Investigating endocrine and physiological parameters of captive American kestrels exposed by diet to selected organophosphate flame retardants

Seasonal variations of organophosphate esters (OPEs) in atmospheric deposition, and their contribution to soil loading

Organophosphate esters (OPEs) are ubiquitous in surface soil, and atmospheric deposition is considered to be the major pollution source. However, the research on the environmental transport behaviors of OPEs between atmospheric deposition and soil is very limited. In this study, we investigated the contamination levels and seasonal variations of OPEs in atmospheric deposition samples (n = 33) collected from an area of South China every month between February 2021 and January 2022, and evaluated the contribution of OPEs in atmospheric deposition to soil. The concentrations of ∑21target-OPEs ranged from 3670 to 18,600 ng/g dry weight (dw), with a mean of 8200 ng/g dw (median: 7600 ng/g dw). ∑21target-OPEs concentrations in all atmospheric deposition samples exhibited significant seasonal differences (p < 0.05) with higher concentrations observed in winter and lower concentrations in summer. Tris(2,4-di-tert-butylphenyl) phosphate (TDTBPP) was the most dominant target OPE in atmospheric deposition (4870 ng/g dw), and its seasonal variation trend was consistent with ∑21OPEs (p < 0.05). Simultaneously, in order to further explore the effect of atmospheric deposition on the levels of OPEs in soil of the study region, input fluxes and accumulation increments were estimated. Ten OPEs (including seven target OPEs and three suspect OPEs) exhibited high input flux means and accumulation increments, indicating that these compounds are prone to accumulate in soil via atmospheric deposition. It is noteworthy that the non-target phosphonate analyte bis(2,4-di-tert-butylphenyl) dibutyl ethane-1,2-diylbis(phosphonate) (BDTBPDEDBP) was detected at highest median concentration (8960 ng/g dw) in atmospheric deposition. Correspondingly, the average input flux and accumulation increment of BDTBPDEDBP were higher than those of all target and suspect OPEs. Collectively, this study quantifies the environmental transport behavior of OPEs between atmospheric deposition and soil, and provides new evidences for the fact that atmospheric deposition is the important pollution source of OPEs in soil.

Tris(2-ethylhexyl) phosphate induces cytotoxicity in TM3 Leydig cells by modulating autophagy and endoplasmic reticulum stress

Tris (2-ethylhexyl) phosphate (TEHP) is a frequently used organophosphorus flame retardant with significant ecotoxicity and widespread human exposure. Recent research indicates that TEHP has reproductive toxicity. However, the precise cell mechanism is not enough understood. Here, by using testicular mesenchymal stromal TM3 cells as a model, we reveal that TEHP induces apoptosis. Then RNA sequencing analysis, immunofluorescence, and western blotting results show that THEP inhibits autophagy flux and enhances endoplasmic reticulum (ER) stress. Moreover, the activation of the ER stress is critical for TEHP-induced cell injury. Interestingly, TEHP-induced ER stress is contributed to autophagic flux inhibition. Furthermore, pharmacological inhibition of autophagy aggravates, and activation of autophagy attenuates TEHP-induced apoptosis. In summary, these findings indicate that TEHP triggers apoptosis in mouse TM3 cells through ER stress activation and autophagy flux inhibition, offering a new perspective on the mechanisms underlying TEHP-induced interstitial cytotoxicity in the mouse testis.

Tris(2-chloroethyl) phosphate (TCEP) exposure inhibits the epithelial-mesenchymal transition (EMT), mesoderm differentiation, and cardiovascular development in early chicken embryos

Tris(2-chloroethyl) phosphate (TCEP) is an organophosphorus flame retardant used worldwide and has been detected in the tissues and eggs of wild birds. Our previous study reported that exposure to TCEP induced developmental delay and cardiovascular dysfunction with attenuated heart rate and vasculogenesis in early chicken embryos. This study aimed to investigate the molecular mechanisms underlying the cardiovascular effects of TCEP on chicken embryos using cardiac transcriptome analysis and to examine whether TCEP exposure affects epithelial-mesenchymal transition (EMT) and mesoderm differentiation during gastrulation. Transcriptome analysis revealed that TCEP exposure decreased the expression of cardiac conduction-related genes and transcription factors on day 5 of incubation. In extraembryonic blood vessels, the expression levels of genes related to fibroblast growth factor (FGF) and vascular endothelial growth factor (VEGF) were significantly reduced by TCEP exposure and vasculogenesis was suppressed. TCEP exposure also attenuated Snail family transcriptional repressor 2 (SNAI2) and T-box transcription factor T (TBXT) signaling in the chicken primitive streak, indicating that TCEP inhibits EMT and mesoderm differentiation during gastrulation at the early developmental stage. These effects on EMT and mesoderm differentiation may be related to subsequent phenotypic defects, including suppression of heart development and blood vessel formation.

Unravelling bioaccumulation, depletion and metabolism of organophosphate triesters in laying hens: Insight of in vivo biotransformation assisted by diester metabolites

Organophosphate triesters (tri-OPEs) threaten human health through dietary exposure, but little is known about their feed-to-food transfer and in vivo behavior in farm animals. Herein 135 laying hens were fed with contaminated feed (control group, low-level group and high-level group) to elucidate the bioaccumulation, distribution, and metabolism of the six most commonly reported tri-OPEs. The storage (breast muscle), metabolism and mobilization (liver and blood) and non-invasive (feather) tissues were collected. The exposure-increase (D1∼14) and depuration-decrease (D15∼42) trends indicated that feed exposure caused tri-OPE accumulation in animal tissues. Tissue-specific and moiety-specific behavior was observed for tri-OPEs. The highest transfer factor (TF) and transfer rate (TR) were observed in liver (TF: 14.8%∼82.3%; TR: 4.40%∼24.5%), followed by feather, breast muscle, and blood. Tris(2-chloroisopropyl) phosphate (TCIPP) had the longest half-life in feather (72.2 days), while triphenyl phosphate (TPhP) showed the shortest half-life in liver (0.41 days). Tri-OPEs' major metabolites (organophosphate diesters, di-OPEs) were simultaneously studied, which exhibited dose-dependent and time-dependent variations following administration. In breast muscle, the inclusion of di-OPEs resulted in TF increases of 735%, 1108%, 798%, and 286% than considering TCIPP, tributyl phosphate, tris(2-butoxyethyl) phosphate and tris(2-ethylhexyl) phosphate alone. Feather was more of a proxy of birds' long-term exposure to tri-OPEs, while short-term exposure was better reflected by di-OPEs. Both experimental and in silico modeling methods validated aryl-functional group facilitated the initial accumulation and metabolism of TPhP in the avian liver compared to other moiety-substituted tri-OPEs.

Influence of watershed characteristics and human activities on the occurrence of organophosphate esters related to dissolved organic matter in estuarine surface water

Organophosphate esters (OPEs) are widespread in aquatic environments and pose potential threats to ecosystem and human health. Here, we profiled OPEs in surface water samples of heavily urbanized estuaries in eastern China and investigated the influence of watershed characteristics and human activities on the spatial distribution of OPEs related to dissolved organic matter (DOM). The total OPE concentration ranged from 22.3 to 1201 ng/L, with a mean of 162.6 ± 179.8 ng/L. Chlorinated OPEs were the predominant contaminant group, accounting for 27.4-99.6 % of the total OPE concentration. Tris(2-chloroisopropyl) phosphate, tris(1,3-dichloro-2-propyl) phosphate, and tributyl phosphate were the dominant compounds, with mean concentrations of 111.2 ± 176.0 ng/L, 22.6 ± 21.5 ng/L, and 14.8 ± 14.9 ng/L, respectively. Variable OPE levels were observed in various functional areas, with significantly higher concentrations in industrial areas than in other areas. Potential source analysis revealed that sewage treatment plant effluents and industrial activities were the primary OPE sources. The total OPE concentrations were negatively correlated to the mean slope, plan curvature, and elevation, indicating that watershed characteristics play a role in the occurrence of OPEs. Individual OPEs (triisobutyl phosphate, tris(2-butoxyethyl) phosphate, tris(2-chloroethyl) phosphate, and tricresyl phosphate) and Σalkyl-OPEs were positively correlated to the night light index or population density, suggesting a significant contribution of human activity to OPE pollution. The co-occurrence of OPEs and DOM was also observed, and the fluorescence indices of DOM were found to be possible indicators for tracing OPEs. These findings can elucidate the potential OPE dynamics in response to DOM in urbanized estuarine water environments with intensive human activities.

