Effects of tris(1,3-dichloro-2-propyl) phosphate and tris(1-chloropropyl) phosphate on cytotoxicity and mRNA expression in primary cultures of avian hepatocytes and neuronal cells

Development and Validation of an Analytical Method to Quantitate Tris(chloroisopropyl)phosphate in Rat and Mouse Plasma using Gas Chromatography with Flame Photometric Detection

Tris(chloropropyl)phosphate (TCPP) is an organophosphorus flame retardant (OPFR) and plasticizer increasingly used in consumer products and as a replacement for brominated flame retardants. Commercially available TCPP is a mixture of four structural isomers the most abundant of which is tris(1-chloro-2-propyl)phosphate (TCPP-1). Although there is a widespread use of TCPP and potential for human exposure, there is limited data on the safety or toxicity of TCPP. The National Toxicology Program is conducting long-term studies to examine the toxicity of the TCPP in rats after lifetime exposure, including perinatal oral exposure. Quantitative estimates of internal dose are essential to interpret toxicological findings in rodents. To aid in this, a method was fully validated to quantitate the most abundant isomer, TCPP-1, in female Harlan Sprague Dawley (HSD) rat and B6C3F1 mouse plasma with partial validation in male rat plasma, and male and female mouse plasma. The method used protein precipitation using trichloroacetic acid followed by the extraction with toluene, and analysis by gas chromatography with flame photometric detection. The performance of the method was evaluated over 5-70 ng TCPP-1/mL plasma. The method was linear (r ≥ 0.99), accurate (inter-day relative error: ≤ ± -7.2) and precise (inter-batch relative standard deviation: ≤27.5%). The validated method has lower limits of quantitation and detection of ~5 and 0.9 ng/mL, respectively, in female HSD rat plasma and can be used on samples as small as 50 μL demonstrating the applicability to plasma samples from toxicology studies.

Organophosphate Ester, 2-Ethylhexyl Diphenyl Phosphate (EHDPP), Elicits Cytotoxic and Transcriptomic Effects in Chicken Embryonic Hepatocytes and Its Biotransformation Profile Compared to Humans

The effects of 2-ethylhexyl diphenyl phosphate (EHDPP) on cytotoxicity and mRNA expression, as well as its metabolism, were investigated using a chicken embryonic hepatocyte (CEH) assay. After incubation for 36 h, the lethal concentration 50 (LC₅₀) was 50 ± 11 μM, suggesting that EHDPP is one of a small cohort of highly toxic organophosphate esters (OPEs). By use of a ToxChip polymerase chain reaction (PCR) array, we report modulation of 6, 11, or 16/43 genes in CEH following exposure to 0.1, 1, or 10 μM EHDPP, respectively. The altered genes were from all nine biological pathways represented on the ToxChip including bile acids/cholesterol regulation, glucose metabolism, lipid homeostasis, and the thyroid hormone pathway. After incubation for 36 h, 92.5% of EHDPP was transformed, and one of its presumed metabolites, diphenyl phosphate (DPHP), only accounted for 12% of the original EHDPP concentration. Further screening by use of high-resolution mass spectrometry revealed a novel EHDPP metabolite, hydroxylated 2-ethylhexyl monophenyl phosphate (OH-EHMPP), which was also detected in a human blood pool. Additional EHDPP metabolites detected in the human blood pool included EHMPP and DPHP. Overall, this study provided novel information regarding the toxicity of EHDPP and identified a potential EHDPP metabolite, OH-EHMPP, in both avian species and humans.

Prenatal exposure to organophosphate esters and cognitive development in young children in the Pregnancy, Infection, and Nutrition Study

Organophosphate esters (OPEs) are a class of chemicals commonly used as flame retardants and plasticizers. OPEs are applied to a wide variety of consumer products and have a propensity to leach from these products. Consequently, OPEs are ubiquitous contaminants in many human environments and human exposure is pervasive. Accumulating evidence suggests that OPEs are capable of interfering with childhood cognitive development through both neurologic- and endocrine-mediated mechanisms. However, observational evidence of cognitive effects is limited. We used data collected in the third phase of the Pregnancy, Infection, and Nutrition Study to investigate cognitive effects of prenatal exposure to OPEs. In a spot prenatal maternal urine sample, we measured the following OPE metabolites: diphenyl phosphate (DPHP), bis(1,3-dichloro-2-propyl phosphate) (BDCIPP), isopropyl-phenyl phenyl phosphate (ip-PPP), and 1-hydroxyl-2-propyl bis(1-chloro-2-propyl) phosphate (BCIPHIPP). We assessed children's language and multi-faceted and overall cognitive development between two and three years of age using the MacArthur-Bates Communicative Development Inventories (MB-CDI) and the Mullen Scales of Early Learning (MSEL). We used linear regression to estimate the change in children's scores on these developmental assessments per interquartile range (IQR) increase in log-transformed, specific-gravity-corrected prenatal OPE metabolite concentrations, adjusted for maternal age, education, income, race/ethnicity, BMI, and child's sex. A total of 149 children had both OPE metabolite measurements and MB-CDI scores, and 227 children had both OPE metabolite measurements and MSEL scores. We observed that higher concentrations of ip-PPP (ng/ml) were associated with lower scores on the MSEL Cognitive Composite Score (β = -2.61; 95% CI: -5.69, 0.46), and separately on two of the four MSEL Scales that comprise the Cognitive Composite, specifically the Fine Motor Scale (β = -3.08; 95% CI: -5.26, -0.91) and the Expressive Language Scale (β = -1.21; 95% CI: -2.91, 0.49). We similarly observed that prenatal ip-PPP concentrations were inversely associated with age-standardized scores on the MB-CDI Vocabulary assessment (β = -1.19; 95% CI: -2.53, 0.16). Other OPE metabolites were not strongly associated with performance on either assessment. Our results suggest that isopropylated triarylphosphate isomers, the presumed parent compounds of ip-PPP, may adversely impact cognitive development, including fine motor skills and early language abilities. Our study contributes to the growing body of observational evidence that suggests prenatal exposure to OPEs may adversely affect cognitive development.

Prioritization of 10 organic flame retardants using an avian hepatocyte toxicogenomic assay

As the number of chemicals developed and used by industry increases, the inherent limitations of traditional toxicology approaches become an unavoidable issue. To help meet the demand for toxicity evaluation, new methods, such as high-throughput toxicity screening, are currently being developed to permit rapid determination of toxic, molecular, and/or biochemical effects of a wide range of chemicals. In the present study, we demonstrate the utility of an avian in vitro toxicogenomics screening approach to determine the cytotoxic and transcriptomic effects of 10 organic flame retardants (OFRs) currently of international priority for ecological risk evaluation to prioritize and inform future toxicological studies. Hepatocytes from 2 avian species, chicken and double-crested cormorant, were prepared and exposed for 24 h to various concentrations (0-300 μM) of the following 10 OFRs: Chemical Abstracts Service registration numbers 29761-21-5, 56803-37-3 (p-tert-butylphenyl diphenyl phosphate [BPDP]), 65652-41-7, 68937-41-7 (phenol, isopropylated, phosphate [3:1] [IPPP]), 95906-11-9, 19186-97-1, 26040-51-7, 35948-25-5, 21850-44-2, and 25713-60-4. Cell viability, the 7-ethoxyresorufin-O-deethylase assay, and transcriptomic analysis using species-specific ToxChip polymerase chain reaction arrays were performed to evaluate the in vitro effect of these OFRs. Of the 10 OFRs assessed, BPDP and IPPP elicited the strongest cytotoxic and transcriptomic responses in both chicken and double-crested cormorant hepatocytes and are therefore recommended as priority candidates for further wildlife toxicological investigations. Environ Toxicol Chem 2018;37:3134-3144. © 2018 Crown in the right of Canada. Published by Wiley Periodicals Inc. on behalf of SETAC.

Exposure to tris(1,3-dichloro-2-propyl) phosphate for Two generations decreases fecundity of zebrafish at environmentally relevant concentrations

Previous studies reported that exposure to environmentally relevant concentrations of TDCIPP significantly decreased the number of cumulative eggs in zebrafish, but effects on the quantity of eggs and sperms remained unknown. Therefore, in this study, effects of TDCIPP on yolk diameter, surface morphology of eggs, sperm density and total motility were evaluated. First generation (F0) zebrafish larvae (Danio rerio) were exposed to 0, 50, 500 or 5000 ng/L tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) from 14 days post fertilization (dpf) to 120 dpf. The F0 generation of zebrafish were paired and F1 generation of embryos were collected and continuously exposed to the same concentrations of TDCIPP until 150 dpf. TDCIPP bioconcentration in the whole body as well as effects on survival and fecundity were evaluated in F1 generation. Exposure to TDCIPP resulted in an accumulation of the chemical and decreased survival of F1 generation of zebrafish. TDCIPP decreased cumulative production and changed surface morphology of eggs in females. In males, TDCIPP decreased total motility of sperm but did not affect sperm density. These effects on quality of egg and sperm might be responsible for the decreased hatching rates observed in cross mating experiments. Furthermore, TDCIPP exposure resulted in down-regulated gene expression related to gonadal development and maturation of germ cells in females or/and males, and the down-regulation was correlated to decreased fecundity. Taken together, the results suggested that exposure to TDCIPP could decrease the quantity of eggs and sperms by down-regulating the expression of genes related to gonadal development and maturation of germ cells in zebrafish.

