Developmental exposure of zebrafish larvae to organophosphate flame retardants causes neurotoxicity

Exposure to organophosphate esters and maternal-child health

Organophosphate esters (OPEs) are a class of chemicals now widely used as flame retardants and plasticizers after the phase-out of polybrominated diphenyl ethers (PBDEs). However, OPEs carry their own risk of developmental toxicity, which poses concern for recent birth cohorts as they have become ubiquitous in the environment. In this review, we summarize the literature evaluating the association between OPE exposure and maternal, perinatal, and child health outcomes. We included original articles investigating associations of OPE exposure with any health outcome on pregnant women, newborns, children, and adolescents. We found 48 articles on this topic. Of these, five addressed maternal health and pregnancy outcomes, 24 evaluated prenatal OPE exposure and child health, 18 evaluated childhood OPE exposure and child/adolescent health, and one article evaluated both prenatal and childhood OPE exposure. These studies suggest that OPE exposure is possibly associated with a wide range of adverse health outcomes, including pregnancy loss, altered gestational duration and smaller birthweight, maternal and neonatal thyroid dysfunction, child metabolic dysregulation and abnormal growth, impaired neurodevelopment, and changes in immune response. Many of the reported outcomes associated with OPE exposure varied by child sex. Findings also varied substantially by OPE metabolite and exposure time. The OPEs most frequently measured, detected, and found to be associated with health outcomes were triphenyl phosphate (TPHP, metabolized to DPHP) and tris(1,3-dichloro-2-propyl) phosphate (TDCIPP, metabolized to BDCIPP). The extensive range of health outcomes associated with OPEs raises concern about their growing use in consumer products; however, these findings should be interpreted considering the limitations of these epidemiological studies, such as possible exposure misclassification, lack of generalizability, insufficient adjustment for covariates, and failure to consider chemical exposures as a mixture.

Integrated Approach for Testing and Assessment for Developmental Neurotoxicity (DNT) to Prioritize Aromatic Organophosphorus Flame Retardants

Organophosphorus flame retardants (OPFRs) are abundant and persistent in the environment but have limited toxicity information. Their similarity in structure to organophosphate pesticides presents great concern for developmental neurotoxicity (DNT). However, current in vivo testing is not suitable to provide DNT information on the amount of OPFRs that lack data. Over the past decade, an in vitro battery was developed to enhance DNT assessment, consisting of assays that evaluate cellular processes in neurodevelopment and function. In this study, behavioral data of small model organisms were also included. To assess if these assays provide sufficient mechanistic coverage to prioritize chemicals for further testing and/or identify hazards, an integrated approach to testing and assessment (IATA) was developed with additional information from the Integrated Chemical Environment (ICE) and the literature. Human biomonitoring and exposure data were identified and physiologically-based toxicokinetic models were applied to relate in vitro toxicity data to human exposure based on maximum plasma concentration. Eight OPFRs were evaluated, including aromatic OPFRs (triphenyl phosphate (TPHP), isopropylated phenyl phosphate (IPP), 2-ethylhexyl diphenyl phosphate (EHDP), tricresyl phosphate (TMPP), isodecyl diphenyl phosphate (IDDP), tert-butylphenyl diphenyl phosphate (BPDP)) and halogenated FRs ((Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP), tris(2-chloroethyl) phosphate (TCEP)). Two representative brominated flame retardants (BFRs) (2,2'4,4'-tetrabromodiphenyl ether (BDE-47) and 3,3',5,5'-tetrabromobisphenol A (TBBPA)) with known DNT potential were selected for toxicity benchmarking. Data from the DNT battery indicate that the aromatic OPFRs have activity at similar concentrations as the BFRs and should therefore be evaluated further. However, these assays provide limited information on the mechanism of the compounds. By integrating information from ICE and the literature, endocrine disruption was identified as a potential mechanism. This IATA case study indicates that human exposure to some OPFRs could lead to a plasma concentration similar to those exerting in vitro activities, indicating potential concern for human health.

Bioaccumulation of Chloropyrifos Organo-pesticide and Its Toxicogenic Association with Antioxidant GSTP1 in Pakistani Pest Control Workers

Synthetic pesticides are employed to enhance agricultural production. Chronic exposure to organophosphate (OP) pesticides may be a source of health problems. The present study was designed to examine an association of GSTP1 (rs1695) polymorphism with OP pesticide chronic exposure. A case-control study was recruited with 250 subjects comprising exposed (n = 100) and controls (n = 150). A survey was conducted to determine the pesticide type to which workers had exposed. According to recorded survey assessment, two compounds of OP pesticides chloropyrifos and malathion were investigated in the blood samples of exposed study subjects using high-performance liquid chromatography (HPLC). For screening of genetic polymorphism in GSTP1 (rs1695) polymerase chain reaction, restriction length polymorphism (PCR-RFLP) and agarose gel electrophoresis were performed. Statistically, data were analyzed using SPSS v. 20.0 and MedCal© software. Total chrom© navigator programmer was used for detection of OP residues in serum and local pesticide solution. chloropyrifos-OP pesticide residues were detected in serum of estimated chronically exposed subjects at 206 nm HPLC optimal conditions. The pattern of GSTP1 (rs1695) genotypic frequencies depicted that heterozygous genotype was higher in Chloropyrifos exposed subjects (0.56) when compared with controls (0.44). Statistical outcomes showed an insignificant association with GSTP1 (rs1695) polymorphism and chloropyrifos-OP pesticide toxicity (Fisher's exact test 1.0, p = 0.25). An insignificant allelic investigation reflected a protective effect of mutant allele G against chloropyrifos-OP pesticide toxicity in exposed subjects. Findings may be helpful in identifying bioaccumulated pesticide residues, but in studied Pakistani exposed workers, no significant association of GSTP1 (rs1695) variant with chloropyrifos-OPs was demonstrated.

Potential adverse outcome pathway of neurodevelopmental toxicity, inflammatory response, and oxidative stress induction mediated by three alkyl organophosphate flame retardants in zebrafish larvae

Following restrictions on polybrominated flame retardants, trimethyl phosphate (TMP), triethyl phosphate (TEP), and tris(2-butoxyethyl) phosphate (TBEP) have been frequently used as plasticizers for fire-resistant plastics. This study investigated the neurodevelopmental effects, inflammatory response, and oxidative stress induction of three alkyl organophosphate flame retardants using a zebrafish embryo/larvae model. After exposure of zebrafish embryos to TMP, TEP, and TBEP (0, 0.02, 0.2, 2, 20, and 200 μg L-1) for 96 h, survival, development, swimming behavior, changes in acetylcholinesterase (AChE) activity, dopamine, tumor necrosis factor-alpha (TNF-α), interleukin (IL), reactive oxygen species (ROS), and antioxidant enzyme activities were observed. Concentrations of TMP, TEP, and TBEP were also measured in the whole body of exposed larvae. Our results showed that exposure to 200 μg L-1 TEP and ≥20 μg L-1 TBEP significantly reduced larval body length; however, TMP had no significant effects on developmental parameters up to 200 μg L-1. After 96 h of exposure to TBEP, total distance moved, mean velocity, AChE, and dopamine concentrations were significantly decreased. Exposure to TEP and TBEP decreased the expression of genes that regulate central nervous system development (e.g. gap43 and mbpa), whereas ROS, antioxidant enzymes, TNF-α, and IL-1β concentrations were significantly increased. Notably, pretreatment with an antioxidant N-acetylcysteine reduced neurotoxicity and oxidative stress caused by TEP and TBEP. The results of this study demonstrated that exposure to TEP and TBEP causes oxidative stress and has adverse effects on the neurobehavioral and immune system of zebrafish, leading to hypoactivity and ultimately impairing development.

Inhibition of autophagosome-lysosome fusion contributes to TDCIPP-induced Aβ1-42 production in N2a-APPswe cells

Alzheimer's disease is the most common form of dementia and is characterized by cognitive impairment. The disruption of autophagosome-lysosome function has been linked to the pathogenesis of Alzheimer's disease. Tris (1,3-dichloro-2-propyl) phosphate (TDCIPP) is a widely used organophosphorus flame retardant that has the potential to cause neuronal damage. We found that TDCIPP significantly increased the expression of β-site amyloid precursor protein (APP)-cleaving enzyme 1 (BACE1), presenilin-1 (PS1) and Aβ42. Proteomic studies with TMT labeling revealed changes in the profiles of N2a-APPswe cells after exposure to TDCIPP. Proteomic and bioinformatics analyses revealed that lysosomal proteins were dysregulated in N2a-APPswe cells after treatment with TDCIPP. The LC3, P62, CTSD, and LAMP1 levels were increased after TDCIPP exposure, and dysregulated protein expression was validated by Western blotting. The exposure to TDCIPP led to the accumulation of autophagosomes, and this phenomenon was enhanced in the presence of chloroquine (CQ). Our results revealed for the first time that TDCIPP could be a potential environmental risk factor for AD development. The inhibition of autophagosome-lysosome fusion may have a significant impact on the generation of Aβ1-42 in response to TDCIPP.

