Fipronil-induced toxic effects in zebrafish (Danio rerio) larvae by using digital gene expression profiling

Transcriptomic Point of Departure (tPOD) of androstenedione in zebrafish embryos as a potential surrogate for chronic endpoints

The transcriptomic Point of Departure (tPOD) is increasingly used in ecotoxicology to derive quantitative endpoints from RNA sequencing studies. Utilizing transcriptomic data in zebrafish embryos as a New Approach Methodology (NAM) is beneficial due to its acknowledgment as an alternative to animal testing under EU Directive 2010/63/EU. Transcriptomic profiles are available in zebrafish for various modes of action (MoA). The limited literature available suggest that tPOD values from Fish Embryo Toxicity (FET) tests align with, but are generally lower than, No Observed Effect Concentrations (NOEC) from long-term chronic fish toxicity tests. In studies with the androgenic hormone androstenedione in a Fish Sexual Development Test (FSDT), a significant shift in the sex ratio towards males was noted at all test concentrations, making it impossible to determine a NOEC (NOEC <4.34 μg/L). To avoid additional animal testing in a repetition of the FSDT and adhere to the 3Rs principle (replacement, reduction, and refinement), a modified zebrafish FET (zFET) was conducted aiming to determine a regulatory acceptable effect threshold. This involved lower concentration ranges (20 to 6105 ng/L), overlapping with the masculinization-observed concentrations in the FSDT. The tPOD analysis in zFET showed consistent results with previous FSDT findings, observing strong expression changes in androgen-dependent genes at higher concentrations but not at lower ones, demonstrating a concentration-response relationship. The tPOD values for androstenedione were determined as 24 ng/L (10th percentile), 60 ng/L (20th gene), and 69 ng/L (1st peak). The 10th percentile tPOD value in zFET was 200 times lower than the lowest concentration in the FSDT. Comparing the tPOD values to literature suggests their potential to inform on the NOEC range in FSDT tests.

Hazardous fipronil insecticide effects on aquatic animals' health: Historical review and trends

Fipronil (FIP) is a broad-spectrum and highly efficient insecticide used against several arthropod pests, such as parasitic mites and insect pests affecting both animals and plants. Given its several benefits, FIP is widely used in the agricultural and veterinary medicine fields, but its indiscriminate use can have ecotoxic effects on non-target species. Thus, the current study aimed to summarise and critically analyse FIP's ecotoxicity in aquatic animals. Data referring to bibliometric parameters (publication year and geographical distribution), experimental conditions (field and laboratory, FIP type, animal class, species, habitat, and exposure conditions), and biomarkers (oxidative stress, DNA damage, neurotoxicity, and morphological changes) were summarised and critically analysed. Ecotoxicological studies were mainly conducted with insects, crustaceans, molluscs, and fish. Exposure to pure FIP or FIP-based commercial formulation can induce mortality and have sublethal effects on non-target organisms, such as increased reactive oxygen species (ROS), oxidative damage, genotoxicity (DNA damage), neurotoxicity, and morphological changes. The herein reviewed data have evidenced high median lethal FIP concentration (LC50) in vertebrates in comparison to invertebrates. The current findings confirmed that FIP can have several effects on aquatic organisms, besides suggesting potential ecotoxicological risks posed by this insecticide.

Neurotoxicity of Some Environmental Pollutants to Zebrafish

The aquatic environment encompasses a wide variety of pollutants, from plastics to drug residues, pesticides, food compounds, and other food by-products, and improper disposal of waste is the main cause of the accumulation of toxic substances in water. Monitoring, assessing, and attempting to control the effects of contaminants in the aquatic environment are necessary and essential to protect the environment and thus human and animal health, and the study of aquatic ecotoxicology has become topical. In this respect, zebrafish are used as model organisms to study the bioaccumulation, toxicity, and influence of environmental pollutants due to their structural, functional, and material advantages. There are many similarities between the metabolism and physiological structures of zebrafish and humans, and the nervous system structure, blood-brain barrier function, and social behavior of zebrafish are characteristics that make them an ideal animal model for studying neurotoxicity. The aim of the study was to highlight the neurotoxicity of nanoplastics, microplastics, fipronil, deltamethrin, and rotenone and to highlight the main behavioral, histological, and oxidative status changes produced in zebrafish exposed to them.