Prenatal exposure to organophosphates and associations with birthweight and gestational length

Organophosphate esters (OPEs) are often used as flame retardants and plasticizers. Animal data suggest exposure to OPEs could impact children's growth and development, yet impacts on human birth outcomes are understudied. We evaluate impacts of OPE exposure on the timing of delivery and infant's birthweight in the Pregnancy Infection and Nutrition Study (PIN). North Carolina women enrolled in PIN in early pregnancy and participated in follow-up through delivery. Analyses were limited to mothers recruited from 2002 to 2005, whose children participated in additional follow-up in early childhood (n = 349). Mothers collected urine samples in which OPE metabolites were assessed and birth outcomes were abstracted from medical records. Bis(1,3-dichloro-2-propyl) phosphate (BDCIPP), diphenyl phosphate (DPHP), isopropyl-phenyl phenyl phosphate (ip-PPP), bis(1-chloro-2-propyl) 1-hydroxy-2-propyl phosphate (BCIPHIPP) were detected in >80% of samples. Average birthweight and gestational age were 3326 g and 39.1 weeks, respectively. As data suggest that the mechanisms of action by which OPEs impact birth outcomes may be fetal sex dependent, we conducted sex-stratified statistical analyses. Women with the highest ip-PPP concentrations delivered girls 1 week earlier than women with lower levels (95% Confidence Interval (CI): -1.85, -0.15). Women with BDCIPP levels above the median had 3.99 (95% CI: 1.08, 14.78) times the odds of delivering their daughters preterm. Similarly, higher ip-PPP levels were associated with lower birthweight, but not after standardizing for gestational age. Among males, maternal ip-PPP was associated with decreased odds of preterm birth (OR = 0.21, 95% CI: 0.06, 0.68). DPHP and BCIPHIPP levels were not associated with outcomes in either sex. Results indicate that prenatal OPE exposure may impact timing of birth, though results are imprecise. Given widespread OPE exposure and the urgent need to identify and mitigate causes of preterm birth, further investigation is warranted.

Effect of the flame retardant tris (1,3-dichloro-2-propyl) phosphate (TDCPP) on Na+-K+-ATPase and Cl- transport in HeLa cells

Tris (1, 3-dichloro-2-propyl) phosphate (TDCPP) is one of the most diffused phosphorus flame retardants in the environment and is highly persistent and abundant in residential dust samples. To date the cellular targets and mechanisms underlying its toxic effects are not completely understood. The aim of this work was to study the effects of TDCPP on ion transport mechanisms fundamental for the cellular ionic homeostasis, such as Na⁺-K⁺-ATPase and Cl^- transport. HeLa cells were used as experimental model. TDCPP showed a dose-dependent effect on cell viability in cells exposed for 24 h as assessed by MTT test (IC₅₀ = 52.5 µM). The flame retardant was able to exert a dose and time-dependent inhibition on the Na⁺-K⁺-ATPase activity. A short-term exposure (1 h) was able to exert a significant inhibition at 75 and 100 µM TDCPP, suggesting that TDCPP is able to directly interfere with the Na⁺-K⁺-ATPase phosphate catalytic activity. The sensitivity of the pump to lower TDCPP concentrations increased with the increase of the time of exposure. Following 24 h exposure a significant inhibition of about 40% was evident already at 10 µM and the IC₅₀ value observed was 12.8 ± 6.0 µM. Moreover, TDCPP was also able to impair the NKCC mediated Cl^- transport in HeLa cells, as assessed in YFP-H148Q/I152L-expressing HeLa cells. Following 1 h exposure TDCPP significantly inhibited the transport by about 30%. The kinetic analysis demonstrated a noncompetitive mechanism of inhibition. In conclusion, results demonstrated the impairment of ion transport mechanisms fundamental for ion homeostasis by TDCPP on HeLa cells.

Effects of tris(1-chloro-2-propyl)phosphate and tris(2-chloroethyl)phosphate on cell viability and morphological changes in peripheral blood mononuclear cells (in vitro study)

Organophosphorus flame retardants (OPFRs) are a group of chemicals widely used in various everyday use products. Tris(2-chloroethyl)phosphate (TCEP) and tris(1-chloro-2-propyl)phosphate (TCPP) are one of the commonly used chemicals belonging to this group. Due to the need of limitation of the use of polybrominated diphenyl ethers (PBDEs) as retardants, the share of the compounds tested in our experiments in chemicals production systematically increases. There is limited information about the influence of halogenated OPFRs on living cells, especially on the immune system cells. That is why the aim of this study was to assess the impact of TCEP and TCPP on viability and morphological alterations of human peripheral blood mononuclear cells (PBMCs). The cells were incubated with selected flame retardants in the concentrations ranging from 0.001 to 1 mM for 24 h. It was found that TCEP at 1 mM and TCPP at 0.5 mM decreased viability of PBMCs, while only TCPP induced morphological alterations in the incubated cells. The results of our experiments suggest that TCPP is more cytotoxic than TCEP, which can be explained by the presence of methyl groups in the molecule of this compound. Similar to other studies, our data also suggest that OPFRs are suitable replacements for PBDEs.

Ubiquitous Flame-Retardant Toxicants Impair Spermatogenesis in a Human Stem Cell Model

Sperm counts have rapidly declined in Western males over the past four decades. This rapid decline remains largely unexplained, but exposure to environmental toxicants provides one potential explanation for this decline. Flame retardants are highly prevalent and persistent in the environment, but many have not been assessed for their effects on human spermatogenesis. Using a human stem cell-based model of spermatogenesis, we evaluated two major flame retardants, hexabromocyclododecane (HBCDD) and tetrabromobisphenol A (TBBPA), under acute conditions simulating occupational-level exposures. Here we show that HBCDD and TBBPA are human male reproductive toxicants in vitro. Although these toxicants do not specifically affect the survival of haploid spermatids, they affect spermatogonia and primary spermatocytes through mitochondrial membrane potential perturbation and reactive oxygen species generation, ultimately causing apoptosis. Taken together, these results show that HBCDD and TBBPA affect human spermatogenesis in vitro and potentially implicate this highly prevalent class of toxicants in the decline of Western males' sperm counts.

Exposure to organophosphate flame retardants in spray polyurethane foam applicators: Role of dermal exposure

BACKGROUND

Spray polyurethane foam (SPF) is a highly effective thermal insulation material that has seen considerable market growth in the past decade. Organophosphate flame retardants (PFRs) are added to SPF formulations to meet fire code requirements. A common flame retardant used in SPF formulations is tris 1-chloro 2-propyl phosphate (TCIPP), a suspected endocrine disruptor. Exposure monitoring efforts during SPF applications have focused primarily on the isocyanate component, a potent respiratory and dermal sensitizer. However, to our knowledge, there is no monitoring data for TCIPP.

OBJECTIVE

To characterize occupational exposures to TCIPP and other flame retardants during SPF insulation.

METHODS

Workers at four SPF insulation sites and one foam removal site (total n = 14) were recruited as part of this pilot study. Personal inhalation exposure to TCIPP was monitored with a CIP-10MI inhalable sampler and potential dermal exposure was assessed through the use of a glove dosimeter. Biomarkers of TCIPP and three other PFRs were measured in urine collected from workers pre-and post-shift. Linear mixed effect models were used to analyze associations of urinary biomarkers with inhalation and dermal exposures and paired t-tests were used to examine the difference on the means of urinary biomarkers pre-and post-shift. Chemical analysis of all species was performed with liquid chromatography-electrospray ionization tandem mass spectrometry.

