Halogen-free organophosphorus flame retardants caused oxidative stress and multixenobiotic resistance in Asian freshwater clams (Corbicula fluminea)

Weight of evidence evaluation of the metabolism disrupting effects of triphenyl phosphate using an expert knowledge elicitation approach

Identification of Endocrine-Disrupting Chemicals (EDCs) in a regulatory context requires a high level of evidence. However, lines of evidence (e.g. human, in vivo, in vitro or in silico) are heterogeneous and incomplete for quantifying evidence of the adverse effects and mechanisms involved. To date, for the regulatory appraisal of metabolism-disrupting chemicals (MDCs), no harmonised guidance to assess the weight of evidence has been developed at the EU or international level. To explore how to develop this, we applied a formal Expert Knowledge Elicitation (EKE) approach within the European GOLIATH project. EKE captures expert judgment in a quantitative manner and provides an estimate of uncertainty of the final opinion. As a proof of principle, we selected one suspected MDC -triphenyl phosphate (TPP) - based on its related adverse endpoints (obesity/adipogenicity) relevant to metabolic disruption and a putative Molecular Initiating Event (MIE): activation of peroxisome proliferator activated receptor gamma (PPARγ). We conducted a systematic literature review and assessed the quality of the lines of evidence with two independent groups of experts within GOLIATH, with the objective of categorising the metabolic disruption properties of TPP, by applying an EKE approach. Having followed the entire process separately, both groups arrived at the same conclusion, designating TPP as a "suspected MDC" with an overall quantitative agreement exceeding 85%, indicating robust reproducibility. The EKE method provides to be an important way to bring together scientists with diverse expertise and is recommended for future work in this area.

Exposure to high concentrations of triphenyl phosphate altered functional performance, liver metabolism and intestinal bacterial composition of aquatic turtles

Organophosphorus flame retardants, such as triphenyl phosphate (TPhP), exist ubiquitously in various environments owing to their widespread usage. Potential toxic effects of residual flame retardants on cultured non-fish species are not concerned commonly. TPhP-induced physiological and biochemical effects in an aquatic turtle were evaluated here by systematically investigating the changes in growth and locomotor performance, hepatic antioxidant ability and metabolite, and intestinal microbiota composition of turtle hatchlings after exposure to different TPhP concentrations. Reduced locomotor ability and antioxidant activity were only observed in the highest concentration group. Several metabolic perturbations that involved in amino acid, energy and nucleotide metabolism, in exposed turtles were revealed by metabolite profiles. No significant among-group difference in intestinal bacterial diversity was observed, but the composition was changed markedly in exposed turtles. Increased relative abundances of some bacterial genera (e.g., Staphylococcus, Vogesella and Lawsonella) probably indicated adverse outcomes of TPhP exposure. Despite having only limited impacts of exposure at environmentally relevant levels, our results revealed potential ecotoxicological risks of residual TPhP for aquatic turtles considering TPhP-induced metabolic perturbations and intestinal bacterial changes.

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.

Critical review on organophosphate esters in water environment: Occurrence, health hazards and removal technologies

Organophosphate esters (OPEs), which are phosphoric acid ester derivatives, are anthropogenic substances that are widely used in commerce. Nevertheless, there is growing public concern about these ubiquitous contaminants, which are frequently detected in contaminated water sources. OPEs are mostly emitted by industrial operations, and the primary routes of human exposure to OPEs include food intake and dermal absorption. Because of their negative effects on both human health and the environment, it is clear that innovative methods are needed to facilitate their eradication. In this study, we present a comprehensive overview of the existing characteristics and origins of OPEs, their possible impacts on human health, and the merits, drawbacks, and future possibilities of contemporary sophisticated remediation methods. Current advanced remediation approaches for OPEs include adsorption, degradation (advanced oxidation, advanced reduction, and redox technology), membrane filtration, and municipal wastewater treatment plants, degradation and adsorption are the most promising removal technologies. Meanwhile, we proposed potential areas for future research (appropriate management approaches, exploring the combination treatment process, economic factors, and potential for secondary pollution). Collectively, this work gives a comprehensive understanding of OPEs, providing useful insights for future research on OPEs pollution.

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.

A multibiomarker approach to assess the ecotoxicological effects of diclofenac on Asian clam Corbicula fluminea (O. F. Müller, 1774)

Diclofenac (DCF), one of the most current and widely used nonsteroidal anti-inflammatory drugs (NSAIDs), has been frequently detected in aquatic environments worldwide. However, the ecotoxicological effects of DCF on freshwater invertebrates remain largely unknown. In the present study, Corbicula fluminea were exposed to environmentally relevant concentrations of DCF (0, 2, 20, and 200 μg/L) for 28 days, and the potential adverse effects of DCF on siphoning behavior, antioxidant responses, and apoptosis were investigated. Our results showed that the siphon efficiencies of clams were significantly suppressed under DCF stress. DCF exerted neurotoxicity via reducing the activity of acetylcholinesterase (AChE) in gills and digestive gland of C. fluminea. Exposure to DCF induced antioxidant stress and increased malondialdehyde (MDA) levels in both gills and digestive gland of C. fluminea. Transcriptional alterations of apoptosis-related genes indicated that DCF might induce apoptosis by triggering mitochondrial apoptotic pathway. These findings can improve our understanding of the ecological risk of DCF in freshwater ecosystems.

Regional distribution of the plastic additive tris(butoxyethyl) phosphate in Nanyang Lake estuary, China, and toxic effects on Cyprinus carpio

There is increasing concern regarding the toxicological effects of plastic additives on humans and aquatic organisms. This study investigated effects of the plastic additive tris(butoxyethyl) phosphate (TBEP) on Cyprinus carpio by measuring concentration distribution of TBEP in the Nanyang Lake estuary, as well as toxic effects of varying doses of TBEP exposure on carp liver. This also included measuring responses of superoxide dismutase (SOD), malondialdehyde (MDA), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and cysteinyl aspartate-specific protease (caspase). Concentrations of TBEP in the polluted water environment (water company inlets, urban sewage pipes, etc.) in the survey area were as high as 76.17-3875.29 μg/L, and 3.12 μg/L in the river flowing through the urban area, and 1.18 μg/L in the estuary of the lake. In the subacute toxicity test, SOD activity in liver tissue with an increase in TBEP concentration was reduced significantly, while the MDA content continued to increase with an increase in TBEP concentration. Inflammatory response factors (TNF-α and IL-1β) and apoptotic proteins (caspase-3 and caspase-9) gradually increased with increasing concentrations of TBEP. Additionally, reduced organelles, increased lipid droplets, swelling of mitochondria, and disorder of mitochondrial cristae structure were observed in liver cells of TBEP-treated carp. Generally, TBEP exposure induced severe oxidative stress in carp liver tissue, resulting in release of inflammatory factors and inflammatory response, mitochondrial structure changes, and the expression of apoptotic proteins. These findings benefit our understanding about the toxicological effects of TBEP in aquatic pollution.

Associations between neonicotinoids metabolites and hematologic parameters among US adults in NHANES 2015-2016

Hematologic parameters are important indicators for monitoring the physiological changes and human health. Neonicotinoids (NEOs) exhibit toxic effects and can affect hematologic parameters. However, the effects of exposure to NEOs metabolites on hematologic parameters in the general population remain unknown. We examined the relationship between NEOs metabolites and hematologic parameters using a cross-sectional study design in 1397 adults of the National Health and Nutrition Examination Survey (NHANES) 2015-2016. The levels of NEOs metabolites in urine and hematologic makers were measured. Multivariate linear regression models were performed to examine the relationship between exposure to NEOs metabolites and hematologic parameters. Detectable urine levels of clothianidin (CLO) was inversely associated with hematocrit (β =  - 0.689; 95% CI: - 1.335, - 0.042). Detectability of 5-hydroxy-imidacloprid (HIMI) was inversely correlated with basophil percentage (β =  - 0.093; 95% CI: - 0.180, - 0.007). N-Desmethyl-acetamiprid (NDE) was related to reduced white blood cells (WBC) (β =  - 0.419; 95% CI: - 0.764, - 0.074) and neutrophil counts (β =  - 0.349; 95% CI: - 0.623, - 0.074). Imidacloprid-equivalent total neonicotinoids (IMIeq) was negatively related to red blood cells (RBC) (β =  - 0.058; 95% CI: - 0.097, - 0.020), hemoglobin (β =  - 0.149; 95% CI: - 0.282, - 0.015), and hematocrit (β =  - 0.484; 95% CI: - 0.855, - 0.113). We also observed that exposure to NEOs metabolites was sex specifically related to hematologic alterations. For example, IMIeq was associated with reduced basophil counts (β =  - 0.016; 95% CI: - 0.028, - 0.003), basophil percentage (β =  - 0.092; 95% CI: - 0.169, - 0.016), RBC (β =  - 0.097; 95% CI: - 0.156, - 0.038), hemoglobin (β =  - 0.200; 95% CI: - 0.355, - 0.045), and hematocrit (β =  - 0.605; 95% CI: - 1.111, - 0.098) only in males. These results provide the first evidence that exposure to NEOs metabolites can disturb hematologic homeostasis in the general population, and the effects may be sex specific.

