmental water samples was developed based on meltblown nonwoven fabric solid-phase extraction combining with gas chromatography-electron capture detection. As the core material of medical mask, meltblown nonwoven fabric is made of polypropylene superfine fibers which are randomly distributed and bonded together with a relatively large specific surface area and good permeability. Polypropylene as a high molecular hydrocarbon-based polymer, has the characteristics of good hydrophobicity and lipophilicity, which can be applied for separation and enrichment of hydrophobic substances in food, environment and biology samples. The meltblown nonwoven fabric is soft and can fill the solid-phase extraction cartridge tightly. This aspect also makes it suitable to be used as an ideal solid-phase extraction sorbent. A series of parameters influencing the extraction efficiency were investigated, and under the optimized conditions, fipronil and its three metabolites had good linear relationship in the range of 0.2-100 μg/L with correlation coefficient R² more than 0.999. The recoveries at three spiked concentrations were in the range of 99.2-107.3% with the relative standard deviations less than 9.8% (intra-day) and 8.1% (inter-day). The limit of detection for the four target analytes were in the range of 0.02-0.06 μg/L. Finally, this method was successfully applied in the analysis of fipronil and its three metabolites in various types of environmental water samples. This article is protected by copyright. All rights reserved.

Occurrence of Phenylpyrazole and Diamide Insecticides in Lactating Women and Their Health Risks for Infants

To investigate the exposure of infants to phenylpyrazole and diamide insecticides during lactation, we collected 3467 breast milk samples of lactating women from 100 cities of 24 provinces in China and prepared 100 pooled samples together city-by-city. Among phenylpyrazole insecticides, fipronil and its metabolites (63-100%) were widely detected in breast milk, with total detection concentrations ranging from 178 to 2947 ng/L (median: 921 ng/L). Among diamide insecticides, chlorantraniliprole and flubendiamide were detected in breast milk, but their detection frequencies (20-85%) and concentration levels (nondetected to 89.9 ng/L) were far lower than those of total fipronils. The average estimated daily intake of infants exposed to total fipronils through breast milk is 209 ng/kg-bw/day by upper-bound scenario evaluation, which is higher than the acceptable daily intake (200 ng/kg-bw/day). This study indicates that infants have far higher exposure levels to fipronil than adults, while exposure levels to other types of phenylpyrazoles and diamide insecticides are low.

Fipronil and its metabolites in human seminal plasma from Shijiazhuang, north China

Fipronil (FP) is an emerging insecticide which could induce reproductive toxicity in male rats at very low dosage, but the occurrence of FP and its transformation products (FPs) in human seminal plasma and their impacts on human semen quality have not been documented. In this study, FPs including FP, fipronil desulfinyl (FP-DES), fipronil sulfone (FP-SFO), fipronil amide (FP-AM), and fipronil sulfide (FP-SFI), were measured in seminal plasma samples (n = 200), which were collected from Shijiazhuang, north China. The cumulative concentration of FPs (ΣFPs), in the seminal plasma samples ranged from 0.003 to 0.180 ng/mL (median: 0.043 ng/mL). FP-SFO was the major target analyte (median: 0.040 ng/mL), accounting for approximately 42.3-100.0% of the ΣFPs. Significantly higher exposure levels of FPs were found in the overweight or obese group (≥25 kg/m²) vs. the normal BMI group (18.5-25 kg/m²) (ΣFPs: 0.047 vs. 0.033 ng/mL), never smoking group vs. current smoking group (ΣFPs: 0.057 vs. 0.037 ng/mL), and low sexual frequency group (<1 time/week) vs. high sexual frequency group (≥3 times/week) (ΣFPs: 0.048 vs. 0.030 ng/mL). No significant association between FPs and impaired semen quality parameter was found in this study. This is the first time to report FPs' occurrence in human seminal plasma and variations in their concentrations among people with different demographic and behavioral characteristics. Further studies on adverse effects of exposure to FPs on reproductive function are needed.

The exposure levels and health risk assessment of antibiotics in urine and its association with platelet mitochondrial DNA methylation in adults from Tianjin, China: A preliminary study

There has been extensive research on antibiotics exposure in adults by biomonitoring, but the biological mechanisms and potential risks to human health remain limited. In this study, 102 adults aged 26-44 years in Tianjin were studied and 23 common antibiotics in urine were analyzed by Liquid chromatography-mass spectrometry (LC-MS). All antibiotics were detected in urine, with an overall detection frequency of 40.4% (the detection frequencies of phenothiazines, quinolones, sulfonamides, tetracyclines, and chloramphenicol were 77%, 54%, 24%, 28%, and 49%, respectively.). Ofloxacin and enrofloxacin had the highest detection frequencies (85% and 81%), with median concentrations of 0.26 (IQR: 0.05-1.36) and 0.09 (IQR: 0.03-0.14) ng/mL, respectively. Based on health risk assessment, the predicted estimated daily exposures (EDEs) ranged from 0 μg/kg/day to 13.98 μg/kg/day. The hazard quotient (HQ) values of all the antibiotics except ofloxacin and ciprofloxacin were bellow one, which are considered safe. For all blood samples, the mitochondrial DNA (mtDNA) methylation levels in the MT-ATP6 (ranging between 3.86% and 34.18%) were slightly higher than MT-ATP8 and MT-ND5 (ranging between 0.57% and 9.32%, 1.08% and 19.62%, respectively). Furthermore, mtDNA methylation from MT-ATP6, MT-ATP8 and MT-ND5 were measured by bisulfite-PCR pyrosequencing. The association (P < 0.05) was found between mtDNA methylation level (MT-ATP8 and MT-ND5) and individual antibiotics including chlorpromazine, ciprofloxacin, enrofloxacin, norfloxacin, pefloxacin, sulfaquinoxaline, sulfachloropyridazine, chloramphenicol, and thiamphenicol, indicating that persistent exposure to low-dose multiple antibiotics may affect the mtDNA methylation level and in turn pose health risks.