Impact of Exposure to a Mixture of Organophosphate Esters on Adrenal Cell Phenotype, Lipidome, and Function

Organophosphate esters (OPEs) are used primarily as flame retardants and plasticizers. Previously, we reported that adrenal cells are important targets of individual OPEs. However, real-life exposures are to complex mixtures of these chemicals. To address this, we exposed H295R human adrenal cells to varying dilutions (1/1000K to 1/3K) of a Canadian household dust-based OPE mixture for 48 hours and evaluated effects on phenotypic, lipidomic, and functional parameters. Using a high-content screening approach, we assessed phenotypic markers at mixture concentrations at which there was greater than 70% cell survival; the most striking effect of the OPE mixture was a 2.5-fold increase in the total area of lipid droplets. We then determined the response of specific lipid species to OPE exposures with novel, nontargeted lipidomic analysis of isolated lipid droplets. These data revealed that house dust OPEs induced concentration-dependent alterations in the composition of lipid droplets, particularly affecting the triglyceride, diglyceride, phosphatidylcholine, and cholesterol ester subclasses. The steroid-producing function of adrenal cells in the presence or absence of a steroidogenic stimulus, forskolin, was determined. While the production of 17β-estradiol remained unaffected, a slight decrease in testosterone production was observed after stimulation. Conversely, a 2-fold increase in both basal and stimulated cortisol and aldosterone production was observed. Thus, exposure to a house dust-based mixture of OPEs exerts endocrine-disrupting effects on adrenal cells, highlighting the importance of assessing the effects of environmentally relevant mixtures.

A quantitative proteomic study reveals oxidative stress and synapse-related proteins contributed to TDCIPP exposure induced neurotoxicity

Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) has been consistently identified in various environmental media and biological specimens. Current understanding of the in vivo toxicities of TDCIPP is limited, especially for potential for neurotoxic and cognitive impairment effects. To better evaluate the potential adverse effect of the chemical on learning and memory, Sprague Dawley (SD) rats were administered TDCIPP via gavage at doses of 40, 120, and 360 mg/kg/day for a period of 90 days. Quantitative proteomic analysis, immunohistochemistry, and Western blotting were employed to assess alterations in proteins following exposure to TDCIPP. An open field test and the Morris Water Maze were used to assess anxiety and spatial learning memory capacity. Administration of TDCIPP induced anxiety and cognitive impairments in rats. Additionally, a noteworthy decrease in the number of neurons was observed in the hippocampal CA3 and dentate gyrus (DG) regions. Proteomic and bioinformatic analyses revealed dysregulation of numerous hippocampal proteins, particularly those associated with synapses (PKN1) or oxidative stress (GSTM4, NQO1, and BMAL1), which was further confirmed by Western blot analysis. In sum, the cognitive impairment of rats caused by TDCIPP exposure was associated with dysregulation of synaptic and oxidative stress-related proteins.

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.

The Organophosphate Esters Used as Flame Retardants and Plasticizers Affect H295R Adrenal Cell Phenotypes and Functions

Adverse effects associated with exposure to brominated flame retardants have led to regulations for their use and their replacement with organophosphate esters (OPEs). However, little is known about the impact of OPEs on the adrenal, a vital endocrine gland. Here, we used a high-content screening approach to elucidate the effects of OPEs on H295R human adrenal cell phenotypic endpoints and function. The effects of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), a legacy brominated flame retardant, on H295R cell cytotoxicity, oxidative stress, mitochondria, lysosomes, and lipid droplets were compared with those of 6 OPEs. Most OPEs reduced oxidative stress, increased the numbers of mitochondria, decreased lysosomes, and increased lipid droplets. Two potency ranking approaches, the lowest benchmark concentration/administered equivalent dose methods and Toxicological Prioritization Index analyses, revealed that the triaryl-OPEs (isopropylated triphenyl phosphate [IPPP], tris(methylphenyl) phosphate [TMPP], and triphenyl phosphate [TPHP]) and 1 nontriaryl OPE (tris(1,3-dichloro-2-propyl) phosphate [TDCIPP]) were more potent than BDE-47. The steroidogenic activity of adrenal cells in the presence or absence of forskolin, a steroidogenic stimulus, was determined after exposure to triaryl-OPEs. The basal production of cortisol and aldosterone was increased by IPPP but decreased by TPHP or TMPP exposure; the response to forskolin was not affected by these OPEs. All 3 triaryl OPEs altered the expression of rate-limiting enzymes involved in cholesterol and steroid biosynthesis; CYP11B1 and CYP11B2 were the most prominently affected targets. The OPE chemical-specific effects on cortisol and aldosterone production were best explained by alterations in STAR expression. Thus, the adrenal may be an important target for these endocrine-disrupting chemicals.

Independent and combined effects of exposure to organophosphate esters on thyroid hormones in children and adolescents

Toxicological studies suggest that organophosphate esters (OPEs) may impair thyroid function. Epidemiological evidence, related to children and adolescents, has not been reported, and little is known about the combined effects of exposure to OPE mixtures. In this study, we collected information of 1156 children and adolescents (aged 6-18 years, 48.4% males) from a cross-sectional study in Liuzhou, China, and measured the levels of 15 urinary OPE metabolites and 5 serum thyroid hormones. Multivariate linear regression and quantile g-computation (QGC) approach were used to examine the associations which adjusted for demographic and lifestyle characteristics. Few participants had levels of triiodothyronine (T3) and free thyroxine (FT4) outside age-specific pediatric ranges. QGC analyses showed that individuals in the second, third, and fourth quartiles (Q2-Q4) of exposure had 3.93% (2.14%, 5.75%), 8.01% (4.32%, 11.8%), and 12.3% (6.54%, 18.3%) higher T3 than those in the first quartile (Q1), with similar pattern for free triiodothyronine (FT3). Individuals in Q2 and Q3 had higher thyroid-stimulating hormone (TSH) than those in Q1, but no differences were observed in TSH between Q1-Q4. In contrast, compared to the lowest quartile, FT4 was lower for those in Q2 (- 1.54%; 95% CI: - 3.02%, -0.04%), Q3 (-3.07%; 95% CI: -5.95%, -0.09%), and Q4 (-4.56%; 95% CI: - 8.80%, - 0.13%). These associations were consistent with the results from multivariate linear regression. When stratified by sex, OPE exposure (individual or mixtures) was associated with increased T3 and FT3 in males and decreased FT4 in females. This study provides the first evidence to characterize the thyroid-disrupting effects of OPE exposure in children and adolescents.

Organophosphate flame retardants and plastics in soil from an abandoned e-waste recycling site: significant ecological risks derived from plastic debris

The distribution of 9 organophosphate flame retardants (OPFRs) was determined in plastic debris and soil samples separated from twenty soil samples collected from an abandoned e-waste recycling area. Tris-(chloroisopropyl) phosphate (TCPP) and triphenyl phosphate (TPhP) were the main chemicals, with median concentrations of 124-1930 ng/g and 143-1170 ng/g in soil, and 712-803 ng/g and 600-953 ng/g in plastics, respectively. Plastics contributed less than 10% of the total OPFR mass in bulk soil samples. No apparent OPFR distribution trend was observed in different sizes of plastics and soil. The ecological risks of plastics and OPFRs were estimated by the species sensitivity distributions (SSDs) method, which resulted in lower predicted no-effect concentrations (PNECs) of TPhP and decabromodiphenyl ether 209 (BDE 209) than the standard values derived from limited toxicity tests. In addition, the PNEC of polyethene (PE) was lower than the plastic concentration in the soil of a previous study. TPhP and BDE 209 had high ecological risks with risk quotients (RQs) > 0.1, and RQ of TPhP was among the highest values in literature.

Insights into the geographical distribution, bioaccumulation characteristics, and ecological risks of organophosphate esters

Organophosphate esters (OPEs), as flame retardants and plasticizers, have been numerously explored regarding the occurrence and ecotoxicology. Given their toxicity, persistency and bio-accumulative potential, however, they may pose negative effects on ecosystems, regarding which is a growing global concern. Accordingly, the present review systematically analyses the recent literature to (1) elucidate their worldwide distribution, bioaccumulation, and biomagnification potential, (2) determine their interim water quality criteria (i.e., effect thresholds), and (3) preliminarily assess the ecological risks for 32 OPEs in aquatic ecosystems. The results showed that the spatiotemporal distribution of OPEs was geographically specific and closely related to human activities (i.e., megacities), especially halogenated-OPEs. We also found that precipitation of airborne particulates could affect the concentrations of OPEs in soil, and there was a positive correlation between the bioaccumulation and hydrophobicity of OPEs. Tris(2-ethylhexyl) phosphate may exhibit high bioaccumulation in aquatic organisms. A substantial difference was found among interim water quality criteria for OPEs, partly attributable to the variation of their available toxicity data. Tris(phenyl) phosphate (TPHP) and tris(1,3-dichloroisopropyl) phosphate with the lowest predicted no-effect concentration showed the strongest toxicity of growth and reproduction. Through the application of the risk quotient and joint probability curve, TPHP and tris(chloroethyl) phosphate tended to pose moderate risks, which should receive more attention for risk management. Future research should focus on knowledge gaps in the mechanism of biomagnification, derivation of water quality criteria, and more precise assessment of ecological risks for OPEs.

