Phenylpyrazole Insecticide Research Articles

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.

RDL A301S alone does not confer high levels of resistance to cyclodiene organochlorine or phenyl pyrazole insecticides in Plutella xylostella

Mutations in the GABA-gated chloride channel are associated with resistance to cyclodiene organochlorine and phenyl pyrazole insecticides. The best characterised of these is A301S, which was initially identified in a Dieldrin resistant strain of Drosophila melanogaster. The orthologous mutation has been found in a variety of different crop pests including the diamond back moth Plutella xylostella. However, the contribution of this mutation to resistance in this species remains unclear. We have used the CRISPR/Cas9 system in order to edit Plutella xylostella PxGABARalpha1 to Serine at the 301 orthologous position (282 in PxGABARalpha1) in an insecticide sensitive strain isolated from Vero Beach (VB) USA. In this edited line, no high level of resistance is conferred to Dieldrin, Endosulfan or Fipronil, rather only a subtle shift in sensitivity which could not confer commercially important resistance. We conclude that the high level of commercial resistance to cyclodiene organochlorine and phenyl pyrazole insecticides observed in some field isolates of Plutella xylostella cannot arise from A282S in PxGABARalpha1 alone.

Nematicidal activity of fipronil against Pratylenchus zeae in sugarcane

Abstract No nematicide has been registered for controlling plant-parasitic nematodes in sugarcane in Japan. Greenhouse and field experiments were conducted to evaluate the efficacy of the phenylpyrazole insecticide fipronil (0.3–0.45 kg a.i./ha) against the root-lesion nematode, Pratylenchus zeae, which is an important plant-parasitic nematode species associated with sugarcane (Saccharum spp. hybrids) in Okinawa, Japan. Both experiments showed a reduction of P. zeae population densities in sugarcane roots to 27 to 56% of the non-treated control after 7 wk in the greenhouse experiment and 3 months in the field experiment (two trials). In contrast, P. zeae population densities in soil were not reduced by the fipronil treatment. At harvest, sugarcane yields in the field experiment were significantly increased by 6 to 8% in the fipronil treated plots compared to the non-treated control. The data showed that fipronil reduced numbers of P. zeae in sugarcane roots at the early stage of sugarcane seedling growth resulting in increased sugarcane yields. This is the first report of nematicidal activity of fipronil against P. zeae under field conditions.

Butylene fipronil induces apoptosis in PC12 murine nervous cells via activation of p16-CDK4/6-cyclin D1 and mitochondrial apoptotic pathway.

Butylene fipronil (BFPN) is a phenylpyrazole insecticide, acting at the γ-aminobutyric acid (GABA) receptor. Here, we show that BFPN inducedcytotoxicity in PC12 murinenervous cells, which lacks GABA receptor. Treatment with BFPN for 48 hours significantly enhanced G0/G1 arrest and induced apoptosis. BFPN decreased the expression of cyclin-dependent kinase (CDK4 and CDK6) and increased P16 and cyclin D1. Simultaneously, Bcl-2 protein was declined while Bax and cytochrome c were significantly enhanced in BFPN-treated groups. The apoptotic enzymes caspase-8, -9, and -3 were also activated by BFPN. Furthermore, treatment with BFPN significantly stimulated reactive oxygen species (ROS) generation, and pretreatment with antioxidant diphenyleneiodonium, substantially reduced cell death. Overall, these results suggest that BFPN is effective to induce G0/G1-phase arrest and apoptosis in PC12 murine nervous cell. Stimulating ROS generation and activation of P16-CDK4/6-cyclin D1 and mitochondrial apoptotic pathway may participate in the cytotoxicity of BFPN.

Advance electrochemical oxidation of fipronil contaminated wastewater by graphite anodes and sorbent nano hydroxyapatite

ABSTRACTDegradation of C12H4Cl2F6N4OS phenylpyrazole insecticide (Fipronil) by advance electrochemical oxidation in aqueous water solution was studied. The process efficiency was figured based on the COD, chloride, and fluoride reduction from fipronil. Further, we tried to highlight the importance of nano-hydroxyapatite (n-Hap) as a cost-effective nano sorbent for removal of fluoride from fipronil. From the advance electrochemical oxidation experiment, it was found that the COD removal was 79%, chloride 52%, and fluoride 80%. The intermediate of fipronil compounds was examined by GC-MS. The final results conclude that advance electrochemical oxidation process was effective for removal of fipronil synthetic wastewater.