Chiral resolution of the insecticide fipronil enantiomers and the simultaneous determination of its major transformation products by high-performance liquid chromatography interfaced with mass spectrometry

A high-performance liquid chromatography-mass spectrometry (HPLC-MS) method was developed using a chiral column based on amylose tris(3-chloro-5-methylphenylcarbamate) for analysis of fipronil (a popular insecticidal nerve agent) and the related transformation products. The optimized method reached the goal of the simultaneous and complete separation of the multiple fiproles in a single run, including the chiral separation of fipronil enantiomers, fipronil metabolites, and photoproducts. The efficacy of such a method was demonstrated by its application in analyzing a series of fipronil samples exposed to sunlight conditions. In general terms, our study provided experimental approaches and an efficient analytical tool for monitoring the environmental fate of fipronil as well as its multitransformation products upon its applications either in agricultural or any other areas.

Tracking the environmental fate of fipronil and three of its metabolites in garlic based on sampling rate-corrected in vivo solid phase microextraction combined with gas chromatography-mass spectrometry

In this study, a sampling rate-corrected in vivo solid-phase microextraction-gas chromatography-mass spectrometry method (SR-in vivo SPME-GC-MS) was constructed to simultaneously detect fipronil and three of its metabolites in garlic, and their environmental behavior was long-term monitored in in vivo mode. All of three fipronil metabolites were more difficult to degrade than the parent pesticide. The final degradation rates of the metabolites in garlic were in the range of 4.4%-25.1%, much lower than that of the parent (78.6%-85.8%). While their total residues amount was about 3 times as high as fipronil, exceeding the maximum residue limits regulated by China and the European Union. The steady-state concentrations of fipronil and its metabolites in garlic were positively correlated with the pesticide stress dose. In short, the established in vivo tracking method is efficient and convenient. The features of simple operation, fast analysis, acceptable sensitivity, non-harmful or non-lethal to plants, available repeated and long-term monitoring of the same organism make it attractive for in vivo tracking assay, it is of great significance for the guidance of rational use of fipronil and protection of food safety.

Human Exposure of Fipronil Insecticide and the Associated Health Risk

Fipronil, as an emerging phenylpyrazole insecticide, is ubiquitous in the environment and food due to its broad spectrum and persistent characteristics, but the research on pathways of human exposure to fipronil and the associated health risk is relatively unclear. In this regard, we summarize potential human exposures to fipronil through ingestion and inhalation, as well as results of human biomonitoring studies. This scientific information will contribute to future assessment of fipronil exposure and subsequent characterization of human health risks. Additionally, this Perspective highlights the lack of epidemiological studies and total diet studies for the general population on fipronil.

Target and Suspect Screening of Urinary Biomarkers for Current-use Pesticides: Application of a Simple Extraction Method

Pesticide residues pose a great threat to human health. Biomonitoring with urine samples has often been used to assess pesticide exposure to humans, and identifying appropriate biomarkers is a premise of success. Current-use pesticides (CUPs) including neonicotinoids tend to be transformed in an organism, and thus the biomonitoring studies focusing on parent compounds alone may underestimate their risk. It is imperative to develop effective methods to analyze CUPs and their metabolites simultaneously and to identify viable metabolites as urinary biomarkers. For analyzing xenobiotics in urine, we optimized CH₃ COCH₃ -MgSO₄ extraction coupled with a high-performance liquid chromatography-tandem mass spectrometry detection method. The method had sensitive method detection limits (0.11-1.39 ng/ml), low matrix effects, and satisfactory recovery and precision (49.4% ± 7.2%-99.8% ± 17.8%) for neonicotinoids and their metabolites. Application of the method for real samples showed that children living in rural areas in South China were ubiquitously exposed to CUPs, including neonicotinoids, fipronil, and chlorpyrifos, and urinary residues were mainly in the form of metabolites. Suitable biomarkers were identified for individual neonicotinoids, including imidacloprid-olefin and imidacloprid-guanidine for imidacloprid, acetamiprid-N-desmethyl for acetamiprid, thiacloprid-amide for thiacloprid, and N-desmethyl-thiamethoxam and thiamethoxam for thiamethoxam. Three metabolites were mainly reported in urine samples, including imidacloprid-urea, thiacloprid-amide, and N-desmethyl-thiamethoxam. In addition, the method was also applied for suspect screening, and an additional metabolite (clothianidin-desmethyl-nitrosoguanidine) was identified, showing its potential application in suspect analysis. Environ Toxicol Chem 2022;41:73-80. © 2021 SETAC.

Development of an analytical method based on solid-phase extraction and LC-MS/MS for the monitoring of current-use pesticides and their metabolites in human urine

Pyrethroids, organophosphorus pesticides and fipronil have been listed as priority chemicals in human biomonitoring studies because of their wide use and potential health effects in humans. The determination of 13 pesticides, including pyrethroids (deltamethrin, cypermethrin, permethrin, cyfluthrin, bifenthrin), organophosphorus (chlorpyrifos, chlorpyrifos-methyl, and malathion), fipronil, neonicotinoids (imidacloprid, acetamiprid and thiacloprid) and triazole (prothioconazole), together with 13 corresponding metabolites in human urine samples was achieved by solid-phase extraction and analysis by liquid chromatography coupled to tandem mass spectrometry. All targeted compounds, except malathion dicarboxylic acid, were measured with a mean within-accuracy (n = 5) of 71%-114% (RSD: 1%-14%) and between-run (n = 15) accuracy of 80%-118% (RSD: 2%-14%). Limits of quantitation of the targeted analytes ranged from 0.1 to 16 pg/mL. The detection result of urine samples from 25 volunteers indicated that the detection frequencies of 3,5,6-trichloro-2-pyridinol (median: 448 pg/mL), 6-chloropyridine-3-carboxylic acid (median: 193 pg/mL), 2-methyl-3-phenylbenzoic acid (median: 181 pg/mL), 3-phenoxybenzoic acid (median: 99 pg/mL), 2-isopropyl-6-methyl-4-pyrimidinol (median: 77 pg/mL), cyfluthrin (median: 59 pg/mL), cis-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylic acid (cis-DCCA, median: 53 pg/mL), trans-DCCA (median: 25 pg/mL), prothioconazole (median: 21 pg/mL), imidacloprid (median: 7 pg/mL), and prothioconazole-desthio (median: 1 pg/mL) were > 50%. The obtained results show that the validated method is suitable for the human biomonitoring of these current-use pesticides and their metabolites.