Organophosphate esters cause thyroid dysfunction via multiple signaling pathways in zebrafish brain

Organophosphate esters (OPEs) are widespread in various environmental media, and can disrupt thyroid endocrine signaling pathways. Mechanisms by which OPEs disrupt thyroid hormone (TH) signal transduction are not fully understood. Here, we present in vivo-in vitro-in silico evidence establishing OPEs as environmental THs competitively entering the brain to inhibit growth of zebrafish via multiple signaling pathways. OPEs can bind to transthyretin (TTR) and thyroxine-binding globulin, thereby affecting the transport of TH in the blood, and to the brain by TTR through the blood-brain barrier. When GH3 cells were exposed to OPEs, cell proliferation was significantly inhibited given that OPEs are competitive inhibitors of TH. Cresyl diphenyl phosphate was shown to be an effective antagonist of TH. Chronic exposure to OPEs significantly inhibited the growth of zebrafish by interfering with thyroperoxidase and thyroglobulin to inhibit TH synthesis. Based on comparisons of modulations of gene expression with the Gene Ontology and Kyoto Encyclopedia of Genes and Genomes databases, signaling pathways related to thyroid endocrine functions, such as receptor-ligand binding and regulation of hormone levels, were identified as being affected by exposure to OPEs. Effects were also associated with the biosynthesis and metabolism of lipids, and neuroactive ligand-receptor interactions. These findings provide a comprehensive understanding of the mechanisms by which OPEs disrupt thyroid pathways in zebrafish.

Bioaccumulation and potential risk of organophosphate flame retardants in coral reef fish from the Nansha Islands, South China Sea

Organophosphate flame retardant (OPFR) pollution in marine environment has attracted increasing attention in recent years. Coral reefs are regarded as significant marine ecosystems, however, research on OPFR contamination in coral reefs is limited. In the present work, 9 OPFR compounds were analyzed in fish samples collected from the Zhubi Reef and Yongshu Reef of the Nansha Islands, South China Sea, to evaluate the biomagnification and potential threats of OPFRs in the coral reef ecosystems. ∑OPFR concentrations in the coral reef fish ranged from 38.7 to 2090 ng/g lipid weight (lw), with an average of 420 ± 491 ng/g lw. Alkyl OPFRs were more abundant than chlorinated OPFRs and aryl OPFRs. Individually, TBEP and TCPP were the two most abundant OPFR compounds. Biomagnification potential was indicated for TCPP, TCEP, TBP, TBEP and TEHP along the marine food web, with trophic magnification factors being greater than one. The estimated dietary intakes of OPFRs via coral fish consumption were 0-1.11 ng/kg bw/d and 0.01-2.06 ng/kg bw/d, respectively, for rural and urban residents. Additionally, the hazard quotients of OPFR compounds ranged from 2 × 10^-7 to 7.41 × 10^-5 for rural residents and from 4 × 10^-7 to 1.37 × 10^-4 for urban residents. Although the risk to human health from exposure to OPFRs via consuming coral reef fish from the South China Sea was low, further investigation of these chemicals is still recommended.

Organophosphate esters in surface soils from a heavily urbanized region of Eastern China: Occurrence, distribution, and ecological risk assessment

Organophosphate esters (OPEs) pose increasing concerns for their widespread distribution in soil environments and potential threat to human health. In this study, we investigated the occurrence and associated risks of seven OPEs in surface soils and the potential influence of human activities on soil OPE contamination in a heavily urbanized region of the Yangtze River Delta in Eastern China. All target OPEs were detected in the soil samples (100% of samples) reflecting their widespread distribution in the study region. The total OPE concentration (the sum of the seven OPEs) ranged from 162.7 to 986.0 ng/g on a dry weight basis, with a mean value of 469.3 ± 178.6 ng/g. Tris (2-butoxyethyl) phosphate was the main compound, accounting for 67-78% of the total OPE concentration. Ecological risk assessment showed that tris(2-chloroisopropyl) phosphate, tris(2,3-dichloropropyl) phosphate, tris(2-butoxyethyl) phosphate, and tris(2-ethylhexyl) phosphate posed a medium potential risk to terrestrial biota (0.1 < risk quotient <1). The human exposure estimation showed insignificant risks to local population. Redundancy analysis revealed that the individual and total OPE contaminations were positively correlated with human activity parameters. The total OPE concentrations were positively correlated to population density (R² = 0.38, P < 0.001), and urban land use percentage (R² = 0.39, P < 0.001), while negatively correlated to forest land use percentage (R² = 0.59, P < 0.001), suggesting a significant contribution of human disturbance to OPE pollution. These results can facilitate OPE contamination control and promote sustainable soil management in urbanized and industrialized regions.

Thyroid disruption and oxidative stress in American kestrels following embryonic exposure to the alternative flame retardants, EHTBB and TBPH

Brominated flame retardant chemicals, such as 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (EHTBB) (CAS #: 183658-27-7) and bis(2-ethylhexyl)-2,3,4,5-tetrabromophthalate (TBPH) (CAS #: 26040-51-7), have been detected in avian tissues and eggs from remote regions. Exposure to EHTBB and TBPH has been shown to cause oxidative stress and altered thyroid function in rodents and fish, yet no controlled studies have examined potential adverse effects of exposure in birds. Because flame retardants have been detected in wild raptors, we used American kestrels (Falco sparverius) as a model raptor to determine whether in ovo exposure to EHTBB or TBPH affected growth, hatching success, oxidative stress, or thyroid function. We exposed kestrel embryos to nominal concentrations (10, 50, or 100 ng g^-1 egg weight) of EHTBB and TBPH via egg-injection on embryonic day 5. Embryonic exposure (~23 d) to EHTBB increased thyroid gland mass, reduced glandular colloid and total thyroxine (T4) in hatchling males and females, whereas deiodinase enzyme activity increased in males but decreased in females. Hatchlings exposed to TBPH in ovo exhibited reduced colloid and increased oxidative stress. Although exposure to EHTBB and TBPH caused several physiological effects (e.g., heart and brain mass), only exposure to 50 ng g^-1 EHTBB appeared to reduce hatching success. Our results suggest these flame retardants may be hazardous for predatory birds. Future research should evaluate long-term survival and fitness consequences in birds exposed to these chemicals.

Seasonal variation, source identification, and risk assessment of organophosphate ester flame retardants and plasticizers in surficial sediments from Liao River estuary wetland, China

Organophosphate ester (OPE) flame retardants and plasticizers in surficial sediments were collected in Liao River estuarine wetland during the dry, flood, and level periods to understand the seasonal variation, potential sources, and environmental risks. The concentrations of ∑₁₃OPEs ranged from 19.5 to 67.0 ng g^-1 dry weight (dw), with an average concentration of 30.6 ng g^-1 dw. OPEs pollution displayed a seasonal variation, the concentrations of OPEs in dry period > level period > flood period. Tributyl-n-phosphate was the predominant OPEs, which accounts for 29.7% of ∑₁₃OPEs. Principal component analysis and positive matrix factorization suggested that the pollution sources of OPEs also varied seasonally. The ecological risk of OPEs to aquatic organisms was low, and the non-carcinogenic and carcinogenic risks to human beings were also far below the acceptable level. 2-Ethylhexyl diphenyl phosphate was the major compound causing ecological and non-carcinogenic risk, while tris-(2-chloroethyl) phosphate had the highest carcinogenic risk.

Distribution and sources of ordinary monomeric and emerging oligomeric organophosphorus flame retardants in Haihe Basin, China

With the banning of poly-brominated diphenyl ethers, organophosphorus flame retardants (OPFRs) have gained great development space as their alternatives. In this study, the concentration and partition of nine ordinary monomeric OPFRs and two emerging oligomeric OPFRs (Resorcinol bis(diphenyl phosphate) (RDP) and bisphenol A bis(diphenyl phosphate) (BDP) in the Haihe Basin of China were studied, and their possible sources were analyzed. The ƩOPFRs in the surface water, sediments and suspended particulate matters (SPMs) in Haihe Basin were 80.1-777 ng/L, 18.9-86.5 ng/g dw and 6.40-234 ng/g dw, respectively. The detection frequencies of both oligomeric OPFRs exceeded 85%, suggesting their environmental contamination was widespread. The mean concentrations of RDP and BDP were 2.09 and 6.03 ng/L in the surface water, 0.91 and 5.09 ng/g dw in the sediments, 1.08 and 2.61 ng/g dw in SPMs, respectively. With Cl-OPFRs being predominant in all the three media, the proportions of alkyl-OPFRs, aryl-OPFRs, and oligomeric OPFRs in the sediments and SPMs were remarkably higher than those in surface water, suggesting that non-halogenated OPFRs preferred to distribute in solid phases. The water-sediment/SPM partition coefficients, logK_oc, of the OPFRs were calculated based on the paired samples. The logK_oc values of RDP and BDP were reported for the first time, and their logK_{oc water-sediment} were 4.36 ± 0.47 and 4.76 ± 0.25 and their logK_{oc water-SPM} were 3.77 ± 0.45 and 4.00 ± 0.47, respectively. The obtained logK_oc values were correlated with their octanol-water partition coefficient (logK_ow) significantly. It suggested that their partition to sediment or SPM was dominated by hydrophobic interaction. Principal component analysis indicated that the emissions from manufacturing plants and airport operation might be two important sources of OPFRs in the Haihe Basin of China.