Neurotoxic effects of 2-ethylhexyl diphenyl phosphate exposure on zebrafish larvae: Insight into inflammation-driven changes in early motor behavior

The extensive utilization and potential adverse impacts of the replacement flame-retardant 2-Ethylhexyl Diphenyl Phosphate (EHDPP) have raised concerns. Currently, there is limited knowledge regarding the developmental, neurological, and immunotoxic consequences of EHDPP exposure, as well as its potential behavioral outcomes. In this study, we undertook a comprehensive examination and characterization of the toxic effects over the EHDPP concentration range of 14-1400 nM. Our findings unveiled that EHDPP, even at an environmentally relevant concentration of 14 nM, exhibited excitatory neurotoxicity, eliciting a 13.5 % increase in the swimming speed of zebrafish larvae. This effect might be attributed to the potential influence of EHDPP on the release of neurotransmitters like serotonin and dopamine, which, in turn, mediated anxiety-like behavior in the zebrafish larvae. Conversely, sublethal dose EHDPP (1400 nM) exposure significantly suppressed the swimming vigor of zebrafish larvae, accompanied by morphological changes, abnormal behaviors, and alterations in intracerebral molecules. Transcriptomics revealed the underlying mechanism. The utilization of pathway inhibitors reshaped the inflammatory homeostasis and alleviated the toxicity induced by EHDPP exposure, anchoring the pivotal role played by the TLR4/NF-κB signaling pathway in EHDPP-induced adverse changes in zebrafish behavior and neurophysiology. This study observed the detrimental effects of EHDPP on fish sustainability at environmentally relevant concentrations, highlighting the practical significance for EHDPP risk management. Elucidating the toxic mechanisms of EHDPP will contribute to a deeper comprehension of how environmental pollutants can intricately influence human health.

Tris(1,3-dichloro-2-propyl) phosphate induces endoplasmic reticulum stress and mitochondrial-dependent apoptosis in mouse spermatocyte GC-2 cells

Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) is a frequently detected organophosphorus flame retardants (OPFRs) in various environmental media, and has been evidenced as reproductive toxicity. However, its adverse effects on spermatogenic cells are unknown. In this study, mouse spermatocyte GC-2spd (GC-2) cells were selected as an in vitro model, and the impact of mitochondrial structure and function, endoplasmic reticulum (ER) stress, cell apoptosis and the related molecular mechanisms were investigated. Our study indicated that cell viability was decreased significantly in a dose-dependent manner after TDCIPP treatment with the half lethal concentration (LC50) at 82.8 μM, 50.0 μM and 39.6 μM for 24 h, 48 h and 72 h, respectively. An apoptosis was observed by Annexin V-FITC/PI stain. In addition, fragmentation of mitochondrial structure, an increase of mitochondrial membrane potential (MMP), reduction of cellular adenosine triphosphate (ATP) content, release of cytochrome c and activation of Caspase-3 and Caspase-9 activity implicated that Caspase-3 dependent mitochondrial pathway might play a key role in the process of GC-2 cell apoptosis. Furthermore, ER stress induction was convinced by altered morphology of ER and up-regulation of ER targeting genes, including (Bip, eIF2α, ATF4, XBP1, CHOP, ATF6 and Caspase-12). Taken together, these results demonstrate that both mitochondrial apoptotic pathways and ER stress apoptotic pathways might play important roles in the process of apoptosis in GC-2 cells induced by TDCIPP treatment. Therefore, the potential reproductive toxicity of TDCIPP should not be ignored.

Chronic exposure to tris (2-chloroethyl) phosphate (TCEP) induces brain structural and functional changes in zebrafish (Danio rerio): A comparative study on the environmental and LC50 concentrations of TCEP

Tris (2-chloroethyl) phosphate (TCEP) is a crucial organophosphorus flame retardant widely used in many industrial and commercial products. Available reports reported that TCEP could cause various toxicological effects on organisms, including humans. Unfortunately, toxicity data for TCEP (particularly on neurotoxicity) on aquatic organisms are lacking. In the present study, Danio rerio were exposed to different concentrations of TCEP for 42 days (chronic exposure), and oxidative stress, neurotoxicity, sodium, potassium-adenosine triphosphatase (Na+, K+-ATPase) activity, and histopathological changes were evaluated in the brain. The results showed that TCEP (100 and 1500 µg L-1) induced oxidative stress and significantly decreased the activities of antioxidant enzymes (SOD, CAT and GR) in the brain tissue of zebrafish. In contrast, the lipid peroxidation (LPO) level was increased compared to the control group. Exposure to TCEP inhibited the acetylcholinesterase (AChE) and Na+,K+-ATPase activities in the brain tissue. Brain histopathology after 42 days of exposure to TCEP showed cytoplasmic vacuolation, inflammatory cell infiltration, degenerated neurons, degenerated purkinje cells and binucleate. Furthermore, TCEP exposure leads to significant changes in dopamine and 5-HT levels in the brain of zebrafish. The data in the present study suggest that high concentrations of TCEP might affect the fish by altering oxidative balance and inducing marked pathological changes in the brain of zebrafish. These findings indicate that chronic exposure to TCEP may cause a neurotoxic effect in zebrafish.

Optimization and verification of selective removal of organophosphate esters from wastewater by molecularly imprinted adsorbent

Tributyl phosphate (TNBP), a new type of flame retardant, is an emerging pollutant and has been frequently detected in various matrices such as wastewater. Efficient removal of TNBP is critical for wastewater treatment. In this study, molecularly imprinted polymer (MIP) was prepared using precipitation polymerization for selective adsorption of TNBP. The results showed that MIP had a porous structure and formed effective imprinting cavities, which was primarily responsible for its superior adsorption ability. The adsorption of TNBP by MIP was carried out following both the pseudo-secondary kinetic model and the Langmuir isothermal adsorption model. MIP adsorbed TNBP rapidly and reached adsorption equilibrium within 30 min with 923 μmol g-1 at 298 K. The adsorption capacity and adsorption rate of MIP were respectively 2 and 5.49 times those of non-molecularly imprinted polymers. In addition, MIP could effectively counter disturbances from external parameters like temperature and pH, exhibiting strong environmental flexibility. MIP can specifically adsorb organophosphate esters, and can selectively adsorb TNBP under the interference of coexisting contaminants such as1,3-diphenylguanidine and isazofos. In actual bodies of water, MIP's highly selective adsorption of TNBP retains its advantage. The selective adsorption of MIP was mainly due to the common phosphate skeleton, and the specific substituent of organophosphate esters played an important role in the imprinting process. Hydrogen bonding might be involved in the polymerization process of TNBP with acrylamide and the adsorption process of TNBP by MIP.MIP exhibited good reuse efficiency, the total adsorption capacity decreased by no more than 25% after 7 reuse cycles. This study provides a simple and efficient method for selective removal of organophosphate from wastewater.

Proposal for priority emerging pollutants in the Nakdong river, Korea: Application of EU watch list mechanisms

The Nakdong River, the longest in Korea, has received numerous pollutants from heavily industrialized and densely populated areas while being used as a drinking water source. A number of research have reported occurrences of emerging pollutants (EPs) in the river. The results requested efficient monitoring and systematic management strategies such as EU watch list under Water Framework Directive. The aim of this study is to propose a watch list through preliminary monitoring of the river and risk-based prioritization approach. As candidates for monitoring target, 632 substances were selected based on literature and database searches. Among them, 175 substances were subjected to target screening method whereas 457 were evaluated via suspect screening. A risk-based prioritization was applied to substances quantified through target screening based on concentrations, and a scoring-based prioritization was applied to substances tentatively identified through suspect screening. Sampling campaigns (n = 12) were conducted from October 2020 to September 2021, at 8 sampling sites along the river. As a result, 130 target substances were quantified above the LOQ. Among the 21 substances whose priority score was assigned through risk-based prioritization, telmisartan and iprobenfos were identified with very high environmental risk while candesartan, TBEP, imidacloprid, azithromycin and clotrimazole were classified with high or intermediate risk. As result of the scoring system for 39 tentatively identified substances, 6 substances (benzophenone, caprolactam, metolachlor oxanilic acid, heptaethylene glycol, octaethylene glycol and pentaethylene glycol), which were then confirmed with reference standards, showed a potential environmental risk. Those substances prioritized through target and suspect screening followed by scoring systems can be a subset for the watch list and potential targets for nationwide water quality monitoring program in the future.

Deriving seawater quality criteria of tris(2-chloroethyl) phosphate for ecological risk assessment in China seas through species sensitivity distributions

Tris(2-chloroethyl) phosphate (TCEP), one of the widely used organophosphorus flame retardants (OPFRs), has been frequently detected in the marine environment in the seas off China. The existing freshwater biotoxicity data are not suited to derivation of the seawater quality criteria of TCEP and evaluating the associated ecological risks. This study aimed at deriving water quality criteria (WQC) of TCEP for marine organisms based on species sensitivity distribution (SSD) approach using the acute toxicity data generated from multispecies bioassays and chronic toxicity data by converting acute data with the acute-to-chronic ratios (ACRs); the derived WQC were then used to evaluate the ecological risk for TCEP in China Seas. According to median effective concentration (EC50) and median lethal concentration (LC50), TCEP had a moderate or low toxicity to eight marine species selected, among which mysid Neomysis awatschensis (96h-LC50 of 39.65 mg/L) and green alga Platymonas subcordiformis (96-h EC50 of 395.42 mg/L) were the most sensitive and the most tolerant, respectively. The acute and chronic hazardous concentrations of TCEP for 5% of marine species (HC5) were estimated to be 29.55 and 2.68 mg/L, respectively. The short-term and long-term WQC were derived to be 9.85 and 0.89 mg/L, respectively. The risk quotient (RQ) values indicated that TECP at current levels poses a negligible risk to marine ecosystems in China. These results will provide valuable reference for the government to establish a seawater quality standard for TCEP.