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.

Toxicity assessment of carvacrol and its acetylated derivative in early staged zebrafish (Danio rerio): Safer alternatives to fipronil-based pesticides?

Fipronil is a broad-spectrum pesticide presenting high acute toxicity to non-target organisms, particularly to aquatic species. Natural compounds stand out as promising alternatives to the use of synthetic pesticides such as fipronil. Thus, our study aimed to compare the toxicity of carvacrol (natural), acetylcarvacrol (semisynthetic), and fipronil (synthetic) to early staged zebrafish. We conducted a series of toxicity assays at concentrations ranging from 0.01 μM to 25 μM for fipronil and 0.01 μM to 200 μM for carvacrol and acetylcarvacrol, depending on the assay, after 7-days post-fertilization (dpf). The potency (EC50) of fipronil was ∼1 μM for both deformities and mortality at 7 dpf, whereas EC50 was >50 μM for carvacrol and >70 μM for acetylcarvacrol. Fipronil at 0.1 and 1 μM caused a decrease in body length and swim bladder area of larvae at 7dpf, but no difference was observed for either carvacrol or acetylcarvacrol. Based upon the visual motor response test, fipronil induced hypoactivity in larval zebrafish at 1 μM and acetylcarvacrol induced hyperactivity at 0.1 μM. Anxiolytic-type behaviors were not affected by any of these chemicals. All chemicals increased the production of reactive oxygen species at 7 dpf, but not at 2 dpf. Genes related to swim bladder inflation, oxidative stress, lipid metabolism, and mitochondrial activity were measured; only fipronil induced upregulation of atp5f1c. There were no changes were observed in oxygen consumption rates of fish and apoptosis. Taken together, our data suggest that carvacrol and its derivative may be safer replacements for fipronil due to their lower acute toxicity.

Developmental toxicity of fipronil and its two metabolites towards zebrafish (Danio rerio) embryos

Fipronil (FIL) use is currently regulated in several countries due to its specific toxicity to bees. This study investigated the possible developmental toxicities as well as the acute toxicities of FIL, fipronil sulfide (FIL-SI), and fipronil sulfone (FIL-SO) to zebrafish (Danio rerio) embryos. At concentrations up to 5000 μg L-1, FIL- and FIL-SI-treated embryos exhibited significant mortality at 96 h postfertilization. Body length was significantly shortened with increasing concentrations in FIL- and FIL-SI-treated embryos. However, FIL-SO-treated embryos exhibited low mortality with high hatching rates. Body length was also significantly shortened in FIL-SO-treated embryos. Regarding the number of intersegmental vessels (ISVs), all chemical-treated embryos showed high ISV numbers with increasing concentrations of each chemical. FIL and FIL-SI induced abnormal heart formation with heart dysfunction in embryos, whereas FIL-SO did not induce any difference in heart development compared with the control. Abnormal heart formation may be related to the upregulation of nppa responsible for the expression of natriuretic peptides in embryos. Embryonic acetylcholinesterase activity was decreased gradually according to the increase in FIL and FIL-SI concentrations, whereas FIL-SO did not cause any change in enzyme activity. Il-1β responsible for the occurrence of injury or infection was highly upregulated in FIL-SI- and FIL-SO-treated embryos. Therefore, reduction to FIL-SI may be associated with FIL toxicity, whereas oxidation to FIL-SO may be a detoxification route in the environment.