Maternal Urinary Organophosphate Esters and Alterations in Maternal and Neonatal Thyroid Hormones

Production of organophosphate esters (OPEs), which represent a major flame-retardant class present in consumer goods, has increased over the past 2 decades. Experimental studies suggest that OPEs may be associated with thyroid hormone disruption, but few human studies have examined this association. We quantified OPE metabolites in the urine of 298 pregnant women from Cincinnati, Ohio, in the Health Outcomes and Measures of the Environment Study (enrolled 2003-2006) at 3 time points (16 and 26 weeks' gestation, and at delivery), and thyroid hormones in 16-week maternal and newborn cord sera. Urinary bis(1,3-dichloro-2-propyl)-phosphate concentrations were generally associated with decreased triiodothyronine and thyroxine levels and increased thyroid-stimulating hormone levels in maternal and newborn thyroid hormones in quartile dose-response analyses and multiple informant models. There was weaker evidence for thyroid hormone alterations in association with diphenyl-phosphate and di-n-butyl-phosphate. Bis-2-chloroethyl-phosphate was not associated with alterations in thyroid hormones in any analyses. We did not observe any evidence of effect modification by infant sex. These results suggest that gestational exposure to some OPEs may influence maternal and neonatal thyroid function, although replication in other cohorts is needed.

Long-Range Transport, Trophic Transfer, and Ecological Risks of Organophosphate Esters in Remote Areas

Organophosphate esters (OPEs) have been a focus in the field of environmental science due to their large volume production, wide range of applications, ubiquitous occurrence, potential bioaccumulation, and worrisome ecological and health risks. Varied physicochemical properties among OPE analogues represent an outstanding scientific challenge in studying the environmental fate of OPEs in recent years. There is an increasing number of studies focusing on the long-range transport, trophic transfer, and ecological risks of OPEs. Therefore, it is necessary to conclude the OPE pollution status on a global scale, especially in the remote areas with vulnerable and fragile ecosystems. The present review links together the source, fate, and environmental behavior of OPEs in remote areas, integrates the occurrence and profile data, summarizes their bioaccumulation, trophic transfer, and ecological risks, and finally points out the predominant pollution burden of OPEs among organic pollutants in remote areas. Given the relatively high contamination level and bioaccumulation/biomagnification behavior of OPEs, in combination with the sensitivity of endemic species in remote areas, more attention should be paid to the potential ecological risks of OPEs.

Hepatic Gene Expression Profiling of Atlantic Cod (Gadus morhua) Liver after Exposure to Organophosphate Flame Retardants Revealed Altered Cholesterol Biosynthesis and Lipid Metabolism

Since the phasing out and eventual ban on the production of organohalogen flame retardants, the use of organophosphate flame retardants (OPFRs) has increased rapidly. This has led to the detection of OPFRs in various environments including the Arctic. Two of the most prevalent OPFRs found in the Arctic are tris(2-chloroisopropyl) phosphate (TCPP), and 2-ethylhexyl diphenyl phosphate (EHDPP). The impacts of exposure to OPFRs on Arctic organisms is poorly understood. The objective of the present study was to determine the effects of exposure to TCPP, EHDPP, and a mixture of OPFRs on gene expression patterns in Atlantic cod, Gadus morhua. Precision-cut liver slices from Atlantic cod in vitro were exposed to either TCPP or EHDPP alone or in a mixture and sampled at 2 different time points to quantify gene expression patterns using RNA sequencing. We exposed the liver slices to 2 concentrations of TCPP and EHDPP, one of which was chosen based on the levels found in the Arctic environment. The RNA sequencing results demonstrated differential expression of hundreds of genes in response to exposure. The genes representing cholesterol biosynthesis and lipid metabolism pathway were significantly enriched in all the treatment groups. Almost all the cholesterol biosynthesis genes were significantly down-regulated in response to OPFR exposure. The effects on these pathways could involve various physiological processes including reproduction, growth, and behavior as well as adaptation to changing temperatures. Membrane fluidity is an important adaptive mechanism among aquatic organisms. Altered cholesterol homeostasis could have long-term consequences by altering the adaptive potential of aquatic organisms to changing water temperatures, particularly those living in polar environments. These results suggest that OPFRs could have unique effects on the organisms living in the Arctic compared with other environments. Further studies are needed to understand the long-term impacts of exposure to environmentally realistic concentrations using laboratory and field-based studies. Environ Toxicol Chem 2021;40:1639-1648. © 2021 SETAC.

The potential connections of adverse outcome pathways with the hazard identifications of typical organophosphate esters based on toxicity mechanisms

Following the world-wide ban of brominated flame retardants (BFRs), organophosphate esters (OPEs), which could potentially affect human health and ecosystem safety, have been frequently detected in various environmental media. However, the knowledge regarding the underlying toxicity effects of OPEs remains limited. In order to address these issues, this study reviewed the related reports which have been published in recent years. This analysis process included 12 OPEs, 10 model organisms, and 15 cell lines, which were used to systematically examine the mechanisms of endocrine disruption, neurotoxicity, hepatotoxicity, and cardiotoxicity, as well as reproductive and developmental toxicity. Subsequently, an adverse outcome pathway (AOP) framework of the toxicological effects of OPEs was built. The results demonstrated that multiple different pathways may lead to a single same adverse outcome (AO), and there was a certain degree of correlation among the different AOs. It was found that among all the 12 OPEs, tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) may potentially be the most toxic. In addition, rather than the parent chemicals, the metabolites of OPEs may also have different degrees of toxicity effects on aquatic organisms and humans. Overall, the results of the present study also suggested that an AOP framework should be built via fully utilizing the existing toxicity data of OPEs based on in vivo-in vitro-in silico to completely and deeply understand the toxic mechanisms of OPEs. This improved knowledge could then provide a theoretical basis for ecological risk assessments and water quality criteria research in the near future.

Effects of an Environmentally Relevant Mixture of Organophosphate Esters Derived From House Dust on Endochondral Ossification in Murine Limb Bud Cultures

Organophosphate esters (OPEs) are used widely as flame retardants and plasticizers but much remains unknown about their potential toxicity. Previously, we reported that 4 individual OPEs suppress endochondral ossification in murine limb bud cultures. However, real-life exposure is to complex OPE mixtures. In the present study, we tested the hypothesis that a Canadian household dust-based OPE mixture will affect endochondral ossification in gestation day 13 CD1 mouse embryo limb buds expressing fluorescent markers for the major cell populations involved in the process: collagen type II alpha 1-enhanced cyan fluorescent protein (proliferative chondrocytes), collagen type X alpha 1-mCherry (hypertrophic chondrocytes), and collagen type I alpha 1-yellow fluorescent protein (osteoblasts). Limbs were cultured for 6 days in the presence of vehicle or dilutions of the OPE mixture (1/1 000 000, 1/600 000, and 1/300 000). All 3 OPE mixture dilutions affected cartilage template development and the progression of endochondral ossification, as indicated by the fluorescent markers. The expression of Sox9, the master regulator of chondrogenesis, was unchanged, but the expression of Runx2 and Sp7, which drive chondrocyte hypertrophy and osteoblastogenesis, was dilution-dependently suppressed. RNA-seq revealed that exposure to the 1/300 000 dilution of the OPE mixture for 24 h downregulated 153 transcripts and upregulated 48 others by at least 1.5-fold. Downregulated transcripts were enriched for those related to the immune system and bone formation. In contrast, upregulated transcripts were enriched for those with stress response functions known to be regulated by ATF4 activation. Thus, exposure to the mixture of OPEs commonly found in house dust may have adverse effects on bone formation.

Endocrine and physiological responses of hatchling American kestrels (Falco sparverius) following embryonic exposure to technical short-chain chlorinated paraffins (C10-13)

Short chain chlorinated paraffins (SCCPs) are complex mixtures of polychlorinated n-alkanes, shown to bioaccumulate but with unknown effects in wild birds. The present study examined development-related effects of SCCPs on captive American kestrels (Falco sparverius) treated in ovo on embryonic day (ED) 5 by injection with technical Chloroparaffin® (C_10-13, 55.5% Cl) at environmentally relevant nominal (measured) concentrations of 10 (10), 50 (29) or 100 (97) ng ΣSCCP/g egg ww, and artificially incubated until hatching (ED27-ED29). The SCCP concentrations measured in the yolk sacs of the hatchling kestrels bracketed concentrations reported in the eggs of wild birds. Uptake and deposition of these SCCPs differed between male and female hatchlings, with only males showing differences in SCCP concentrations, being highest in the high-dose males than each of the other male groups. Embryonic exposure to SCCPs suppressed glandular total thyroxine (TT4) (20-33%) and reduced circulating triiodothyronine (TT3) (37-40%) in male hatchlings only when compared to control males, but had no effect on glandular TT3 or circulating TT4 in male or female kestrels. Histological assessments of thyroid glands showed that both sexes experienced significant structural changes indicative of gland activation. These thyroid glandular changes and the variations in SCCP concentrations were related to circulating TT3 in female hatchlings. Hepatic deiodinase enzyme (D1, D2) activities were stable and no SCCP-related changes were observed in hatching success, hatchling size, or immune organ size. However, several of the thyroid function indicators were correlated with hatchling size and smaller bursas and spleens, possibly indirectly through SCCP-induced changes in thyroid function. Because changes in thyroid function were evident at concentrations measured in wild bird eggs, similar changes may occur in wild nestlings. The potential impact of these changes on thyroid-mediated growth and survival in wild birds requires further investigation.