Fiprole insecticide resistance of Laodelphax striatellus: electrophysiological and molecular docking characterization of A2'N RDL GABA receptors.

Phenylpyrazole (fiprole) insecticides, including ethiprole, fipronil and flufiprole with excellent activity on rice planthoppers, are very important in Asia but resistance has developed after decades of use. The molecular mechanism of fipronil- but not ethiprole-resistance has been previously studied in rice planthoppers. In our laboratory, a small brown planthopper Laodelphax striatellus strain with ethiprole-resistance was cultured and the molecular mechanisms of ethiprole resistance and of cross-resistance among fiprole insecticides were investigated. Ethiprole-resistant L. striatellus has >5000-fold resistance compared to the susceptible strain, and exhibits around 200-fold cross-resistance with fipronil and flufiprole. RDL genes were isolated from susceptible and ethiprole-resistant L. striatellus and expressed in Xenopus oocytes. Electrophysiological studies showed fiprole insecticides inhibited γ-aminobutyric acid (GABA)-induced current with IC50 = 0.1-1.4 μM to LsRDL-S homomers. In LsRDL-R with A2'N mutation, only 1-13% inhibition was observed on treatment with 10 μM ethiprole, fipronil or flufiprole. Homology models indicate A2'N mutation allows crosslinking hydrogen bonding between Asn sidechains at the 2' position around the channel pore, blocking insecticides from interacting near this position. In contrast, insecticides showed favorable binding near A2' in wild-type L. striatellus. Cross-resistance is increasing for fiprole insecticides in L. striatellus and management strategies are necessary to minimize resistance. © 2018 Society of Chemical Industry.

Thymoquinone and diallyl sulfide protect against fipronil-induced oxidative injury in rats.

Fipronil (FPN) is a phenylpyrazole insecticide, widely used for agricultural and veterinary activities. Early reports indicated that FIP organ toxicity is primarily mediated by the induction of oxidative stress. Both thymoquinone (TQ) and diallyl sulfide (DAS) are natural antioxidants with established health benefits. This study investigated the potential ameliorative effects of DAS and TQ against FPN-induced toxicity in rats. Thirty-two male Wistar rats (150-180g) were randomized into four treatment groups, receiving (I) saline, (II) FPN (10mg/kg bw), (III) FPN with DAS (200mg/kg bw), and (IV) FPN with TQ (10mg/kg bw). All treatments were administered once daily for 28days. The results showed that compared to the control rats, FPN-treated rats had significantly increased (p < 0.05) serum levels of uric acid, urea, creatinine, cholesterol, aspartate transferase, alanine transferase, alkaline phosphatase, lactate dehydrogenase, and γ-glutamyl transferase. Moreover, FPN significantly reduced (p < 0.05) the serum levels of total proteins, albumin, and triglycerides. In addition, compared with the control group, FPN-treated rats had significantly elevated (p < 0.05) malondialdehyde and nitric oxide levels, as well as significantly reduced glutathione concentration and activities of glutathione peroxidase, superoxide dismutase, and catalase enzymes in the hepatic, renal, and brain tissues. Cotreatment with DAS or TQ significantly ameliorated (p < 0.05) the FPN-induced alterations in all the previously mentioned parameters with more frequent restoration of normal control ranges in the TQ group. In conclusion, both DAS and TQ alleviated the oxidative injury of FPN, probably by enhancing tissue antioxidant defenses.

Interactions of Fipronil within Fish and Insects: Experimental and Molecular Modeling Studies.

Fipronil is an efficient phenylpyrazole insecticide that acts on insect γ-aminobutyric acid (GABA) receptors (GABARs) and has low toxicity to mammals but high toxicity to nontarget organisms such as fish. To develop novel efficient low-toxicity insecticides, it is necessary to determine the detailed toxic mechanism at the molecular target level. In this work, methods including affinity chromatography, fluorescent-labeled binding assays, and molecular modeling were integrated to explore the binding of fipronil to GABARs in fish ( Aristichthys nobilis) and insects ( Musca domestica). Affinity chromatography revealed that fipronil acts on two different subunits of GABARs in fish and M. domestica. Moreover, fluorescence assays revealed that fipronil exhibits similar affinity to the two GABARs. The Kd and Bmax of fipronil binding to the A. nobilis GABAR were 346 ± 6 nmol/L and 40.6 ± 3.5 pmol/mg of protein, respectively. And the Kd and Bmax of fipronil binding to the GABAR in M. domestica brain were 109 ± 9 nM and 21.3 ± 2.5 pmol/mg of protein, respectively. In addition, similar fipronil binding positions but different binding modes were observed in docking studies with Brachydanio rerio var. and M. domestica GABARs. These findings indicated similar interactions of fipronil with fish and insects, leading to high toxicity. The different binding features of fipronil between the two species might be helpful for the design and development of highly selective insecticides with low toxicity to fish.