Benzotriazole UV stabilizer-induced genotoxicity in freshwater benthic clams: A survey on apoptosis, oxidative stress, histopathology and transcriptomics

Benzotriazole UV stabilizer-329 (UV-329) is frequently detected in various environmental and biological matrices. However, the toxicity effect on freshwater benthos induced by UV-329 has rarely been described. In this study, genotoxicity, apoptosis, oxidative stress, histopathological alterations, siphoning behavior, and bioaccumulation in the gill and digestive gland of Corbicula fluminea exposed to UV-329 at 10, 100, and 1000 μg/L for 21 days were investigated. Toxicity screening using transcriptomics confirmed that UV-329 preferentially stimulated cellular process-related pathways including gap junctions, apoptosis, phagosomes and necroptosis. The transcript levels of a large number of apoptosis genes were significantly upregulated. This apoptosis mechanism was further confirmed by the fact that UV-329 exposure significantly increased the percentage of apoptotic cells, activated caspase-3, -8, and -9, and affected the antioxidant enzyme activities. Following exposure to 1000 μg/L UV-329, significant histological alterations were reflected in the corrosion of cilia, cellular swelling of epithelial cells in the gills, degeneration of digestive tubules, and necrosis of epithelial cells in the digestive glands. These results may aid in elucidating the toxicity mechanism of UV329 in bivalves and evaluating the hazards of UV-329 in benthic ecosystems.

Feeding behavior, microcystin accumulation, biochemical response, and ultramicrostructure changes in edible freshwater bivalve Corbicula fluminea exposed to Microcystis aeruginosa

As filter-feeders, bivalves naturally come into direct contact with microcystins (MCs) in eutrophic water bodies suffering from cyanobacteria blooms. To date, however, no studies have quantified the dynamics of microcystin accumulation and depuration in the edible freshwater bivalve Corbicula fluminea when exposed to dense bloom concentrations of Microcystis aeruginosa, while considering dynamic changes of biochemical indexes and feeding structure. In the present study, the bioaccumulation and detoxification of microcystin-LR (MC-LR) in C. fluminea were investigated. Our results showed that C. fluminea would graze equally efficiently on green algae and M. aeruginosa, irrespective of whether the M. aeruginosa strains were toxic or non-toxic. MCs could be accumulated and depurated by C. fluminea efficiently. In addition, linear and exposure time-dependent MC-LR accumulation patterns were observed in C. fluminea. Activities of biotransformation (glutathione S-transferase, GST) and antioxidant enzymes (superoxide dismutase, SOD, and catalase, CAT) and malondialdehyde (MDA) contents in various tissues of treated clams were stimulated by MCs in a tissue-specific manner. Our findings indicated that C. fluminea hepatopancreas was the primary target organ for MC-LR detoxification processes, as evidenced by a significant increase in GST activity. Besides, gills and mantle were more sensitive than the other tissues to oxidative stress in the initial microcystin exposure period with a significant increase in SOD activity. The scanning electron microscopy (SEM) observations revealed that the lateral cilia in the gill aperture were well developed during the MCs exposure period, which could perform the filter-feeding function instead of the damaged frontal cilium. This study provides insight into the possible tolerance of C. fluminea exposed to dense bloom concentrations of M. aeruginosa.

Physiological and proteomic responses of Chlamydomonas reinhardtii to arsenate and lead mixtures

Arsenic (As) and lead (Pb) are frequently emitted from various sources into environment, but microbial responses to their combined toxicity have not been systematically investigated. In this study, Chlamydomonas reinhardtii was exposed to two levels of arsenate (As (V), 50, 500 μg/L), Pb (II) (500, 5000 μg/L) and their mixture (50 μg/L As (V) + 500 μg/L Pb (II); 500 μg/L As (V) + 5000 μg/L Pb (II)). The growth of C. reinhardtii was inhibited more remarkably by As (V) than by Pb (II). The As stress was alleviated by Pb in the 50 μg/L As (V) + 500 μg/L Pb (II) treatment, but was enhanced upon the 500 μg/L As (V) + 5000 μg/L Pb (II) exposure, with more pronounced changes in a number of physiological parameters of the algal cells. Proteomic results showed that 71 differently expressed proteins (DEPs) in the treatment of 50 μg/L As (V) + 500 μg/L Pb (II), and 167 DEPs were identified in that of 500 μg/L As (V) + 5000 μg/L Pb (II). These proteins were involved in energy metabolism, photosynthetic carbon fixation, reactive oxygen scavenging and defense, and amino acid synthesis. Taken together, these physiological and proteomic data demonstrated that C. reinhardtii could resist the As (V) and Pb (II) combined treatments through extracellular complexation and intracellular pathways.

Sub-chronic ecotoxicity of triphenyl phosphate to earthworms (Eisenia fetida) in artificial soil: Oxidative stress and DNA damage

As a flame retardant, triphenyl phosphate (TPHP) is commonly added to various daily products. Due to its easy diffusion, TPHP pollution has become a global concern. Despite the wide focus on environmental risk, the sub-chronic ecotoxicity of TPHP in soil organisms remains unclear. In this study, the artificial soil exposure method was used to analyze the oxidative stress and DNA damage in earthworms with 0, 20, 40, 60 and 80 mg/kg TPHP treatments through the response of reactive oxygen species (ROS), antioxidant and detoxifying enzymes, malondialdehyde (MDA) and olive tail moment (OTM) at 7, 14, 21 and 28 days. Throughout the experimental period, the results showed that the ROS content in earthworms treated with 20, 40, 60 and 80 mg/kg TPHP treatments increased by 9.43-18.37 %, 6.07-25.73 %, 7.71-42.61 % and 8.22-46.70 %, respectively, compared to the control treatment. Meanwhile, the activities of antioxidant and detoxification enzymes in earthworms with all TPHP treatments were significantly activated after exposure for 7 and 14 days, and then inhibited at 21 and 28 days. Despite the protection of antioxidant enzymes and detoxification enzymes, MDA content in earthworms with the 20 mg/kg treatment still significantly increased at 7 and 14 days of exposure, as well as in the other three treatments. Compared to the control treatment, the obviously higher OTM values in earthworms with TPHP treatments possibly indicated a genotoxicity of TPHP in earthworms. Furthermore, the integrated biomarker response index (IBRv2) revealed that earthworms showed an obvious biochemical response TPHP-contaminated soil, which was strongly correlated with TPHP concentrations and exposure time. This study provides insights into the TPHP hazard in the soil environment and offers a reference to assess its environmental risk to soil ecosystems.

Toxic effect of triphenyl phosphate (TPHP) on Cyprinus carpio and the intestinal microbial community response

Triphenyl phosphate (TPHP) is a kind of organophosphorus flame retardants, and its use is increasing annually. However, the toxic effect associated with exposure to it has not been adequately investigated. Therefore, in this study, we determined the toxic dose of TPHP in the economic fish species, Cyprinus carpio. Acute and subacute toxicity tests were conducted, and the enrichment of TPHP in the gills, brain, intestines, and liver were determined by Liquid Chromatography-Mass Spectrometry, and the response of carp gut microbial community to TPHP stress was determined using 16 S rRNA gene high-throughput sequencing. Results showed that the 96-h LC₅₀ of TPHP in carp was 7 mg/L. At the 7 d, the order of TPHP absorption was as follows (from highest to lowest): gills > intestine > liver > brain, but at the 28 d and the purification period, the order of TPHP absorption was brain > gills > intestine > liver. TPHP exposure at 3.5 mg/L decreased α-diversity of the intestinal microbial community (p < 0.05), and altered community composition, in particular the relative abundance of dominant microbial populations. Functional profiles of the microbial communities predicted based on 16 S rRNA gene data showed upregulation in the degradation of exogenous substances and energy metabolism of the TPHP-treated groups (p < 0.05), suggesting that intestinal microbial taxa play a role in reducing TPHP toxicity. The results provide insights that could facilitate risk assessments of TPHP pollutants in aquatic environments and the management of associated water pollution.