Transcriptomic, proteomic and metabolomic profiling unravel the mechanisms of hepatotoxicity pathway induced by triphenyl phosphate (TPP)

Triphenyl phosphate (TPP) has been found in various environmental media and in biota suggesting widespread human exposure. However, there is still insufficient information on the hepatotoxicity mechanisms of health risk exposed to TPP. In this study, TPP could induce human normal liver cell (L02) apoptosis, injury cell ultrastructure and elevate the levels of reactive oxygen species (ROS). The integrated multi-omic (transcriptomic, proteomic, and metabolomic) analysis was used to further investigate the mechanisms. Transcriptomic analysis revealed that TPP exposure markedly affected cell apoptosis, oncogene activation, REDOX homeostasis, DNA damage and repair. Additionally, proteomic analysis found that the related proteins associated with apoptosis, oxidative stress, metabolism and membrane structure were affected. And metabolomic analysis verified that the related metabolic pathways, such as glycolysis, citrate cycle, oxidative phosphorylation, lipid and protein metabolism, were also significantly disrupted. Based on the multi-omic results, a hypothesized network was constructed to discover the key molecular events in response to TPP and illustrate the mechanism of TPP-induced hepatotoxicity in L02 cells. Therefore, molecular responses could be elucidated at multiple biological levels, and multi-omic analysis could provide scientific tools for exploring potential mechanisms of toxicity and chemical risk assessment.

Animal-Derived and Plant-Derived Protein Supplement Feeds Are Important Sources of Organophosphate Esters in the Food Supply

Animal protein supplement feeds (APFs) are important raw feed materials for livestock. APFs might be susceptible to organophosphate esters (OPEs) but have not been paid attention yet. In the present study, animal-derived (meat meal, feather meal, and blood meal) and plant-derived APFs were all found to contain detectable levels of OPEs, with 16 target OPEs ranging from 12.6 ng/g dry weight (dw) to 301 ng/g dw. Meat meal contained the highest OPE level (mean: 117 ± 75.6 ng/g dw), followed by feather meal (54.6 ± 30.0 ng/g dw), plant-derived feed (41.9 ± 16.0 ng/g dw), and blood meal (28.0 ± 12.0 ng/g dw). Considering its widespread consumption, plant-derived APFs might be an important source of OPE exposure for livestock. Dust adhesion contributed to OPE contamination both in feather meal and plant-derived APFs. Congener patterns varied among the different APFs. Tris(2-chloroisopropyl) phosphate dominated in the plant-derived feed and blood meal, while tris(2-chloroethyl) phosphate and triphenyl phosphate were the major contributors in meat meal and feather meal, respectively. Tributyl phosphate and tri-iso-butyl phosphate were found to be statistically correlated in all APFs (p < 0.01), indicating their similar behavior and common sources. The protein-associated transport pathways of OPEs need to be studied separately for different protein matrices in the future.

In Vitro Immunotoxicity of Organophosphate Flame Retardants in Human THP-1-Derived Macrophages

Scarce attention has been paid to the immunotoxicity of organophosphate flame retardants (PFRs), which poses a challenge to the systematic assessment of their health risks. In this study, a battery of in vitro immunotoxicity screening assays, including adhesion, phagocytosis, and 48 cytokine/chemokine production, was measured after exposing THP-1-derived macrophages to six selected common PFRs (TPHP, TDCPP, TNBP, TOCP, TCEP, and TBOEP) at a noncytotoxic concentration (≤50 μM). Our results showed that TPHP and TBOEP partially attenuated the adhesion and phagocytosis of the THP-1 mφs and that TDCPP caused a functional loss of phagocytosis, implying the potential immunosuppression. In contrast, TNBP and TOCP may cause an immunostimulation by significantly promoting cell adhesion and enhancing phagocytic efficiency. Additionally, the results from a cytokine/chemokine secretion analysis revealed the proinflammatory properties of TDCPP, TPHP, and TBOEP. TOCP was thought to disrupt the inflammatory balance by inhibiting both proinflammatory and antiinflammatory cytokines. TCEP showed no effect on adhesion or phagocytosis and little modulation of cytokine release at this experimental concentration. Overall, this study supports that PFRs can be immunotoxic to macrophages in different ways and provides evidence for developing more sensitive in vitro immunotoxicity bioassay methods.

Distribution, source apportionment and ecological risks of organophosphate esters in surface sediments from the Liao River, Northeast China

A total of 24 surface sediment samples were collected from Liao River, Northeast China. The concentration, spatial distribution, potential source, and ecological risk of 13 organophosphate esters (OPEs) flame retardants and plasticizers were analyzed. The total concentrations of OPEs varied considerably, ranging from 19.7 to 234 ng g^-1 dry weight (dw), with the mean concentrations of 64.2 ± 52.2 ng g^-1 dw. The OPEs pollution was increasing from upstream to downstream of Liao River. Compared with other sediments of rivers and lakes all over the world, Liao River has been seriously contaminated by OPEs, especially tributyl phosphate (TNBP) and tri-butoxyethyl phosphate (TBOEP). TNBP was the most abundant OPEs, followed by TBOEP and triphenylphosphine oxide. Their mean relative contributions were 26.3%, 12.4% and 11.6%, respectively. Positive matrix factorization indicated that OPEs in sediments from Liao River might be derived from plastic, textile, and polyurethane foam, anti-foam agent, hydraulic fluids, and coatings, indoor release, and chemical process emission. The risk of potential adverse effects of each individually OPEs on aquatic organisms were low (risk quotient less than 0.1). 2-Ethylhexyl diphenyl phosphate was the main substance causing risk.

The interactions of diet-induced obesity and organophosphate flame retardant exposure on energy homeostasis in adult male and female mice

Previously, sex-dependent alterations in energy homeostasis were reported in adult mice fed a standard chow attributed to exposure to a mixture of organophosphate flame retardants (OPFRs) via estrogen receptors (ERα). In this study, adult male and female mice (C57BL/6J; Taconic) were treated with the same mixture of OPFRs (1 mg/kg each of tricresyl phosphate (TCP), triphenyl phosphate (TPP), and tris(1-3-dichloro-2propyl)phosphate (TDCPP)) for 7 weeks on a low-fat diet (LFD, 10% kcal fat) or a high fat (HFD, 45% kcal fat) in a diet-induced obesity model. Consistent with our previous observations, OPFRs altered weight gain in males, differentially with diet, while females remained unaffected. OPFR treatment also revealed sex-dependent perturbations in metabolic activity. During the night (approximately 0100-0400 hr), males exhibited elevated activity and oxygen consumption, while in females these parameters were decreased, irrespective of diet. OPFR disrupted feeding behavior and abolished diurnal water intake patterns in females while increasing nighttime fluid consumption in males. Despite no marked effect of OPFRs on glucose or insulin tolerance, OPFR treatment altered circulating insulin and leptin in females and ghrelin in males. Data indicate that adult OPFR exposure might influence, and perhaps exacerbate, the effects of diet-induced obesity in adult mice by altering activity, ingestive behavior, and metabolism.

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.

Neurotoxicity and related mechanisms of flame retardant TCEP exposure in mice

Objective: To explore the neurotoxicity and mechanism of tris(2-chloroethyl) phosphate (TCEP) exposure in mice.Methods: Total 30 adult Kunming mice were randomly divided into normal control group (0 mg/kg·d), low-dose TCEP group (10 mg/kg·d), and high-dose TCEP group (100 mg/kg·d), and administered continuously by gavage for 30 days.Results: Compared with the control group, the water intake of high-dose TCEP group was declined significantly (p < 0.05), and the organ index of liver and spleen were increased significantly (p < 0.05). In addition, the escape latency of TCEP exposed mice were longer than that in the control group in water maze test (p < 0.05), while the total swimming course of high-dose TCEP group was elevated and the swimming time in target quadrant was obviously shortened compared with the control group (p < 0.05). The serum levels of total-triiodothyronine (TT3) and free triiodothyronine (FT3) were significantly higher in the high-dose TCEP group than in the control group (p＜0.05). Compared with the control group, the activities of glutathione transferase (GST) and super oxide dismutase (SOD) in the high-dose TCEP group were increased, and GST in the low-dose TCEP group were decreased, while the content of malonaldehyde (MDA) in both groups was increased (p＜0.05). In the CCK8 assay, the viability of PC12 cells decreased with an increase of TCEP concentration, indicating a concentration dependent neurotoxicity.Conclusion: TCEP exposure can cause neurotoxicity by increasing thyroid hormones and inducing oxidative damage in mice.

Effects of Organophosphate Ester Flame Retardants on Endochondral Ossification in Ex Vivo Murine Limb Bud Cultures

Phasing out the usage of polybrominated diphenyl ether (PBDE) flame retardants (FRs) in consumer products led to their widespread replacement with organophosphate ester (OPE) FRs, despite scarce safety data. PBDE exposures were associated with the suppression of endochondral ossification but little is known about the effects of OPEs on bones. Here, we used a novel ex vivo murine limb bud culture system to compare the effects of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) with those of several OPEs. Gestation day 13 embryos were collected from transgenic CD1 mice expressing fluorescent markers for the major stages of endochondral ossification: COL2A1-ECFP (chondrogenesis), COL10A1-mCherry (early osteogenesis), and COL1A1-YFP (late osteogenesis). Limbs were excised and cultured for 6 days in the presence of vehicle, BDE-47, or an OPE FR: triphenyl phosphate (TPHP), tert-butylphenyl diphenyl phosphate (BPDP), tris(methylphenyl) phosphate (TMPP), or isopropylated triphenyl phosphate (IPPP). BDE-47 (50 μM) decreased the extent of chondrogenesis in the digits and COL1A1-YFP expression in the radius and ulna relative to control. In comparison, concentrations of ≥1 μM of all 4 OPEs limited chondrogenesis; osteogenesis (both COL10A1-mCherry and COL1A1-YFP fluorescence) was markedly inhibited at concentrations ≥3 μM. The expression of Sox9, the master regulator of chondrogenesis, was altered by BDE-47, TPHP, and BPDP. BDE-47 exposure had minimal impact on the expression of Runx2 and Sp7, which drive osteogenesis, whereas TPHP and BPDP both suppressed the expression of these transcription factors. These data suggest that OPE FRs may be more detrimental to bone formation than their brominated predecessors.