Protective effects of rosuvastatin and vitamin E against fipronil-mediated oxidative damage and apoptosis in rat liver and kidney

Fipronil (FPN) is a phenylpyrazole insecticide that is extensively used in agriculture and veterinary applications. However, FPN is also a potent environmental toxicant to animals and humans. Therefore, the current study aimed to investigate the protective role of rosuvastatin (ROSU) and vitamin E (Vit E) against FPN-induced hepatorenal toxicity in albino rats. Seven groups with eight rats each were used for this purpose; these groups included the control vehicle group that received corn oil, the Vit E group (1000 mg/kg, orally), the ROSU group (10 mg/kg, orally), the FPN group (20 mg/kg, orally), the FPN-ROSU group, the FPN-Vit E group, and the FPN-Vit E-ROSU group. The results revealed that FPN significantly increased serum levels of alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, lactate dehydrogenase, cholesterol, urea, and creatinine. In addition, there were substantial increases in the liver and kidney contents of malondialdehyde and nitric oxide, along with significant decreases in glutathione, superoxide dismutase, catalase, and glutathione peroxidase. FPN also caused histological changes and increased the expression of caspase-3 in the liver and kidney tissues. However, administration of ROSU and Vit E alone or in combination ameliorated the FPN-induced oxidative damage and apoptosis, possibly through their antioxidant properties.

Reproductive and neurobehavioral effects of maternal exposure to ethiprole in F1 -generation mice.

Few published studies are reported for neurobehavioral toxicity of the phenylpyrazole insecticide ethiprole in mammals. This study was designed to evaluate the reproductive and neurobehavioral effects of maternal exposure to ethiprole in mice. Ethiprole was given in the diet to provide levels of 0 (control), 0.0002, 0.001, and 0.005% during the gestation and lactation periods. Selected reproductive and neurobehavioral parameters were measured in the F1 generation. No adverse effect of ethiprole was observed in litter size, litter weight, or sex ratio at birth. The average body weight of male and female offspring was increased significantly in treatment groups at postnatal day (PND) 21. With respect to behavioral developmental parameters, the time of olfactory orientation on PND 14 of male offspring was accelerated significantly in the high-dose group. For movement activity of exploratory behavior of female offspring in the F1 generation, number of horizontal activities increased significantly in the high-dose group and the average speed declined significantly in all treatment groups. After weaning, the rearing time and the average time of rearing lengthened in a significant dose-related trend in adult males and females of the F1 generation. Spontaneous behavior examination indicated that total distance and rearing time increased in the high-dose group, and number of horizontal activities and movement time decreased in a significant dose-related trend through 120 min in the F1 -generation females. The high-dose level of ethiprole in the present study produced several adverse effects in neurobehavioral parameters after weaning without administration in mice.

Insecticidal spectrum of fluralaner to agricultural and sanitary pests

Fluralaner, as an isoxazoline insecticide, has been developed as antiparasitic (namely Bravecto®) with selective toxicity for insect versus mammals. Even though the toxic effect of fluralaner to several insects have been already examined, but also more agricultural and sanitary insects should be tested before it could be used widely. Four insects, including two agricultural insects, one sanitary insect and one stored product insect were tested in the present study. Compared to the broad-spectrum and high activity insecticide of fipronil, fluralaner showed mostly higher activity to tested pests, Chilo suppressalis, Tribolium castaneum, Spodoptera litura except Blattella germanica with topical application. Through summarizing and analyzing various published data, we concluded that, to date, the toxic activity of fluralaner to 19 insects from 11 orders were already examined, and fluralaner displayed excellent activity. Compared to fipronil, fluralaner mostly shows more excellent activity to tested insect with maximal 1.67×104-fold difference so much. In the present study, the toxicity activity of fluralaner was compared to the broad-spectrum phenylpyrazole insecticide fipronil to tested insect pests and the results exhibited that fluralaner would be a novel alternative insecticide with broad insecticidal spectrum and be widely used in more other areas not only as veterinary drug.