Toxicity effects of ciprofloxacin on biochemical parameters, histological characteristics, and behaviors of Corbicula fluminea in different substrates

Antibiotic toxicity and antibiotic resistance have become significant challenges to human health. However, the potential ecotoxicity of sediment-associated antibiotics remains unknown. In this study, biochemical responses, histological changes, and behavioral responses of Corbicula fluminea exposed to sediment-associated ciprofloxacin (CIP) were systemically investigated. Special attention was paid to the influence of different substrate types. Biochemical analyses revealed that the balance of the antioxidant system was disrupted, eventually leading to oxidative damage to the gills and digestive gland with increasing CIP concentration. Severe histopathological changes appeared along with the oxidative damage. An enlargement of the tubule lumen and thinning of the epithelium in the digestive gland were observed under exposure to high CIP concentrations (0.5 and 2.5 μg/g CIP). In a behavioral assay, the filtration rate of C. fluminea in high concentration exposure groups was clearly inhibited. Moreover, from the integrated biomarker response (IBR) index, the toxicity response gradients of the digestive gland (no substrate--NOS > Sand > Sand and kaolinite clay-- SKC > Sand, kaolinite clay, and organic matter--SCO) and gills (NOS > SCO > SKC > Sand) were different among substrate exposure groups. The most serious histopathological damage and highest siphoning inhibition were observed in the NOS group. The changes in the morphological structure of digestive gland cells in C. fluminea were similar in the other three substrate groups. The inhibition of the filtration rate in the higher concentration groups decreased in the order Sand > SKC > SCO.

Gene expression and functional analysis of different heat shock protein (HSPs) in Ruditapes philippinarum under BaP stress

Heat shock proteins (HSPs) are a class of highly conserved proteins which can protect cells against various types of stress. However, little information on the mechanism involved in the organic contaminants stress response of HSPs is available, especially in marine invertebrates. The present study was conducted to evaluate the responses of HSPs in clams (Ruditapes philippinarum) under Benzo[a] pyrene (BaP) exposure. The clams were exposed to BaP (concentrations: 0, 0.1, 1, 10 μg/L) for 15 days. 6 HSPs mRNA were classified, and the results of tissue distribution indicated that 4 HSPs gene expressed most in the digestive glands. The transcription level of 6 HSPs (HSP22-1, HSP22-2, HSP40A, HSP60, HSP70, HSP90) genes and the aryl hydrocarbon receptor signaling pathway-related genes, and detoxification system-related enzymes activities were analyzed at 0, 1, 3, 6, 10 and 15 days. The activities of phase II detoxification metabolic enzymes and signaling pathway related genes in clams were severely affected by BaP stress and presented significant difference. Our result suggested that HSPs were produced in the presence of BaP and participated in the process of detoxification metabolism to a certain extent. Additionally, the transcription of HSP40A gene may be used as a potential biomarker of BaP exposure due to its evident concentration- and time-dependent expression pattern. Overall, the study investigated the classification of HSPs in R. philippinarum, provided information about the expression profiles of various HSPs after BaP exposure and broadened the understanding mechanism of HSPs in detoxification defense system under PAHs stress in mollusks.

Dose-Dependent Molecular Responses of Labeo rohita to Triphenyl Phosphate

Triphenyl phosphate (TPhP) is a broad-spectrum organophosphate compound widely used as an additive in several products to prevent ignition. However, its utilization produces a hazardous impact on various organisms. So far, very few studies have investigated the acute toxicity of TPhP at environmentally relevant concentrations in nontarget aquatic species. This study aimed to assess whether the short-term exposure of TPhP (4, 20, and 100 μg L^-1) affects the oxidative stress, antioxidant activity, biomolecule metabolism, DNA stability, chromosomal integrity, apoptosis, and pathological changes in various organs of Labeo rohita fingerlings. The results illustrated that the reactive oxygen species (ROS) production and lipid peroxidation (LPO) rates were significantly higher in tissues (brain, liver, and kidney) of TPhP-treated groups. Interestingly, superoxide dismutase (SOD) and catalase (CAT) activities were remarkably decreased in tissues following TPhP exposure. The levels of protein, glucose, total cholesterol (TC), triglycerides (TG), low-density lipoprotein (LDL), and high-density lipoprotein (HDL) in various tissues were also found to be significantly altered in TPhP-exposed fish fingerlings. These significant alterations in the antioxidant system and biochemical profile induced genotoxic responses such as DNA and chromosomal damage in the fish fingerlings. Furthermore, the incidence of the observed genotoxic responses was also found to be dose-dependent. Likewise, the apoptotic responses were also significantly altered following TPhP acute exposure in L. rohita fingerlings. The subsequent effects on oxidative stress, antioxidant inhibition, dysregulated biomolecule metabolism, and genotoxicity might be the possible reason for the observed pathological changes in various tissues of L. rohita. Taken together, the present findings showed that the toxicity of TPhP is principally associated with exposure concentrations. Therefore, this study illustrates the toxicity risks of TPhP to vertebrate organisms at real-world concentrations.

Organophosphate (OP) diesters and a review of sources, chemical properties, environmental occurrence, adverse effects, and future directions

Over the course of the continual phase-outs of toxic halogenated flame retardants (HFRs), there has been an increasing demand for organophosphate esters (OPEs) in global FR markets. OPE-FRs have largely been identified as OP triesters, which have a basic chemical structure of O = P(OR)₃. In addition to OP triesters, OPEs can refer to another class of related substances, namely, OP diesters that have a typical chemical structure of O = P(OR)₂(OH)). OP diesters are known as biotic or abiotic degradation products of OP triesters. In recent years, environmental scientists have proven that OP diesters widely exist in a variety of environmental matrices and biotic samples around the world, implying the potential risks from OP diester exposure to biota and humans in the environment. Here, we have reviewed the scientific literature for studies involving OP diesters and up to the end of 2020. The aim of the present review is to assess the present understanding of the physicochemical properties, sources (industrial production and degradation), environmental occurrence of OP diesters, and adverse effects to exposed organisms. Based on the literature in the Web of Science core collection, we found that at least 23 OP diesters have been reported as contaminants in various environments or as degradation products of OP triesters. The physicochemical properties of OP diesters vary depending on their specific chemical structures. OP diesters containing halogen atoms and aryl groups seem to be more persistent (with greater estimated half-life (t_1/2) values) in environmental matrices. There were multiple sources of OP diesters, including industrial production and biotic or abiotic degradation from OP triesters. Specifically, we found that ten OP diesters are produced somewhere in the world, and the total annual output was estimated to be 17,050 metric tons (this number is underestimated due to the limitation of the available information). In addition, the wide application of OP triesters worldwide makes the degradation of OP triesters another critical source of OP diesters to the environment and to organisms. Current monitoring studies have demonstrated that some OP diesters were detectable in the human body (via both blood and urine samples), indoor dust, wastewater, or sewage sludge worldwide. The highest concentrations of diphenyl phosphate (DPHP) in human urine have been reported as high as 727 ng/mL (children (aged 0-5 years) urine samples from Australia). In addition, adverse effects following direct or indirect exposure to 11 OP diesters in organisms (including animals, bacteria, and algae) have been reported, and the recorded adverse outcomes following exposure to OP diesters included developmental toxicity, alteration of gene expression, and disturbance of nuclear receptor activity. Biomonitoring studies regarding human samples have frequently reported statistically significant associations between the concentrations of OP diesters and markers of human health (mainly related to reproductive toxicity). Finally, on the basis of current knowledge on OP diesters, we propose prospects for related research directions in future studies.