Exposure to fipronil induces cell cycle arrest, DNA damage, and apoptosis in porcine trophectoderm and endometrial epithelium, leading to implantation defects during early pregnancy

Fipronil, a phenyl-pyrazole insecticide, has a wide range of uses, from agriculture to veterinary medicine. Due to its large-scale applications, the risk of environmental and occupational exposure and bioaccumulation raises concerns. Moreover, relatively little is known about the intracellular mechanisms of fipronil in trophoblasts and the endometrium involved in implantation. Here, we demonstrated that fipronil reduced the viability of porcine trophectoderm and luminal epithelial cells. Fipronil induced cell cycle arrest at the sub-G1 phase and apoptotic cell death through DNA fragmentation and inhibition of DNA replication. These reactions were accompanied by homeostatic changes, including mitochondrial depolarization and cytosolic calcium depletion. In addition, we found that exposure to fipronil compromised the migration and implantation ability of pTr and pLE cells. Moreover, alterations in PI3K-AKT and MAPK-ERK1/2 signal transduction were observed in fipronil-treated pTr and pLE cells. Finally, the antiproliferative and apoptotic effects of fipronil were also demonstrated in 3D cell culture conditions. In summary, our results suggest that fipronil impairs implantation potentials in fetal trophectoderm and maternal endometrial cells during early pregnancy.

Insecticide fipronil and its transformation products in human blood and urine: Assessment of human exposure in general population of China

Fipronil (FP) is widely used as a highly effective insecticide worldwide, thereby raising concern about environmental contamination and risk for human health. However, data on the occurrence of FP and its transformation products (FPs) in human blood and urine are limited. In this study, 39 pairs of serum, plasma, blood cells (BCs), and urine samples were collected from adults in Wuhan, central China (2020), in order to characterize the concentration profiles of FPs in different matrices. FPs were also determined in serum samples (n = 226, including 57, 56, 56, and 57 samples for Wuhan, Huangshi, Nanjing, and Zhenjiang, respectively) collected from four cities of China (2015) to characterize the exposure levels of FPs among the general population and potential spatial variations. Fipronil sulfone (FP-SFO) was 100% detectable in blood samples, and it was the predominant metabolite (accounting for 86-95% of the cumulative concentrations of FPs [ΣFPs]), with the median concentrations (ng/mL) of 0.17, 0.16, and 0.03 in serum (range: 0.07-1.53), plasma (range: 0.06-1.41), and BCs (range: 0.01-0.24), respectively. The compositional profiles of FPs in serum, plasma, and BCs were similar; very strong positive correlations were observed between different blood matrices for FP-SFO (r = 0.94-0.97, p < 0.01) but not between blood and urine. The median ΣFPs (ng/mL) in the serum (0.20; range: 0.09-1.56) and the plasma samples (0.19; range: 0.09-1.43) was higher than that in BCs samples (0.04; range: 0.01-0.24). In the urine samples, only the major metabolite FP-SFO was detectable in approximately 10% of the samples. Additionally, the highest median ΣFPs (ng/mL) in the serum samples was found in Nanjing (0.56; range: 0.13-1.88), followed by Wuhan (0.34; range: 0.06-1.02), Huangshi (0.10; range: 0.03-0.60), and Zhenjiang (0.08; range: 0.02-0.42). The level of ΣFPs seemed to increase with city sizes and urbanization scale, though further studies are needed to confirm the variations with larger sample size. The estimated daily intake of ΣFPs based on the median concentration of samples from Nanjing (18.5 ng/kg-bw/d) was higher than that of Wuhan (11.3), Huangshi (3.40), and Zhenjiang (2.80). Dietary intake should be the major exposure route for the general population, while water or indoor dust accounted for <1% of the ΣFPs intake. This pilot study provided the first data on the profiles of FPs in paired human serum, plasma, BCs, and urine samples, and potential spatial variations of ΣFPs in China. FP-SFO and FP desulfinyl should be considered among priority substances worthy to be bio-monitored in China due to its moderated persistence and ubiquitous occurrence in human blood.

Toxic effects of fipronil and its metabolites on PC12 cell metabolism

Fipronil and its metabolites (fipronil sulfone, fipronil sulfide and fipronil desulfinyl) adversely affect the environment and human health. Targeted metabolomics and lipidomics based on ultra-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) was used to analyse the alterations of glycerophospholipids and amino acids after exposure to fipronil and its metabolites at dosages of 0.5, 12.5 and 50 μM for 72 h and to evaluate their different toxic effects. Results showed that fipronil sulfone and fipronil desulfinyl are more toxic than their parent compound, with fipronil desulfinyl as the most toxic and fipronil sulfide as the least toxic. Fipronil and its metabolites affected the metabolism of PC18:1/16:0, PI18:0/20:4, arginine, leucine and tyrosine and the "phenylalanine, tyrosine and tryptophan biosynthesis" pathway, indicating their possible inducing role in cellular macromolecule damage, nerve signal transmission disturbance and energy metabolism disruption caused by oxidative stress. Importantly, fipronil sulfone and fipronil desulfinyl more strongly influenced lipid and amino acid metabolism, mainly reflected in the number of changed glycerophospholipids and differential metabolites associated with oxidative stress, including PS18:0/20:4, glutamate, phenylalanine and histidine for fipronil sulfone and PS18:0/20:4, glutamate, phenylalanine, serine and aspartic acid for fipronil desulfinyl. Therefore, the higher toxicity of fipronil desulfinyl and fipronil sulfone may be also related to oxidative stress. This study provides implications for risk assessment and toxic mechanism research on fipronil and its metabolites.