RESULTS

Geometric mean (GM) concentrations of TCIPP in personal air monitors and glove dosimeters collected from SPF applicators, 294.7 μg/m³ and 18.8 mg/pair respectively. Overall, GM concentrations of the two TCIPP urinary biomarkers BCIPP and BCIPHIPP and (6.2 and 88.8 μg/mL) were 26-35 times higher than reported in the general population. Post-shift levels of TCIPP biomarkers were higher than pre-shift even though workers at insulation sites wore supplied air respirators, gloves and coveralls. The urinary biomarkers for the other PFRs were not elevated post shift. Concentrations of TCIPP on glove dosimeters were positively associated with post-shift urinary TCIPP biomarkers (p < 0.05) whereas concentrations in personal air samples were not.

CONCLUSIONS

High levels of urinary biomarkers for TCIPP among SPF applicators, including post-shift, points to absorption of TCIPP during the work shift, in spite of the use of best industry exposure control practices. Dermal exposure appears to be an important, if not the primary exposure pathway for TCIPP, although inhalation or incidental ingestion of foam particles post-SPF application cannot be ruled out in this pilot study.

Photolysis of highly brominated flame retardants leads to time-dependent dioxin-responsive mRNA expression in chicken embryonic hepatocytes

Tetradecabromo-1,4-diphenoxybenzene (TeDB-DiPhOBz) and 2,2',3,3',4,4',5,5',6,6'-decabromodiphenyl ether (BDE-209) are flame retardant chemicals that can undergo photolytic degradation. The present study compared the time-dependent photolyic degradation of TeDB-DiPhOBz and BDE-209, and dioxin-like product formation as a result of (UV) irradiation (I; irradiation time periods of 0, 1, 4, 15 and 40 days). Photo-degraded product fractions of UV-I-TeDB-DiPhOBz (nominal concentration: 1.9 μM) were administered to chicken embryonic hepatocytes (CEH), and significant induction of CYP1A4/5 mRNA expression was observed for fractions collected at the day 15 and 40 time points (fold change of 7.3/3.6 and 9.1/4.7, respectively). For the UV-I-BDE-209 fractions (nominal concentration: 10 μM), significant CYP1A4/5 up-regulation occurred at all time points, and the fraction collected on day 1 induced the greatest fold change of 510/86, followed by 410/68 (day 4) and 110/26 (day 15), respectively. For the UV-I-BDE-209 fraction collected at day 40, significant CEH cytotoxicity was observed. As a result, CYP1A4/5 expression was determined at a nominal concentration of 1 μM instead of 10 μM and CYP1A4/5 fold changes of 11/8.2 (day 40) were observed. Fractions eliciting the greatest CYP1A4/5 mRNA upregulation were further screened for transcriptomic effects using a PCR array comprising 27 dioxin-responsive genes. A total of 6 and 16 of the 27 target genes were up or down-regulated following UV-I-TeDB-DiPhOBz and UV-I-BDE-209 exposure, respectively. Overall, and regardless of the formation rate, these results raise concerns regarding the potential formation of dioxin-like compounds from flame retardants in products and materials such as plastics, and in natural sunlight irradiation situations in the environment (e.g. in landfill sites or electronic waste facilities).

Organophosphate triesters and selected metabolites enhance binding of thyroxine to human transthyretin in vitro

The toxicological properties of organophosphate (OP) triesters that are used as flame retardants and plasticizers are currently not well understood, though increasing evidence suggests they can affect the thyroid system. Perturbation of thyroid hormone (TH) transport is one mechanism of action that may affect thyroid function. The present study applied an in vitro competitive protein binding assay with thyroxine (T4) and human transthyretin (hTTR) transport protein to determine the potential for the OP triesters, TDCIPP (tris(1,3-dichloro-2-propyl) phosphate), TBOEP (tris(butoxyethyl) phosphate), TEP (triethyl phosphate), TPHP (triphenyl phosphate), p-OH-TPHP (para-hydroxy triphenyl phosphate), and the OP diester DPHP (diphenyl phosphate), to competitively displace T4 from hTTR. Enhancement of T4 binding to hTTR, rather than the hypothesized competition, was observed for the six OP esters and in a concentration-dependent manner. For example, T4-hTTR binding was significantly increased at concentrations of TBOEP as low as 64 nM, and up to 184% of controls at 5000 nM. A plausible explanation of these results, which to our knowledge has not been previously reported, may be allosteric interactions of the OP esters with hTTR allowing T4 to access the second site of the TH binding pocket. These in vitro results suggest a novel mechanism of OP ester toxicity via T4 binding enhancement, and possible dysregulation of T4-hTTR interactions.

Occurrence and spatial distribution of organophosphorus flame retardants and plasticizers in the Bohai and Yellow Seas, China

Seawater samples from 50 sites in the BS and YS were collected to investigate the spatial distribution of 7 OPs. Concentrations of the total OPs (ƩOPs) in the BS and YS ranged from 8.12ngL^-1 to 98.04ngL^-1 with a geometric mean (GM) of 23.70ngL^-1. Tris(1-chloro-2-propyl) phosphate (TCPP) was the dominant compound, followed by tris(2-chloroethyl) phosphate (TCEP) and triphenylphosphine oxide (TPPO). The ƩOPs together with the most commonly detected individual OPs (TCPP, TCEP, tris(1,3-dichloro-2-propyl) phosphate (TDCPP), tri-iso-butyl phosphate (TiBP), triphenyl phosphate (TPhP), and TPPO) tended to decrease from nearshore to offshore and from the surface to the bottom seawaters, indicating major land-based sources. Furthermore, the Yellow Sea Cold Water Mass (YSCWM), Changjiang Diluted Water (CDW), Taiwan Warm Current (TaWC), and Subei Coastal Water (SCW) influenced the horizontal and vertical distributions of the OPs in the study area.

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

Halogen-free organophosphorus flame retardants are widespread in aquatic environments. Although it has been documented that they affect the behavior and reproduction of aquatic species, researches investigating cellular detoxification and the defense system in bivalves are scarce. In this study, adult Asian clams (C. fluminea) were exposed to tris (2-butoxyethyl) phosphate (TBEP) and tributyl phosphate (TBP) at 20, 200, and 2000 μg/L for 28 d. The results showed no noticeable difference in siphoning behavior. However, the siphoning behavior displayed a trend toward a slight decrease in the treatment groups. GR activity was markedly reduced compared with the control groups, whereas the levels of cyp4 significantly increased following the 2000 μg/L TBP treatments (p < 0.05). Moreover, the levels of gsts1 and gstm1 significantly decreased following all TBEP treatments and were significantly inhibited by 20 μg/L TBP (p < 0.05). The adverse effects on antioxidant enzymes suggested that C. fluminea mainly relies on the antioxidant system to reduce damage without an increase in MDA levels following exposure to a low concentration. Moreover, mRNA expression levels of heat shock proteins (hsp 22, 40, 60, 70, and 90) were significantly down-regulated with TBEP and TBP treatments lower than 200 μg/L (p < 0.05), whereas significant up-regulations were observed for hsp 22 and hsp 70 in response to 2000 μg/L TBP treatment (p < 0.05). Up-regulation of ATP-binding cassette (ABC) transporter genes (abcb1 and abcc1) showed that TBEP and TBP could activate the multixenobiotic resistance (MXR) system to discharge xenobiotics in C. fluminea, which kept its shell closed at high concentrations to prevent xenobiotic entry. Our results provide a new insight into the different mechanisms of cellular detoxification and the MXR system of C. fluminea in response to low and high concentrations of TBEP and TBP.

Flame retardant tris(1,3-dichloro-2-propyl)phosphate (TDCPP) toxicity is attenuated by N-acetylcysteine in human kidney cells

Prolonged exposure to the flame retardants found in many household products and building materials is associated with adverse developmental, reproductive, and carcinogenic consequences. While these compounds have been studied in numerous epidemiological and animal models, less is known about the effects of flame retardant exposure on cell function. This study evaluated the toxicity of the commonly used fire retardant tris(1,3-dichloro-2-propyl)phosphate (TDCPP) in cell line derived from the kidney, a major tissue target of organohalogen toxicity. TDCPP inhibited cell growth at lower concentrations (IC₅₀ 27 μM), while cell viability and toxicity were affected at higher concentrations (IC₅₀ 171 μM and 168 μM, respectively). TDCPP inhibited protein synthesis and caused cell cycle arrest, but only at higher concentrations. Additionally, the antioxidant N-acetylcysteine (NAC) reduced cell toxicity in cells treated with TDCPP, suggesting that exposure to TDCPP increased oxidative stress in the cells. In summary, these data show that low concentrations of TDCPP result in cytostasis in a kidney cell line, whereas higher concentrations induce cell toxicity. Furthermore, TDCPP toxicity can be attenuated by NAC, suggesting that antioxidants may be effective countermeasures to some organohalogen exposures.