Organophosphate ester flame retardants and plasticizers in house dust and mental health outcomes among Canadian mothers: A nested prospective cohort study in CHILD

Organophosphate ester flame retardants and plasticizers (OPEs) are common exposures in modern built environments. Toxicological models report that some OPEs reduce dopamine and serotonin in the brain. Deficiencies in these neurotransmitters are associated with anxiety and depression. We hypothesized that exposure to higher concentrations of OPEs in house dust would be associated with a greater risk of depression and stress in mothers across the prenatal and postpartum periods. We conducted a nested prospective cohort study using data collected on mothers (n = 718) in the CHILD Cohort Study, a longitudinal multi-city Canadian birth cohort (2008-2012). OPEs were measured in house dust sampled at 3-4 months postpartum. Maternal depression and stress were measured at 18 and 36 weeks gestation and 6 months and 1 year postpartum using the Centre for Epidemiologic Studies for Depression Scale (CES-D) and Perceived Stress Scale (PSS). We used linear mixed models to examine the association between a summed Z-Score OPE index and continuous depression and stress scores. In adjusted models, one standard deviation increase in the OPE Z-score index was associated with a 0.07-point (95% CI: 0.01, 0.13) increase in PSS score. OPEs were not associated with log-transformed CES-D (β: 0.63%, 95% CI: -0.18%, 1.46%). The effect of OPEs on PSS score was strongest at 36 weeks gestation and weakest at 1 year postpartum. We observed small increases in maternal perceived stress levels, but not depression, with increasing OPEs measured in house dust during the prenatal and early postpartum period in this cohort of Canadian women. Given the prevalence of prenatal and postpartum anxiety and the ubiquity of OPE exposures, additional research is warranted to understand if these chemicals affect maternal mental health.

Elucidating the toxicity mechanisms of organophosphate esters by adverse outcome pathway network

With the widespread use of organophosphate esters (OPEs), the accumulation and toxicity effect of OPEs in biota are attracting more and more concern. In order to clarify the mechanism of toxicity of OPEs to organisms, this study reviewed the OPEs toxicity and systematically identified the mechanism of OPEs toxicity under the framework of adverse outcome pathway (AOP). OPEs were divided into three groups (alkyl-OPEs, aryl-OPEs, and halogenated-OPEs) and biota was divided into aquatic organism and mammals. The results showed that tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) and triphenyl phosphate (TPHP) mainly caused neurotoxicity, reproductive, and hepatotoxicity in different mechanisms. According to the constructed AOP network, the toxicity mechanism of OPEs on aquatic organisms and mammals is different, which is mainly attributed to the different biological metabolic systems of aquatic organisms and mammals. Interestingly, our results indicate that the toxicity effect of the three kinds of OPEs on aquatic organisms is different, while there was no obvious difference in the mechanism of toxicity of OPEs on mammals. This study provides a theoretical basis for OPEs risk assessment in the future.

Predicting the acute toxicity of organophosphate esters (OPEs) to aquatic organisms by modelling the structure-toxicity relationships using partial least square regression

Organophosphate esters (OPEs) have been used worldwide as organophosphate flame retardants (OPFRs) since brominated flame retardants (BFRs) were banned. Due to the toxicity of these OPEs, environmental concerns and ecological risks arose. However, there are still large gaps in the understanding of their toxicity to organisms and the mechanisms of toxicity. After collecting the existing toxicity information and obtaining molecular descriptors of OPEs, a partial least square (PLS) regression model was used in this study to quantify the structure-toxicity relationships of OPEs. Based on the regression results, the acute toxicity of the remaining OPEs lacking acute toxicity data was predicted, and the risk level of total common OPEs was classified. The acute toxicity of 15 chemicals was collected, and >1660 molecular structure descriptors were obtained. The cross-validation results of the partial least square regression indicated that two principal components met the regression requirements with the selected features, and the regression equations of these chemicals were generated with selected molecular descriptors. The influence of physicochemical properties, such as hydrophobicity/molecular weight, in traditional perception of OPE toxicity was not that obvious, and acute toxicity was mainly influenced by the autocorrelation coefficients. However, the regression results indicated that the correlation between autocorrelation coefficients calculated based on different physicochemical properties and toxicity was different. According to the prediction result based on PLS regression, CDP may pose a high risk and halogenated alkyl-substituted OPEs such as TCEP may be less toxic. The results of the present study may help inform the environmental management and risk assessment of emerging chemicals such as OPEs.

Cognitive Performance and Exposure to Organophosphate Flame Retardants in Children: Evidence from a Cross-Sectional Analysis of Two European Mother-Child Cohorts

The knowledge of the effects of organophosphate flame retardants on children's neurodevelopment is limited. The purpose of the present research is to evaluate the association between exposure to organophosphate flame retardants and children's neurodevelopment in two European cohorts involved in the Human Biomonitoring Initiative Aligned Studies. The participants were school-aged children belonging to the Odense Child Cohort (Denmark) and the PCB cohort (Slovakia). In each cohort, the children's neurodevelopment was assessed through the Full-Scale Intelligence Quotient score of the Wechsler Intelligence Scale for Children, using two different editions. The children's urine samples, collected at one point in time, were analyzed for several metabolites of organophosphate flame retardants. The association between neurodevelopment and each organophosphate flame retardant metabolite was explored by applying separate multiple linear regressions based on the approach of MM-estimation in each cohort. In the Danish cohort, the mean ± standard deviation for the neurodevelopment score was 98 ± 12; the geometric mean (95% confidence interval (95% CI)) of bis(1,3-dichloro-2-propyl) phosphate (BDCIPP) standardized by creatinine (crt) was 0.52 µg/g crt (95% CI = 0.49; 0.60), while that of diphenyl phosphate (DPHP) standardized by crt was 1.44 µg/g crt (95% CI = 1.31; 1.58). The neurodevelopment score showed a small, negative, statistically imprecise trend with BDCIPP standardized by crt (β = -1.30; 95%CI = -2.72; 0.11; p-value = 0.07) and no clear association with DPHP standardized by crt (β = -0.98; 95%CI = -2.96; 0.99; p-value = 0.33). The neurodevelopment score showed a negative trend with BDCIPP (β = -1.42; 95% CI = -2.70; -0.06; p-value = 0.04) and no clear association with DPHP (β = -1.09; 95% CI = -2.87; 0.68; p-value = 0.23). In the Slovakian cohort, the mean ± standard deviation for the neurodevelopment score was 81 ± 15; the geometric mean of BDCIPP standardized by crt was 0.18 µg/g crt (95% CI = 0.16; 0.20), while that of DPHP standardized by crt was 2.24 µg/g crt (95% CI = 2.00; 3.52). The association of the neurodevelopment score with BDCIPP standardized by crt was -0.49 (95%CI = -1.85; 0.87; p-value = 0.48), and with DPHP standardized by crt it was -0.35 (95%CI = -1.90; 1.20; p-value = 0.66). No clear associations were observed between the neurodevelopment score and BDCIPP/DPHP concentrations that were not standardized by crt. No clear associations were observed with bis(1-chloro-2-propyl) phosphate (BCIPP) in either cohort, due to the low detection frequency of this compound. In conclusion, this study provides only limited evidence of an inverse association between neurodevelopment and exposure to BDCIPP and DPHP. The timing of exposure and effect modification of other organophosphate flame retardant metabolites and other substances should be the subject of further investigations that address this scientific hypothesis.

Tributyl phosphate can inhibit the feeding behavior of rotifers by altering the axoneme structure, neuronal coordination and energy supply required for motile cilia

Organophosphorus flame retardants (OPFRs) are frequently detected in aquatic environments and can potentially amplify the food chain, posing a potential risk to organisms. Marine invertebrates have primitive nervous systems to regulate behavior, but how they respond to OPFRs that are potentially neurotoxic substances is unclear. This study assessed changes in the feeding behavior of rotifer Brachionus plicatilis exposed to alkyl OPFRs tributyl phosphate (TnBP) (0.376 nM, 3.76 and 22.53 µM) to elucidate the mechanism of behavioral toxicity. TnBP at 22.53 μM reduced the ingestion and filtration rates of rotifers for Chlorella vulgaris and Phaeocystis globosa in a 24-h test and altered rotifer-P. globosa population dynamics in 15-d coculture. Ciliary beat frequency was also reduced, and the expression of genes encoding the cilia axoneme was downregulated. TnBP could inhibit rotifer acetylcholinesterase activity by binding this protein and reduce the expression of the exocytotic membrane protein syntaxin-4, suggesting a disorder in nervous regulation of cilia beat. Moreover, TnBP induced abnormal shape and dysfunction of mitochondria, which caused insufficient energy required for ciliary movement. This study revealed diverse neurotoxicity mechanisms of TnBP, particularly as a potentially competing acetylcholinesterase ligand for aquatic invertebrates. Our research also provides a meaningful reference for OPFR-induced behavioral toxicity assessments.

Temperature- and chemical-induced neurotoxicity in zebrafish

Throughout their lives, humans encounter a plethora of substances capable of inducing neurotoxic effects, including drugs, heavy metals and pesticides. Neurotoxicity manifests when exposure to these chemicals disrupts the normal functioning of the nervous system, and some neurotoxic agents have been linked to neurodegenerative pathologies such as Parkinson's and Alzheimer's disease. The growing concern surrounding the neurotoxic impacts of both naturally occurring and man-made toxic substances necessitates the identification of animal models for rapid testing across a wide spectrum of substances and concentrations, and the utilization of tools capable of detecting nervous system alterations spanning from the molecular level up to the behavioural one. Zebrafish (Danio rerio) is gaining prominence in the field of neuroscience due to its versatility. The possibility of analysing all developmental stages (embryo, larva and adult), applying the most common "omics" approaches (transcriptomics, proteomics, lipidomics, etc.) and conducting a wide range of behavioural tests makes zebrafish an excellent model for neurotoxicity studies. This review delves into the main experimental approaches adopted and the main markers analysed in neurotoxicity studies in zebrafish, showing that neurotoxic phenomena can be triggered not only by exposure to chemical substances but also by fluctuations in temperature. The findings presented here serve as a valuable resource for the study of neurotoxicity in zebrafish and define new scenarios in ecotoxicology suggesting that alterations in temperature can synergistically compound the neurotoxic effects of chemical substances, intensifying their detrimental impact on fish populations.