Assessment of the effects of early life exposure to triphenyl phosphate on fear, boldness, aggression, and activity in Japanese quail (Coturnix japonica) chicks

Triphenyl phosphate (TPHP) is an organophosphate ester (OPE) used as a flame retardant (FR) and plasticizer. TPHP has previously been shown to disrupt behaviour in fish and mammals, but to our knowledge, this is the first study on the behavioural effects of TPHP in birds. Early life stage Japanese quail (Coturnix japonica) were exposed to nominal doses of 0 ng/g (vehicle-control), 5 ng/g (low dose), 50 ng/g (mid dose), and 100 ng/g (high dose) TPHP, both as embryos (via air cell injection prior to incubation) and as chicks (via daily gavage until 5 days post-hatch). The low dose reflects TPHP levels recorded in wild avian eggs, but actual environmental exposure levels may be higher given that TPHP is known to be rapidly metabolized in birds. We previously reported that the chicks exposed to TPHP in this study experienced reduced growth and resting metabolic rate, and sex-specific changes in thyroid function. The current study focuses on behavioural endpoints. We found that high-TPHP chicks exhibited less neophobia than vehicle-controls, and low-TPHP chicks exhibited more aggression towards conspecifics. No differences were observed in the responses of Japanese quail chicks to activity or tonic immobility (fear response) tests. These data add weight of evidence to previous findings suggesting that TPHP, among other OPEs, can disrupt ecologically-relevant behaviours in exposed vertebrates.

Organophosphate flame retardants and bisphenol A in children's urine in Hong Kong: has the burden been underestimated?

The urine levels of organophosphate flame retardants (PFRs) and bisphenol A (BPA) in kindergarten children (n = 31, 4-6 years old, sampling performed in 2016) in Hong Kong were measured. The detection frequency of the target PFRs, tri(2-chloroethyl)phosphate (TCEP), tris(1,3-dichloro-2-propyl) phosphate (TDCIPP), tris(chloroisopropyl)phosphate (TCIPP), triphenyl phosphate (TPHP) and 2-ethylhexyl diphenyl phosphate (EHDPP) ranged from 52% to 84%. The 95th percentile urinary concentrations of TPHP, TDCIPP, TCIPP, EHDPP and TCEP were 1.70, 0.24, 0.03, 0.05, 0.68 and 0.03 ng/mL, respectively. The median urine level of BPA was 1.69 ng/mL, with a detection frequency of 77%. Due to the lack of metabolism information, two scenarios were used to calculate the estimated daily intake (EDI) of these compounds. Back-calculated EDIs of PFRs using the urinary excretion rates from in vivo animal data (scenario 2) were up to 2.97 μg/kg/d (TDCIPP), which was only a little less than that observed in a sample of American infants, and the reference dose (RfD), meaning that the potential health risk of TDCIPP cannot be ignored. Dust ingestion was suggested to be the major pathway of exposure to PFRs, but when the levels in dust and air particles in kindergartens in Hong Kong were used to predict EDIs, these values were nearly half as much as those predicted from urinary TDCIPP in this study. This suggested that children's PFRs burden may be underestimated when considering only PFR levels in dust or air. There is thus a need for further studies with large-scale surveys and investigation of exposure routes.

Early life exposure to triphenyl phosphate: Effects on thyroid function, growth, and resting metabolic rate of Japanese quail (Coturnix japonica) chicks

Triphenyl phosphate (TPHP; CAS # 115-86-6), a commonly used plasticizer and flame retardant, has been reported in wild birds and identified as a potential high-risk chemical. We exposed Japanese quail (Coturnix japonica) by in ovo injection, and once hatched, orally each day for 5 days to safflower oil (controls) or TPHP dissolved in vehicle at low (5 ng TPHP/g), mid (50 ng TPHP/g), or high (100 ng TPHP/g) nominal TPHP doses. The low TPHP dose reflected concentrations in wild bird eggs, with mid and high doses 10x and 20x greater to reflect potential increases in environmental TPHP concentrations in the future. Despite no effects on mRNA expression in thyroid-related genes, TPHP exposure enhanced thyroid gland structure in high TPHP males, but in females, suppressed thyroid gland structure and activity (all TPHP females), and circulating free triiodothyronine (high TPHP females only). Consistent with thyroidal changes, and compared to controls, mid and high TPHP chicks experienced significantly reduced resting metabolic rate (≤13%) and growth (≤53%); mid TPHP males and high TPHP females were significantly smaller. The observed thyroidal effects and suppressed growth and metabolic rate of the quail chicks suggest that TPHP may adversely affect the health of wild birds.

In ovo exposure to brominated flame retardants Part II: Assessment of effects of TBBPA-BDBPE and BTBPE on hatching success, morphometric and physiological endpoints in American kestrels

Tetrabromobisphenol A bis(2,3-dibromopropyl ether) (TBBPA-BDBPE) and 1,2-bis(2,4,6-tribromophenoxy)ethane (BTPBE) are both brominated flame retardants (BFRs) that have been detected in birds; however, their potential biological effects are largely unknown. We assessed the effects of embryonic exposure to TBBPA-BDBPE and BTBPE in a model avian predator, the American kestrel (Falco sparverius). Fertile eggs from a captive population of kestrels were injected on embryonic day 5 (ED5) with a vehicle control or one of three doses within the range of concentrations that have been detected in biota (nominal concentrations of 0, 10, 50 or 100 ng/g egg; measured concentrations 0, 3.0, 13.7 or 33.5 ng TBBPA-BDBPE/g egg and 0, 5.3, 26.8 or 58.1 ng BTBPE/g egg). Eggs were artificially incubated until hatching (ED28), at which point blood and tissues were collected to measure morphological and physiological endpoints, including organ somatic indices, circulating and glandular thyroid hormone concentrations, thyroid gland histology, hepatic deiodinase activity, and markers of oxidative stress. Neither compound had any effects on embryo survival through 90% of the incubation period or on hatching success, body mass, organ size, or oxidative stress of hatchlings. There was evidence of sex-specific effects in the thyroid system responses to the BTBPE exposures, with type 2 deiodinase (D2) activity decreasing at higher doses in female, but not in male hatchlings, suggesting that females may be more sensitive to BTBPE. However, there were no effects of TBBPA-BDBPE on the thyroid system in kestrels. For the BTPBE study, a subset of high-dose eggs was collected throughout the incubation period to measure changes in BTBPE concentrations. There was no decrease in BTBPE over the incubation period, suggesting that BTBPE is slowly metabolized by kestrel embryos throughout their ∼28-d development. These two compounds, therefore, do not appear to be particularly toxic to embryos of the American kestrel.

Flame retardant concentrations and profiles in wild birds associated with landfill: A critical review

Given factors such as their persistence and toxicity, legacy brominated flame retardants (BFRs) like polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCDD), are designated as persistent organic pollutants (POPs) and are subject to regulation. Waste streams likely represent a substantial reservoir of legacy BFRs given that they were once widely applied to goods which are increasingly likely to be obsolete. Waste streams are also increasingly likely to be a source of emerging flame retardants, in particular, novel BFRs (NBFRs), the halogenated norbornene flame retardant Dechlorane Plus (DDC-CO) and the brominated, chlorinated or non-halogenated organophosphate triester flame retardants (PFRs). Many bird populations rely on landfill and its surrounding land-use for inter alia the opportunities it provides for activities such as foraging and resting. However, studies on captive and wild (free-living) birds have demonstrated deleterious effects of several FRs. Globally, approximately 250 bird species, including many of conservation concern, are reported to use landfill and surrounding habitat (including wastewater treatment operations), thus putting birds potentially at risk of exposure to such chemicals. We synthesise and critically evaluate a total of 18 studies covering eight avian species published between 2008 and 2018 (inclusive) across four continents that report flame retardant (FR) burdens in birds utilising landfill. Several such studies found FRs at among the highest concentrations detected in wild biota to date. We recommend that ongoing research be focused on landfill-associated birds, given that landfill is an important source of FRs and other anthropogenic chemicals, and particularly at sites where species are of conservation concern. We suggest ways in which the comparative power of studies could be enhanced in the future, the reporting of a minimum common suite of key chemicals, and where feasible, standardisation of the tissue compartments (i.e., eggs) to be studied. We conclude by identifying future research directions.

Can variability in corticosterone levels be related to POPs and OPEs in feathers from nestling cinereous vultures (Aegypius monachus)?