Athabasca Oil Sands Petcoke Extract Elicits Biochemical and Transcriptomic Effects in Avian Hepatocytes

Petroleum coke or "petcoke" is a granular carbonaceous material produced during the upgrading of heavy crude oils, including bitumen. Petcoke dust was recently reported as an environmental contaminant in the Athabasca oil sands region, but the ecotoxicological hazards posed by this complex bitumen-derived material-including those to avian species-have not been characterized. In this study, solvent extracts (x) of delayed and fluid petcoke (xDP and xFP) were prepared and dissolved in dimethyl sulfoxide. A water-accommodated fraction of delayed petcoke (waDP) was also prepared. Graded concentrations of xDP, xFP, and waDP were administered to chicken and double-crested cormorant hepatocytes to determine effects on 7-ethoxyresorufin-O-deethylase (EROD) activity, porphyrin accumulation, and mRNA expression. Polycyclic aromatic compounds (PACs) were characterized, and xDP, xFP, and waDP had total PAC concentrations of 93 000, 270, and 5.3 ng/mL. The rank order of biochemical and transcriptomic responses was xDP > xFP > waDP (e.g., EROD EC_50s were lower for xDP compared to xFP and waDP). A total of 22, 18, and 4 genes were altered following exposure to the highest concentrations of xDP, xFP, and waDP, respectively, using a chicken PCR array comprising 27 AhR-related genes. To provide more exhaustive coverage of potential toxicity pathways being impacted, two avian ToxChip PCR arrays-chicken and double-crested cormorant-were utilized, and xDP altered the expression of more genes than xFP. Traditional PAC-related toxicity pathways and novel mechanisms of action were identified in two avian species following petcoke extract exposure. Extrapolation to real-world exposure scenarios must consider the bioavailability of the extracted PACs compared to those in exposed organisms.

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.

Parental transfer of tris(1,3-dichloro-2-propyl) phosphate and transgenerational inhibition of growth of zebrafish exposed to environmentally relevant concentrations

Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) is a re-emerging environmental contaminant that has been frequently detected at sub-ppb (<μg/L) concentrations in natural waters. The objective of this study was to evaluate effects of TDCIPP on growth in initial generation (F₀) zebrafish after chronic exposure to environmentally relevant concentrations, and to examine possible parental transfer of TDCIPP and transgenerational effects on growth of first generation (F₁) larvae. When zebrafish (1-month old) were exposed to 580 or 7500 ng TDCIPP/L for 240 days, bioconcentration resulted in significantly less growth as measured by body length, body mass, brain-somatic index (BSI) and hepatic-somatic index (HSI) in F₀ females but not F₀ males. These effects were possibly due to down-regulation of expression of genes along the growth hormone/insulin-like growth factor (GH/IGF) axis. Furthermore, residues of TDCIPP were detected in F₁ eggs after exposure of parents, which resulted in less survival, body length and heart rate in F₁ individuals. Down-regulation of genes in the GH/IGF axis (e.g., gh, igf1) might be responsible for transgenerational toxicity. This study provides the first known evidence that exposure of zebrafish to environmentally relevant concentrations of TDCIPP during development can inhibit growth of offspring, which were not exposed directly to TDCIPP.

Rice ingestion is a major pathway for human exposure to organophosphate flame retardants (OPFRs) in China

Although organophosphate flame retardants (OPFRs) have been shown to accumulate in abiotic and biotic environmental compartments, data about OPFRs concentrations in various foods are limited and are none in humans through diets. In this work, the concentrations of 6 typical OPFRs were investigated in 50 rice samples, 75 commonly consumed foods and 45 human hair samples from China. The dietary intakes of OPFRs for adult people via food ingestion were estimated. The concentrations of ΣOPFRs in foods ranged from 0.004ng/g to 287ng/g. OPFRs were detected in 53.3% of the human hair samples. The highest OPFRs concentrations were found in rice and vegetables. Tri(2-chloroethyl)phosphate(TCEP), tris(2-chloroisopropyl)phosphate(TCIPP), and tri(2-ethyltexyl)phosphate(TEHP) were predominant in all food samples. OPFRs concentrations in foods were not significantly affected by the packaging materials. The mean dietary intakes of ΣOPFRs for adult males and females were 539 and 601ng/kg body weight/day, respectively. The greatest contribution to these values is from rice, accounting for approximately 60% of the total intake, particularly from rice protein. Rice ingestion was considered a potential major pathway for human exposure to OPFRs, and regional differences in the levels of OPFRs in foods and dietary differences should be given more attention in the future.

Multigenerational effects of tris(1,3-dichloro-2-propyl) phosphate on the free-living ciliate protozoa Tetrahymena thermophila exposed to environmentally relevant concentrations and after subsequent recovery

Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) is considered a re-emerging environmental pollutant, and exposure to environmentally relevant concentrations has been shown to cause individual developmental toxicity in zebrafish and the water flea (Daphnia magna). However, multigenerational effects during exposure to TDCIPP and after subsequent recovery were unknown. In the present study, individuals of a model aquatic organism, the ciliated protozoan, T. thermophila were exposed to environmentally-relevant concentrations of TDCIPP (0, 300 or 3000 ng/L) for 60 days (e.g., theoretically 372 generations) followed by a 60-day period of recovery, during which T. thermophila were not exposed to TDCIPP. During exposure and after exposure, effects at the molecular, histological, individual and population levels were examined. Multigenerational exposure to 300 or 3000 ng TDCIPP/L for 60 days significantly decreased numbers of individuals, sizes of individuals, expressed as length and width of bodies, number of cilia, and depth and diameter of basal bodies of cilia, and up-regulated expressions of genes related to assembly and maintenance of cilia. Complete or partial recoveries of theoretical sizes of populations as well as sizes of individuals and expressions of genes were observed during the 60-day recovery period. Effects on number of cilia and depth and diameter of basal body of cilia were not reversible and could still be observed long after cease of TDCIPP exposure. Collectedly, and shown for the first time, multigenerational effects to T. thermophila were caused by exposure to environmentally relevant concentrations of TDCIPP. Also, there were multi-generational effects at the population level that were not caused by carry-over exposure to TDCIPP. The "permanent" alterations and their potential significance are discussed.

Effects of TBEP on the induction of oxidative stress and endocrine disruption in Tm3 Leydig cells

The flame retardant tris (2-butoxyethyl) phosphate (TBEP) is a frequently detected contaminant in the environment. In the cultured TM3 cells (originated from ATCC), effects of TBEP on the induction of oxidative stress and endocrine disruption were evaluated. It was observed that exposure to 100 μg/mL TBEP for 24 h significantly reduced the viability of TM3 cells. The mRNA levels of genes related to oxidative stress including Sod, Gpx1, Cat, and Gsta1 were changed in a dose-dependent and/or time-dependent manner after exposure to 30 and 100 μg/mL TBEP for 6, 12, or 24 h. Moreover, notable decrease in glutathione (GSH) contents and increases in oxidized glutathione (GSSG) contents as well as the antioxidant enzyme activities like superoxide dismutase, catalase, glutathione peroxidase, and glutathione S-transferase were found in the group treated with 100 μg/mL TBEP for 24 h, indicating that TBEP induced oxidative stress in TM3 Leydig cells. In addition, the expression of genes related to testosterone (T) synthesis including cytochrome P450 cholesterol side-chain cleavage enzyme (P450scc), cytochrome P450 17α-hydroxysteroid dehydrogenase (P450-17α), and 17β-hydroxysteroid dehydrogenase (17β-HSD) and T levels in medium were remarkably declined by the treatment of 100 μg/mL TBEP for 24 h. And TBEP could inhibit the expression of P450-17α and 17β-HSD and T levels up-regulated by hCG in TM3 cells. Taken together, these findings indicated that TBEP can induce oxidative stress and alter steroidogenesis in TM3 cells. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1276-1286, 2016.