Enantioselective metabolism of phenylpyrazole insecticides by rat liver microsomal CYP3A1, CYP2E1 and CYP2D2

The stereoselective difference of chiral pesticide enantiomers is an important factor of risk evaluation and the subject has received wide attention. In the present work, enantioselective metabolism of chiral phenylpyrazole insecticides including fipronil, ethiprole and flufiprole in rat liver microsomes was investigated in vitro. The result showed remarkable enantioselectivity for fipronil and ethiprole with the EF values of 0.11-0.58. The metabolite fipronil-sulfone was formed with the degradation of fipronil. R-Ethiprole to S-ethiprole transformation was observed, but not S-ethiprole to R-ethiprole. No enantioselective metabolism was observed for flufiprole with the EF values of 0.49-0.51. The enzymatic assays showed that the inhibition ratio of R-fipronil and S-ethiprole was 1.5-2.1times that of the corresponding enantiomers on CYP2E1 and CYP2D2 activity, leading to the enantioselective metabolism. The result of the homology modeling and molecular docking further revealed that S-fipronil (-7.56 kcal mol^-1) and R-ethiprole (-6.45 kcal mol^-1) performed better binding with CYP2E1 and CYP2D2, respectively. The results provided useful data for the risk evaluation of chiral phenylpyrazole insecticides on ecological safety and human health.

Improving the Screening Analysis of Pesticide Metabolites in Human Biomonitoring by Combining High-Throughput In Vitro Incubation and Automated LC-HRMS Data Processing

There is a current need to monitor human exposure to a large number of pesticides and other chemicals of emerging concern (CECs). This requires screening analysis with high confidence for these compounds and their metabolites in complex matrices, which is hampered by the fact that no reference standards are available for most metabolites. We address this challenge by a high-throughput workflow based on incubation of pesticides (or other CECs) with human liver S9, followed by solid-phase extraction, liquid chromatography-high-resolution mass spectrometry (LC-HRMS) analysis, and automated data processing to generate a database (retention time, precursor m/z, and MS² spectral library) for the annotation in human samples. The metabolite prioritization consists of statistical comparisons and mass defect and m/z range filtering to obtain a subset of probable phase I metabolites, for which molecular formulas and likely metabolic transformation are retrieved. We tested the workflow on 22 pesticides, for which we could determine 91 metabolite molecular formulas which are only partly covered by the literature and/or predicted by in silico metabolization. Our workflow allows for an efficient generation of metabolite reference information, which can be used directly for annotating LC-HRMS data from human samples. A full structure elucidation of individual metabolites can be limited to those being actually present in human samples.

The effects of fipronil exposure on oxidative stress, non-specific immunity, autophagy, and apoptosis in the common carp

The increase in the area treated with the insecticide fipronil has caused concern for aquatic organisms such as fish. Here, we assessed the effect of fipronil on carp indexes of non-specific immunity, oxidative stress, autophagy, and apoptosis following exposure to 0.074 mg/L and 0.185 mg/L of fipronil in the aqueous environment for 1 day, 3 days, 5 days, and 7 days. It was found that glutathione (GSH), malonaldehyde (MDA), and superoxide dismutase (SOD) in gills were significantly reduced (P < 0.05). The increase in exposure time increases the impact on GSH, SOD, and MDA parameters in the liver and intestine. Liver acid phosphatase (ACP), alkaline phosphatase (AKP), and lysozyme (LZM) activity levels increased significantly in the treatment group on the first day after exposure, except for the 0.074 mg/L group of ACP (P < 0.05). The mRNA expression levels of autophagy-related genes ATG12, ATG5, ATG16L, LC3-II, and BECN1 were generally elevated in the liver and intestine during the initial exposure period (P < 0.05), while mTOR was significantly reduced on the first and third days after treatment (P < 0.05). From the results of Western blotting (WB), we can see that the amount of LC3-II was significantly higher than that of LC3-I at 1, 3, and 5 days of exposure (P < 0.05). Furthermore, the apoptosis-related gene Bcl-2 reached its peak in the liver, intestine, and gill on the first day, and caspase3 was significantly downregulated throughout the exposure period (P < 0.05). The results showed that fipronil was potentially harmful to carp and should be used moderately to reduce the damage to aquatic ecosystems. This study complements the mechanism theory of fipronil on fish toxicology and has a certain value for human health risk assessment.

Ameliorative Role of Cerium Oxide Nanoparticles Against Fipronil Impact on Brain Function, Oxidative Stress, and Apoptotic Cascades in Albino Rats

Fipronil (FIP) is an N-phenylpyrazole insecticide that is used extensively in public health and agriculture against a wide range of pests. Exposure to FIP is linked to negative health outcomes in humans and animals including promoting neuronal cell injury, which results in apoptosis through the production of reactive oxygen species (ROS). Therefore, the purpose of the current study was to investigate the neuroprotective effects of cerium oxide nanoparticles (CeNPs) on neuronal dysfunction induced by FIP in albino rats. Male rats were randomly classified into four groups: control, FIP (5 mg/kg bwt), CeNPs (35 mg/kg bwt), and FIP + CeNPs (5 (FIP) + 35 (CeNPs) mg/kg bwt), which were treated orally once daily for 28 consecutive days. Brain antioxidant parameters, histopathology, and mRNA expression of genes related to brain function were evaluated. The results revealed oxidative damage to brain tissues in FIP-treated rats indicated by the elevated levels of malondialdehyde (MDA) and nitric oxide (NO) levels and reduced activities of antioxidant enzymes such as superoxide dismutase (SOD) and glutathione peroxidase (GPx). On the other hand, the FIP’s group that was treated with CeNPs showed decrease in MDA and NO levels and increase in SOD and GPx enzymes activity. Besides, FIP-treated rats showed decreased butyrylcholinesterase (BuChE) activity in comparison to the FIP + CeNPs group. Moreover, FIP caused up-regulation of the expression of neuron-specific enolase (NSE), caspase-3, and glial fibrillary acidic protein (GFAP) but down-regulation of B-cell lymphoma-2 (BCL-2) expression. But the FIP + CeNPs group significantly down-regulated the GFAP, NSE, and caspase-3 and up-regulated the gene expression of BCL-2. Additionally, the FIP-treated group of rats had clear degenerative lesions in brain tissue that was reversed to nearly normal cerebral architecture by the FIP + CeNPs treatment. Immunohistochemical examination of brain tissues of rats-treated with FIP showed abundant ionized calcium-binding adaptor molecule 1 (Iba-1) microglia and caspase-3 and apoptotic cells with nearly negative calbindin and synaptophysin reaction, which were countered by FIP + CeNPs treatment that revealed a critical decrease in caspase-3, Iba-1 reaction with a strong calbindin positive reaction in most of the Purkinje cells and strong synaptophysin reaction in the cerebrum and cerebellum tissues. Based on reported results herein, CeNPs treatment might counteract the neurotoxic effect of FIP pesticide via an antioxidant-mediated mechanism.