Combined toxicity of micro/nano scale polystyrene plastics and ciprofloxacin to Corbicula fluminea in freshwater sediments

Plastic pollution has become a global environmental threat, and its potential to affect the bioavailability and toxicity of pharmaceuticals to aquatic organism are of growing concern. However, little is known regarding the combined toxicity of micro/nano-plastics and pharmaceuticals to benthic organisms in sediments. Thus, we employed a freshwater benthic bivalve, Corbicula fluminea (C. fluminea), to investigate the individual and co-toxicity of model plastics, microscopic fluorescent polystyrene (PS) (PS nano-plastic (PS-NP) and PS micro-plastic (PS-MP), 80 nm and 6 μm, respectively) and the common antibiotic ciprofloxacin (CIP) in formulated sediments. Our results suggest that oxidative damage and neurotoxicity were confirmed to occur in C. fluminea in all the treatments. The oxidative damage in the digestive glands reduced the clam ability to scavenge free radicals, causing severe tissue damage to the digestive glands of C. fluminea. Filtration rates of C. fluminea were significantly decreased in a concentration-dependent manner across all the treatments, which might be due to the inhibition of acetylcholinesterase activities. Interactions between CIP and micro/nano-plastic were observed, whereby the presence of PS decreased the toxicity of CIP in the digestive glands but aggravated the C. fluminea siphoning inhibition rate in the nano-plastic co-treatments group; in addition, the CIP toxicity to C. fluminea decreased because that the concentration of free dissolved CIP was lowered by micro/nano-PS. Taken together, the current study could contribute greatly to evaluating the ecological risk of CIP and PS in aquatic environments and sheds light on potential issues of food safety caused by both emerging pollutants.

Responses of Asian clams (Corbicula fluminea) to low concentration cadmium stress: Whether the depuration phase restores physiological characteristics

The effect of low concentration Cd stress on bivalves is unclear. In this study, Asian clams (Corbicula fluminea) were continuously exposed to 0, 0.05, 0.10, and 0.20 mg/L Cd for 14 d (exposure phase) and to artificial freshwater for 7 d (depuration phase). A total of 16 variables were measured to explore the toxic effects on C. fluminea. All physiological characteristics were significantly inhibited in the treatments (p < 0.05), and the negative effects of Cd did not return to normal levels in the short term. Tissue damage was found in the feet and gills of C. fluminea in all the treatments. On the 7th day (D7), enzyme activity in all the treatments was significantly higher (p < 0.05) than in the control group. Acetylcholinesterase, superoxide dismutase, and catalase activities were enhanced on D14 in all the treatments. However, only glutathione S-transferase activity was significantly higher in all the treatments (p < 0.05) than in the control group on D21. The instability of the enzymes indicated that the adaptability of C. fluminea became stronger throughout the experiment. In each group, the maximum bioaccumulation of Cd followed the order: 0.20 mg/L > 0.05 mg/L > 0.10 mg/L, which might be caused by the filtration capacity of C. fluminea in the 0.05-mg/L group, which was higher than that of the 0.10-mg/L group. Thus, low Cd concentrations effect the physiological characteristics, tissue health, and antioxidant system of C. fluminea and may require a long recovery time to be restored to normal levels.

Organophosphorus flame retardants are developmental neurotoxicants in a rat primary brainsphere in vitro model

Due to regulatory bans and voluntary substitutions, halogenated polybrominated diphenyl ether (PBDE) flame retardants (FR) are increasingly substituted by mainly organophosphorus FR (OPFR). Leveraging a 3D rat primary neural organotypic in vitro model (rat brainsphere), we compare developmental neurotoxic effects of BDE-47-the most abundant PBDE congener-with four OPFR (isopropylated phenyl phosphate-IPP, triphenyl phosphate-TPHP, isodecyl diphenyl phosphate-IDDP, and tricresyl phosphate (also known as trimethyl phenyl phosphate)-TMPP). Employing mass spectroscopy-based metabolomics and transcriptomics, we observe at similar human-relevant non-cytotoxic concentrations (0.1-5 µM) stronger developmental neurotoxic effects by OPFR. This includes toxicity to neurons in the low µM range; all FR decrease the neurotransmitters glutamate and GABA (except BDE-47 and TPHP). Furthermore, n-acetyl aspartate (NAA), considered a neurologic diagnostic molecule, was decreased by all OPFR. At similar concentrations, the FR currently in use decreased plasma membrane dopamine active transporter expression, while BDE-47 did not. Several findings suggest astrogliosis induced by the OPFR, but not BDE-47. At the 5 µM concentrations, the OPFR more than BDE-47 interfered with myelination. An increase of cytokine gene and receptor expressions suggests that exposure to OPFR may induce an inflammatory response. Pathway/category overrepresentation shows disruption in 1) transmission of action potentials, cell-cell signaling, synaptic transmission, receptor signaling, (2) immune response, inflammation, defense response, (3) cell cycle and (4) lipids metabolism and transportation. Taken together, this appears to be a case of regretful substitution with substances not less developmentally neurotoxic in a primary rat 3D model.

Elucidating multilevel toxicity response differences between tris(1,3-dichloro-2-propyl) phosphate and its primary metabolite in Corbicula fluminea

Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) and its primary metabolite, bis(1,3-dichloro-2-propyl) phosphate (BDCIPP) are frequently detected in aquatic environments. However, information regarding the biotoxicity of these compounds to bivalves is limited. We explored the multilevel physiological responses of Corbicula fluminea to TDCIPP and BDCIPP. The results indicated that TDCIPP/BDCIPP bioaccumulation in bivalves was positively correlated with their hydrophobicity. Furthermore, the higher body burden of TDCIPP in digestive glands led to significantly higher levels of ethoxyresorufin-O-deethylase (EROD), glutathione S-transferase (GST), and P-glycoprotein (p < 0.05). Owing to different molecular structures of inducers, upregulations of cyp4, gstm1, and abcb1 mRNA exhibited different sensitivities to TDCIPP and BDCIPP. Although Phase-I and Phase-II biotransformation and the multixenobiotic resistance (MXR) system were activated to protect bivalves from TDCIPP or BDCIPP, digestive glands produced large amounts of reactive oxygen species (ROS). Moreover, oxidative stress, the percentage of apoptotic cells in digestive glands, and inhibition of siphoning behaviour in TDCIPP treatments were higher than those in BDCIPP treatments (p < 0.05), indicating that TDCIPP was more toxic to bivalves than BDCIPP. Lower bioaccumulation and rapid metabolism of BDCIPP in vivo may contribute to alleviating its toxicity. This research establishes a foundation for further understanding the differences between the toxic mechanisms of TDCIPP and its metabolites.

Transcriptomics and metabolomics reveal Ca2+ overload and osmotic imbalance-induced neurotoxicity in earthworms (Eisenia fetida) under tri-n-butyl phosphate exposure

Tri-n-butyl phosphate (TNBP) is mass-produced and widely utilized in many products, which has increasingly drawn concern about its potential environmental risks. However, little is known about the toxic mechanism on soil-dwelling organisms caused by TNBP. In this study, earthworms (Eisenia fetida) were exposed to environmentally relevant or higher concentrations of TNBP (0, 0.1, 1, and 10 mg/kg) in artificial soil for 14 days. Our results showed that TNBP accumulated in earthworm nervous tissue (cerebral ganglions). In addition, the content of glutamate in cerebral ganglions decreased compared to the control (p < 0.05). The concentration of Ca²⁺ in earthworm cerebral ganglions increased. However, both Na⁺/K⁺-ATPase and Ca²⁺-ATPase activities were significantly reduced compared to the control (p < 0.05), which led to neurotoxicity in earthworm nervous tissue. Furthermore, the transcriptome and metabolomics revealed the toxic mechanism in earthworm nervous tissue caused by TNBP. Results indicated that the main neurotoxicity mechanisms induced by TNBP were an osmotic imbalance and Ca²⁺ overload in cerebral ganglions. Our findings fill a gap in the literature on neurotoxicity mechanisms of earthworm response to TNBP exposure and contribute to a better understanding of the adverse effects of TNBP on soil-dwelling organisms in terrestrial ecological systems.

Suspended sediment exacerbates perfluorooctane sulfonate mediated toxicity through reactive oxygen species generation in freshwater clam Corbicula fluminea

Perfluorooctane sulfonate (PFOS) potentially adsorbs on the surface of suspended sediment (SPS), which can develop a toxic "pool" bioavailable to benthic organisms. In this study, the freshwater clam Corbicula fluminea was employed as a zoobenthos model to study the effects of SPS (collected from the Yellow River) on the bioaccumulation and toxicity (from the molecular level to cellular and physiological levels) caused by PFOS exposure. Besides, the enhanced integrated biomarker response (EIBR) system was applied as an index to evaluate the in-depth toxic effects of PFOS and SPS single and co-exposure at various treatment levels. Our results demonstrated that PFOS-SPS co-exposure (at sub-lethal doses of PFOS) significantly increased the bioaccumulation of PFOS, and induced the elevated levels of reactive oxygen species (ROS), the significantly increased activities of superoxide dismutase (SOD) and catalase (CAT) enzymes, the significantly increased content of malondialdehyde (MDA), and the significantly upregulated expression levels of sod, selenium-dependent glutathione peroxidase (se-gpx), heat shock protein 22 (hsp22), heat shock protein 40 (hsp40) and cytochrome P450 30 (cyp30) genes. Further, the co-exposure induced the significantly higher histopathological alterations in the gonads and digestive glands, and even elevated the inhibition of siphoning behavior in clams. In addition, the EIBR index also revealed the highest values for PFOS and SPS co-exposure, compared to the individual SPS or PFOS exposure. The results indicated that at high levels of PFOS exposure (especially at 1000 μg/L), the presence of SPS might increase the generation of ROS by influencing the bioaccumulation of PFOS, which enhanced the toxicity of PFOS to C. fluminea. These results potentially provide basic information for the comprehensive evaluation of the toxic effects of PFOS on benthos in a multi-sediment river ecosystem.