Retrospective analysis of organophosphate flame retardants in herring gull eggs and relation to the aquatic food web in the Laurentian Great Lakes of North America

With the phase-out and regulation of some flame retardant chemicals, the production and usage of organophosphate triester flame retardants (OPFRs) has increased in recent years. In the present study, 14 OPFRs (either chlorinated, brominated or non-halogenated) were analyzed in egg pools of 10-13 individual herring gull eggs from five colonial nesting sites for 11 years spanning 1990-2010, (for a total of n=55 egg pools) in the Laurentian Great Lakes of North America (Chantry Island, Fighting Island, Agawa Rocks, Toronto Harbour and Gull Island). OPFR profiles varied slightly between colony sites and collection years. For all five sites tris(2-chloroisopropyl) phosphate (TCIPP), tris(2-chloroethyl) phosphate (TCEP) and tris(2-butoxyethyl) phosphate (TBOEP) were detected, while triphenyl phosphate (TPHP) was only quantifiable in eggs from Chantry Island and Gull Island collected in 2008 and 2010. For the 2010 egg pools, the ΣOPFR concentrations were generally low and ranged from 2.02 to 6.69 ng/g wet weight (ww). ΣOPFR concentrations in 2010 were significantly higher (p<0.05) than they were between 1990 and 2004 (4.06 vs. 1.55 ng/g ww, respectively). In a pilot examination of Great Lakes aquatic food webs, 2010-collected alewife and rainbow smelt (major herring gull fish prey) and lake trout from western Lake Erie and Ontario, only contained TBOEP at low to sub ng/g ww concentrations. These results demonstrate that low to sub-ppb concentrations of at least three OPFRs, TCIPP, TCEP and TBOEP, have been persistent in herring gull eggs from the Great Lakes for at least the past 20 years, probably bioaccumulate mainly via the fish diet, and are transferred to the eggs of exposed herring gulls.

The cytotoxicity of organophosphate flame retardants on HepG2, A549 and Caco-2 cells

In order to elucidate the cytotoxicity of organophosphate flame retardants (OPFRs), three human in vitro models, namely the HepG2 hepatoma cells, the A549 lung cancer cells and the Caco-2 colon cancer cells, were chosen to investigate the toxicity of triphenyl phosphate (TPP), tributylphosphate (TBP), tris(2-butoxyexthyl) phosphate (TBEP) and tris (2-chloroisopropyl) phosphate (TCPP). Cytotoxicity was assayed in terms of cell viability, DNA damage status, reactive oxygen species (ROS) level and lactate dehydrogenase (LDH) leakage. The results showed that all these four OPFRs could inhibit cell viability, overproduce ROS level, induce DNA lesions and increase the LDH leakage. In addition, the toxic effects of OPFRs in Caco-2 cells were relatively severer than those in HepG2 and A549 cells, which might result from some possible mechanisms apart from oxidative stress pathway. In conclusion, TBP, TPP, TBEP and TCPP could induce cell toxicity in various cell lines at relatively high concentrations as evidenced by suppression of cell viability, overproduction of ROS, induction of DNA lesions and increase of LDH leakage. Different cell types seemed to have different sensitivities and responses to OPFRs exposure, as well as the underlying potential molecular mechanisms.

Editor's Highlight: Comparative Toxicity of Organophosphate Flame Retardants and Polybrominated Diphenyl Ethers to Caenorhabditis elegans

With the phasing-out of the polybrominated diphenyl ether (PBDE) flame retardants due to concerns regarding their potential developmental toxicity, the use of replacement compounds such as organophosphate flame retardants (OPFRs) has increased. Limited toxicity data are currently available to estimate the potential adverse health effects of the OPFRs. The toxicological effects of 4 brominated flame retardants, including 3 PBDEs and 3,3',5,5'-tetrabromobisphenol A, were compared with 6 aromatic OPFRs and 2 aliphatic OPFRs. The effects of these chemicals were determined using 3 biological endpoints in the nematode Caenorhabditis elegans (feeding, larval development, and reproduction). Because C. elegans development was previously reported to be sensitive to mitochondrial function, results were compared with those from an in vitro mitochondrial membrane permeabilization (MMP) assay. Overall 11 of the 12 flame retardants were active in 1 or more C. elegans biological endpoints, with only tris(2-chloroethyl) phosphate inactive across all endpoints including the in vitro MMP assay. For 2 of the C. elegans endpoints, at least 1 OPFR had similar toxicity to the PBDEs: triphenyl phosphate (TPHP) inhibited larval development at levels comparable to the 3 PBDEs; whereas TPHP and isopropylated phenol phosphate (IPP) affected C. elegans reproduction at levels similar to the PBDE commercial mixture, DE-71. The PBDEs reduced C. elegans feeding at lower concentrations than any OPFR. In addition, 9 of the 11 chemicals that inhibited C. elegans larval development also caused significant mitochondrial toxicity. These results suggest that some of the replacement aromatic OPFRs may have levels of toxicity comparable to PBDEs.

In vitro assessment of thyroid hormone receptor activity of four organophosphate esters

Previous animal experiments have implied that organophosphate esters (OPEs) have a disruption effect on the thyroid endocrine system. However, knowledge of the toxicological mechanism remains limited. In this study, the activities of four OPEs have been characterized against the thyroid hormone (TH) nuclear receptor (TR) using two in vitro models, with the aim of evaluating their toxicity mechanisms towards the TR. The results of a TH-dependent cell proliferation assay showed that tris(2-chloro-1-(chloromethyl)ethyl)phosphate (TDCPP) could induce cell growth, while the other three OPEs had no effect. The results of a luciferase reporter gene assay revealed that all four of the OPEs tested in the current study showed agonistic activity towards TRβ, with TDCPP being the most potent one. Moreover, molecular docking revealed that all the tested OPEs could fit into the ligand binding pocket of TRβ, with TDCPP binding more effectively than the other three OPEs. Taken together, these data suggest that OPEs might disrupt the thyroid endocrine system via a mechanism involving the activation of TR.

Differential modulation of neuro- and interrenal steroidogenesis of juvenile salmon by the organophosphates - tris(2-butoxyethyl)- and tris(2-cloroethyl) phosphate

Following the ban of polybrominated diphenyl ether (PBDEs) flame retardants under well-documented toxicity issues, organophosphate such as tris(2-butoxyethyl) phosphate (TBOEP) and tris(2-cloroethyl) phosphate (TCEP) were considered as potential substitutes. Although TBOEP and TCEP are consistently detected in the aquatic environment, there are few data about the possible toxicological effects of these compounds on aquatic organisms, including fish. In the present study, we have investigated the influence of TBOEP and TCEP on neuro- and interrenal steroidogenesis of juvenile Atlantic salmon (Salmo salar), after a seven-day exposure to four different concentrations (0 (control), 0.04, 0.2 and 1mg/L) of each compound. TBOEP and TCEP were diluted in Milli-Q water. The expression of genes involved in steroidogenesis (StAR, cyp19a, cyp19b, cholesterol side-chain cleavage enzyme (P450scc), 3β-hydroxysteroid dehydrogenase (3β-hsd), and 11β-hydroxylase (cyp11β)), were analyzed in the brain and head kidney using real-time PCR. Plasma 11-ketotestosterone (11-KT) analysis was performed using enzyme immunoassay (EIA). Our results showed that TBOEP accumulated more rapidly than TCEP in fish muscle tissue. Surprisingly, TBOEP produced less pronounced effects than TCEP on neural and interrenal steroidogenic responses, despite the observed rapid uptake and bioaccumulation pattern. Specifically, TBOEP produced significant and consistent concentration-specific alterations on neural- and interrenal steroidogenesis. Plasma levels of 11-KT were not significantly altered by any of the exposures. The increased expression of steroidogenic genes demonstrated in the present study could produce time-specific alterations in the production of glucocorticoids and steroid hormones that play integral roles in fish metabolism, stress responses and adaptation, sexual maturation, reproduction and migration with overt consequences on reproductive success and survival.

Review of OPFRs in animals and humans: Absorption, bioaccumulation, metabolism, and internal exposure research

Due to their widespread use, organophosphate flame retardants (OPFRs) are commonly detected in various environmental matrices and have been identified as emerging contaminants. Considering the adverse effects of OPFRs, many researchers have paid their attention on the absorption, bioaccumulation, metabolism and internal exposure processes of OPFRs in animals and humans. In this article, we first review the diverse absorption routes of OPFRs by animals and humans (e.g., inhalation, ingestion, dermal absorption and gill absorption). Bioaccumulation and biomagnification potentials of OPFRs in different types of organisms and food webs are also summarized, based on quite limited available data and results. For metabolism, we review the Phase-I and Phase-II metabolic processes for each type of OPFRs (chlorinated OPFRs, alkyl-OPFRs and aryl-OPFRs) in the animals and humans, as well as toxicokinetic information and putative exposure biomarkers on OPFRs. Finally, we highlight gaps in our knowledge and critical directions for future internal exposure studies of OPFRs in animals and humans.