Comparative pharyngeal cartilage developmental toxicity of bisphenol A, bisphenol S and bisphenol AF to zebrafish (Danio rerio) larvae: A combination of morphometry and global transcriptome analyses

Exposure to BPA is recently shown to affect cartilage development in teleost fishes; whether BPS and BPAF, its two most frequently used phenolic analogues have similar effect, however, remains unclear. Here, we utilize zebrafish (Danio rerio) as an in-vivo larval model for systematic comparison of the pharyngeal arch-derived cartilage developmental toxicity of BPA, BPS and BPAF. Zebrafish are continuously exposed to three bisphenol analogues (3-BPs) at a range of concentrations since the embryonic stage (0.5 hpf), and identified cartilage malformations of the mandibular and hyoid pharyngeal arches at larval stage (120 hpf). BPA and BPAF prolong length and broaden cartilage angles; however, BPS shortens length and narrows the angles of skull cartilages. The results of the comparative transcriptome show that FoxO and MAPK signaling pathways are closely associated with the toxicity of BPA and BPAF, while BPS exposure affects energy metabolism-related pathways. Moreover, exposure to 3-BPs have an impact on the oxidative stress status. Our data collectively indicate that BPS and BPAF may not be safer than BPA regarding the impact on pharyngeal cartilage development in fish model, the mechanisms still need explorations, and that these two analogues should be applied with caution.

Transcriptome reveals overview of Ca2+ dose-dependent metabolism disorders in zebrafish larvae after Cd2+ exposure

Cadmium (Cd), a ubiquitous environmental hazardous heavy metal, poses a significant threat to the health of aquatic organisms, including teleosts. Although the toxic profile of Cd is well recognized, little is known regarding the overall view of toxic responses to varying aquatic environmental parameters (e.g., water hardness) at an individual level. Herein, differences in water hardness were partially mimicked by adjusting Ca²⁺ levels in E3 medium. As an in vivo model, zebrafish embryos were exposed to variable Ca²⁺ levels (NV, normal Ca²⁺; LV, low Ca²⁺; HV, high Ca²⁺) alone or combined with 30.7 µg/L Cd²⁺ (NC, LC, and HC, respectively) until 144 hr post-fertilization. The genome-wide transcriptome revealed differentially expressed genes between groups. Functional enrichment analysis found that biological processes related to metabolism, particularly lipid metabolism, were significantly disrupted in NC and LC treatments, while a remission was observed in the HC group. Biochemical assays confirmed that the decrease in Ca²⁺ enhanced synthesis, inhibited mobilization and increased the storage of lipids in Cd²⁺ treatments. This study suggests that the toxic effect of Cd on biological pathways will be influenced by Ca²⁺, which will improve the toxicological understanding and facilitate accurate assessment of Cd.

Constructing an MCF-7 breast cancer cell-based transient transfection assay for screening RARα (Ant)agonistic activities of emerging phenolic compounds

The screening of compounds with endocrine disrupting effects has been attracting increasing attention due to the continuous release of emerging chemicals into the environment. Testing the (ant)agonistic activities of these chemicals on the retinoic acid receptor α (RARα), a vital nuclear receptor, is necessary to explain their perturbation in the endocrine system in vivo. In the present study, MCF-7 breast carcinoma cells were transiently transfected with a RARα expression vector (pEF1α-RARα-RFP) and a reporter vector containing a retinoic acid reaction element (pRARE-TA-Luc). Under optimized conditions, the performance of the newly constructed system was evaluated for its feasibility in screening the (ant)agonistic effects of emerging phenolic compounds on RARα. The results showed that this transient transfection cell model responded well to stimulation with (ant)agonists of RARα, and the EC₅₀ and IC₅₀ values were 0.87 nM and 2.67 μM for AM580 and Ro41-5253, respectively. Its application in testing several emerging phenolic compounds revealed that triclosan (TCS) and tetrabromobisphenol A (TBBPA) exerted notable RARα antagonistic activities. This newly developed bioassay based on MCF-7 is promising in identifying the agonistic or antagonistic activities of xenobiotics on RARα and has good potential for studying RARα signaling-involved toxicological effects of emerging chemicals of concern.