Effects of tri-n-butyl phosphate (TnBP) on neurobehavior of Caenorhabditis elegans

As an emerging flame retardant, organic phosphate flame retardants have been extensively used worldwide. The aim of this study is to determine the effects of TnBP on neurobehavior of Caenorhabditis elegans (C. elegans) and its mechanisms. L1 larvae of wild-type nematodes (N2) were exposed to TnBP of 0, 0.1, 1, 10, and 20 mg/L for 72 hours. Then, we observed that the body length and body width were inhibited, the head swings were increased, the pump contractions and chemical trend index were reduced, the production of reactive oxygen species (ROS) was increased, and the expression of mitochondrial oxidative stress related genes (mev-1 and gas-1) and P38 MAPK signal pathway-related genes (pmk-1, sek-1, and nsy-1) was altered. After reporter gene strains BZ555, DA1240, and EG1285 were exposed to TnBP of 0, 0.1, 1, 10, and 20 mg/L for 72 hours, the synthesis of dopamine, glutamate, and Gamma-Amino Butyric Acid (GABA) was increased. In addition, the pmk-1 mutants (KU25) led to the sensitivity of C. elegans to TnBP in terms of head swings. The results showed that TnBP had harmful effects on the neurobehavior of C. elegans, oxidative stress might be one of the mechanisms of its neurotoxicity, and P38 MAPK signal pathway might play an important regulatory role in this process. The results revealed the potential adverse effects of TnBP on the neurobehavior of C. elegans.

Influence of Methylene Blue or Dimethyl Sulfoxide on Larval Zebrafish Development and Behavior

The use of larval zebrafish developmental testing and assessment, specifically larval zebrafish locomotor activity, has been recognized as a higher throughput testing strategy to identify developmentally toxic and neurotoxic chemicals. There are, however, no standardized protocols for this type of assay, which could result in confounding variables being overlooked. Two chemicals commonly employed during early-life stage zebrafish assays, methylene blue (antifungal agent) and dimethyl sulfoxide (DMSO, a commonly used vehicle) have been reported to affect the morphology and behavior of freshwater fish. In this study, we conducted developmental toxicity (morphology) and neurotoxicity (behavior) assessments of commonly employed concentrations for both chemicals (0.6-10.0 μM methylene blue; 0.3%-1.0% v/v DMSO). A light-dark transition behavioral testing paradigm was applied to morphologically normal, 6 days postfertilization (dpf) zebrafish larvae kept at 26°C. Additionally, an acute DMSO challenge was administered based on early-life stage zebrafish assays typically used in this research area. Results from developmental toxicity screens were similar between both chemicals with no morphological abnormalities detected at any of the concentrations tested. However, neurodevelopmental results were mixed between the two chemicals of interest. Methylene blue resulted in no behavioral changes up to the highest concentration tested, 10.0 μM. By contrast, DMSO altered larval behavior following developmental exposure at concentrations as low as 0.5% (v/v) and exhibited differential concentration-response patterns in the light and dark photoperiods. These results indicate that developmental DMSO exposure can affect larval zebrafish locomotor activity at routinely used concentrations in developmental neurotoxicity assessments, whereas methylene blue does not appear to be developmentally or neurodevelopmentally toxic to larval zebrafish at routinely used concentrations. These results also highlight the importance of understanding the influence of experimental conditions on larval zebrafish locomotor activity that may ultimately confound the interpretation of results.

Environmental occurrence and ecotoxicity of aquaculture-derived plastic leachates

Plastic products such as fishing nets and foam buoys have been widely used in aquaculture. To enhance the desirable characteristics of the final equipment, plastic gear for aquaculture is mixed with a wide range of additives. Recent studies have shown that additives could be leached out to the environment with a long-term use of aquaculture plastics, forming aquaculture-derived plastic leachates. It should be emphasized that some leachates such as phthalic acid esters (PAEs) and organophosphate esters (OPEs) are endocrine disruptors, which could increase the exposure risk of aquatic products and subsequently display potential threats to human health via food chain. However, systematic studies on the release, occurrence, bioaccumulation, and toxic effects of aquaculture-derived plastic leachates are missing, overlooking their potential sources and ecotoxicological risks in aquatic environments. We have reviewed and compared the concentrations of major plastic leachates in the water environment and organisms of global aquaculture and non-farmed areas, confirming that aquaculture leachate is an important source of contaminants in the environment. Moreover, the toxic effects of aquaculture-derived plastic additives and the related mechanisms are summarized with fish as a representative, revealing their potential health risk. In addition, we proposed current challenges and future research needs, which provides scientific guidance for the use and management of plastic products in aquaculture industries.

Exposure to environmentally relevant concentrations of TnBP results in tissue-specific bio-accumulation and inhibits growth of silver carp (Hypophthalmichthys molitrix)

Tri-n-butyl phosphate (TnBP) is commonly used as flame retardant and rubber plasticizer, and has been widely detected in aquatic organisms and natural waters. However, the potential toxicity of TnBP in fish remains unclear. In the present study, silver carp (Hypophthalmichthys molitrix) larvae were treated with environmentally relevant concentrations (100 or 1000 ng/L) of TnBP for 60 d and then they were depurated in clean water for 15 d, and the accumulation and depuration of the chemical in six tissues of silver carp were measured. Furthermore, effects on growth were evaluated and potential molecular mechanisms were explored. Results indicated that TnBP could be rapidly accumulated and depurated in silver carp tissues. In addition, the bio-accumulation of TnBP displayed tissue-specificity, where intestine contained the greatest and vertebra had the smallest level of TnBP. Furthermore, exposure to environmentally relevant concentrations of TnBP led to time- and concentration-dependent growth inhibition of silver carp, even though TnBP was completely depurated in tissues. Mechanistic studies suggested that exposure to TnBP up- and down-regulated the expression of ghr and igf1 in liver, respectively, and increased GH contents in plasma of silver carp. TnBP exposure also up-regulated the expression of ugt1ab and dio2 in liver, as well as decreased T4 contents in plasma of silver carp. Our findings provide direct evidence of health hazards of TnBP to fish in natural waters, calling for more attention of environmental risks of TnBP in aquatic environment.

The association between organophosphate esters exposure and body mass index in children and adolescents: The mediating effect of sex hormones

Organophosphate esters (OPEs), used as flame retardants and plasticizers, have been indicated to impair growth and development in toxicological studies, but current epidemiological data on their associations with body mass index (BMI) are limited and the underlying biological mechanisms remain unclear. In this study, we aim to explore the association of OPE metabolites with BMI z-score, and assess whether sex hormones mediate the relationships between OPE exposure and BMI z-score. We measured weight and height, and determined OPE metabolites in spot urine samples and sex hormones in serum samples among 1156 children and adolescents aged 6-18 years in Liuzhou city, China. The results showed that di-o-cresyl phosphate and di-pcresyl phosphate (DoCP & DpCP) levels were associated with lower BMI z-score of all participants and a similar pattern of associations were presented in prepubertal boys stratified by sex-puberty groups and male children stratified by sex-age groups. In addition, sex hormone binding globulin (SHBG) were related to reduced BMI z-score among all subgroups including prepubertal boys, prepubertal girls, pubertal boys, and pubertal girls (all P_trend<0.05). We also found that DoCP & DpCP showed positive associations with SHBG among prepubertal boys. Mediation analysis further showed that SHBG mediated 35.0% of the association between DoCP & DpCP and reduced BMI z-score in prepubertal boys. Our results indicated that OPEs may impair growth and development by disrupting the sex hormones in prepubertal boys.

Descriptive analysis of organophosphate ester metabolites in a pan-Canadian pregnancy cohort

Organophosphate esters (OPEs) are widely used in numerous consumer products for their flame retardant and plasticizing properties. Despite potential widespread exposure, biomonitoring data during critical windows of development are scarce and limited to the most widely studied metabolites. We quantified urinary concentrations of multiple OPE metabolites in a vulnerable Canadian population. Using data and biobanked specimens from the Maternal-Infant Research on Environmental Chemicals (MIREC) study (2008-2011), we measured first trimester urinary concentrations of 15 OPE metabolites as well as one flame retardant metabolite and quantified associations with sociodemographic and sample collection characteristics in 1865 pregnant participants. We applied 2 different analytical methods to quantify OPEs, one using UItra-Performance Liquid Chromatography coupled to tandem mass spectrometry (UPLC-MS/MS) and the other using Atmospheric Pressure Gas Chromatography coupled to mass spectrometry (APGC-MS/MS) with sensitive limits of detection (0.008-0.1 μg/L). We modelled associations between sociodemographic and sample collection characteristics and specific gravity-standardized chemical concentrations. Six OPE metabolites were detected in the majority (68.1-97.4 %) of participants. Bis-(2-chloroethyl) hydrogen phosphate had the highest detection rate (97.4 %). Diphenyl phosphate had the highest geometric mean concentration (0.657 μg/L). Metabolites of tricresyl phosphate were detected in few participants. Associations between sociodemographic characteristics varied according to each OPE metabolite. Pre-pregnancy body mass index tended to be positively associated with OPE metabolite concentrations whereas age tended to be inversely associated with OPE concentrations. OPE concentrations were, on average, higher in urine samples collected in the summer than other seasons the winter. We present the largest biomonitoring study of OPE metabolites in pregnant people to date. These findings demonstrate widespread exposure to OPEs and their metabolites and identify subpopulations who may experience heightened exposure.