Biochemical responses of a freshwater fish Cirrhinus mrigala exposed to tris(2-chloroethyl) phosphate (TCEP)

Freshwater fish Cirrhinus mrigala were exposed to tris(2-chloroethyl) phosphate (TCEP) with three different concentrations (0.04, 0.2, and 1 mg/L) for a period of 21 days. During the study period, thyroid-stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4) levels were significantly (p < 0.05) inhibited. The superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), and lipid peroxidation (LPO) levels were increased significantly (p < 0.05) in gills, liver, and kidney tissues, whereas glutathione (GSH) and glutathione peroxidase (GPx) (except liver tissue) activities were inhibited when compared to the control group. Likewise, exposure to TCEP significantly (p < 0.05) altered the biochemical (glucose and protein) and electrolyte (sodium, potassium, and chloride) levels of fish. Light microscopic studies exhibited series of histopathological anomalies in the gills, liver, and kidney tissues. The present study reveals that TCEP at tested concentrations causes adverse effects on fish and the studied biomarkers could be used for monitoring the ecotoxicity of organophosphate esters (OPEs).

Comparison of the Toxicity Effects of Tris(1,3-dichloro-2-propyl)phosphate (TDCIPP) with Tributyl Phosphate (TNBP) Reveals the Mechanism of the Apoptosis Pathway in Asian Freshwater Clams (Corbicula fluminea)

To compare the toxicities of a chlorinated and a nonchlorinated organophosphorus flame retardant (OPFR) in this study, adult calms (Corbicula fluminea) were exposed to tris(1,3-dichloro-2-propyl)phosphate (TDCIPP) and tributyl phosphate (TNBP) at 20, 200, and 2000 μg/L for 30 days. Toxicity screening using transcriptomics indicated that the apoptosis pathway was significantly affected in the groups exposed to 2000 μg/L TDCIPP and TNBP (p ≤ 0.05), and this finding was further confirmed by the protein interaction network. The terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay suggested that TDCIPP and TNBP can cause apoptosis. The significant (p ≤ 0.05) increases in the activities of caspases 3 and 8 obtained with all treatments and in that of caspase 9 obtained with 2000 μg/L exposure treatments indicated the presence of mitochondria-dependent and mitochondria-independent apoptosis. Interestingly, a noticeable dose-dependent increase in DNA damage was observed in all treatments, resulting in apoptosis. Therefore, our results demonstrate that TDCIPP and TNBP induce DNA damage and apoptosis in C. fluminea, which indicates that these chemicals pose an ecological risk to benthic organisms. Moreover, through a similar mechanism of action in apoptosis, TDCIPP induced more serious toxicity than TNBP, which indicated that chlorination or differences in structure-specific metabolism could be key factors influencing toxicity.

In vitro oxidative stress, mitochondrial impairment and G1 phase cell cycle arrest induced by alkyl-phosphorus-containing flame retardants

Phosphorus-containing flame retardants (PFRs) have been frequently detected in various environmental samples at relatively high concentrations and are considered emerging environmental pollutants. However, their biological effects and the underlying mechanism remain unclear, especially alkyl-PFRs. In this study, a battery of in vitro bioassays was conducted to analyze the cytotoxicity, oxidative stress, mitochondrial impairment, DNA damage and the involved molecular mechanisms of several selected alkyl-PFRs. Results showed that alkyl-PFRs induced structural related toxicity, where alkyl-PFRs with higher logKow values induced higher cytotoxicity. Long-chain alkyl-PFRs caused mitochondrial and DNA damage, resulting from intracellular reactive oxygen species (ROS) and mitochondrial superoxide overproduction; while short-chain alkyl-PFRs displayed adverse outcomes by significantly impairing mitochondria without obvious ROS generation. In addition, alkyl-PFRs caused DNA damage-induced cell cycle arrest, as determined by flow cytometry, and transcriptionally upregulated key transcription factors in p53/p21-mediated cell cycle pathways. Moreover, compared to the control condition, triisobutyl phosphate and trimethyl phosphate exposure increased the sub-G1 apoptotic peak and upregulated the p53/bax apoptosis pathway, indicating potential cell apoptosis at the cellular and molecular levels. These results provide insight into PFR toxicity and the involved mode of action and indicate the mitochondria is an important target for some alkyl-PFRs.

Predictors and reproducibility of urinary organophosphate ester metabolite concentrations during pregnancy and associations with birth outcomes in an urban population

BACKGROUND

Organophosphate esters (OPEs) are synthetic chemicals used as flame retardants and plasticizers in a variety of goods. Despite ubiquitous human exposures and laboratory evidence that prenatal OPE exposures may disrupt offspring metabolism, perinatal studies of OPE health effects are limited. The objectives of this study were to: 1) Determine predictors and reproducibility of urinary OPE biomarker concentrations during pregnancy, and 2) Estimate the relation of prenatal OPE exposures with birth outcomes and cord blood adipokine and insulin concentrations.

METHODS

We analyzed five OPE metabolites in urine samples collected at up to three visits during pregnancy from 90 women enrolled in the ORigins of Child Health And Resilience in Development (ORCHARD) pregnancy cohort in Baltimore, MD from 2017 to 2019. To quantify the variability of metabolite concentrations during pregnancy, we calculated intraclass correlation coefficients (ICCs) for each metabolite using mixed effects regression models. Using self-reported questionnaire data collected during gestation, we assessed possible sociodemographic and environmental/behavioral predictors of each OPE metabolite using generalized estimating equations to account for repeated exposure measures. We ascertained birth outcomes of 76 offspring from medical records, including weight-for-gestational age, length, ponderal index, and gestational age. In a subset of 37 infants, we measured cord blood concentrations of leptin, adiponectin, and insulin. To account for repeated exposure measures, we used linear structural equation models to assess the relations of standard deviation (SD) increases in prenatal OPE metabolite factor scores with continuous birth outcomes and cord blood biomarker concentrations.

RESULTS

ICCs ranged from 0.09 for isopropylphenyl-phenyl phosphate (ip-PPP) to 0.59 for bis(1,3-dichloro-2-propyl) phosphate (BDCIPP). We observed little consistency in environmental or behavioral predictors of OPE exposures, although concentrations were generally lower for samples collected in the afternoon compared to morning and winter compared to other seasons. In adjusted analyses, a SD increase in BDCIPP concentration was associated with a 0.06 g/cm3 (95% CI: 0.00, 0.12) greater ponderal index. A SD increase in BDCIPP was associated with a 0.37 (95% CI: - 0.62, - 0.13) SD lower insulin concentration and 0.24 (95% CI: - 0.39, - 0.08) SD lower leptin concentration. Other OPEs were not associated with infant outcomes.

CONCLUSIONS

These findings suggest some OPEs may be metabolic disruptors warranting investigation in larger studies.

Endosulfan exposure alters transcription of genes involved in the detoxification and stress responses in Physella acuta

Endosulfan is a persistent pesticide that has been in use for more than five decades. During this time, it has contaminated soil, air, and water reservoirs worldwide. It is extremely toxic and harmful to beneficial non-target invertebrates, aquatic life, and even humans upon consumption, which is one of the many dangers of this pesticide since it biomagnifies in the food chain. The effects of three endosulfan concentrations (1, 10, and 100 µg/L) on the freshwater snail Physella acuta, an invasive cosmopolitan species, were examined over a week-long exposure period. Alterations in the expression of ten genes related to stress and xenobiotic detoxification were measured against the endogenous controls rpL10 and GAPDH by Real-Time polymerase chain reaction. Four genes are described here for the first time in this species, namely Hsp60, Grp78, GSTk1, and GSTm1. The rest of genes were Hsp90, sHsp16.6, cyp2u1, cyp3a7, cyp4f22, and MRP1. cyp2u1, sHsp16.6, and Grp78 expression were all altered by endosulfan. These results suggest a low pesticide concentration activates the acute response in P. acuta by affecting detoxification and stress responses and alter endoplasmic reticulum function and lipid metabolism. Furthermore, the newly identified genes extend the number of processes and cellular locations that can be analyzed in this organism.