The Potential of Systemic Control of Sand Flies Using Fipronil in the Novel Leishmania major (Kinetoplastida: Trypanosomatidae) Reservoirs Meriones tristrami (Rodentia: Muridea) and Meriones crassus (Rodentia: Muridea)

Leishmania major (Yakimoff & Schokhor, 1914), an important causative agent of Old World Cutaneous Leishmaniasis (CL), is transmitted by sand flies among a limited number of gerbilline reservoir-species. We can take advantage of this strong dependency to break the pathogen transmission cycle by using systemic insecticides that render the host toxic to the blood-feeding vector. We evaluated the potential of this approach with two novel reservoir species, incriminated for CL expansion in several sites in the Middle East. Specifically, we evaluated: 1) the residuality of the systemic insecticide fipronil in Meriones tristrami (Thomas, 1892) fed on fipronil-treated baits and 2) the treatments' adulticide effect on sand flies that blood fed on treated and untreated M. tristrami and M. crassus (Sundevall, 1842). We fed M. tristrami with food pellets containing 0.1 g/kg fipronil and used gas chromatograph-mass spectrometery analysis and bioassays to examine its residual toxicity to blood-feeding female sand flies. In M. tristrami, fipronil was rapidly metabolized to fipronil sulfone, found in the blood, urine, and feces for ≥31 d after fipronil admission. The survival of sand flies that blood fed on fipronil-treated M. tristrami and M. crassus was significantly reduced for at least 15 and 9 d respectively, after fipronil admission. These results hold promise for the potential contribution of systemic control approaches to CL integrated management strategies against novel CL (due to L. major) outbreaks in Israel and elsewhere.

An update of the Worldwide Integrated Assessment (WIA) on systemic insecticides. Part 1: new molecules, metabolism, fate, and transport

With the exponential number of published data on neonicotinoids and fipronil during the last decade, an updated review of literature has been conducted in three parts. The present part focuses on gaps of knowledge that have been addressed after publication of the Worldwide Integrated Assessment (WIA) on systemic insecticides in 2015. More specifically, new data on the mode of action and metabolism of neonicotinoids and fipronil, and their toxicity to invertebrates and vertebrates, were obtained. We included the newly detected synergistic effects and/or interactions of these systemic insecticides with other insecticides, fungicides, herbicides, adjuvants, honeybee viruses, and parasites of honeybees. New studies have also investigated the contamination of all environmental compartments (air and dust, soil, water, sediments, and plants) as well as bees and apicultural products, food and beverages, and the exposure of invertebrates and vertebrates to such contaminants. Finally, we review new publications on remediation of neonicotinoids and fipronil, especially in water systems. Conclusions of the previous WIA in 2015 are reinforced; neonicotinoids and fipronil represent a major threat worldwide for biodiversity, ecosystems, and all the services the latter provide.

Occurrence of the insecticide fipronil and its degradates in indoor dust from South, Central, and North China

No known data are available regarding the occurrence of fipronil (FP) in indoor dust in China, despite the fact that it is an emerging insecticide that is used extensively. In this study, FP and its derivatives (FPs), including fipronil sulfone (FP-SFO), fipronil sulfide, fipronil desulfinyl, and fipronil amide, were determined in indoor dust samples (n = 436) collected from three different cities in China between 2016 and 2019, namely Shenzhen (February and September 2019), Wuhan (October 2016, October 2018, and August 2019), and Taiyuan (October 2016), located in south, central, and north China, respectively. FP and FP-SFO were the major target analytes detected in all dust samples, accounting for approximately 68.6-90.1% of the cumulative concentration of FPs (ΣFPs). The ΣFPs values for the dust samples ranged from not detected (ND) to 33.6 μg/g (median ± median absolute deviation [MAD]: 7.12 ± 6.44 ng/g), with a detection frequency of 95.6%. The median value of the ΣFPs of the dust samples collected from Shenzhen (22.6 ± 15.6 ng/g) was higher than that found in the dust samples collected in Taiyuan 2016 (1.87 ± 1.65 ng/g) and Wuhan (6.43 ± 5.62 ng/g). Significantly higher ΣFPs were observed in the dust samples collected in urban areas than in the rural areas of Taiyuan and Wuhan. Furthermore, an increasing trend of FP (from 2016 to 2018) in the rural areas of Wuhan, and a seasonal variation (summer > autumn) in FP, FP-SFO, and ΣFPs in the dust samples from urban areas of Wuhan were observed. The estimated daily intake of FPs via dust ingestion for people in Shenzhen was approximately 12 times higher than in Taiyuan based on the samples analyzed. This is the first study to describe the occurrence and spatiotemporal variations of FPs in indoor dust in China.

Spatial variation of fipronil and its derivatives in tap water and ground water from China and the fate of them during drinking water treatment in Wuhan, central China

Fipronil (FP) is an emerging insecticide, however, its occurrence in drinking water and source water is limited. In this work, a total of 789 tap water and 95 ground water samples were collected from China in June 2019 in order to assess occurrence of FP and its derivatives (FPs). FPs were also analyzed in source, treated (n = 10, July), and tap water samples (n = 81, July and October 2019) originating from the central Yangtze River and its tributary, the Hanshui River in Wuhan. The sum concentrations of FPs (ΣFPs) in the tap water in China ranged from not detected (ND) to 5.07 (median: 0.03 ng/L), with FP found in 55.3% of the samples, and other targets ≤ 50.0%. Significant regional variations in the ΣFPs values were found between East China (75th percentile: 0.31 ng/L) and Northwest China (0.04), as well as between East China and North China (0.04). Similar ΣFPs values were found for ground water and tap water. The estimated daily intake of ΣFPs via water ingestion was below 200 pg/kg-bw/day for all age groups and was lower than the reference dose for FP (0.2 μg/kg-bw/day). Additionally, FPs were found in all of the source water samples collected in Wuhan with concentrations in the range of 0.84-2.72 ng/L for ΣFPs (median: 2.39). Most of these FPs were removed during water treatment. Higher concentration of ΣFPs in tap water was observed in July (median: 0.04 ng/L) compared to that in October (ND). This is the first study on the occurrence of FPs in the Yangtze River, the fate of FPs during the tap water treatment, and the regional distribution of FPs in tap water from China.