A rapid evidence assessment of the potential risk to the environment presented by active ingredients in the UK's most commonly sold companion animal parasiticides

A number of parasiticides are commercially available as companion animal treatments to protect against parasite infestation and are sold in large volumes. These treatments are not intended to enter the wider environment but may be washed off or excreted by treated animals and have ecotoxic impacts. A systematic literature review was conducted to identify the existing evidence for the toxicity of the six most used parasiticides in the UK: imidacloprid, fipronil, fluralaner, afoxolaner, selamectin, and flumethrin. A total of 17,207 published articles were screened, with 690 included in the final evidence synthesis. All parasiticides displayed higher toxicity towards invertebrates than vertebrates, enabling their use as companion animal treatments. Extensive evidence exists of ecotoxicity for imidacloprid and fipronil, but this focuses on exposure via agricultural use and is not representative of environmental exposure that results from use in companion animal treatments, especially in urban greenspace. Little to no evidence exists for the ecotoxicity of the remaining parasiticides. Despite heavy usage, there is currently insufficient evidence to understand the environmental risk posed by these veterinary treatments and further studies are urgently needed to quantify the levels and characterise the routes of environmental exposure, as well as identifying any resulting environmental harm.

Evaluation of fentanyl toxicity and metabolism using a zebrafish model

The increased abuse of novel drugs has created a critical need for cheap and rapid in vivo models to understand whole organism drug-induced toxicity and metabolic impacts. One such model is zebrafish, which share many similarities to human. Assays have been developed for behavioral, toxicity, and metabolism elucidation following chemical exposure. The zebrafish model provides the advantage of assessing these parameters within a single study. Previous zebrafish studies have evaluated the behavioral effects of fentanyl, but not developmental toxicity and its relation to metabolism. In this study, we evaluate the effects of fentanyl on the development of wild-type (TL strain) zebrafish and its metabolism over 4 days. Fertilized eggs were exposed to six concentrations of fentanyl (0.01, 0.1, 1, 10, 50, and 100 μM) through embryo media incubated at 28-29°C. Observations included egg coagulation, somite formation, heartbeat, tail and yolk morphology, pericardial formation, and swim bladder inflation. The incubation media was analyzed for the presence of metabolites using a targeted metabolomics approach. Fentanyl concentration caused significant effects on survival and development, with notable defects to the tail, yolk, and pericardium at 50 and 100 μM. Despropionyl fentanyl (4-ANPP), β-hydroxy fentanyl, and norfentanyl were detected in zebrafish larvae. We present a single in vivo model to assess toxicity and metabolism of fentanyl exposure in a vertebrate model system. Our findings provide a foundation for further investigations into fentanyl's mechanism of action and translation to human drug exposure.

Direct analysis of metabolites in the liver tissue of zebrafish exposed to fiproles by internal extractive electrospray ionization mass spectrometry

Exploring the metabolic disturbance of fipronil and its derivatives in aquatic organisms may provide a more comprehensive understanding of the impact of fipronil on the ecological environment. In this work, internal extractive electrospray ionization mass spectrometry (iEESI-MS) was used to directly analyze metabolites in the liver tissue of zebrafish exposed to fipronil and its three derivatives. Partial least squares-discriminant analysis (PLS-DA) revealed that 32 signals were considered as differential signals in zebrafish after the exposure treatment of fipronil and its derivatives, including phosphatidylcholines (PCs), lysophosphatidylcholines (LPCs), phosphatidylethanolamines (PEs), fatty acids and so on. The pathway analysis result showed that both fipronil and its derivatives have a significant impact on the glycerophospholipid metabolism of zebrafish. Besides, the intensities of PC signals in the liver samples of each group showed such a trend: mixed fiprole exposed group > fipronil sulfone exposed group ≈ fipronil sulfide exposed group > fipronil exposed group > fipronil desulfinyl exposed group > control group, indicating that mixed exposure of fipronil and its derivatives exhibited more significant metabolic disturbance in zebrafish. Taken together, iEESI-MS is applied to environmental toxicology and investigating the metabolic disturbance induced by fipronil and its derivatives in aquatic organisms, providing a new analytical method for this field.