Urinary concentrations of organophosphate esters in relation to semen quality: A cross-sectional study

Organophosphate esters (OPEs) are widely used as flame retardants and plasticizers in consumer products. Toxicological studies have indicated that OPEs may affect male reproductive health, but human evidence is inconclusive. In this study, we explored associations of individual and mixtures of OPE exposure with semen quality among 1015 Chinese men from an infertility clinic. After adjusting for potential confounders, we observed that higher diphenyl phosphate (DPHP) and [Bis(2-methylphenyl) phosphate (BMPP)] exposure was associated with increased odds ratios (ORs) of having below-reference total sperm count. Higher bis (2-butoxyethyl) phosphate (BBOEP) exposure was associated with increased ORs of having below-reference progressive motility and total motility. For semen quality parameters modeled as continuous outcomes, inverse associations with individual OPE were still observed. In addition, urinary 1-hydroxy-2-propyl bis (1-chloro-2-propyl) phosphate (BCIPHIPP) concentrations were inversely associated with the percentage of normal morphology while positively associated with the percentage of abnormal heads. Quantile g-computation regression analyses showed that exposure to higher OPE mixtures was associated with lower total sperm motility and normal morphology. Our results indicated that both individual and mixtures of OPE exposure were associated with reduced semen quality.

Occurrence, spatial distribution, and potential risks of organic micropollutants in urban surface waters from qinghai, northwest China

Lack of knowledge on the destiny of organic micropollutants (OMPs) in the Tibetan Plateau region of China prevents the public from being aware of the need for protecting these unique aquatic ecosystems that are precious water resources and source areas of the Yellow River. To address this knowledge gap, this study systematically investigated the multi-residue analysis, distribution, and potential risks of six types of OMPs, namely, neonicotinoid pesticides (NEOs), fungicides, organophosphate esters (OPEs), organophosphorus pesticides (OPPs), psychoactive substances (PSs), and antidepressants (ADs), in surface waters of major cities in Qinghai. A total of 31 compounds, consisting of 8 NEOs, 1 fungicide, 12 OPEs, 2 OPPs, 5 PSs, and 3 ADs, were detected in >50% of the sites, showing their ubiquitous nature in the study area. Results showed that the total OMP concentration in surface water was 28.3-908 ng/L, and OPEs were the dominant composition (48.6%-97.4%). The risk quotient values of the detected diazinon and dursban regularly exceeded 1 for aquatic organisms at all sampling sites, indicating moderate-high chronic ecological risk. The joint probability curves showed that dursban and NEOs have higher risk levels than other OMPs. Although the results of the non-carcinogenic total hazard quotient of the OMPs in the surface water was less than 1 in all age groups and the carcinogenic risk was lower than the negligible risk level, the potential risks to children and infants were considerably greater and should not be underestimated. In addition to pollutant concentration and exposure duration, ingestion rate and body weight (BW) are also important factors affecting health risk, with BW having a negative effect. To the best of the authors' knowledge, this report is the first to describe OMP pollution in Qinghai, and the results provide new insight into the ecological security of the water resources of the Tibetan Plateau.

In vitro neurotoxic potential of emerging flame retardants on neuroblastoma cells in an acute exposure scenario

Since 2004, some legacy flame retardants (FRs) were restricted or removed from the European markets due to their concern on human health. Both organophosphorus FRs (OPFRs) and novel brominated FRs (NBFRs) have replaced them because they are presumably safer and less persistent emerging FRs (EFRs) and their exposure is currently occurring in indoor environments at high levels. Little is known about the neurotoxic potential risk of these EFRs in humans. The present study was aimed at assessing the acute neurotoxicity potential of Tris(1, 3-dichloro-2-propyl)phosphate (TDCPP), triphenyl phosphate (TPhP), Bis(2-ethylhexyl)tetrabromophthalate (BEH-TEBP) and 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (EH-TBB) on human neuroblastoma cells (SH-SY5Y). SH-SY5Y were exposed to these EFRs at low concentrations -ranging 2.5-20 μM. during 2-24 h. We investigated viability, mitochondrial function, oxidative stress, inflammatory response, as well as neural plasticity and development. The results have demonstrated that selected EFRs (TDCPP, TPhP, EH-TBB and BEH-TBP) did not impair neural function on SH-SY5Y as acute response. To the best of our knowledge, this has been the first study focused on evaluating the neural affection of TPhP on SH-SY5Y cells and of EH-TBB and BEH-TBP on neural cells. We also assessed for the first time almost all endpoints after FR exposure on neural cell lines.

Developmental exposure to the flame retardant, triphenyl phosphate, causes long-lasting neurobehavioral and neurochemical dysfunction

BACKGROUND

Human exposures to organophosphate flame retardants result from their use as additives in numerous consumer products. These agents are replacements for brominated flame retardants but have not yet faced similar scrutiny for developmental neurotoxicity. We examined a representative organophosphate flame retardant, triphenyl phosphate (TPP) and its potential effects on behavioral development and dopaminergic function.

METHODS

Female Sprague-Dawley rats were given low doses of TPP (16 or 32 mg kg^-1  day^-1 ) via subcutaneous osmotic minipumps, begun preconception and continued into the early postnatal period. Offspring were administered a battery of behavioral tests from adolescence into adulthood, and littermates were used to evaluate dopaminergic synaptic function.

RESULTS

Offspring with TPP exposures showed increased latency to begin eating in the novelty-suppressed feeding test, impaired object recognition memory, impaired choice accuracy in the visual signal detection test, and sex-selective effects on locomotor activity in adolescence (males) but not adulthood. Male, but not female, offspring showed marked increases in dopamine utilization in the striatum, evidenced by an increase in the ratio of the primary dopamine metabolite (3,4-dihydroxyphenylacetic acid) relative to dopamine levels.

CONCLUSIONS

These results indicate that TPP has adverse effects that are similar in some respects to those of organophosphate pesticides, which were restricted because of their developmental neurotoxicity.

Parental whole life-cycle exposure to tris (2-chloroethyl) phosphate (TCEP) disrupts embryonic development and thyroid system in zebrafish offspring

Tris (2-chloroethyl) phosphate (TCEP), an emerging environmental pollutant, has been frequently detected in natural waters. The objective of this study was to investigate possible parental transfer of TCEP and transgenerational effects on the early development and thyroid hormone homeostasis in F1 larvae following parental whole life-cycle exposure to TCEP. To this end, zebrafish (Danio rerio) embryos were exposed to environmentally relevant concentrations (0.8, 4, 20 and 100 μg/L) of TCEP for 120 days until sexual maturation. Parental exposure to TCEP resulted in significant levels of TCEP, developmental toxicity including decreased survival and final hatching rates, accelerated heart rate and elevated malformation rate, as well as induction of oxidative stress and cell apoptosis in F1 offspring. In F1 eggs, declined thyroxin (T4) levels were observed, consistent with those in plasma of F0 adult females, indicating the maternal transfer of thyroid endocrine disruption to the offspring. In addition, mRNA levels of several genes along the hypothalamic-pituitary-thyroid (HPT) axis were significantly modified in F1 larvae, which could be linked to transgenerational developmental toxicity and thyroid hormone disruption. For the first time, we revealed that the parental exposure to environmentally relevant levels of TCEP could cause developmental toxicity and thyroid endocrine disruption in subsequent unexposed generation.

Potential adverse outcome pathways with hazard identification of organophosphate esters

Data-driven analysis and pathway-based approaches contribute to reasonable arrangements of limited resources and laboratory tests for continuously emerging commercial chemicals, which provides opportunities to save time and effort for toxicity research. With the widespread usage of organophosphate esters (OPEs) on a global scale, the concentrations generally reached up to micromolar range in environmental media and even in organisms. However, potential adverse effects and toxicity pathways of OPEs have not been systematically assessed. Therefore, it is necessary to review the current situation, formulate the future research priorities, and characterize toxicity mechanisms via data-driven analysis. Results showed that the early toxicity studies focused on neurotoxicity, cytotoxicity, and metabolic disorders. Then the main focus shifted to the mechanisms of cardiotoxicity, endocrine disruption, hepatocytes, reproductive and developmental toxicity to vulnerable sub-populations, such as infants and embryos, affected by OPEs. In addition, several novel OPEs have been emerging, such as bis(2-ethylhexyl)-phenyl phosphate (HDEHP) and oxidation derivatives (OPAsO) generated from organophosphite antioxidants (OPAs), leading to multiple potential ecological and human health risks (neurotoxicity, hepatotoxicity, developmental toxicity, etc.). Notably, in-depth statistical analysis was promising in encapsulating toxicological information to develop adverse outcome pathways (AOPs) frameworks. Subsequently, network-centric analysis and quantitative weight-of-evidence (QWOE) approaches were utilized to construct and evaluate the putative AOPs frameworks of OPEs, showing the moderate confidences of the developed AOPs. In addition, frameworks demonstrated that several events, such as nuclear receptor activation, reactive oxygen species (ROS) production, oxidative stress, and DNA damage, were involved in multiple different adverse outcome (AO), and these AOs had certain degree of connectivity. This study brought new insights into facilitating the complement of AOP efficiently, as well as establishing toxicity pathways framework to inform risk assessment of emerging OPEs.

Prenatal Exposure of Organophosphate Esters and Its Trimester-Specific and Gender-Specific Effects on Fetal Growth

The toxicity of organophosphate esters (OPEs) on embryonic development is well noted in animal experiments, but epidemiological studies are still lacking. This study evaluated the prenatal exposure of OPEs and its trimester-specific and gender-specific effects on fetal growth. The correlations between OPE exposure and fetal growth were investigated by linear mixed-effect models and multivariable linear regression analyses. Prenatal exposure to tributyl phosphate (TBP) was negatively associated with a z-score of fetal abdominal circumference (AC), biparietal diameter (BPD), femur length (FL), and head circumference (HC). In the second trimester, the serum concentration of TBP was inversely related to the z-score of AC, BPD, and HC. In the third trimester, serum concentration of TBP was inversely related to AC, BPD, and FL z-scores. Prenatal exposure to tri-m-cresyl phosphate (TMCP) was inversely related to the z-score of AC, BPD, and HC. In the second trimester, TMCP was negatively correlated with AC, BPD, FL, and HC z-scores. After stratification by gender, male fetuses were more sensitive to OPE exposure. The above results remained robust after excluding pregnant women who gave preterm birth or those with low or high pre-pregnancy BMI. Our findings suggested that health effects of typical OPEs, particularly TBP and TMCP, should be taken into consideration in future works.