Fipronil Tablets: Development and Pharmacokinetic Profile in Beagle Dogs

Increased human-pet interactions have led to concerns related to the prevention and treatment of ectoparasite infestations. Fipronil (FIP) is a widely used ectoparasiticide in veterinary medicine available for topical administration; however, its use may cause damage to the owners and the environment. The aim of the study was to develop immediate-release tablets of FIP, as well as to determine its pharmacokinetic properties after oral administration in beagle dogs. The prepared FIP tablets were evaluated for pre-compression (angle of repose, speed flow, and Carr's index) and post-compression (weight variation, friability, thickness, hardness, disintegration time, and dissolution rate) parameters. Orally administered FIP at a dose of 2 mg/kg was rapidly absorbed with C_máx of 3.13 ± 1.39 μg/mL at 1.83 ± 0.40 h post treatment (P.T.) and metabolized with 1.27 ± 1.04 μg/mL at 2.33 ± 0.82 h P.T. for fipronil sulfone (SULF) (the primary metabolite). The elimination of FIP and SULF occurred slowly and had maintained quantifiable plasma levels in the blood for up to 28 days P.T. The goal of the study is aligned with the concept of One Health, which aims to collaboratively achieve the best health for people, animals, and the environment. Therefore, the use of FIP tablets for the control of ectoparasites in dogs may be a safer alternative for owners and the environment.

A first approach using micellar electrokinetic capillary chromatography for the determination of fipronil and fipronil-sulfone in eggs

Fipronil is an insecticide that is not approved in the European Union in food. In 2017, fipronil was involved in a European health alert due to its presence in fresh hen eggs because of an illicit use in poultry farms, so reliable methods are needed to determine fipronil and its main metabolites in these matrixes. In this work, we report the first approach to the study of fipronil and two metabolites, fipronil-sulfone and fipronil-sulfide by CE. MEKC mode was employed using a solution of 50 mM ammonium perfluorooctanoate pH 9.0 with 10% (v/v) methanol as background electrolyte. The proposed method was combined with a simple sample treatment based on salting-out assisted LLE (SALLE) using acetonitrile as extraction solvent and ammonium sulfate as salt. The SALLE-MEKC-UV method allowed the simultaneous quantification of fipronil and fipronil-sulfone. Validation parameters yielded satisfactory results, with precision, expressed as relative SD, below 14% and recoveries higher than 83%. Limits of detection were 90 µg/kg for fipronil and 150 µg/kg for fipronil-sulfone, so in terms of sensitivity further studies of sample treatments allowing extra preconcentration or the use of more sensitive detection, such as MS, would be needed.

In vitro biotransformation of pharmaceuticals and pesticides by trout liver S9 in the presence and absence of carbamazepine

The aim of the present study was to develop (i) a technique for identifying metabolites of organic contaminants by using an in vitro system of trout S9 and liquid chromatography-high-resolution mass spectrometry-based identification method and (ii) to apply this technique to identify the interactive potential of carbamazepine on the formation rate of other metabolites. The pharmaceuticals carbamazepine and propranolol and the pesticides azoxystrobin, diazinon, and fipronil were selected as test contaminants. As a result, a total of ten metabolites were identified for the five parent substances, six of which were confirmed using reference standards. Metabolic reactions included hydroxylation, epoxidation, S-oxidation, and dealkylation. The metabolic transformation rate ranged from 0.2 to 3.5 pmol/mg protein/min/μmol substrate. In the binary exposure experiment with increasing carbamazepine concentration, the formation rates of diazinon and fipronil metabolites (MDI2 and MFP2, respectively) increased, while formation of metabolites of propranolol and azoxystrobin (MPR1, MPR2, MPR3, and MAZ1) slowed down. Meanwhile, S9 pre-exposed to carbamazepine produced diazoxon, a toxic metabolite of diazinon, and pyrimidinol, a less toxic metabolite, more rapidly. These results suggest that carbamazepine, a perennial environmental pollutant, might modulate the toxicity of other substances such as diazinon but further in vivo studies are needed.

Fate of UV filter Ethylhexyl methoxycinnamate in rat model and human urine: Metabolism, exposure and demographic associations

Ethylhexyl methoxycinnamate (EHMC) is one of the most frequently used UV filters in sunscreens and other cosmetic products. Its ubiquitous presence in various environmental matrices and its endocrine disrupting properties have been widely reported. However, we know little about the effect of EHMC exposure on humans, mainly due to its fast metabolism. In this study, urine and plasma of EHMC-dosed rats were analysed to identify its major metabolites. Five metabolites were found, with four firstly reported. Two metabolites were putatively identified as 4-methoxycinnamic acid (4-MCA) and 4'-methoxyacetophenone (4'-MAP). Quantitative results revealed that their excretion concentrations were much higher than the parent compound. Because of these high concentrations, for the human biomonitoring study, EHMC and these two metabolites were detected simultaneously in urine samples from Chinese children and adolescents. The results indicated wide exposure to EHMC, 4-MCA and 4'-MAP. The correlation between urinary concentration of EHMC and 4-MCA as well as 4-MCA and 4'-MAP provided important clues as to the sources and metabolic pathways among these three compounds. Several demographic factors were also assessed with the exposure level. As the first human exposure study of EHMC in a Chinese population, this report would help to establish an exposure database facilitating health risk assessment of EHMC.