Reproductive and Neurobehavioral Effects of Ethiprole Administered to Mice in the Diet.

Few studies were found for neurobehavioral toxicity of the phenylpyrazole insecticide ethiprole in mammals. This study was designed to evaluate the reproductive and neurobehavioral effects of ethiprole exposure in mice. Ethiprole was given in the diet to provide levels of 0 (control), 0.0003, 0.0009, and 0.0027% from 5 weeks of age of the F0 generation to 11 weeks of age of the F1 generation in mice. Selected reproductive and neurobehavioral parameters were measured. Movement time increased with a significant dose-related trend, and frequencies of mice with urination increased in the high-dose group of adult males in the F0 generation. The average body weight of male and female offspring increased significantly in treatment groups at postnatal days (PNDs) 7, 14, and 21. Surface righting on PND 7 of male offspring was accelerated in a significant dose-related trend. In female offspring, olfactory orientation on PND 14 was accelerated significantly on the route of higher-dose groups, and time of all treatment groups. Total distance, movement time, average speed, and average time of movement significantly decreased, and frequencies of mice with urination increased in a significant dose-related trend in male offspring in the F1 generation. Longitudinal patterns of spontaneous behavior differed in the number of horizontal activities, movement time, and average speed in treatment groups in males. The number of horizontal activities of females decreased in a significant dose-related trend through 120 min. The dose levels of ethiprole in the present study produced several adverse effects in neurobehavioral parameters in mice. Birth Defects Research 109:1568-1585, 2017. © 2017 Wiley Periodicals, Inc.

Ingestion Toxicity of Fipronil on Reticulitermes speratus kyushuensis (Isoptera: Rhinotermitidae) and Its Applicability as A Termite Bait

Historical wooden buildings in Korea are being damaged by Reticulitermes speratus kyushuensis Morimoto, a type of subterranean termite, and the scale of this damage is increasing gradually because of global warming. This study evaluated the ingestion toxicity of the phenylpyrazole insecticide fipronil to R. s. kyushuensis and its applicability as termite bait with the aim of controlling termite colonies more efficiently. An ingestion toxicity assessment was conducted and the LT50 was determined to be 4.43 day at concentrations of 10 ppm, indicating a slow-acting effect; therefore, 10 ppm was selected as an appropriate dose. A field applicability assessment was conducted in which the number of foraging workers and the rate at which the termites fed decreased 2 weeks after baiting, and termite colony activity was no longer apparent after 4 weeks demonstrating the efficacy of fipronil at eliminating colonies. Taken together, these results, indicate that low-dose fipronil eliminated R. s. kyushuensis colonies faster than insect growth regulators; therefore, it is expected to be useful when trying to conserve historical wooden buildings.

Involvement of vimentin in neurite outgrowth damage induced by fipronil in SH-SY5Y cells

Fipronil, a phenylpyrazole insecticide, is more selective in its potency towards insects than humans and is thus commonly used. In this study, we demonstrated that exposure to fipronil may pose a human health risk. We observed in vitro the shortening of neurite outgrowths of SH-SY5Y neuroblastoma cells upon treatment with fipronil, even at a non-cytotoxic concentration. Fipronil induced apoptosis involving caspase-6, which is an apoptotic effector highly implicated in neurodegenerative diseases. Moreover, at a concentration that did not induce apoptosis, mitochondrial dysfunction and autophagic vacuole formation were detected. Interestingly using proteomics, we identified vimentin to be dramatically expressed by SH-SY5Y cells as a response to fipronil treatment. Not only did the expression of total vimentin increase, different isoforms were observed, indicating alterations in post-translational modifications. Vimentin was localized at the neurite outgrowth, possibly to repair the damage in cellular structure. However at high concentrations of fipronil, vimentin was found in less defined fibrils, in bridge-like formation, and dense surrounding vacuoles. In all, our results indicate that vimentin plays an important role in fipronil-induced neurotoxicity in SH-SY5Y cells.

Cross-resistance to three phenylpyrazole insecticides and A2'N mutation detection of GABA receptor subunit in fipronil-resistant Laodelphax striatellus (Hemiptera: Delphacidae).