Persistent organic pollutants (POPs) are still globally distributed and some have been shown to interact with the endocrine system of birds. However, the relationship between POPs and the stress response mediated by the hypothalamic-pituitary-adrenal (HPA) axis is still poorly understood. Raising concerns are now focused on the toxic properties of emergent organophosphate ester flame retardants (OPEs), but whether OPEs interact with the HPA axis response has not yet been investigated. We measured corticosterone concentrations in feathers (CORTf) as a long-term biomarker of the bird HPA axis response and we investigated their relationship with POP and OPE concentrations in down feathers of nestling cinereous vultures (Aegypius monachus). We also examined whether high contaminant burden and high CORTf concentrations impacted the duration of chick development. The most predominant compounds were the following: p,p'-DDE (3.28 ± 0.26 ng g^-1 dw) > γ-HCH (0.78 ± 0.09 ng g^-1 dw) > BDE-99 (0.73 ± 0.09 ng g^-1 dw) > CB-153 (0.67 ± 0.04 ng g^-1 dw). The most persistent POP compounds (CB-170, -177, -180, -183, -187, -194 and p,p'-DDE) were associated (P = 0.02) with high concentrations of CORTf (range: 0.55-6.09 pg mm^-1), while no relationship was found when OPEs were tested (P > 0.05). Later egg-laying was positively associated to high levels of CORTf (P = 0.02) and reduced duration of chick development (P < 0.001), suggesting a beneficial effect of the HPA axis response on the growth of the chicks. In addition, males with high concentrations of the most persistent POP compounds tended to show a reduced duration of the nestling period (P = 0.05) and an equal fledging success than chicks with lower levels. These findings suggest that POPs, but not OPEs, may interact with the HPA axis response of chicks, although levels were not high enough to cause detrimental consequences.

Changes in thyroid function of nestling tree swallows (Tachycineta bicolor) in relation to polycyclic aromatic compounds and other environmental stressors in the Athabasca Oil Sands Region

In the Canadian Athabasca Oil Sands Region (AOSR), nestling tree swallows (Tachycineta bicolor) raised near mining-related activities accumulated greater concentrations of polycyclic aromatic compounds (PACs) that contributed to their poorer condition, growth, and reproductive success. Here, we report changes in thyroid function of the same 14 day old (do) nestlings (N ≤ 68) at these mining-related sites (OS1, OS2) compared to reference nestlings (REF1), and in relation to multiple environmental stressors that influence avian thyroid function. Thyroid function was compromised for OS1 nestlings but generally comparable between OS2 and REF1 chicks. In 2012, circulating total triiodothyronine (TT3) and thyroxine (TT4) were similar among all nestlings. The OS1 chicks had more active thyroid glands based on histological endpoints. Hepatic T4 outer-ring deiodinase (T4-ORD) activity was suppressed in OS1 and OS2 chicks. Despite inter-annual differences, OS1 chicks continued experiencing compromised thyroid function with significantly higher circulating TT4 and more active thyroid glands in 2013. The OS2 chicks had less active thyroid glands, which conceivably contributed to their suppressed growth (previously reported) relative to the heavier OS1 nestlings with more active thyroid glands. Thyroid gland activity was more influenced by the chicks' accumulation of (muscle), than exposure (feces) to naphthalene, C2-naphthalenes, and C1-fluorenes. Of four major volatile organic contaminants, sulfur dioxide (SO₂) primarily influenced thyroid gland activity and structure, supporting previous findings with captive birds. When collectively considering environmental-thyroidal stressors, chicks had a greater thyroidal response when they experienced colder temperatures, accumulated more C2-naphthalenes, and consumed aquatic-emerging insects with higher PAC burdens than terrestrial insects (carbon (δ¹³C)). We hypothesize that the more active thyroid glands and higher circulating TT4 of the OS1 chicks supported their growth and survival despite having the highest PAC burdens, whereas the lack of thyroid response in the OS2 chicks combined with high PAC burdens, contributed to their smaller size, poorer condition and poorer survival.

Urinary metabolites of organophosphate flame retardants in 0-5-year-old children: Potential exposure risk for inpatients and home-stay infants

Organophosphate flame retardants (OPFRs) have been commonly observed in indoor dust, food, and drinking water in China, but little is known about their exposure levels or factors leading to exposure in Chinese children. In this study, we measured eight metabolites of OPFRs (mOPFRs) in 227 urine samples collected from 0- to 5-year-old children in China. The high detection rates of mOPFRs (60%-100%) in the collected urine samples demonstrated the widespread exposure of this population to OPFRs. The median concentrations indicated that bis(2-chloroethyl)phosphate (BCEP, 0.85 ng/mL) and diphenyl phosphate (DPHP, 0.27 ng/mL) were the dominant chlorinated mOPFRs and nonchlorinated mOPFRs, respectively. Interestingly, the median urinary levels of bis(1-chloro-2-propyl)phosphate (BCIPP, 6.48 ng/mL) and bis(2-butoxyethyl)phosphate (BBOEP, 0.31 ng/mL) in inpatient infants were one order of magnitude higher (p < 0.01) than those observed in outpatient infants. For home-stay participants, furthermore, infants (0-1 year) had the highest median levels of BCIPP (0.72 ng/mL) and dibutyl phosphate (DBP, 0.14 ng/mL) among the three age groups (i.e., 0-1, >1-3, and >3-5 years), and significantly (p < 0.05) negative age-related relationships were found for both urinary mOPFRs. Two set of data on estimated daily intakes (EDIs) were calculated based on the fraction of OPFR excreted as the corresponding mOPFR (F_UE) in human liver microsomes (EDI_HLM) and S9 fraction (EDI_S9) system, respectively. In general, children have relatively high EDIs of tris(2-chloroethyl)phosphate (TCEP: EDI_HLM = 485 ng/kg bw/day, EDI_S9 = 261 ng/kg bw/day). Furthermore, 17% or 21% of inpatient infants had EDIs that exceeded the reference dose, whereas this value was reduced to 13% in outpatient infants; and this value decreased with age among all home-stay children (0-5 years). Our results indicated that inpatient and home-stay infants had a higher potential risk of OPFR exposure. To our knowledge, this is the first study to identify the elevated urinary levels of mOPFRs in inpatients.

Sex-specific responses in neuroanatomy of hatchling American kestrels in response to embryonic exposure to the flame retardants bis(2-ethylhexyl)-2,3,4,5-tetrabromophthalate and 2-ethylhexyl-2,3,4,5-tetrabromobenzoate

Bis(2-ethylhexyl)-2,3,4,5-tetrabromophthalate (BEH-TEBP) and 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (EH-TBB), flame retardant components of FireMaster 550® and 600® have been detected in tissues of wild birds. To address the paucity of information regarding potential impacts of flame retardants on the brain, brain volume regions of hatchling American kestrels (Falco sparverius) were evaluated following in ovo injection at embryonic day 5 with safflower oil or to 1 of 3 doses of either BEH-TEBP (12, 60, or 107 ng/g egg) or EH-TBB (11, 55, or 137 ng/g egg). The doses for both chemicals reflected concentrations reported in wild birds. The volumes of the hippocampus and telencephalon and volumetric differences between left and right hemispheres were measured in hatchlings (embryonic day 28). A sex-specific effect of BEH-TEBP on relative hippocampus volume was evident: the hippocampus was significantly enlarged in high-dose females compared to control females but smaller in low-dose females than the other females. There was no significant effect of EH-TBB on hippocampus volume in female kestrel hatchlings or of either chemical in male hatchlings and no effects of these concentrations of EH-TBB or BEH-TEBP on telencephalon volume or the level of symmetry between the hemispheres of the brain. In sum, embryonic exposure of female kestrels to these BEH-TEBP concentrations altered hippocampus volume, having the potential to affect spatial memory relating to ecologically relevant behavior such as prey capture, predator avoidance, and migration. Environ Toxicol Chem 2018;37:3032-3040. © 2018 SETAC.

Occurrence and distribution of organophosphate flame retardants (OPFRs) in soil and outdoor settled dust from a multi-waste recycling area in China

Distribution of 12 organophosphate flame retardants (OPFRs) was determined in soil and outdoor settled dust samples collected from a multi-waste (electronic, plastic, and rubber wastes and abandoned household-appliances and vehicles) recycling area, that encompassed different modes of operation i.e. open (ORS) and semi-closed recycling (SCRS). Among the twelve OPFRs analyzed, eleven were detected at a frequency of 75%-100% in all soil and dust samples. In soil samples, ΣOPFR concentrations were significantly higher at ORS (122-2100ng/g) than at SCRS (58.5-316ng/g) and nearby farmlands (37.7-156ng/g). The ΣOPFR concentrations in dust samples were higher than those in soil samples with spatial distribution similar to that observed for soil, decreasing from ORS (1390-42,700ng/g) to SCRS (914-7940ng/g). Tris(2-chloroisopropyl) phosphate (TCIPP) was the major OPFRs in both soil (<MDL-1370ng/g) and dust (39.9-16,300ng/g) samples. Chlorinated OPFRs [TCIPP, tris(1,3-dichloroisopropyl) phosphate (TDCIPP) and tris(2-chloroethyl) phosphate (TCEP)] and aryl-OPFRs [triphenyl phosphate (TPHP), tris(methylphenyl) phosphate (TMPP)] exhibited spatial difference between ORS and SCRS. Principle component analysis (PCA) of OPFR concentrations revealed that TCIPP, TDCIPP, TPHP, TMPP originated from similar sources. TMPP was assessed to pose eco-toxicological risk (risk quotient values: RQs) in the soil ecosystem. The median estimated daily intake (EDI) of OPFRs via soil and outdoor settled dust ingestion (based on average ingestion rate) was 3.14×10^-1ng/kgbw/day for adults at ORS. Our results suggest that waste recycling is an important source of chlorinated- and aryl-OPFRs in the environment.