Prenatal Exposure to Organophosphate Flame Retardants and the Risk of Low Birth Weight: A Nested Case-Control Study in China

Organophosphate flame retardants (OPFRs), used as flame retardants and plasticizers, have been suggested to impair fetal growth and development in toxicological studies, but epidemiological data are extremely limited. This study was designed to explore whether prenatal exposure to OPFRs was associated with an increased risk of low birth weight (LBW) using a nested case-control design based on the ongoing prospective birth cohort in Wuhan, China. A total of 113 cases and 226 matched controls recruited from this cohort project in 2014-2016 were included. OPFR metabolite concentrations in maternal urine samples collected in the third trimester were determined, and birth outcomes were extracted from medical records. Compared with the lowest tertile of diphenyl phosphate (DPHP) concentrations, pregnant women with the highest tertile of DPHP had a 4.62-fold (95% confidence interval (CI): 1.72, 12.40) significantly increased risk for giving birth to LBW infants, with a significant dose-response relationship (p-trend < 0.01). After stratification by newborn sex, the significant positive association of DPHP levels with LBW risk was merely observed among female newborns. Our results suggest a positive association between maternal urinary DPHP concentrations and LBW risk for the first time, and the effect appears be sex-specific.

Low concentration of 2,4,6-tribromophenol (TBP) represents a risk to South American silver catfish Ramdia quelen (Quoy and Gaimard, 1824) population

The 2,4,6-tribromophenol (TBP) is an environmental persistent pollutant widely used as flame retardant, antimicrobial and insecticide agent in wood preservation and plastic production. Currently, TBP is found in environmental compartments such as soil, freshwater, groundwater, sewage sludge and domestic dust, but the effects to biota and the risk of exposure to aquatic vertebrates are still scarce. In the present study, Rhamdia quelen fish embryos (8 h post-fertilization - hpf) were exposed to 0.3 and 3.0 μg L^-1 of TBP until 96 hpf. Biochemical biomarkers, hatching, survival and larvae/embryo malformations were evaluated after exposure. Additionally, a mathematical model was proposed to evaluate the effects along further generations. The results showed that TBP decreased the survival level but did not cause significant difference in the hatching rates. After 72 and 96 hpf, individuals from the highest tested concentration group showed more severe malformations than individuals from control and the lower concentrations groups. The deformities were concentrated on the embryos facial region where the sensorial structures related to fish behavior are present. The biochemical biomarkers revealed both oxidative stress and neurotoxicity signs after exposure to the contaminant, while the application of the mathematical model showed a decrease of population in both tested TBP concentrations. In conclusion, the current results demonstrated that TBP is toxic to R. quelen embryos and represents a risk to population after early life stage exposure.

Effect of imidacloprid on the behavior, antioxidant system, multixenobiotic resistance, and histopathology of Asian freshwater clams (Corbicula fluminea)

In the current study, to investigate the effect of imidacloprid on benthic bivalves, adult Asian clams (Corbicula fluminea) were exposed to 0, 20, 200, and 2000 μg/L imidacloprid for 30 d. Imidacloprid significantly inhibited the siphoning and burrowing behaviour (p < 0.05) of the clams. Significant histopathological changes were associated with degeneration of the cilium, the contraction and adhesion of the lymphocyte, and the swelling of epithelium cells in gills, and there was notable degeneration in the digestive tubules, haemolytic infiltration in the connective tissue and epithelial cell necrosis in the digestive glands in the 2000 μg/L treatment group. The activity of AChE in the digestive glands was significantly inhibited at all treatment levels, whereas this inhibition was observed in gills only in the 2000 μg/L treatment (p < 0.05). Additionally, indicators of the antioxidant system (e.g., SOD, CAT, and GST activity) and MDA content were significantly increased in the gills and digestive glands with all treatments (p < 0.05). Moreover, the mRNA expression levels of Hsp genes (hsp 22, hsp 40, hsp 60, hsp 70, hsp 90) and multixenobiotic resistance (MXR) system-related genes (abcb1, abcc1) were significantly downregulated (p < 0.05). Therefore, our results suggest that imidacloprid changes the oxidative stress, cellular detoxification, and MXR system of C. fluminea. Our findings provide new insights into the effects of neonicotinoids on benthic bivalves such as C. fluminea.

Organophosphate Ester Flame Retardants: Are They a Regrettable Substitution for Polybrominated Diphenyl Ethers?

As the use of polybrominated diphenyl ethers (PBDEs), and the entire class of organohalogen flame retardants, is declining, the use of organophosphate esters flame retardants (OPFRs) is increasing. In this paper, we ask whether OPFRs are a better choice than PBDEs. To address this question, we compared OPFRs with PBDEs for a wide range of properties. OPFRs exposure is ubiquitous in people and in outdoor and indoor environments, and are now often found at higher levels compared to PBDE peak exposure levels. Furthermore, data from toxicity testing, epidemiological studies, and risk assessments all suggest that there are health concerns at current exposure levels for both halogenated and non-halogenated OPFRs. Obtaining the scientific evidence needed for regulation of OPFRs can take many years. Given the large number of OPFRs in use, manufacturers can move towards healthier and safer products by developing innovative ways to reduce fire hazard for electronics enclosures, upholstered furniture, building materials and other consumer products without adding flame retardant chemicals.

Transcriptomic responses of the clam Meretrix meretrix to the organophosphorus pesticide (dimethoate)

Organophosphorus pesticides (OPs) play a certain role in promoting the development of agriculture and forestry, but they may cause potential harm to aquatic life when entering rivers and polluting water sources. Previous researches have shown that OPs participate in the regulation mechanism of aquatic organisms. Here, our aim is to determine the underlying mechanisms of one OP (dimethoate) at the transcriptional level using the clam Meretrix meretrix. 4119 DEGs were obtained from high-throughput RNA sequencing data. Then, expression profiles of some genes were verified by qPCR, which showed a positive correlation with the RNA sequencing results. 14,481 simple sequence repeats were also identified and could be further used as molecular markers. In addition, some oxidative, immune, and stress-related genes were further discussed and could also be used as biomarkers to indicate the biological response of dimethoate. This study will help to better understand the clam's response mechanism to dimethoate stress.

Toxicokinetic patterns, metabolites formation and distribution in various tissues of the Chinese rare minnow (Gobiocypris rarus) exposed to tri(2‑butoxyethyl) phosphate (TBOEP) and tri-n-butyl phosphate (TNBP)

Alkylated organophosphate esters (alkyl-OPEs) are widely used and extensively detected in aquatic organisms. This work investigated the tissue-specific toxicokinetics of two common alkyl-OPEs, tri(2‑butoxyethyl) phosphate (TBOEP) and tri‑n‑butyl phosphate (TNBP) in Chinese rare minnow (Gobiocypris rarus) through a 50 day uptake and depuration experiment. The tissue-specific bioconcentration factor (BCF) values for the two alkyl-OPEs ranged from 1 to 30 L/kg wet weight (ww), with the kidney and ovary as the tissues with the highest accumulation. The tissue BCFs only exhibited a significant correlation with lipid contents only in storage tissues (i.e., muscle, brain, ovary and testis), indicating that lipids might not be the major contributor to tissue distribution of TBOEP and TNBP. However, the contribution of blood perfusion and active transport to tissue-specific OPE accumulation needs to be further investigated. Lower accumulation of metabolites than parent chemicals was observed, with metabolite parent concentration factors (MPCFs) <1. Di-alkyl phosphate (DAP), bis(2‑butoxyethyl) phosphate (BBOEP) and di(n-butyl) phosphate (DNBP) were the most abundantly formed metabolites of TBOEP and TNBP in various tissues, followed by the monohydroxylated OPEs (OH-OPEs). However, bis(2‑butoxyethyl) hydroxyethyl phosphate (BBOEHEP), was detected at much lower levels in the tissues. All the investigated metabolites showed high production rates (k_{prod,metabolites}) in the fish liver, followed by the GI tract and the kidney, indicating the importance of the hepatobiliary and urinary systems in eliminating the metabolites. Our study suggested that metabolism plays an important role in eliminating these two alkyl-OPEs in rare minnow and results in different tissue distribution mechanisms for metabolites and their compounds.