Short-term effects of pesticide fipronil on behavioral and physiological endpoints of Daphnia magna

Fipronil (FIP) is an organic pesticide with many practical uses. Although some results indicated toxic effects in some terrestrial and aquatic animal species, little is known on its influence on behavioral and physiological endpoints of cladocerans. The aim of our study was to determine the short-term effects of FIP at concentrations of 0.1 μg/L, 1 μg/L, 10 μg/L, and 100 μg/L on Daphnia magna sublethal indices: behavioral (swimming speed, distance traveled) and physiological endpoints (heart rate, post-abdominal claw activity and thoracic limb movements). The results showed that FIP induced reduction of swimming speed and distance traveled in a concentration- and time-dependent manner at all the concentrations used. The lowest concentration of the insecticide temporarily stimulated post-abdominal claw activity after 24 h and thoracic limb activity after 48 h; however, the highest concentrations reduced all the studied physiological endpoints. IC50 values showed that thoracic limb activity, swimming speed, and distance traveled were most sensitive to FIP after 24-h exposure. The most sensitive parameter after 48 h and 72 h was swimming speed and post-abdominal claw activity, respectively. The study indicated that (i) behavioral and physiological endpoints of Daphnia magna are reliable and valuable sublethal indicators of toxic alterations induced by FIP; however, they respond with different sensitivity at various times of exposure, (ii) FIP may alter cladoceran behavior and physiological processes at concentrations detected in the aquatic environment; therefore, it should be considered as an ecotoxicological hazard to freshwater cladocerans.

Residual molecular and behavioral effects of the phenylpyrazole pesticide fipronil in larval zebrafish (Danio rerio) following a pulse embryonic exposure

Pesticides are typically applied to crops as acute applications, and residual effects of such intermittent exposures are not often characterized in developing fish. Fipronil is an agricultural pesticide that inhibits γ-amino-butyric acid (GABA) gated chloride channels. In this study, zebrafish (Danio rerio) embryos were exposed for 48 h (starting at ~3 h post fertilization, hpf) to various concentrations of fipronil (0.02 μg/L up to 4000 μg/L). Following this acute exposure, a subset of fish was transferred to clean water for a 7-day depuration phase. We hypothesized that a pulse exposure to fipronil during critical periods of central nervous system development would adversely affect fish later in life. After a 48 hour pulse exposure, survival was reduced in embryos exposed to 2 μg fipronil/L or greater. However, there was no further mortality during the depuration phase, nor were there changes in body length nor notochord length in larvae 9 dpf (days post-fertilization) compared to controls. Additional experiments were carried out at higher concentrations over 96 h (up to 4 dpf) to also elucidate developmental effects and teratogenicity of fipronil (43.7 μg/L up to 4370 μg/L). Fipronil at these higher concentrations significantly impacted the development of zebrafish, and the following morphometric and teratogenic effects were observed in 4 dpf fish; reduced body length, yolk sac and pericardial edema, reduced midbrain length, reduced optic and otic diameter, and truncation of the lower jaw. In depurated fish, we hypothesized that there would exist residual effects of exposure at the molecular level. Transcriptome profiling was therefore conducted on 9 dpf depurated larvae exposed initially for 48 h to one dose of either 0.2 μg/L, 200 μg/L or 2000 μg/L fipronil. The expression of gene networks associated with glycogen and omega-3-fatty acid metabolism were decreased in larvae exposed to each of the three concentrations of fipronil, suggesting metabolic disruption. Moreover, transcriptomics revealed that fipronil suppressed gene networks related to light-dark adaptation, photoperiod sensing, and circadian rhythm. Based on these data, we tested fish for altered behavioral responses in a Light-Dark preference test. Larvae exposed to >200 μg fipronil/L as embryos showed fewer number of visits (20-30% less) to the dark zone compared to controls. Larvae also spent a lower amount of time in the dark zone compared to controls, suggesting that fipronil strengthened dark avoidance behavior which is indicative of anxiety. This study demonstrates that a short pulse exposure to fipronil can affect transcriptome networks for metabolism, circadian rhythm, and response to light in fish after depuration, and these molecular responses are hypothesized to be related to aberrant behavioral effects observed in the light-dark preference test.