Bioaccumulation, biotransformation and toxic effect of fipronil in Escherichia coli

Fipronil is a highly effective, broad-spectrum insecticide used to control pests, globally. The increased usage has led to contamination of soil, water, fruits, and vegetables. The wide and frequent usage of fipronil across the globe calls for attention regarding risk assessment of undesirable effects on non-target microorganisms. In this context, the present study was carried to understand the impact of fipronil on non-pathogenic Escherichia coli. The non-pathogenic E. coli are important commensal of the intestinal tract of humans and animals and are also indicator organisms in the environment. Our study indicates that exposure of E. coli to fipronil (100 μM concentration) leads to significant reactive oxygen species production, loss of membrane potential and viability. Further, we have witnessed the bioaccumulation and biotransformation of fipronil by E. coli at non-lethal concentrations. The bio-transformed products (fipronil sulfone and fipronil sulfide) are also the major metabolites (along with amide) reported in the feces of the mammals when exposed to fipronil. Thus, there is a possibility that the gut E. coli might play a role in the degradation and thereby removal of fipronil. In addition, the bioaccumulation of fipronil in bacteria is of concern and need to be further explored because it can lead to biomagnification in the higher trophic level and can disturb the ecological balance. In our knowledge, this is the first report on the determination of fipronil and its metabolites in bacteria through GC-MS/MS.

Inflammatory and oxidative injury is induced in cardiac and pulmonary tissue following fipronil exposure in Japanese quail: mRNA expression of the genes encoding interleukin 6, nuclear factor kappa B, and tumor necrosis factor-alpha

The phenylpyrazole insecticide, fipronil, isused for the eradication of insects in agriculture, which also exposes various non-target groups such as birds and animals. Our aim was to assess the cardiac and pulmonary consequences of sub-acute administration of fipronil (¹∕₅ LD₅₀; 2.26 mg/kg) in the Japanese quail for fifteen days and to determine the tissue recovery over a period of 60 days. Fipronil exposure led to a significant decrease in the body weight of the treated birds. Its exposure also induced cardiac and pulmonary damage of varying degrees. Fipronil increased the lipid peroxide (LPO) and nitric oxide (NO) contents as well as indices of tissue injury in the serum of exposed birds. Furthermore, it decreased the antioxidant indices in both the organs. Most of these changes gradually reversed and the histological changes, particularly of the heart, reversed completely by day-60 of recovery. Furthermore, alterations in the mRNA gene expressions of Nuclear factor kappa B (NF-κB), Interleukin 6 (IL-6), and Tumor necrosis factor-alpha (TNF-α) were monitored by quantitative polymerase chain reaction (RT-PCR). In both the tissues, a significant up-regulation of the transcripts was recorded after fipronil administration, which was reversed during the recovery period in the heart tissue except for TNF-α, while the transcripts in the lung tissue declined non-significantly. This study showed that the exposure of Japanese quail to fipronil has a profound negative impact on heart and lung including oxidative injury and tissue inflammation. Fipronil can induce the activity of NF-κB inflammatory -signaling pathway that play a role in the associated tissue inflammation. Although most of the cardiac changes could be reversed after a recovery period of sixty days, the pulmonary changes did not reverse much.

In vitro inhibition of human CYP2D6 by the chiral pesticide fipronil and its metabolite fipronil sulfone: Prediction of pesticide-drug interactions

Fipronil is a chiral insecticide employed worldwide in crops, control of public hygiene and control of veterinary pests. Humans can be exposed to fipronil through occupational, food, and environmental contamination. Therefore, the risk assessment of fipronil in humans is important to protect human health. Fipronil sulfone is the major metabolite formed during fipronil metabolism by humans. Since the CYP450 enzymes are the main ones involved in drug metabolism, the evaluation of their inhibition by fipronil and its main metabolite is important to predict drug-pesticide interactions. The aim of this work was to investigate the inhibition effects of rac-fipronil, S-fipronil, R-fipronil and fipronil sulfone on the main human CYP450 isoforms. The results showed that CYP2D6 is the only CYP450 isoform inhibited by these xenobiotics. In addition, no enantioselective differences were observed in the inhibition of CYP450 isoforms by fipronil and its individuals' enantiomers. Rac-fipronil, S-fipronil and R-fipronil are moderate CYP2D6 inhibitors showing a competitive inhibition profile. On the other hand, the metabolite fipronil sulfone showed to be a strong inhibitor of CYP2D6 also by competitive inhibition. These results highlight the importance of metabolite evaluation on pesticide safety since the metabolism of fipronil into fipronil sulfone increases the risk of pesticide-drug interactions for drugs metabolized by CYP2D6.

Investigation of etoxazole metabolites in citrus, soil and earthworms by ultra-performance liquid chromatography with time-of-flight mass spectrometry

Etoxazole is a newly registered and widely used acaricide. However, its metabolites were not fully understood and might exhibit similar or even higher toxicity than parent compound. Therefore, in this study, the metabolites of etoxazole in citrus, soil and earthworms were firstly identified by an ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-QTOF/MS). Four potential metabolites in citrus, 11 in soil, and 8 in earthworms were determined. These metabolites were then further structural elucidated based on the fragment pathways, and accurate mass measurement. The distributions of etoxazole and its main metabolites (M1, M2, M3, M4 and M5) which were identified as the dehydrogenation, hydrolysis, oxidation products of etoxazole (M0) were also monitored in citrus, soil and earthworms at different exposure periods. The 45 days exposure experiment showed that M0 gradually decreased in citrus and soil samples by 80% and 28% of the initial amounts, respectively. In earthworm samples, M0 accumulated in the bodies of the worms during 24 days exposure and then decreased with time. The dissipation rate of etoxazole were citrus > earthworms > soil. Concentrations of M1 and M3 in soil were found continuously increased with time during the experimental period. Moreover, the persistence of M1 in earthworm samples was also observed. Great attention should be paid to these two compounds due to their potential risks to both environmental and human health.