Associations between urinary organophosphate ester metabolites and measures of adiposity among U.S. children and adults: NHANES 2013-2014

BACKGROUND

Organophosphate esters (OPEs) are synthetic chemicals found in many consumer products, including furniture, electronics, processed foods, and building materials. Emerging in vitro and in vivo studies suggest that OPEs are metabolism disrupting compounds; however, epidemiologic studies investigating their associations with adiposity markers are sparse.

OBJECTIVE

We examined cross-sectional associations between OPE biomarkers and adiposity measures among U.S. children and adults participating in the National Health and Nutrition Examination Survey (NHANES: 2013-2014).

METHODS

Concentrations of five OPE metabolites were quantified in urine: diphenyl phosphate (DPHP), bis(1,3-dichloro-2-propyl) phosphate (BDCPP), bis(2-chloroethyl) phosphate (BCEP), dibutyl phosphate (DBUP), and bis(1-chloro-2-propyl) phosphate (BCPP). We conducted covariate-adjusted logistic and linear regressions to examine associations between log2-transformed and dichotomized OPE metabolite concentrations and obesity, body mass index (BMI), and waist circumference (WC), separately among 784 children (6-19 years) and 1672 adults (≥20 years). We also assessed heterogeneity of associations by sex.

RESULTS

DBUP concentrations were inversely associated with the prevalence odds of being obese vs. normal weight in children (adjusted Prevalence Odds Ratio, aPOR: 0.82, 95% Confidence Interval, 95% CI: 0.70, 0.95) and adults (aPOR: 0.83, 95% CI: 0.72, 0.96). DBUP was also significantly associated with lower BMI z-scores (β:-0.08, 95% CI:-0.17, 0.01) and WC (β:-0.71, 95% CI: -1.49, 0.07) in children. BCEP concentrations were associated with increased prevalence odds of being overweight vs. normal weight (aPOR: 1.15, 95% CI: 1.01, 1.32) among children; similar, albeit not statistically significant, relationships were observed with other child adiposity outcomes. Among adults, detectable BCPP concentrations were associated with increased prevalence odds of being obese vs. normal weight (aPOR: 1.70, 95% CI: 1.21, 2.38) and having a high vs. normal WC (aPOR: 1.51, 95% CI: 1.11, 2.07) as well as higher BMI (β: 1.31, 95% CI: 0.30, 2.33). Other OPE metabolites were not consistently associated with adiposity measures among adults. Although associations of BCPP exposure with adiposity outcomes were generally inverse among boys, but not girls, we did not observe consistent evidence of sexually-dimorphic associations for other OPE metabolites.

CONCLUSIONS

Exposure to select OPEs may be differentially associated with body size among children and adults. Given the cross-sectional design of the present study, future prospective studies are needed to confirm these findings.

A pilot study of metabolites of organophosphorus flame retardants in paired maternal urine and amniotic fluid samples: potential exposure risks of tributyl phosphate to pregnant women

Organophosphorus flame retardants (OPs) are of wide concern due to their presence in human urine and their considerable endocrine disruption and neuro-development toxicity. It has been confirmed that electronic waste (e-waste) dismantling activities have contributed to human exposure to OPs. However, assessments of OP exposure and the health risks for pregnant women and fetuses living in areas associated with e-waste dismantling have been impeded by a lack of data. In this study, six OP metabolites (mOPs) were measured in paired maternal urine and amniotic fluid samples collected from an e-waste dismantling area in Guangdong Province, China. All mOPs were detectable in maternal urine, whereas two were found in amniotic fluid. Dibutyl phosphate (DBP) was the predominant mOP in both maternal urine (geometric mean (GM): 2.9 ng ml-1) and amniotic fluid (1.3 ng ml-1); and diphenyl phosphate (DPHP) was the secondary one found (0.94 ng ml-1 in maternal urine, 0.12 ng ml-1 in amniotic fluid). The GM urinary concentrations of DBP and DPHP were two and seven times higher than those in amniotic fluid, respectively. The estimated daily intakes (EDIs) of triphenyl phosphate (TPHP) and tributyl phosphate (TnBP) by pregnant women were calculated from their daily urine excretion rate as fractions of OP metabolized to the corresponding metabolite (FUE). Our results showed high exposure levels to TPHP (median: 273 or 613 ng per kg bw per day) and TnBP (404 ng per kg bw per day) for pregnant women living in the e-waste associated area. Most importantly, 13% of mothers had EDITnBP levels that exceeded the reference dose (RfD: 2400 ng per kg bw per day), suggesting potential health risks from TnBP exposure for pregnant women living in areas associated with e-waste dismantling. This study, as a pilot study, presents the first measurements of mOPs in human amniotic fluid.

Combined toxicity of organophosphate flame retardants and cadmium to Corbicula fluminea in aquatic sediments

Organophosphate flame retardants (OPFRs), as alternatives to polybrominated biphenyl ethers (PBDEs), are frequently detected in various environmental matrices. Owing to urbanization and industrial pollution, co-contamination of OPFRs and heavy metals is ubiquitous in the environment. The toxicity of OPFRs in aqueous phase is a significant concern, but uncertainty still exists regarding the co-toxicity to benthic organisms of OPFRs and metals in sediments. Hence, we explored the physiological response of Corbicula fluminea to OPFRs and Cd in sediments. The results indicated that the antioxidant system in the clams was stimulated in the presence of OPFRs and Cd, and the oxidative stress increased with increasing concentrations of OPFRs. In contrast, the cytochrome P450 (CYP450) content and acetylcholinesterase (AChE) activity were reduced by exposure to both OPFRs and Cd. The cytochrome P450 4 family (CYP4) mRNA expression and OPFR toxicity were lower than those in previously reported experiments conducted in the water phase. Moreover, the expression levels of metallothionein (MT) and AChE mRNA decreased when OPFRs and Cd were present together. The highest integrated biomarker response (IBR) index (IBR = 15.41) was observed in the presence of 45 mg kg^-1 Cd + 200 mg kg^-1 OPFRs, rather than the 45 mg kg^-1 Cd + 400 mg kg^-1 OPFRs treatment (IBR = 9.48). In addition, CYP450 and AChE in the digestive glands of C. fluminea exhibited significant correlations with the concentration of the OPFR/Cd mixture (p < 0.01) and could be effective biomarkers for OPFR and Cd co-contamination. The results potentially contribute to more realistic predictions and evaluations of the environmental risks posed by OPFRs in aquatic sediments contaminated with heavy metals, particularly with respect to the risk to benthic organisms.

Gene expression and genotoxicity in Manila clam (Ruditapes philippinarum) modulated by sediment contamination and lagoon dynamics in the Po river delta

The lagoons of the Po River delta are potentially exposed to complex mixtures of contaminants, nevertheless, there is a substantial lack of information about the biological effects of these contaminants in the Po delta lagoons. These environments are highly dynamic and the interactions between chemical and environmental stressors could prevent the proper identification of biological effects and their causes. In this study, we aimed to disentangle such interactions focusing on Manila clams, previously exposed to six lagoons of the Po delta, adopting three complementary tools: a) the detailed description via modelling techniques of lagoon dynamics for salinity and water temperature; b) the response sensitivity of a number of target genes (ahr, cyp4, ρ-gst, σ-gst, hsp22, hsp70, hsp90, ikb, dbh, ach, cat, Mn-sod, Cu/Zn-sod, cyp-a, flp, grx, TrxP) investigated in clam digestive glands by Real Time PCR; and c) the relevance of DNA adducts determined in clams as markers of exposure to genotoxic chemicals. The lagoons showed specific dynamics, and two of them (Marinetta and Canarin) could induce osmotic stress. A group of genes (ahr, cyp4, Mn-sod, σ-gst, hsp-22, cyp-a, TrxP) seemed to be associated with overall lagoon characteristics as may be described by salinity and its variations. Lagoon modelling and a second group of genes (hsp70, hsp90, cat, ikb, ach, grx, Cu/Zn-sod) also suggested that moderate increases of river discharge may imply worse exposure conditions. Oxidative stress seemed to be associated with such events but it was slightly evident also under normal exposure conditions. DNA adduct formation was mainly associated with overwhelmed antioxidant defences (e.g. low Cu/Zn-sod) or seemingly with their lack of response in due time. In Po delta lagoons, Manila clam can be affected by chemical and environmental factors which can contribute to induce oxidative stress, DNA adduct formation and, ultimately, to affect clam condition and health.