Evaluation of the spinal effects of phthalates in a zebrafish embryo assay

Phthalates (phthalate esters, PAEs) are commonly used as plasticizers and are emerging concerns worldwide for their potential influence on the environment and general public health. Thus, identification of the negative effects and involved mechanisms of PAEs is necessary. Herein, we found that embryonic exposure of zebrafish to di-(2-ethylhexyl) phthalate (DEHP) and di-butyl phthalate (DBP) significantly induced spinal defects, such as inhibited spontaneous movement at 24 h post-fertilization (hpf), spine curvature and body length decrease at 96 hpf. The transcriptional level of the genes that are related to the development of the notochord (col8a1a and ngs), muscle (stac3, klhl41a and smyd2b) and skeleton (bmp2, spp1) were significantly altered by DEHP and DBP at 50 and 250 μg/L, which might be associated with the observed morphological changes. Notably, DBP and DEHP altered the locomotor activity of zebrafish larvae at 144 hpf, which might be due to the abnormal development of the spine and skeletal system. In conclusion, phthalates caused spinal birth defects in zebrafish embryos, induced transcriptional alterations of the spinal developmental genes, and led to abnormal behavior.

Parental exposure to bisphenol A affects pharyngeal cartilage development and causes global transcriptomic changes in zebrafish (Danio rerio) offspring

BACKGROUND

As one of the most common endocrine-disrupting chemicals (EDCs), bisphenol A (BPA) is a threat to aquatic ecosystems. Despite a rich literature addressing the adverse effects of BPA on various systems in fish models, the potential impact of parental BPA exposure on offspring pharyngeal cartilage development is poorly understood.

METHODS

Adult zebrafish (F0) were exposed to BPA (1.0 μM) or control for 7 days. Eggs (F1) were collected and exposed to BPA (control, 0.05, 0.1, 1, 10 μM) until 120 h post-fertilization. Histomorphometrical essay was used to quantitatively and qualitatively assess the effects of BPA on pharyngeal cartilage development. RNA sequencing (RNA-seq) was used to discover differentially expressed genes (DEGs), and KEGG pathway and GO enrichment analysis were performed to interpret functional ontology.

RESULTS

Parental BPA exposure affected hatchability and heart rates of F1 progeny. By pathology analysis, parental BPA exposure caused craniofacial deformity, characterized by wider angles of cartilage elements, disrupted pharyngeal chondrocytes and promoted apoptosis and elongation of head length. RNA-seq suggested that many DEGs were involved in multiple biological processes and signaling pathways; defense responses, reactive oxygen species metabolic process, apoptosis, p53 signaling pathway and MAPK signaling pathway were closely associated with the toxicity of parental BPA exposure.

CONCLUSIONS

Parental BPA exposure affected chondrogenesis in the viscerocranium of zebrafish offspring and led to global transcriptomic changes involved in apoptosis, hyperplasia and oxidative stress. These newly identified gene expression patterns, pathways and gene networks of zebrafish eleutheroembryos after early-life waterborne BPA exposure, may lead to severe and permanent morphological and functional consequences.