Laodelphax striatellus (Fallén) is an important pest of crops in East Asia. Over the past decade, phenylpyrazole insecticides, which target the insect GABA receptor, have increasingly been used as alternatives against rice planthoppers. Cross-resistance to ethiprole and butene-fipronil was detected in a laboratory-selected fipronil-resistant strain of L. striatellus (LsFR). Compared with a fipronil-susceptible strain (LsFS), LsFR had obtained a high-level resistance to fipronil (112.1-fold) and moderate resistance to ethiprole (24.5-fold) and butene-fipronil (14.7-fold). For the resistance of field populations, LC50 values of ethiprole were remarkably higher than the other two analogues in Gaochun and Yancheng populations in 2016. Significant correlations were demonstrated between the LC50 values of three phenylpyrazole insecticides (R = 0.944-0.998, P = 0.007-0.016). Additionally, an AS-PCR assay was developed to detect the A2'N mutant GABA receptor in L. striatellus strains or populations. It was noteworthy that mutation frequencies of 19.2 and 3.6% appeared in Lujiang and Gaochun populations in 2016, respectively. Furthermore, there was an extremely significant difference in genomic expression of Lsrdl between the LsFS and LsFR individuals (1.85-fold, F = 26.8, P = 0.0008). This study could help us better understand the cross-resistance mechanisms in L. striatellus, and be beneficial for proposing effective pest management strategies of phenylpyrazole resistance. © 2016 Society of Chemical Industry.

Influence of the RDL A301S mutation in the brown planthopper Nilaparvata lugens on the activity of phenylpyrazole insecticides

We discovered the A301S mutation in the RDL GABA-gated chloride channel of fiprole resistant rice brown planthopper, Nilaparvata lugens populations by DNA sequencing and SNP calling via RNASeq. Ethiprole selection of two field N. lugens populations resulted in strong resistance to both ethiprole and fipronil and resulted in fixation of the A301S mutation, as well as the emergence of another mutation, Q359E in one of the selected strains. To analyse the roles of these mutations in resistance to phenylpyrazoles, three Rdl constructs: wild type, A301S and A301S+Q359E were expressed in Xenopus laevis oocytes and assessed for their sensitivity to ethiprole and fipronil using two-electrode voltage-clamp electrophysiology. Neither of the mutant Rdl subtypes significantly reduced the antagonistic action of fipronil, however there was a significant reduction in response to ethiprole in the two mutated subtypes compared with the wild type. Bioassays with a Drosophila melanogaster strain carrying the A301S mutation showed strong resistance to ethiprole but not fipronil compared to a strain without this mutation, thus further supporting a causal role for the A301S mutation in resistance to ethiprole. Homology modelling of the N. lugens RDL channel did not suggest implications of Q359E for fiprole binding in contrast to A301S located in transmembrane domain M2 forming the channel pore. Synergist bioassays provided no evidence of a role for cytochrome P450s in N. lugens resistance to fipronil and the molecular basis of resistance to this compound remains unknown. In summary this study provides strong evidence that target-site resistance underlies widespread ethiprole resistance in N. lugens populations.

Developmental effects of fipronil on Japanese Medaka (Oryzias latipes) embryos

Pesticides in urban runoff are a major source of pollutants in aquatic ecosystems. Fipronil, a phenylpyrazole insecticide, found in structural pest control products, turf grass control, and home pet flea medication, has recently increased in use and is commonly detected in urban runoff. However, little is known about the effects of fipronil on aquatic organisms at early developmental stages. Here, we evaluated toxicity of fipronil to embryos of Japanese Medaka (Oryzias latipes, Qurt strain) using a high-throughput 96-well plate toxicity test. Male and female embryos (<6 h post fertilization) were exposed to concentrations of fipronil ranging from 0.1 to 910 μg L−1 for 14 days or until hatching. Embryos were subjected to gross and microscopic examinations of developmental adverse effects as well as transcriptome analysis using RNA-seq. Results indicated a positive dose-response in reduced hatching success, increased gross deformity (tail curvature) at a lowest-observed-effect concentration (LOEC) of 200 μg L−1 and delayed hatching (∼1 day at the highest concentration, LOEC = 600 μg L−1). The transcriptome analysis indicated that fipronil exposure enhanced expression of titin and telethonin, which are responsible for muscle development. It is therefore possible that the formation of a tail curvature is due to asymmetrical overgrowth of muscle. Our results indicate that sub-lethal effects occur in embryonic stages of an aquatic vertebrate following exposure to high concentrations of fipronil, although no adverse effects at the highest published environmentally relevant concentration (6.3 μg L−1) were observed.