Oxidative stress, cell cycle arrest, DNA damage and apoptosis in adult zebrafish (Danio rerio) induced by tris(1,3-dichloro-2-propyl) phosphate

Tris(1,3-dichloro-2-propyl)phosphate (TDCPP) is an additive flame retardant of high production volume, and frequently detected in biota and environment. However, knowledge on its potential risk and toxicological mechanism still remains limited. In this study, DNA damage, transcriptomic responses and biochemical changes in the liver of zebrafish (Danio rerio) induced by TDCPP were investigated. Zebrafish was exposed to 45.81μg/L (1/100 (96h-LC₅₀)) and 229.05μg/L (1/20 (96h-LC₅₀)) TDCPP for 7 d. The reactive oxygen species (ROS) and GSH contents, in addition to antioxidant enzyme activities in the liver changed significantly, and the mRNA levels of genes related to oxidative stress were alerted in a dose-dependent and/or sex-dependent manner after exposure to TDCPP. Significant DNA damage in zebrafish liver was found, and olive tail moment increased in a concentration-dependent manner. Moreover, exposure of TDCPP at 45.81μg/L level activated the cell cycle arrest, DNA repair system and apoptosis pathway in male zebrafish, and 229.05μg/L TDCPP exposure inhibited those pathways in both male and female zebrafish. The cell apoptosis was confirmed in TUNEL assay as higher incidence of TUNEL-positive cells were observed in zebrafish exposed to 229.05μg/L TDCPP. Our results also indicated that males were more sensitive to TDCPP exposure compared with females. Taken together, our results showed that TDCPP could induce oxidative stress, cell cycle arrest, DNA damage and apoptosis in adult zebrafish liver in sex- and concentration-dependent manners.

Spatiotemporal patterns and relationships among the diet, biochemistry, and exposure to flame retardants in an apex avian predator, the peregrine falcon

Flame retardants (FR) are industrial chemicals and some are proven environmental contaminants that accumulate in predatory birds. Few studies have examined the influence of diet on FR profiles in nestling raptors and the possible physiological implications of such FR exposure. The objectives of this research were (1) to determine spatial patterns of ≤ 48 polybrominated diphenyl ether (PBDE) congeners and ≤ 26 non-PBDE FRs, including organophosphate esters (OPEs), in nestling peregrine falcons (Falco peregrinus) across the Canadian Great Lakes-St. Lawrence River Basin (GL-SLR; 2010) and in the eastern Canadian Arctic (2007); (2) to identify temporal changes in FR concentrations from the mid-2000s to 2010 in GL-SLR peregrine nestlings; (3) to investigate the role of diet using stable isotopes on exposure patterns of quantifiable FRs; and (4) to assess possible associations between circulating FRs and total (T) thyroxine (TT₄) and triiodothyronine (TT₃), tocopherol, retinol and oxidative status (isoprostanes). The summed concentrations of the top 5 PBDEs (Σ₅) (BDE-47, -99, -100, -154, -153) were significantly higher in rural nestlings than urban nestlings in the GL-SLR, followed by the eastern Arctic nestlings. The PBDE congener profile of rural nestlings was dominated by BDE-99 (34‰), whereas BDE-209 (31‰) became dominant in the 2010 urban PBDE profile marking a shift since the mid-2000s. Low (ppb) concentrations of 25 novel non-PBDE FRs (e.g., 1,2-bis-(2,4,6-tribromophenoxy)ethane (BTBPE), decabromodiphenylethane (DBDPE)) were measured in the nestlings in at least one region, with the first report in peregrines of 15 novel non-PBDE FRs (e.g., 2-ethyl-1-hyxyl 2,3,4,5-tetrabromobenzoate (EHTBB), pentabromo allyl ether (PBPAE), tetrabromoethylcyclohexane (α-, β-DBE-DBCH)) as well as of tris (2-butoxyethyl) phosphate (TBOEP) (0-7.5ng/g ww) > tris(2-chloroisopropyl) phosphate (TCIPP) (0.1-5.5ng/g ww) > tris(2-chloroethyl) phosphate (TCEP) (0.02-2.0ng/g ww) > tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) (0-1.0ng/g ww). Within the GL-SLR, the urban nestlings' diet had significantly more terrestrial sources (greater δ¹³C values) than the broader, more aquatic-based diet of rural peregrines. Dietary source (δ¹³C) was significantly associated with concentrations of Σ₅PBDE, BDE-209, EHTBB, and 2,2-4,4',5,5'-hexabromobiphenyl (BB-153), with trophic level (δ¹⁵N) also positively associated with BDE-209 levels. Compared to urban nestlings, the rural nestlings had significantly lower circulating concentrations of thyroxine (TT₄), triiodothyronine (TT₃), a greater proportion of TT₃ relative to TT₄ (TT₃:TT₄), tocopherol and oxidative status (isoprostanes), but higher retinol levels; the most recalcitrant PBDE congener, BDE-153, in combination with low concentrations of some novel FRs, particularly octabromotrimethylphenyllindane (OBIND), may influence circulating thyroid hormones, especially TT₄, and retinol levels of peregrine falcon nestlings. These associations of FR-endocrine-biochemical measures suggest possible exposure-related changes in these birds and further study is warranted.

Birds and flame retardants: A review of the toxic effects on birds of historical and novel flame retardants

Flame retardants (FRs) are a diverse group of chemicals, many of which persist in the environment and bioaccumulate in biota. Although some FRs have been withdrawn from manufacturing and commerce (e.g., legacy FRs), many continue to be detected in the environment; moreover, their replacements and/or other novel FRs are also detected in biota. Here, we review and summarize the literature on the toxic effects of various FRs on birds. Birds integrate chemical information (exposure, effects) across space and time, making them ideal sentinels of environmental contamination. Following an adverse outcome pathway (AOP) approach, we synthesized information on 8 of the most commonly reported endpoints in avian FR toxicity research: molecular measures, thyroid-related measures, steroids, retinol, brain anatomy, behaviour, growth and development, and reproduction. We then identified which of these endpoints appear more/most sensitive to FR exposure, as determined by the frequency of significant effects across avian studies. The avian thyroid system, largely characterized by inconsistent changes in circulating thyroid hormones that were the only measure in many such studies, appears to be moderately sensitive to FR exposure relative to the other endpoints; circulating thyroid hormones, after reproductive measures, being the most frequently examined endpoint. A more comprehensive examination with concurrent measurements of multiple thyroid endpoints (e.g., thyroid gland, deiodinase enzymes) is recommended for future studies to more fully understand potential avian thyroid toxicity of FRs. More research is required to determine the effects of various FRs on avian retinol concentrations, inconsistently sensitive across species, and to concurrently assess multiple steroid hormones. Behaviour related to courtship and reproduction was the most sensitive of all selected endpoints, with significant effects recorded in every study. Among domesticated species (Galliformes), raptors (Accipitriformes and Falconiformes), songbirds (Passeriformes), and other species of birds (e.g. gulls), raptors seem to be the most sensitive to FR exposure across these measurements. We recommend that future avian research connect biochemical disruptions and changes in the brain to ecologically relevant endpoints, such as behaviour and reproduction. Moreover, connecting in vivo endpoints with molecular endpoints for non-domesticated avian species is also highly important, and essential to linking FR exposure with reduced fitness and population-level effects.

A Review of Organophosphate Esters in the Environment from Biological Effects to Distribution and Fate

Organophosphate esters (OPEs) are synthetic phosphoric acid derivatives used in a wide variety of applications including as flame retardants and plasticizers. Their production and usage has increased in recent years, due to the phase-out of other flame retardant formulations (e.g., polybrominated diphenyl ethers). As such, there has been a recent push to understand the global distribution of OPEs and their behaviour in biota. Multiple studies have been published over the last few years pertaining to OPE concentrations in biotic and abiotic environmental compartments, as well as the metabolism of OPEs in biota. This paper aims to provide a brief review of the occurrence and levels of OPEs in the environment, as well as recent developments concerning the elucidation of OPE metabolism in biota.

In ovo tris(2-butoxyethyl) phosphate concentrations significantly decrease in late incubation after a single exposure via injection, with no evidence of effects on hatching success or latent effects on growth or reproduction in zebra finches

Zebra finch (Taeniopygia guttata) eggs were injected with the organophosphate triester flame retardant tris(2-butoxyethyl) phosphate (TBOEP) at 0 μg/g, 0.01 μg/g, 1 μg/g, 10 μg/g, or 50 μg/g egg. Subsets of high-dose eggs were collected throughout incubation to measure TBOEP, which started declining in late incubation and then decreased rapidly to 28% of injected concentration by hatching. The authors found no effects of TBOEP on survival, growth, or reproduction even at very high doses. Environ Toxicol Chem 2017;36:83-88. © 2016 SETAC.