Use of a Novel Double-Crested Cormorant ToxChip PCR Array and the EROD Assay to Determine Effects of Environmental Contaminants in Primary Hepatocytes

In vitro screening tools and 'omics methods are increasingly being incorporated into toxicity studies to determine mechanistic effects of chemicals and mixtures. To date, the majority of these studies have been conducted with well-characterized laboratory animal models. In the present study, well-established methods developed for chicken embryonic hepatocyte (CEH) studies were extended to a wild avian species, the double-crested cormorant (DCCO; Phalacrocorax auritus), in order to compare the effects of several environmental contaminants on cytotoxicity, ethoxyresorufin O-deethylase (EROD) activity, and mRNA expression. Five organic flame retardants and one plasticizer decreased cormorant hepatocyte viability in a similar manner to that observed in previous studies with CEH. EROD activity was induced in a concentration-dependent manner following exposure to two dioxin-like chemicals and the calculated EC50 values were concordant with domestic avian species from similar species sensitivity categories. Transcriptomic effects were determined using a novel DCCO PCR array, which was designed, constructed and validated in our laboratory based on a commercially available chicken PCR array. The DCCO array has 27 target genes covering a wide range of toxicity pathways. Gene profiles were variable among the 10 chemicals screened; however, good directional concordance was observed with regard to results previously obtained in CEH. Overall, the application of well-established methods (i.e., CEH and chicken PCR array) to the double-crested cormorant demonstrated the portability of the techniques to an indicator species of ecological relevance.

Effects of tris(1,3-dichloro-2-propyl)phosphate on pathomorphology and gene/protein expression related to thyroid disruption in rats

Previous studies demonstrated that tris(1,3-dichloro-2-propyl)phosphate (TDCIPP) caused adverse effects on thyroid hormone (TH) imbalance in aquatic and avian organisms. This study focused on the effects of TDCIPP on thyroid function and hormone homeostasis in mammals. Pubertal female Sprague-Dawley rats were orally administered 50, 100, or 250 mg per kg per d of TDCIPP from postnatal day (PND) 22 to PND42 for 21 days. The serum triiodothyronine (T3) levels increased significantly at 250 mg per kg per d of TDCIPP. There were no significant differences in the body weight, serum thyroxine (T4) and free thyroxine (FT4) levels between the control and TDCIPP treated groups. There were significant dose-dependent increases in the mRNA and protein expression levels of genes related to drug metabolism (cytochrome-p450-3A1, CYP3A1) and TH clearance (udp-glucuronosyltransferase-1A6, UGT1A6) in the liver. Treatment with TDCIPP increased hepatic type 1 deiodinase (DIO1) mRNA at 250 mg per kg per d but down-regulated hepatic TH receptor beta (TRβ) mRNA expression. In addition, TDCIPP exposure induced slight thyroid follicular hyperplasia, and several genes involved in TH biosynthesis (NIS, TPO, Tg) were altered at 100 and 250 mg per kg per d of TDCIPP. Nevertheless, serum thyroid stimulating hormone (TSH) levels and the receptor (TSHr) mRNA significantly decreased at only the low dose group. Based on these results, we certified that TDCIPP disturbs the normal bioprocess on TH synthesis, biotransformation or clearance, and hepatic detoxification of pubertal female SD rats, causing thyroid function disorder.

Acute Exposure to Tris(1,3-dichloro-2-propyl) Phosphate (TDCIPP) Causes Hepatic Inflammation and Leads to Hepatotoxicity in Zebrafish

Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) has been frequently detected in environmental media and has adverse health effect on wildlife and humans. It has been implicated to have hepatotoxicity, but its molecular mechanisms remain unclear. In the present study, adult male zebrafish were exposed to TDCIPP and global hepatic gene expression was examined by RNA-Seq and RT-qPCR in order to understand the molecular mechanisms of TDCIPP-induced hepatotoxicity. Our results indicated that TDCIPP exposure significantly up-regulated the expression of genes involved in endoplasmic reticulum stress and Toll-like receptor (TLR) pathway, implying an inflammatory response, which was supported by up-regulation of inflammation-related biomaker genes. Hepatic inflammation was further confirmed by histological observation of increase of infiltrated neutrophils and direct observation of liver recruitment of neutrophils labeled with Ds-Red fluorescent protein of Tg(lysC:DsRed) zebrafish upon TDCIPP exposure. To further characterize the hepatotoxicity of TDCIPP, the expression of hepatotoxicity biomarker genes, liver histopathology and morphology were examined. The exposure to TDCIPP significantly up-regulated the expression of several biomarker genes for hepatotoxicity (gck, gsr and nqo1) and caused hepatic vacuolization and apoptosis as well as increase of the liver size. Collectively, our results suggest that exposure to TDCIPP induces hepatic inflammation and leads to hepatotoxicity in zebrafish.

Lipid peroxidation and oxidative stress responses in juvenile salmon exposed to waterborne levels of the organophosphate compounds tris(2-butoxyethyl)- and tris(2-chloroethyl) phosphates

There is limited knowledge on the toxicological, physiological, and molecular effects attributed to organophosphate (OP) compounds currently used as flame retardants or additives in consumer products. This study investigated the effects on oxidative stress and lipid peroxidation in juvenile Atlantic salmon liver and brain samples after exposure to two OP compounds, tris(2-butoxyethyl) phosphate (TBOEP) and tris(2-chloroethyl) phosphate (TCEP). In this study, groups of juvenile Atlantic salmon were exposed using a semistatic experimental protocol over a 7-d period to 3 different concentrations (0.04, 0.2, or 1 mg/L) of TBOEP and TCEP. When toxicological factors such as bioaccumulation and bioconcentration, and chemical structural characteristics and behavior, including absorption to solid materials, are considered, these concentrations represent environmentally relevant concentrations. The concentrations of the contaminants were derived from levels of their environmental occurrence. The expression of genes related to oxidative stress-glutathione peroxidase (GPx), glutathione reductase (GR), glutathione S-transferase (GST)-and to lipid peroxidation-peroxisome proliferator-activated receptors (PPAR)-were determined using quantitative (real-time) polymerase chain reaction (PCR). The presence of PPAR proteins was also investigated using immunochemical methods. Levels of thiobarbituric acid-reactive substances (TBARS) in liver were used as a measure of lipid peroxidation. Overall, our data show an increase in lipid peroxidation, and this was associated with an augmented expression of genes from the glutathione family of responses. Interestingly, PPAR expression in liver after exposure to TBOEP and TCEP was consistently decreased compared to controls, while expression in brain did not show a similar trend. The results suggest that OP contaminants may induce oxidative stress and thus production of reactive oxygen substances (ROS), and modulate lipid peroxidation processes in organisms.

Environmentally Relevant Concentrations of the Flame Retardant Tris(1,3-dichloro-2-propyl) Phosphate Inhibit Growth of Female Zebrafish and Decrease Fecundity

Bioconcentrations of tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) in brain, gonad, and liver as well as effects on fecundity and development of zebrafish (Danio rerio) were determined. Zebrafish (1-month old) were exposed to environmentally relevant concentrations of 29 ± 2.1, 600 ± 21, or 6300 ± 130 ng TDCIPP/L. After 120 days of exposure, TDCIPP accumulated in the brain, gonad, and liver with bioconcentration factors of 460, 38, and 87 in females and 26, 55, and 110 in males, respectively. TDCIPP accumulated to a greater extent in brains of females than those of males. Exposure to 6300 ± 130 ng TDCIPP/L resulted in significantly (P < 0.05) fewer eggs being produced, but the histology of the gonad, plasma concentrations of estradiol and 11-ketotestosterone, and expression of genes involved in hypothalamic-pituitary-gonadal-liver axis were not significantly (P > 0.05) different between individuals exposed to TDCIPP and the unexposed control fish. Exposure to TDCIPP resulted in shorter body length, lighter body mass, and lower gonadal-somatic index in females. These effects were possibly due to down-regulation of expression of genes along the growth hormone/insulin-like growth factor (GH/IGF) axis. Correlations between the production of eggs and developmental parameters or expression of genes along the GH/IGF axis further suggested that environmentally relevant concentrations of TDCIPP could have adverse effects on reproduction, possibly due to the inhibition of the growth of females.

Effects of Tris(1,3-dichloro-2-propyl) Phosphate on Growth, Reproduction, and Gene Transcription of Daphnia magna at Environmentally Relevant Concentrations

The synthetic flame retardant tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) has been frequently detected in natural waters, and its maximum concentration ever reported is 377 ng/L. However, information on the adverse effects of environmentally relevant concentrations of TDCIPP on aquatic organisms are totally unknown. In this study, <12-h old water fleas, D. magna, were exposed to concentrations of 0, 65±7.1, 550±33, or 6500±1400 ng/L TDCIPP, and dose- and time-dependent effects on reproduction and development were evaluated. Sequences of genes of D. magna were obtained from the National Center for Biotechnology Information and were used to develop PCR arrays for D. magna. Arrays were then used to study transcriptional responses of D. magna to TDCIPP. Exposure to environmentally relevant concentrations of TDCIPP significantly decreased fecundity as well as length of F0 and F1 generations. Transcriptional responses showed that, of the 155 genes tested, expressions of 57 genes were significantly changed, and some changes occurred following exposure to environmentally relevant concentrations (i.e., 65±7.1 and 550±23 ng/L). Furthermore, pathways related to protein synthesis and metabolism and endocytosis were considered to be significantly affected in a dose- and time-dependent manner and might be responsible for TDCIPP-induced reproductive and developmental toxicities.