Toxicity profiling of flame retardants in zebrafish embryos using a battery of assays for developmental toxicity, neurotoxicity, cardiotoxicity and hepatotoxicity toward human relevance

Following the voluntary phase-out of brominated flame retardants (BFRs) due to their environmental persistence and toxicity, the organophosphorus flame retardants (OPFRs) are emerging replacements. However, there is limited information on the potential human health effects of the OPFRs. Zebrafish embryos are a viable vertebrate model organism with many advantages for high throughput testing toward human hazard assessment. We utilized zebrafish embryos to assess developmental toxicity, neurotoxicity, cardiotoxicity and hepatotoxicity, of eight replacement OPFRs: (triphenyl phosphate [TPHP], isopropylated phenyl phosphate [IPP], 2-ethylhexyl diphenyl phosphate [EHDP], tert-butylated phenyl diphenyl phosphate [BPDP], trimethyl phenyl phosphate [TMPP], isodecyl diphenyl phosphate [IDDP], tris(1,3-dichloroisopropyl) phosphate [TDCIPP], and tris(2-chloroethyl) phosphate [TCEP]) and two BFRs (3,3',5,5'- tetrabromobisphenol A [TBBPA] and 2,2'4,4'-brominated diphenyl ether [BDE-47]). To determine potential effects on teratogenicity, embryos were exposed to flame retardants (FRs) at 4 h post fertilization (hpf) to 4 days post fertilization (dpf) and morphological alterations and corresponding survival were evaluated at 2 and 4 dpf. Internal concentrations were measured in larvae used in this assay by liquid chromatography-mass spectrometry. Locomotor activity was assessed in larvae treated for 48 h (from 3 dpf to 5 dpf), followed by hepatotoxicity evaluation. Finally, alterations in heart rate and rhythmicity were assessed to determine cardiotoxicity in 48 hpf embryos exposed to compounds for 3 h. Results suggest that several OPFRs (BPDP, EHDP; IPP, TMPP; TPHP and TDCIPP) produced adverse effects in multiple target organs at concentrations comparable to the two BFRs. As these OPFRs have the capacity to disrupt an integrated vertebrate model, they potentially have the capacity to affect mammalian biology. Then, we compared the lowest effective levels (LEL) in zebrafish with estimated or measured human plasma concentrations using biomonitoring data (human plasma, breast milk, handwipe samples and house dust) and a high throughput toxicokinetic (HTTK) model. Results indicate that for some compounds, the nominal LELs were within the range of human exposures, while internal LELs in zebrafish are above internal exposures in humans. These findings demonstrate the value of the zebrafish model as a relevant screening tool and support the need for further hazard characterization of the OPFRs.

The neuropeptides of Asian freshwater clam (Corbicula fluminea) as new molecular biomarker basing on the responses of organophosphate chemicals exposure

In the present study, to discover new biomarker of Asian freshwater clam (Corbicula fluminea) to assess impact of environmental pollutions, cholecystokinin (CCK), conopressin, and Neuropeptide FF (FFamide) in C. fluminea were selected as potent biomarkers. Therefore, their full-length cDNAs were cloned and characterized to investigate the molecular characteristics and expression patterns of neuropeptides in C. fluminea. According to the sequence analysis, CCK, conopressin, and FFamide encoded proteins of 173, 152, and 90 amino acids, respectively. Moreover, the multiple sequence alignment revealed that the bioactive regions of these neuropeptides were well conserved among different invertebrates. In addition, under basal conditions, CCK, conopressin and FFamide mRNA were mainly expressed in the visceral mass, whereas the FFamide mRNA was rarely detected in the foot and mantle. Exposure to 20 and 200 μg/L Tris (2-butoxyethyl) phosphate (TBOEP) and tri-butyl-phosphate (TBP) exposure significantly up-regulated the expression of the CCK and FFamide mRNAs in the visceral mass (p < 0.05), whereas no significant changes in conopressin mRNA levels were observed in response to any treatment. Therefore, CCK and FFamide of C. fluminea neuropeptides are feasible new biomarkers for screening and assessing responses to organophosphate chemicals.

Biological toxicity response of Asian Clam (Corbicula fluminea) to pollutants in surface water and sediment

As a typical test species, Asian Clam (Corbicula fluminea) is widely used in the identification and evaluation of freshwater toxicity. This study provides a summary of the research published from 1979 to 2018. The focus was on the bioaccumulation, morphological and behavioral changes, and biochemical index alterations of Corbicula fluminea to target pollutants (i.e., ammonia, metal(loid)s, and organic chemicals) in surface water and sediment. The applications on the evaluation of actual aquatic pollution, determination of toxicological mechanisms, prediction of toxicity, and bioremediation are also specifically discussed. The primary purpose is to facilitate the comprehensive understanding and accurate application of Corbicula fluminea in freshwater ecotoxicological studies.

Characterized in Vitro Metabolism Kinetics of Alkyl Organophosphate Esters in Fish Liver and Intestinal Microsomes

Tris(2-butoxyethyl) phosphate (TBOEP) and tris( n-butyl) phosphate (TNBP) are the most commonly used alkyl organophosphate esters (alkyl-OPEs), and they increasingly accumulate in organisms and create potential health hazards. This study examined the metabolism of TNBP and TBOEP in Carassius carassius liver and intestinal microsomes and the production of their corresponding monohydroxylated and dealkylated metabolites. After 140 min of incubation with fish liver microsomes, the rapid depletion of TNBP and TBOEP were both best fitted to the Michaelis-Menten model (at administrated concentrations ranging from 0.5 to 200 μM), with a CL_int (intrinsic clearance) of 3.1 and 3.9 μL·min^-1·mg^-1 protein, respectively. But no significant ( P > 0.05) biotransformation was observed for these compounds in intestinal microsomes at any administrated concentrations. In fish liver microsomes assay, bis(2-butoxyethyl) hydroxyethyl phosphate (BBOEHEP) and bis(2-butoxyethyl) 3-hydroxyl-2-butoxyethyl phosphate (3-OH-TBOEP) were the most abundant metabolites of TBOEP, and dibutyl-3-hydroxybutyl phosphate (3-OH-TNBP) was the predominant metabolite of TNBP. Similarly, the apparent V_max values (maximum metabolic rate) of BBOEHEP and 3-OH-TNBP were also respectively highest among those of other metabolites. Further inhibition studies were conducted to identify the specific cytochrome P450 (CYP450) isozymes involved in the metabolism of TNBP and TBOEP in liver microsomes. It was confirmed that CYP3A4 and CYP1A were the significant CYP450 isoforms catalyzing the metabolism of TNBP and TBOEP in fish liver microsomes. Overall, this study emphasized the importance of hydroxylated metabolites as biomarkers for alkyl-OPEs exposure, and further research is needed to validate the in vivo formation and toxicological implications of these metabolites.

Multigenerational effects evaluation of the flame retardant tris(2-butoxyethyl) phosphate (TBOEP) using Daphnia magna

Tris(2-butoxyethyl) phosphate (TBOEP) is an organophosphate ester used as substitute following the phase-out of brominated flamed retardants. Because of its high production volume and its use in a broad range of applications, this chemical is now frequently detected in the environment and biota. However, limited information is available on the long-term effects of TBOEP in aquatic organisms. In this study, Daphnia magna were exposed over three 21d generations to an environmentally relevant concentration of TBOEP (10μg/L) and effects were evaluated at the gene transcription, protein, and life-history (i.e., survival, reproduction and growth) levels. Chronic exposure to TBEOP did not impact survival or reproduction of D. magna but affected the growth output. The mean number of molts was also found to be lower in daphnids exposed to the chemical compared to control for a given generation, however there were no significant differences over the three generations. Molecular responses indicated significant differences in the transcription of genes related to growth, molting, ecdysteroid and juvenile hormone signaling, proteolysis, oxidative stress, and oxygen transport within generations. Levels of mRNA were also found to be significantly different for genes known to be involved in endocrine-mediated mechanisms such as reproduction and growth between generations F0, F1, and F2, indicating effects of parental exposure on offspring. Transcription results were supported by protein analyses with the significant decreased in catalase (CAT) activity in F1 generation, following the decreased transcription of cat in the parental generation. Taken together, these multi-biological level results suggest long-term potential endocrine disruption effects of TBOEP in D. magna exposed to an environmentally relevant concentration. This study highlights the importance of using chronic and multigenerational biological evaluation to assess risks of emerging chemicals.