Comparison of fipronil sources in North Carolina surface water and identification of a novel fipronil transformation product in recycled wastewater

Fipronil is a phenylpyrazole insecticide that is widely used in residential and agricultural settings to control ants, roaches, termites, and other pests. Fipronil and its transformation products have been found in a variety of environmental matrices, but the source[s] which makes the greatest contribution to fipronil in surface water has yet to be determined. A sampling effort designed to prioritize known fipronil inputs (golf courses, residential areas, biosolids application sites and wastewater facilities) was conducted in North Carolina to learn more about the origins of fipronil in surface water. High resolution mass spectrometry (HRMS) analysis indicated that fipronil and its known derivatives were routinely present in all samples, but concentrations were substantially elevated near wastewater treatment plant outfalls (range 10–500ng/L combined), suggesting that they predominate as environmental sources. Corresponding recycled wastewater samples, which were treated with NaOCl for disinfection, showed disappearance of fipronil and all known degradates. HRMS and nuclear magnetic resonance (NMR) analysis techniques were used to determine that all fipronil-related compounds are oxidized to a previously unidentified fipronil sulfone chloramine species in recycled wastewater. The implications of the presence of a new fipronil-related compound in recycled wastewater need to be considered.

Insecticides in sediment cores from a rural and a suburban area in South China: A reflection of shift in application patterns

A shift in pesticide application pattern has occurred in recent decades, yet little information is available in the consequence of this shift. To better understand how the shift is reflected in aquatic environment, two sediment cores were collected from a rural (RLY) and a suburban (SGZ) river in South China. A variety of legacy organochlorine pesticides (OCPs) and current-use pesticides (CUPs), including organophosphate, pyrethroid and phenylpyrazole insecticides were quantified at distinct increments of the sediment cores. Total insecticide concentrations were in the ranges of 67.6–1671 and 99.2–231ng/g dry weight in RLY and SGZ with pyrethroids and organochlorines being the dominant components, respectively. In general, the shifting profile of sediment-bound insecticides from legacy OCPs to CUPs over time followed their historical application pattern, but significant differences were noted between the temporal profiles of the rural and suburban cores in regards to concentrations and composition of insecticides. The observed difference between the suburban and rural cores was synchronous with land use pattern and local economic changes. A steep increased occurrence of CUPs in the 1990s was observed in the RLY core, which is consistent with the onset of economic growth in this area. In contrast, the suburban SGZ area has been historically contaminated by legacy OCPs, with fresh input of OCPs in SGZ believed to be caused by soil erosion, caused by land reclamation activities associated with urban expansion. The current study shows the shift in insecticide application pattern from legacy OCPs to CUPs leading to an elevated CUP occurrence in the environment. It also suggests a stronger need for understanding not only environmental fate and risk, but also how their use pattern and land use changes impact the occurrence of pesticides.

Experimental and density functional study on electronic structure and electronic circular dichroism of the phenylpyrazole insecticides enantiomers and the probable chiral catabolites

The stable conformations of three phenylpyrazole insecticides enantiomers and their probable chiral catabolites, marked A, B, C, a, b and c, are identified via Monte Carlo searching with the MMFF94 molecular mechanics force field. The electronic circular dichroism of flufiprole (A) and ethiprole (B) was recorded. Moreover, the DFT method is utilized to optimize for the searched conformers. Then, the electronically excited states involving the first 30 excited states were computed using the time-dependent density functional theory method. The conformations selected to investigate in this article were the most stable conformers, and the UV and ECD spectra were in accord with the experimental values. The delocalized transition between benzene ring and pyrazole groups causes the strong absorptions of the electronic transitions at the UV–visible range. Three bands appear in the ECD spectra, in which the lower-energy ECD band is a delocalized πpy → πph* electronic transition. In addition, the higher and highest energy bands originate from the localized πph → πph* electronic transition. The calculated UV and ECD spectra were in good accordance with reported experimental values. Since the ECD spectrum at the B3LYP/6-311++G** level is indistinctively different from that at the B3LYP/6-31+G* level, it is necessary for the diffuse functions to be added to the 6-311++G** basis set, especially considering the solvent effect.