Bioconcentration, metabolism and alterations of thyroid hormones of Tris(1,3-dichloro-2-propyl) phosphate (TDCPP) in Zebrafish

Tris(1,3-dichloro-2-propyl) phosphate (TDCPP) is an organophosphate widely used as a flame retardant, and has frequently been detected in the environment and biota. The present study investigates the bioconcentration and metabolism of TDCPP in fish. Zebrafish embryos (from 2h post-fertilization) were exposed to TDCPP (0, 4, 20 and 100μg/L) for six months. Exposure to TDCPP significantly induced phase I metabolic enzymes 7-ethoxyresorufin O-deethylase (EROD) and 7-methoxyresorufin O-demethylase (MROD) in fish. The mRNA expression of genes related to Phase I and II metabolic enzymes, such as cyp1a1, cyp1b1, cyp1c1 and ugt1ab were also significantly upregulated. Exposure to TDCPP significantly reduced plasma thyroxine (T4) and 3,5,3'-triiodothyronine (T3) levels in females. Chemicals analysis indicated significant levels of TDCPP and its metabolite, bis (1,3-dichloro-2-propyl) phosphate (BDCPP), in the liver. The present study reveals that exposure to low concentrations of TDCPP can cause bioconcentration in fish, and TDCPP can be readily metabolized in liver.

Neurotoxicological and thyroid evaluations of rats developmentally exposed to tris(1,3-dichloro-2-propyl)phosphate (TDCIPP) and tris(2-chloro-2-ethyl)phosphate (TCEP)

Tris(1,3-dichloro-2-propyl)phosphate (TDCIPP) and tris(2-chloro-2-ethyl)phosphate (TCEP) are organophosphorous flame retardants with widespread usage and human exposures through food, inhalation, and dust ingestion. They have been detected in human tissues including urine and breast milk. Reports of disrupted neural growth in vitro, abnormal development in larval zebrafish, and altered thyroid hormones in several species have raised concern for neurodevelopmental toxicity. This is especially the case for TDCIPP, which is more potent and has more activity in those assays than does TCEP. We evaluated the potential for developmental neurotoxicity of TDCIPP and TCEP in a mammalian model. Pregnant Long-Evans rats were administered TDCIPP (15, 50, or 150 mg/kg/day) or TCEP (12, 40, 90 mg/kg/day) via oral gavage from gestational day 10 to weaning. Corn oil was the vehicle control in both studies. Body weight and righting reflex development were monitored in all pups. A subset of offspring at culling and weaning, and dams at weaning, were sacrificed for serum and organ collection for measurement of brain, liver, and thyroid weights, serum thyroid levels, and serum and brain acetylcholinesterase activities. Brain weights were also measured in a group of adult TDCIPP-treated offspring. One male and one female from each litter were allocated for behavioral testing at several ages: standard locomotor activity (preweaning, postweaning, adults), locomotor activity including a lighting change mid-way (postweaning, adults), elevated zero maze (postweaning, adults), functional observational battery (FOB; postweaning, adults), and Morris water maze (place learning, reference and working memory; adults). Neither chemical produced changes in maternal body weight or serum thyroid hormones, but relative liver weight was increased at the high doses of both TDCIPP and TCEP. In offspring, there were no effects on viability, litter size, or birth weight. With TDCIPP, absolute liver weights were lower at weaning and weight gain was lower in the high-dose offspring until about two months of age. Thyroid hormones and brain weights were not altered and acetylcholinesterase (both brain and serum) was not inhibited by either chemical. TDCIPP-treated offspring showed slight differences in floating in the water maze, hindlimb grip strength, and altered activity habituation, whereas TCEP-treated rats showed differences in quadrant time (probe) and middle-zone preference in the water maze. Regarding these few changes, the effects were minimal, mostly not related to dose, and did not appear treatment-related or biologically significant. Overall, these data do not support the potential for thyrotoxicity or developmental neurotoxicity produced by TDCIPP or TCEP.

Biochemical and Transcriptomic Effects of Herring Gull Egg Extracts from Variably Contaminated Colonies of the Laurentian Great Lakes in Chicken Hepatocytes

Determining the effects of complex mixtures of environmental contaminants poses many challenges within the field of ecotoxicology. In this study, graded concentrations of herring gull egg extracts, collected from five Great Lakes breeding colonies with variable burdens of organohalogen contaminants (OHCs), were administered to chicken embryonic hepatocytes to determine effects on 7-ethoxyresorufin-O-deethylase (EROD) activity, porphyrin accumulation, and mRNA expression. EROD activity and porphyrin accumulation permitted the ranking of colonies based on the efficacy of eliciting an aryl hydrocarbon receptor-mediated response. An avian ToxChip polymerase chain reaction (PCR) array provided more exhaustive coverage in terms of potential toxicity pathways being affected, including xenobiotic and lipid metabolism and the thyroid hormone pathway. Herring gull eggs from Channel Shelter Island (CHSH, Lake Huron) and Gull Island (GULL, Lake Michigan) had among the highest OHC burdens, and extracts elicited a biochemical and transcriptomic response greater than that of extracts from the other three, less polluted colonies. For example, EROD EC50 values and porphyrin ECthreshold values were lower for CHSH and GULL extracts than for the other colonies. Extracts from CHSH and GULL altered 15 and 13 of 27 genes on the PCR array compared to no more than eight genes for the less contaminated sites. The combination of a well-established avian in vitro assay, two well-characterized biochemical assays, and the avian ToxChip PCR array permitted the geographical discrimination of variably contaminated herring gull eggs from the Great Lakes. Such high-throughput assays show potential promise as cost-effective tools for determining toxic potencies of complex mixtures in the environment.

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

Organophosphate triesters are high production volume additive flame retardants (OPFRs) and plasticizers. Shown to accumulate in abiotic and biotic environmental compartments, little is known about the risks they pose. Captive adult male American kestrels (Falco sparverius) were fed the same dose (22 ng OPFR/g kestrel/d) daily (21 d) of tris(2-butoxyethyl) phosphate (TBOEP), tris(2-chloroethyl) phosphate (TCEP), tris(2-chloroisopropyl) phosphate (TCIPP), or tris(1,2-dichloro-2-propyl) phosphate (TDCIPP). Concentrations were undetected in tissues (renal, hepatic), suggesting rapid metabolism. There were no changes in glutathione status, indicators of hepatic oxidative status, or the cholinergic system (i.e., cerebrum, plasma cholinesterases; cerebrum muscarinic, nicotinic receptors). Modest changes occurred in hepatocyte integrity and function (clinical chemistry). Significant effects on plasma free triiodothyronine (FT3) concentrations occurred with exposure to TBOEP, TCEP, TCIPP, and TDCIPP; TBOEP and TCEP had additional overall effects on free thyroxine (FT4), whereas TDCIPP also influenced total thyroxine (TT4). Relative increases (32%-96%) in circulating FT3, TT3, FT4, and/or TT4 were variable with each OPFR at 7 d exposure, but limited thereafter, which was likely maintained through decreased thyroid gland activity and increased hepatic deiodinase activity. The observed physiological and endocrine effects occurred at environmentally relevant concentrations and suggest parent OPFRs or metabolites may have been present despite rapid degradation.

TPP and TCEP induce oxidative stress and alter steroidogenesis in TM3 Leydig cells

Effects of triphenyl phosphate (TPP) and tris-(2-chloroethyl) phosphate (TCEP) exposure on induction of oxidative stress and endocrine disruption were investigated in TM3 cells. After 24h exposure, cell growth declined and morphology changed in TPP and TCEP treated groups with high dosages. Significant increases in superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX) and glutathione S-transferase (GST) activities and their respective gene expressions in a dose-dependent and/or time-dependent manner in TPP or TCEP groups. Moreover, the expression of main genes related to testosterone (T) synthesis including cytochrome P450 cholesterol side-chain cleavage enzyme (P450scc), cytochrome P450 17α-hydroxysteroid dehydrogenase (P450-17α), 3β-hydroxysteroid dehydrogenase (3β-HSD) and 17β-hydroxysteroid dehydrogenase (17β-HSD) were dramatically reduced by TPP and TCEP treatments, especially with the high dosage for 24h. TPP and TCEP treatments for 24h caused significant decreases in T levels in the medium. Furthermore, co-treatments of hCG with TPP or TCEP could inhibit hCG-induced changes in the expression of P450scc, P450-17α and 17β-HSD and T levels. Taken together, TPP and TCEP could induce oxidative stress and endocrine disruption in TM3 cells.