The adverse effects of fluxapyroxad on the neurodevelopment of zebrafish embryos

Fluxapyroxad (Flu), one of the succinate dehydrogenase-inhibited (SDHI) fungicides, has been extensively used in crop fungal disease control. Despite its increasing use in modern agriculture and long-term retention in the environment, the potentially toxic effects of Flu in vivo, especially on neurodevelopment, remain under-evaluated. In this study, zebrafish embryos were exposed to Flu at concentrations of 0.5, 0.75, and 1 mg/L for 96 h to evaluate the neurotoxicity of Flu. The results showed that Flu caused concentration-dependent malformations, including shorter body length, smaller head and eyes, and yolk sac edema. After exposure to Flu, larval zebrafish exhibited severe motor aberrations. Flu at a concentration of 1 mg/L significantly decreased dopamine level and notably altered acetylcholinesterase (AChE) activity and acetylcholine (ACh) content. Abnormal central nervous system (CNS) neurogenesis and disordered motor neuron development were observed in Tg (HUC-GFP) and Tg (hb9-GFP) zebrafish in Flu-treated groups. The expression of key genes involved in neurotransmission and neurodevelopment further proved that Flu impaired the zebrafish nervous system. This work contributes to our understanding of the neurotoxic effects and mechanisms induced by Flu in zebrafish and may help us take precautions against the neurotoxicity of Flu.

A systematic scoping review of epidemiological studies on the association between organophosphate flame retardants and neurotoxicity

Organophosphate flame retardants (OPFRs) are increasingly and widely used as substitutes for brominated flame retardants in daily life. The chemical structure of OPFRs is very similar to that of organophosphorus pesticides, leading to concerns about their neurotoxicity. A few epidemiological studies have been published with inconsistent results on this topic, and a systematic scoping review is needed to provide an overview or map of the current evidence on the relationship of OPFRs with neurodevelopmental toxicity. Therefore, MEDLINE (accessed through PubMed), Web of Science, and CNKI (Chinese National Knowledge Infrastructure) were systematically searched for articles published in the last two decades. Nine eligible articles were included in the present systematic scoping review for adherence to the predefined PECOS (population, exposure, comparison, outcome, study design) statement. Six studies were conducted in the USA, and the remaining three studies were conducted in Austria, Norway and China. A total of 2 581 children (1 203 females and 1 378 males) were included. Half of the included studies focused on the adverse effects of OPFR exposure on cognition in children, while others primarily focused on the behaviors of children. In summary, the current evidence suggests inverse associations between early-life exposure to OPFRs and the childhood intelligence quotient and internalizing behavior and positive relationships of OPFR exposure with externalizing behavior. However, some differences in the timing of sample collection for exposure measurements, in the individual OPFR metabolites available, in the neurodevelopmental scales for outcome measurement, and in the statistical methods used to analyze the data are noted. In addition, further studies are warranted to evaluate some important issues, such as sex differences in the association, exposure-sensitive periods, and cumulative exposure risk assessment.

Organophosphate Esters in Foodstuffs from Multiple Provinces in China: Possible Sources during Food Processing and Implications for Human Exposure

With increasing application of organophosphate esters (OPEs) as flame retardants and plasticizers in the world, the health and ecological risks posed by these chemicals have raised people's concern over the years. Despite the fact that dietary intake is an important pathway for human exposure to OPEs, monitoring on OPEs in foodstuffs is scarce. In this study, we measured 14 OPEs in both packaged (n = 229) and fresh (n = 58) foodstuffs collected across China with a new method that was developed by two-stage solid-phase extraction. The total concentrations of OPEs (ΣOPEs) in 12 categories of packaged foodstuffs and 5 categories of fresh foodstuffs were in the range of 0.212-273 ng/g wet weight (ww) [geometric mean (GM): 5.06 ng/g ww] and 0.189-2.82 ng/g ww (GM: 0.618 ng/g ww), respectively. Significantly higher levels of ΣOPEs were found in packaged food categories of fruits and meat than those in the corresponding fresh ones, implying the extra introduction of OPEs during the processing and storage of foodstuffs. Correlation analysis showed that the GM concentrations of individual OPEs in animal-derived foods with few industrial processing were positively correlated with their annual production volumes in China in 2020, emphasizing the significance of natural sources of OPEs in these food samples. Elevated levels of ΣOPEs (range: 8.94-4120 and GM: 274 ng/g) were found in food-packaging materials, and the predominant OPE analogues were consistent with those found in packaged food samples. The result implies that the food-packaging material can be an important contamination source of OPEs in packaged foodstuffs, which is in particular true for triphenyl phosphate, tris(2-chloroisopropyl) phosphate, tris(2-chloroethyl) phosphate, and 2-ethylhexyl diphenyl phosphate. The median daily intake of ΣOPEs via food was estimated as 65.4 ng/kg bw/day for adults in China, and the category of cereals was the major contributor (72.7%) of the dietary exposure to OPEs. The exposure risk of OPEs via food intake was generally low for the Chinese population. Overall, this study establishes a baseline concentration for OPEs in Chinese foodstuffs and uncovers food contact material as a potential source of OPEs in foods. It is expected that the research in terms of food safety and OPE contamination will benefit from this work.

Sources, behaviors, transformations, and environmental risks of organophosphate esters in the coastal environment: A review

The rapid growth in the global production of organophosphate esters (OPEs) has resulted in their high environmental concentrations. The low removal rate of OPEs makes the effluents of wastewater treatment plants be one of the major sources of OPEs. Due to relatively high solubility and mobility, OPEs can be carried to the coastal environment through river discharge and atmospheric deposition. Therefore, the coastal environment can be an important OPE sink. Previous studies have shown that OPEs were widely detected in coastal atmospheres, water, sediments, and even aquatic organisms. OPEs can undergo various environmental processes in the coastal environment, including adsorption/desorption, air-water exchange, and degradation. In addition, bioaccumulation of OPEs was observed in coastal biota but current concentrations would not cause significant ecological risks. More efforts are required to understand the environmental behaviors of OPEs and address resultant environmental and health risks, especially in the complicated environment.

Penetration of Organophosphate Triesters and Diesters across the Blood-Cerebrospinal Fluid Barrier: Efficiencies, Impact Factors, and Mechanisms

The penetration of organophosphate triesters (tri-OPEs) and diesters (di-OPEs) across the blood-brain barrier and their influencing factors remain unclear in humans. In this study, 21 tri-OPEs and 8 di-OPEs were measured in 288 paired serum and cerebrospinal fluid (CSF) samples collected in Jinan, China. Six tri-OPEs were frequently detected in both serum and CSF, with median concentrations ranging from 0.062 to 1.62 and 0.042-1.11 ng/mL, respectively. Their penetration efficiencies across the blood-CSF barrier (BCSFB) (R_CSF/serum, C_CSF/C_serum) were calculated at 0.667-2.80, and these efficiencies first increased and then decreased with their log K_ow values. The reduced penetration efficiencies of triphenyl phosphate (TPHP) and 2-ethylhexyl diphenyl phosphate (EHDPP) may be attributed to their strong binding affinities for human serum albumin and p-glycoprotein due to their high hydrophobicity and aryl structure, as indicated by molecular docking. This suggests that active efflux transport may be involved in the penetration of TPHP and EHDPP in addition to passive diffusion similar to the other four tri-OPEs. Di-OPEs were found in few serum samples and even fewer CSF samples, indicating their limited BCSFB permeability. This may be due to their high polarity, low hydrophobicity, and ionic state in blood. This study has important implications for understanding the neurotoxicity of tri-OPEs and di-OPEs and the underlying mechanisms.

Tri-n-butyl phosphate delays tissue repair by dysregulating neutrophil function in zebrafish

Tri-n-butyl phosphate (TnBP) is a widely used organophosphate ester, but its effects on the regenerative process under damaging circumstances remain unknown. In the present study, zebrafish larvae were exposed to 0, 50, 100, 200 and 1000 μg/L TnBP, and the caudal fins were cut at 72 hours post fertilization (hpf). First, after exposure to TnBP, the number of total neutrophils decreased together with decreased neutrophils in the tail, and TnBP inhibited chemotaxis. Second, reactive oxygen species (ROS) levels in the zebrafish decreased greatly. Following exposure to TnBP, transcription levels of many genes regulating fin regeneration, such as fgf20a, fgfr1a, bmp2a and bmp4, were significantly downregulated, while inflammatory factors such as cxcl8a, cxcl18b, il-6, and tnfa were abnormally upregulated. In addition, TnBP inhibited the regenerative area after caudal fin amputation. The inflammatory state was adverse during the regenerative process. In summary, TnBP exposure is immunotoxic and decreases oxidative stress in injured zebrafish larvae.