Developmental toxicity of fipronil in early development of zebrafish (Danio rerio) larvae: Disrupted vascular formation with angiogenic failure and inhibited neurogenesis

Fipronil has been widely used in agriculture to prevent aggressive insects from damaging agricultural products. Fipronil residues circulate in the environment and they have been detected in non-targeted organisms in aquatic environments. To study the effect of fipronil toxicity on environmental health, 6 h post fertilization (hpf) zebrafish embryos were treated with fipronil for 72 h. LC₅₀ value was obtained by applying varying concentrations of fipronil to zebrafish embryos for 72 h. As zebrafish embryos are useful vertebrate models for studying developmental and genetic findings in toxicology research, they were exposed to fipronil to study detailed elucidating mechanisms with hazardous end points of toxicity. Cell cycle arrest-related apoptosis supported pathological alterations, such as increased mortality, shortened body length, and reduced hatchability. Furthermore, observed heart defects, including edema and irregular heartbeat were caused due to abnormal blood circulation. In transgenic zebrafish models (fli1:eGFP and olig2:dsRED), disrupted blood vessel formations were indicated by eGFP⁺ endothelial cells. Moreover, neurogenic defects were observed by studying dsRED⁺ motor neurons and oligodendrocytes. This study demonstrates fipronil accumulation in aquatic environment and its ability to impair essential processes, such as angiogenesis and neurogenesis during early developmental stage of zebrafish, along with general developmental toxicity.

Comparative analysis on the sorption kinetics and isotherms of fipronil on nondegradable and biodegradable microplastics

Biodegradable plastics have been introduced and widely used as a promising alternative to traditional nondegradable plastics. However, the differences in sorption behavior of pesticides on nondegradable and biodegradable microplastics has been insufficiently studied. Here, four types of nondegradable [polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC), polypropylene (PP)] and two types of biodegradable [polylactic acid (PLA), polybutylene succinate (PBS)] microplastics were selected to investigate the sorption mechanism of fipronil based on their sorption kinetics and isotherms. The results indicated that the sorption rates of PLA and PBS were much higher than those of PE, PP, PVC and PS and that the sorption capacities of fipronil on microplastics followed the order of PBS > PLA > PP > PE > PS > PVC. The sorption kinetics followed a pseudo-second-order kinetics model (R² = 0.953-0.998) for all tested microplastics. External mass transport and intraparticle diffusion were the main rate controlling steps of the sorption of fipronil on microplastics. Furthermore, isotherm results indicated that a Langmuir model provided the best fit for fipronil sorption on PE, PS, PVC and PP (R² = 0.997-0.999), while a Freundlich model was the most appropriate model for PLA and PBS (R² = 0.998-0.999). The presence of surface O-containing functional groups and the spatial arrangement of rubbery domains are likely to affect the sorption process. The results from this work suggest that microplastics, especially biodegradable ones, may play an important role in the fate and transport of pesticides, and their effects on soil organisms (e.g., earthworms) require further investigation.

Transcriptomic responses of Caco-2 cells to Lactobacillus rhamnosus GG and Lactobacillus plantarum J26 against oxidative stress

Oxidative stress is the basic reason for aging and age-related diseases. In this study, we investigated the protective effect of 2 strains of lactic acid bacteria (LAB), Lactobacillus rhamnosus GG and L. plantarum J26, against oxidative stress in Caco-2 cells, and gave an overview of the mechanisms of lactic acid bacteria antioxidant activity using digital gene expression profiling. The 2 LAB strains provided significant protection against hydrogen peroxide (H₂O₂)-induced reduction in superoxide dismutase activity and increase in glutathione peroxidase activity in Caco-2 cells. However, inactive bacteria had little effect on alleviating oxidation stress in Caco-2 cells. Eight genes related to oxidative stress-FOSB, TNF, PPP1R15A, NUAK2, ATF3, TNFAIP3, EGR2, and FBN2-were significantly upregulated in H₂O₂-induced Caco-2 cells compared with untreated Caco-2 cells. After incubation of the H₂O₂-induced Caco-2 cells with L. rhamnosus GG and L. plantarum J26, 5 genes (TNF, EGR2, NUAK2, FBN2, and TNFAIP3) and 2 genes (NUAK2 and FBN2) were downregulated, respectively. In addition, the Kyoto Encyclopedia of Genes and Genomes indicated that some signaling pathways associated with inflammation, immune response, and apoptosis, such as Janus kinase/signal transducers and activators of transcription (Jak-STAT), mitogen-activated protein kinase (MAPK), nuclear factor-κB, and tumor necrosis factor, were all negatively modulated by the 2 strains, especially L. rhamnosus GG. In this paper, we reveal the mechanism of LAB in relieving oxidative stress and provide a theoretical basis for the rapid screening and evaluation of new LAB resources.