Effects of Tris(1,3-dichloro-2-propyl) Phosphate (TDCPP) in Tetrahymena Thermophila: Targeting the Ribosome

Tris(1,3-dichloro-2-propyl) phosphate (TDCPP) has been frequently detected in the environment, and exposure to TDCPP appears widespread. It has been implicated to cause toxicity in vertebrates, but its potential to affect lower-trophic-level species remains unknown. In the present study, the ciliated protozoan, Tetrahymena thermophila, was used as a model to evaluate toxic effects of TDCPP and explore molecular mechanisms by integrating phenotypic observation, RNA-Seq and transmission electron microscopy (TEM) Imaging technologies. Exposure to 0.01, 0.1 or 1 μM TDCPP for 5 days significantly decreased the relative biomass by reducing number of cells, size of cells and quantity of cilia in a dose-dependent manner. RNA-Seq analysis demonstrated that expression of twenty-one ribosome protein genes was down-regulated and these genes were enriched in “ribosome” term in KEGG pathway analysis. Furthermore, down-regulation of genes expressing ribosome proteins was accompanied by decreased ribosome quantity in rough endoplasmic reticulum and cytoplasm and enlarged ribosome size. Therefore, taken together, the data from the present study suggest that exposure to TDCPP affects growth and reproduction of Tetrahymena thermophila by targeting the ribosome. This information might provide insights into critical mechanisms of toxic action in other species and lead to useful bioindicators of exposure to TDCPP.

Bioconcentration and transfer of the organophorous flame retardant 1,3-dichloro-2-propyl phosphate causes thyroid endocrine disruption and developmental neurotoxicity in zebrafish larvae

Organophosphate flame retardants are emerging environmental contaminants, although knowledge of their health risks is limited. Here, thyroid hormone homeostasis and neuronal development was studied in the progeny of adult zebrafish exposed to tris(1,3-dichloro-2-propyl) phosphate (TDCPP). Adult zebrafish were exposed to TDCPP (0, 4, 20, and 100 μg/L) for 3 months. Increased generation of reactive oxygen species and reduced survival rates was observed in exposed F1 larvae. We also observed a significant decrease in plasma thyroxine and 3,5,3'-triiodothyronine levels in F0 females and F1 eggs/larvae. The mRNA and protein expression of factors associated with neuronal development (e.g., α1-tubulin, myelin basic protein, and synapsin IIa) were significantly downregulated in exposed F1 larvae, as was the level of the neurotransmitters dopamine, serotonin, gamma amino butyric acid, and histamine. Larval locomotion was significantly decreased in exposed fish, but there was no effect on acetylcholinesterase activity. Bioconcentration of TDCPP was observed in F0 fish. TDCPP was also detected in F1 eggs following parental exposure, indicating maternal transfer of this compound. This study uniquely shows that TDCPP can be transferred to the offspring of exposed adults, causing thyroid endocrine disruption and developmental neurotoxicity.

Comparing the effects of tetrabromobisphenol-A, bisphenol A, and their potential replacement alternatives, TBBPA-bis(2,3-dibromopropyl ether) and bisphenol S, on cell viability and messenger ribonucleic acid expression in chicken embryonic hepatocytes

A market for alternative brominated flame retardants (BFRs) has emerged recently due to the phase out of persistent and inherently toxic BFRs. Several of these replacement compounds have been detected in environmental matrices, including wild birds. A chicken embryonic hepatocyte (CEH) assay was utilized to assess the effects of the BFR, tetrabromobisphenol-A (TBBPA), and its replacement alternative, tetrabromobisphenol A bis(2,3-dibromopropyl ether [TBBPA-DBPE]) on cell viability and messenger ribonucleic acid (mRNA) expression. Bisphenol A (BPA) and 1 of its replacement alternatives, bisphenol S (BPS), were also screened for effects. Both TBBPA and BPA decreased CEH viability with calculated median lethal concentration (LC50) values of 40.6 μM and 61.7 μM, respectively. However, the replacement alternatives, TBBPA-DBPE and BPS, did not affect cell viability (up to 300 μM). Effects on mRNA expression were determined using an Avian ToxChip polymerse chain reaction (PCR) array and a real-time (RT)-PCR assay for the estrogen-responsive genes, apolipoproteinII (ApoII) and vitellogenin (Vtg). A luciferase reporter gene assay was used to assess dioxin-like effects. Tetrabromobisphenol-A altered mRNA levels of 4 genes from multiple toxicity pathways and increased luciferase activity in the luciferase reporter gene assay, whereas its alternative, TBBPA-DBPE, only altered 1 gene on the array, Cyp1a4, and increased luciferase activity. At 300 μM, a concentration that decreased cell viability for TBBPA and BPA, the BPA replacement, BPS, altered the greatest number of transcripts, including both ApoII and Vtg. Bisphenol A exposure did not alter any genes on the array but did up-regulate Vtg at 10 μM. Characterization of the potential toxicological and molecular-level effects of these compounds will ideally be useful to chemical regulators tasked with assessing the risk of new and existing chemicals.

Bioconcentration, metabolism and neurotoxicity of the organophorous flame retardant 1,3-dichloro 2-propyl phosphate (TDCPP) to zebrafish

Organophosphate flame retardants are ubiquitous environmental contaminants; however, knowledge is limited regarding their environmental health risks and toxicity. Here, we investigated the effects of acute and long-term exposure to tris(1,3-dichloro-2-propyl) phosphate (TDCPP) to the nervous system of zebrafish. Zebrafish embryos (2 h post-fertilization) were exposed to TDCPP (0-100 μg/L) for 6 months up until sexual maturation. Concentrations of TDCPP and its metabolic product (bis(1,3-dichloro-2-propyl) phosphate, BDCPP) were measured in the tissues of 5 day post-fertilization (dpf) larvae. There was no effect on locomotion, acetylcholinesterase activity, levels of the neurotransmitters dopamine and serotonin, and expression of mRNAs and proteins related to central nervous system development (e.g., myelin basic protein, α1-tubulin) in any exposure group. However, in adult fish, reductions of dopamine and serotonin levels were detected in the brains of females but not males. Downregulation of nervous system development genes was observed in both the male and female brain tissues. TDCPP concentrations were measured in adult fish tissues including the brain, and greater levels were detected in females. Our results showed that females are more sensitive to TDCPP stress than males in terms of TDCPP-induced neurotoxicity. We demonstrate that long-term exposure to lower concentrations of TDCPP in fish can lead to neurotoxicity.

Time-dependent effects of the flame retardant tris(1,3-dichloro-2-propyl) phosphate (TDCPP) on mRNA expression, in vitro and in ovo, reveal optimal sampling times for rapidly metabolized compounds

The flame retardant, tris(1,3-dichloro-2-propyl) phosphate (TDCPP), was previously shown to affect chicken embryo growth, gallbladder size, and lipid homeostasis. A microarray study, however, revealed only modest transcriptional alterations in liver tissue of pipping embryos (days 20-21), which was attributed to the rapid metabolism of TDCPP throughout incubation. To identify the most appropriate sampling time for rapidly metabolized compounds, the present study assessed the time-dependent effects of TDCPP on 27 genes, in ovo (50 µg [116 nmol] TDCPP/g egg) and in vitro (10 µM), using a chicken ToxChip polymerase chain reaction array. The greatest magnitude in dysregulation (up to 362-fold) occurred on day 8 of incubation (in ovo) with alterations of genes involved in phase I, II, and III metabolism, among others. Gallbladder hypotrophy was observed by embryonic day 12, corroborating the finding in pipping embryos from our previous study. From days 12 to 19, genes involved in lipid homeostasis, steroid hormone metabolism, and oxidative stress were affected. In chicken embryonic hepatoctyes (CEHs), TDCPP was completely metabolized to bis(1,3-dichloro-2-propyl) phosphate (BDCPP) within 36 h, but transcriptional changes remained significant up to 36 h. These changes were not attributed to BDCPP exposure as it only altered 1 gene (CYP1A4). An 18-h exposure in CEHs altered the greatest number of genes, making it an appropriate time point for high-throughput chemical screening; however, depending on the biological pathways of interest, shorter or longer incubation times may be more informative. Overall, TDCPP elicits the transcriptional and phenotypic alterations observed in vitro and in ovo, whereas its major metabolite, BDCPP, is far less biologically active.