Insights into the mechanisms of tris(2-chloroethyl) phosphate-induced growth inhibition in juvenile yellow catfish Pelteobagrus fulvidraco

With the gradual elimination of brominated flame retardants (BFRs), the production and application of tris (2-chloroethyl) phosphate (TCEP), as a substitute of BFRs, has increased greatly. The objective of the present study was to comprehensively explore the potential adverse effects of TCEP on fish growth and the possible underlying mechanisms. To this end, juvenile yellow catfish (Pelteobagrus fulvidraco) were exposed to environmentally relevant concentrations of TCEP (0, 1, 10 and 100 µg/L) for 30 days. The results showed that exposure to high concentrations of TCEP (10 and 100 µg/L) significantly decreased body weight, body length and specific growth rate (SGR). Plasma IGF-I levels and hepatic mRNA levels of igf1 and igf1r were all reduced, while the transcriptional levels of IGFBPs (igfbp2, igfbp3, igfbp5) were significantly up-regulated in the liver of yellow catfish under exposure to 10 and 100 µg/L TCEP. TCEP-induced growth inhibition might be related to somatostatin (SS) signaling system, as evidenced by elevated mRNA transcriptions of ss in brain and its receptors (sstr2, sstr3, sstr5) in liver. In addition, fish exposed to high concentrations of TCEP displayed multiple histological alterations in liver. Taken together, these findings suggested that TCEP (>10 µg/L) might exert its inhibitory effect on fish growth through interfering with the GH/IGF axis and SS signaling system, and by impairing hepatic structures.

Developmental Neurotoxicity and Behavioral Screening in Larval Zebrafish with a Comparison to Other Published Results

With the abundance of chemicals in the environment that could potentially cause neurodevelopmental deficits, there is a need for rapid testing and chemical screening assays. This study evaluated the developmental toxicity and behavioral effects of 61 chemicals in zebrafish (Danio rerio) larvae using a behavioral Light/Dark assay. Larvae (n = 16–24 per concentration) were exposed to each chemical (0.0001–120 μM) during development and locomotor activity was assessed. Approximately half of the chemicals (n = 30) did not show any gross developmental toxicity (i.e., mortality, dysmorphology or non-hatching) at the highest concentration tested. Twelve of the 31 chemicals that did elicit developmental toxicity were toxic at the highest concentration only, and thirteen chemicals were developmentally toxic at concentrations of 10 µM or lower. Eleven chemicals caused behavioral effects; four chemicals (6-aminonicotinamide, cyclophosphamide, paraquat, phenobarbital) altered behavior in the absence of developmental toxicity. In addition to screening a library of chemicals for developmental neurotoxicity, we also compared our findings with previously published results for those chemicals. Our comparison revealed a general lack of standardized reporting of experimental details, and it also helped identify some chemicals that appear to be consistent positives and negatives across multiple laboratories.

Alkyl organophosphate flame retardants (OPFRs) induce lung inflammation and aggravate OVA-simulated asthmatic response via the NF-кB signaling pathway

Alkyl organophosphate flame retardants (OPFRs), tri-n-butyl phosphate (TnBP) and tris(2-butoxyethyl) phosphate (TBOEP), are ubiquitously detected in indoor and outdoor environments and their inhalation may result in lung damage. This study examined pulmonary toxicity after exposure to TnBP or TBOEP and investigated aggravation of inflammation and immunoreaction by TnBP in an ovalbumin (OVA)-induced mice model. Transcriptomics were used to further reveal the underlying mechanism. Exposure to TnBP or TBOEP resulted in pathological damage, including edema and thickened alveolar septum. In comparison with the control, enhanced levels of superoxide dismutase (SOD) (p < 0.01 in TnBP (High) group and p < 0.05 in TBOEP (High) group), glutathione peroxidase (GSH-px) (p < 0.05), malondialdehyde (MDA) (p < 0.01), and cytokines under a dose-dependent relationship were noted, and the expression of the Fkbp5/Nos3/MAPK/NF-кB signaling pathway (p < 0.01) was upregulated in the TnBP and TBOEP groups. Moreover, the combined exposure of TnBP and OVA exacerbated the allergic inflammatory response, including airway hyperresponsiveness, leukocytosis, cellular exudation and infiltration, secretion of inflammatory mediators, and higher expression of IgE (p < 0.01). Transcriptomics results demonstrated that the PI3K/Akt/NF-кB signal pathway was involved in TnBP-aggravated asthmatic mice. Exposure to TnBP or TBOEP resulted in oxidative damage and leukocyte-induced lung injury. TnBP can further facilitate OVA-induced asthma through an inflammatory response. This study is the first to reveal the pulmonary toxicity and potential mechanism induced by OPFRs through an in-vivo model.

The Ahr2-Dependent wfikkn1 Gene Influences Zebrafish Transcriptome, Proteome, and Behavior

The aryl hydrocarbon receptor (AHR) is required for vertebrate development and is also activated by exogenous chemicals, including polycyclic aromatic hydrocarbons (PAHs) and TCDD. AHR activation is well-understood, but roles of downstream molecular signaling events are largely unknown. From previous transcriptomics in 48-hours post fertilization (hpf) zebrafish exposed to several PAHs and TCDD, we found wfikkn1 was highly co-expressed with cyp1a (marker for AHR activation). Thus, we hypothesized wfikkn1's role in AHR signaling, and showed that wfikkn1 expression was Ahr2 (zebrafish ortholog of human AHR)-dependent in developing zebrafish exposed to TCDD. To functionally characterize wfikkn1, we made a CRISPR-Cas9 mutant line with a 16-bp deletion in wfikkn1's exon, and exposed wildtype and mutants to DMSO or TCDD. 48-hpf mRNA sequencing revealed over 700 genes that were differentially expressed (p < 0.05, log2FC > 1) between each pair of treatment combinations, suggesting an important role for wfikkn1 in altering both the 48-hpf transcriptome and TCDD-induced expression changes. Mass spectrometry-based proteomics of 48-hpf wildtype and mutants revealed 325 significant differentially expressed proteins. Functional enrichment demonstrated wfikkn1 was involved in skeletal muscle development and played a role in neurological pathways after TCDD exposure. Mutant zebrafish appeared morphologically normal but had significant behavior deficiencies at all life stages, and absence of Wfikkn1 did not significantly alter TCDD-induced behavior effects at all life stages. In conclusion, wfikkn1 did not appear to be significantly involved in TCDD's overt toxicity but is likely a necessary functional member of the AHR signaling cascade.

Impact of airborne total suspended particles (TSP) and fine particulate matter (PM2.5 )-induced developmental toxicity in zebrafish (Danio rerio) embryos

Airborne total suspended particles (TSP) and particulate matter (PM_2.5 ) threaten global health and their potential impact on cardiovascular and respiratory diseases are extensively studied. Recent studies attest premature deaths, low birth weight, and congenital anomalies in the fetus of pregnant women exposed to air pollution. In this regard, only few studies have explored the effects of TSP and PM_2.5 on cardiovascular and cerebrovascular development. As both TSP and PM_2.5 differ in size and composition, this study is attempted to assess the variability in toxicity effects between TSP and PM_2.5 on the development of cardiovascular and cerebrovascular systems and the underlying mechanisms in a zebrafish model. To explore the potential toxic effects of TSP and PM_2.5 , zebrafish embryos/larvae were exposed to 25, 50, 100, 200, and 400 μg/ml of TSP and PM_2.5 from 24 to 120 hpf (hours post-fertilization). Both TSP and PM_2.5 exposure increased the rate of mortality, malformations, and oxidative stress, whereas locomotor behavior, heart rate, blood flow velocity, development of cardiovasculature and neurovasculature, and dopaminergic neurons were reduced. The expression of genes involved in endoplasmic reticulum stress (ERS), Wnt signaling, and central nervous system (CNS) development were altered in a dose- and time-dependent manner. This study provides evidence for acute exposure to TSP and PM_2.5 -induced cardiovascular and neurodevelopmental toxicity, attributed to enhanced oxidative stress and aberrant gene expression. Comparatively, the effects of PM_2.5 were more pronounced than TSP.

A worldwide review of currently used pesticides' monitoring in agricultural soils

The adverse effects of pesticides on the agricultural ecosystem have been matter of concern in recent decades. However, attention has mostly been directed to highly persistent chemicals leading to underestimating currently used pesticides. In this review we present an overview of the studies on monitoring currently used pesticides in agricultural soils around the world published in the last 50 years. Furthermore, all data available in the articles has been integrated into one united data set. Finally, an overall meta-analysis on the prepared data set was performed. The result of the meta-analysis has been presented in this article. It was revealed that the occurrence of currently used pesticides in the soil of agricultural regions was alarming in many countries, establishing the need for long-term monitoring programs, especially in regions with intensive agricultural activities, in order to determine real-world currently used pesticides fate and accumulation in the soil.

Electrochemical (Bio)Sensors for the Detection of Organophosphorus Pesticides Based on Nanomaterial-Modified Electrodes: A Review

Organophosphorus pesticides were easily remained in fruits and vegetables which would be harm to the environmental safety and human health. In recent years, due to the simple preparation process, fast response and high sensitivity, the electrochemical (bio)sensors have received increasing attention, which were extensively used as the sensing platform for the detection of OPPs. The mechanisms for the determination of OPPs mainly included redox of nitrophenyl OPPs, enzyme hydrolysis and inhibition, immunosensor, aptasensor. Nowadays, the mainly explored electrode material has focused on metal-organic frameworks, metal and metal derivatives, carbon materials (carbon nanotube, graphene, g-C3N4), MXene, etc. These nanomaterials played important roles in the electrochemical (bio)sensors, which included: (a) as an electrocatalyst to promote the redox reaction, (b) as a carrier to load the enzyme or aptamer, (c) as a recognizer to identify the targets. The nanomaterials-based electrochemical (bio)sensor was a rapid, cost-effective methods to detect OPPs with high sensitivity. Besides, this review compared the analytical performance of different nanomaterials-based electrochemical (bio)sensors, and also identified the key challenges in the future. It would provide new ideas and insights to the further development and application of electrochemical (bio)sensors and the detection of pesticides in real samples.