Induction of Amyloid-β42 Production by Fipronil and Other Pyrazole Insecticides

Generation of amyloid-β peptides (Aβs) by proteolytic cleavage of the amyloid-β protein precursor (AβPP), especially increased production of Aβ42/Aβ43 over Aβ40, and their aggregation as oligomers and plaques, represent a characteristic feature of Alzheimer's disease (AD). In familial AD (FAD), altered Aβ production originates from specific mutations of AβPP or presenilins 1/2 (PS1/PS2), the catalytic subunits of γ-secretase. In sporadic AD, the origin of altered production of Aβs remains unknown. We hypothesize that the 'human chemical exposome' contains products able to favor the production of Aβ42/Aβ43 over Aβ40 and shorter Aβs. To detect such products, we screened a library of 3500 + compounds in a cell-based assay for enhanced Aβ42/Aβ43 production. Nine pyrazole insecticides were found to induce a β- and γ-secretase-dependent, 3-10-fold increase in the production of extracellular Aβ42 in various cell lines and neurons differentiated from induced pluripotent stem cells derived from healthy and FAD patients. Immunoprecipitation/mass spectrometry analyses showed increased production of Aβs cleaved at positions 42/43, and reduced production of peptides cleaved at positions 38 and shorter. Strongly supporting a direct effect on γ-secretase activity, pyrazoles shifted the cleavage pattern of another γ-secretase substrate, alcadeinα, and shifted the cleavage of AβPP by highly purified γ-secretase toward Aβ42/Aβ43. Focusing on fipronil, we showed that some of its metabolites, in particular the persistent fipronil sulfone, also favor the production of Aβ42/Aβ43 in both cell-based and cell-free systems. Fipronil administered orally to mice and rats is known to be metabolized rapidly, mostly to fipronil sulfone, which stably accumulates in adipose tissue and brain. In conclusion, several widely used pyrazole insecticides enhance the production of toxic, aggregation prone Aβ42/Aβ43 peptides, suggesting the possible existence of environmental "Alzheimerogens" which may contribute to the initiation and propagation of the amyloidogenic process in sporadic AD.

Occurrence of Fipronil in residential house dust in the presence and absence of pets: a hint for a comprehensive toxicological assessment

The presence of the insecticide Fipronil and its main products of toxicological relevance, namely Sulfone and Desulfinyl, was assessed in 161 residential house dust samples in the absence (N = 101) and presence (N = 60) of cats and dogs in Italy. High-resolution mass spectrometry analysis revealed a significant difference (p < 0.001) in the dust contamination in the presence of pets (median: 467 vs. 24 ng/g dry weight), even if the highest value was found in the absence of pets (82,069 vs. 67,799 ng/g dry weight). Fipronil intake estimates from dust in toddlers, computed according to US-EPA and EU-ECHA guidelines, ranged from 333 to 556 and from 20 to 34 ng/kg per day for acute and chronic scenario, respectively. Dust seemed not able itself to lead to Fipronil overexposure with respect to acute and chronic toxicity health-based guidance values. Kittens were potentially overexposed to Fipronil under both acute (26,076 ng/kg per day) and chronic (1,633 ng/kg per day) scenarios. The mild symptomatology associated with acute intoxication could possibly determine case underreporting within pharmacosurveillance schemes. Its administration was estimated in 7.3-9.7 tons per year. Such a range suggests its prudent use under strict veterinary control to prevent pest resistance and ecotoxicological outcomes.

Mass defect filtering for suspect screening of halogenated environmental chemicals: A case study of chlorinated organophosphate flame retardants

RATIONALE

Organophosphate flame retardants (OPFRs) are a class of flame retardants widely found in environmental and biological matrices that have been extensively studied due to their adverse health effects in humans. OPFRs are loosely bound chemicals that can detach from treated products and be released into indoor and outdoor environments, where they have the potential to further undergo transformation and degradation processes, in particular the chlorinated OPFRs (Cl-PFRs). Their detection remains a moving target for analysts, and traditional targeted mass spectrometry methods are suitable only for those compounds with authentic standards.

METHODS

Mass defect filter (MDF) is a strategy to filter molecular features using thresholds applied to the mass defect value of a target ion or molecular feature of interest. We have developed an MDF strategy for the detection and tentative identification of twelve potential Cl-PFR transformation products in a study mixture of six known Cl-PFRs using MS/MS data acquired on a high-resolution mass spectrometer. Most compounds in the Cl-PFRs family share a ClO₄ P group as a core structure, of which modification results in a significant shift in the exact masses of the resulting compounds but show only a minimal shift in their mass defects. Subsequently, the MDF strategy was employed to tentatively identify Cl-PFRs retrospectively in six human urine samples that had previously been analyzed.

RESULTS

MDF in combination with product ion filtering for the characteristic [H₂ O₃ P]⁺ and [H₄ O₄ P]⁺ ions and neutral loss filtering for the characteristic C_n H_2n-x Cl_x group resulted in revealing suspects and homologues in the Cl-PFRs family. Furthermore, the MDF of the product ions detected additional Cl-PFR-related compounds that differed significantly in the exact masses of both precursor and product ions but had minimal shift in the mass defects of product ions. The mass defect of one or more common product ions helped to detect a few Cl-PFR analogs that had not been identified by MDF of the core structure precursor ion.

CONCLUSIONS

MDF helped to detect some Cl-PFRs present in lower concentrations, which went undetected without data filters. MDF also helped to detect chromatographic peaks for Cl-PFR homologues that are likely structural analogs that resulted from impurities and/or derivatives and transformation products. The methodology was applied to demonstrate and tentatively detect known and suspect Cl-PFRs in human urine samples retrospectively.

The Terminalia laxiflora modulates the neurotoxicity induced by fipronil in male albino rats

The extensive use of fipronil (FPN) may trigger hazards to more than insects. The present investigation was carried out to evaluate the abrogating role of Terminalia laxiflora (TL) methanol extract (TLE) against the neurotoxic effects provoked by FPN. Fourty male albino rats were assigned into four equal groups. The first group served as control, the second one was orally administered FPN (10.5 mg/kg BW), the third group was given combination of FPN and TLE) (100 mg/kg BW), and the fourth one was orally given TLE. Our findings highlighted the efficacy of TLE as a neuroprotectant through a significant reduction in malondialdehyde (MDA) content by 25.8%, elevations of the reduced glutathione (GSH) level, catalase (CAT,) and superoxide dismutase (SOD) activities by 30.9, 41.2, and 48.2% respectively. Consequently, the relative mRNA levels of both Bax and caspase-3 were down-regulated by 40.54% and caspase-3 by 30.35% compared with the control group. Moreover, restoration of the pathological tissue injuries were detected. In conclusion, TLE proved to be a potent neuroprotective agent against the FPN-induced toxicity.