Maternal exposure to fipronil results in sulfone metabolite enrichment and transgenerational toxicity in zebrafish offspring: Indication for an overlooked risk in maternal transfer?

Ecotoxicological studies show the association between pesticide pollution and transgenerational toxicity in aquatic organisms. However, a less considered risk is that many pesticides can be metabolized and transferred to offspring as new toxicants. In this study, we used zebrafish to evaluate the maternal transfer risk of fipronil (FIP), which is a great threat to aquatic organisms with toxic metabolite formation. After 28-day exposure to environmentally relevant concentrations (1.0, 5.0 and 10.0 μg/L) of FIP in adult female zebrafish (F0), the toxicants off-loading and transgenerational toxicity in offspring were studied. High burdens of FIP and its sulfone metabolite were found in both F0 and the embryos (F1), resulting in increased CYP450 activity. The residual levels of the metabolite were higher than those of the parent compound. Chiral analysis further showed a preferential accumulation of S-enantiomer of FIP in both F0 and F1. Maternal exposure to FIP increased the malformation rate and decreased the swim speed in larvae. Additionally, after exposure, the levels of thyroid hormones (THs), including triiodothyronine (T3) and thyroxine (T4), decreased in both generations, particularly in the F1. Gene transcription expression along the hypothalamic-pituitary-thyroid (HPT) axis was also significantly affected. Maternal exposure to FIP increased sulfone metabolite enrichment and cause multiple toxic effects in F1. Findings from this study highlight the key role of biologically active product formation in the maternal transfer of pollutants and associated risk assessment.

Ecotoxicological effects of fipronil, neem cake and neem extract in edaphic organisms from tropical soil

Veterinary medicines are widely applied for the treatment and prevention of animal diseases. Consequently, animal manure contains significant amounts of environmental pollutants that are potential sources of environmental pollution when inappropriately applied in soils. This work aimed to evaluate ecotoxicological effects of doses of commercial fipronil, neem cake and neem extract in the survival and reproduction of earthworms (Eisenia andrei), enchytraeidae (Enchytraeus crypticus) and springtails (Folsomia candida) in Oxisol and tropical artificial soil (TAS). Applications of fipronil, neem cake and extract in soil were carried out according to standardized ISO methodologies by using a random experimental design with five replicates. Toxic effects of fipronil for springtails in Oxisol and TAS were observed with LC₅₀ of 0.26 mg kg^-1 (0.18-0.35 mg kg^-1) and 0.29 mg kg^-1 (0.22-0.37 mg kg^-1), respectively. It was not observed significant toxic effects of fipronil for earthworms and enchytraeidae in both soils. However, significant amounts of juvenile earthworm and adult enchytraeidae decreased in fipronil doses higher than 10 mg kg^-1. Neem cake and extract were not toxic for earthworms and enchytraeidae but, significant amounts of juvenile springtails decreased in neem cake doses from 500 to 1000 mg kg^-1. It can be concluded that the use of veterinary medicines containing synthetic compounds for preventing diseases in animals needs to be controlled to avoid environmental pollution after applying manure in soil. Veterinary medicines containing natural compounds as neem cake and extract are eco-friendly and could be efficiently applied in soil in a sustainable way.