Dietary Exposure to Flame Retardant Tris (2-Butoxyethyl) Phosphate Altered Neurobehavior and Neuroinflammatory Responses in a Mouse Model of Allergic Asthma

Tris (2-butoxyethyl) phosphate (TBEP) is an organophosphate flame retardant and used as a plasticizer in various household products such as plastics, floor polish, varnish, textiles, furniture, and electronic equipment. However, little is known about the effects of TBEP on the brain and behavior. We aimed to examine the effects of dietary exposure of TBEP on memory functions, their-related genes, and inflammatory molecular markers in the brain of allergic asthmatic mouse models. C3H/HeJSlc male mice were given diet containing TBEP (0.02 (TBEP-L), 0.2 (TBEP-M), or 2 (TBEP-H) μg/kg/day) and ovalbumin (OVA) intratracheally every other week from 5 to 11 weeks old. A novel object recognition test was conducted in each mouse at 11 weeks old. The hippocampi were collected to detect neurological, glia, and immunological molecular markers using the real-time RT-PCR method and immunohistochemical analyses. Mast cells and microglia were examined by toluidine blue staining and ionized calcium-binding adapter molecule (Iba)-1 immunoreactivity, respectively. Impaired discrimination ability was observed in TBEP-H-exposed mice with or without allergen. The mRNA expression levels of N-methyl-D aspartate receptor subunits Nr1 and Nr2b, inflammatory molecular markers tumor necrosis factor-α oxidative stress marker heme oxygenase 1, microglia marker Iba1, and astrocyte marker glial fibrillary acidic protein were significantly increased in TBEP-H-exposed mice with or without allergen. Microglia and mast cells activation were remarkable in TBEP-H-exposed allergic asthmatic mice. Our results indicate that chronic exposure to TBEP with or without allergen impaired object recognition ability accompanied with alteration of molecular expression of neuronal and glial markers and inflammatory markers in the hippocampus of mice. Neuron-glia-mast cells interaction may play a role in TBEP-induced neurobehavioral toxicity.

Effects of common environmental endocrine-disrupting chemicals on zebrafish behavior

Environmental endocrine-disrupting chemicals (EDCs), a type of exogenous organic pollutants, are ubiquitous in natural aquatic environments. Therefor, this review focused on the use of the zebrafish as a model to explore the effect of different EDCs on behavior, as well as the molecular mechanisms that drive these effects. Furthermore, our study summarizes the current knowledge on the neuromodulatory effects of different EDCs in zebrafish. This study also reviews the current state of zebrafish behavior research, in addition to the potential mechanisms of single and mixed pollutant-driven behavioral dysregulation at the molecular level, as well as the applications of zebrafish behavior experiments for neuroscience research. This review broadens our understanding of the influence of EDCs on zebrafish behavior and provides guidance for future research.

Imidacloprid and thiamethoxam affect synaptic transmission in zebrafish

Imidacloprid (IMI) and thiamethoxam (THM) are two commonly applied neonicotinoid insecticides. IMI and THM could cause negative impacts on non-target organisms like bees. However, the information about neurotoxicity of IMI and THM in fish is still scarce. Here we investigated the effects of IMI and THM on locomotor behavior, AChE activity, and transcription of genes related to synaptic transmission in zebrafish exposed to IMI and THM with concentrations of 50 ng L^-1 to 50,000 ng L^-1 at 14 day post fertilization (dpf), 21 dpf, 28 dpf and 35 dpf. Our results showed that IMI and THM significantly influenced the locomotor activity in larvae at 28 dpf and 35 dpf. THM elevated AChE activity at 28 dpf. The qPCR data revealed that IMI and THM affected the transcription of marker genes belonging to the synapse from 14 dpf to 35 dpf. Furthermore, IMI and THM mainly affected transcription of key genes in γ-aminobutyric acid, dopamine and serotonin pathways in larvae at 28 dpf and 35 dpf. These results demonstrated the neurotoxicity of IMI and THM in zebrafish. The findings from this study suggested that IMI and THM in the aquatic environment may pose potential risks to fish fitness and survival.

Evaluation of the acute toxicity and neurodevelopmental inhibition of perfluorohexanoic acid (PFHxA) in zebrafish embryos

Perfluorohexanoic acid (PFHxA), a widely used emerging alternative for 8-carbon PFAAs, has been detected at a high level in the water environment. While its toxicity and environmental health risk are still largely unknown in aquatic life. The present study aimed to evaluated the possible developmental neurotoxicity induced by PFHxA exposure (0, 0.48, 2.4, and 12 mg/L for 120 h) in the zebrafish embryo. Here, both developmental endpoints, neurotransmitters concentrations, locomotor behavior were analyzed. No significant effects on mortality, malformation rate, and growth delay were detected in the low dose treatment groups except for in the high dose group (12 mg/L). A significant increase in swimming speed were noted in the 0.48 mg/L group. Other changes including neurotransmitters concentrations and green fluorescent protein (GFP) expression in Tg (HuC-GFP) zebrafish larvae were significantly increased in 12 mg/L group. Beyond that, genes related to neurodevelopment were significantly decreased in larvae. Moreover, downregulations of protein expression levels of α1-tubulin, elavl3, and gap43 were identified. These results demonstrate that the PFAAs alternative PFHxA have no significant neurodevelopmental effects on zebrafish larvae under acute low-dose exposure, while, it is important to note that PFHxA perform inhibiting effects on neurotransmitter and central nervous system under a relatively high dose. This in vivo study could provide reliable toxicity information for risk assessments of PFHxA on aquatic ecosystems. CAPSULE: PFHxA have no significant neurodevelopmental effects on zebrafish larvae under acute low-dose exposure, while exposed with relatively high-dose, could induced the alternations of neurotransmitter concentrations as well as the genes involved in the early developmental stages of zebrafish, leading to the impairment of the nervous system in zebrafish larvae.

Beyond Cholinesterase Inhibition: Developmental Neurotoxicity of Organophosphate Ester Flame Retardants and Plasticizers

BACKGROUND

To date, the toxicity of organophosphate esters has primarily been studied regarding their use as pesticides and their effects on the neurotransmitter acetylcholinesterase (AChE). Currently, flame retardants and plasticizers are the two largest market segments for organophosphate esters and they are found in a wide variety of products, including electronics, building materials, vehicles, furniture, car seats, plastics, and textiles. As a result, organophosphate esters and their metabolites are routinely found in human urine, blood, placental tissue, and breast milk across the globe. It has been asserted that their neurological effects are minimal given that they do not act on AChE in precisely the same way as organophosphate ester pesticides.

OBJECTIVES

This commentary describes research on the non-AChE neurodevelopmental toxicity of organophosphate esters used as flame retardants and plasticizers (OPEs). Studies in humans, mammalian, nonmammalian, and in vitro models are presented, and relevant neurodevelopmental pathways, including adverse outcome pathways, are described. By highlighting this scientific evidence, we hope to elevate the level of concern for widespread human exposure to these OPEs and to provide recommendations for how to better protect public health.

DISCUSSION

Collectively, the findings presented demonstrate that OPEs can alter neurodevelopmental processes by interfering with noncholinergic pathways at environmentally relevant doses. Application of a pathways framework indicates several specific mechanisms of action, including perturbation of glutamate and gamma-aminobutyric acid and disruption of the endocrine system. The effects may have implications for the development of cognitive and social skills in children. Our conclusion is that concern is warranted for the developmental neurotoxicity of OPE exposure. We thus describe important considerations for reducing harm and to provide recommendations for government and industry decision makers. https://doi.org/10.1289/EHP9285.

Effects of tris (2-chloroethyl) phosphate (TCEP) on survival, growth, histological changes and gene expressions in juvenile yellow catfish Pelteobagrus fulvidraco

Tris (2-chloroethyl) phosphate (TCEP) is an emerging aquatic environmental pollutant. In the present study, juvenile yellow catfish (Pelteobagrus fulvidraco) were exposed to environmentally relevant concentrations of TCEP for 30 days. The results showed that TCEP exposure decreased the survival rate (100 μg/L), body weight (10 and 100 μg/L) and specific growth rate (10 and 100 μg/L) of juvenile yellow catfish. Exposure to TCEP resulted in pronounced damages of gill structures. Gene transcription analysis showed that the antioxidant capacity of the liver and gills was affected; CYP1A1 might contribute to phase I metabolism of TCEP in the liver rather than CYP1B1; TCEP stress might increase the demand of ion transport in fish gill; TCEP could stimulate the immune response and might induce apoptosis via a p53-Bax pathway and caspase-dependent pathway in gills. Collectively, these findings provide new insights into the toxic effects of TCEP on fish.

Gene co-expression network analysis in zebrafish reveals chemical class specific modules

BACKGROUND

Zebrafish is a popular animal model used for high-throughput screening of chemical hazards, however, investigations of transcriptomic mechanisms of toxicity are still needed. Here, our goal was to identify genes and biological pathways that Aryl Hydrocarbon Receptor 2 (AHR2) Activators and flame retardant chemicals (FRCs) alter in developing zebrafish. Taking advantage of a compendium of phenotypically-anchored RNA sequencing data collected from 48-h post fertilization (hpf) zebrafish, we inferred a co-expression network that grouped genes based on their transcriptional response.

RESULTS

Genes responding to the FRCs and AHR2 Activators localized to distinct regions of the network, with FRCs inducing a broader response related to neurobehavior. AHR2 Activators centered in one region related to chemical stress responses. We also discovered several highly co-expressed genes in this module, including cyp1a, and we subsequently show that these genes are definitively within the AHR2 signaling pathway. Systematic removal of the two chemical types from the data, and analysis of network changes identified neurogenesis associated with FRCs, and regulation of vascular development associated with both chemical classes. We also identified highly connected genes responding specifically to each class that are potential biomarkers of exposure.

CONCLUSIONS

Overall, we created the first zebrafish chemical-specific gene co-expression network illuminating how chemicals alter the transcriptome relative to each other. In addition to our conclusions regarding FRCs and AHR2 Activators, our network can be leveraged by other studies investigating chemical mechanisms of toxicity.