Human internal exposure to organophosphate esters: A short review of urinary monitoring on the basis of biological metabolism research

Associations of gestational exposure to organophosphate esters with thyroid hormones in cord plasma and the safety threshold of exposure in pregnant women

BACKGROUND

As a class of synthetic chemicals, organophosphate esters (OPEs) were shown to have thyroid hormones (THs) disrupting potentials in animal studies, while epidemiological evidence on gestational exposure to OPEs and thyroid disruption is limited. Besides, assessment on the safety threshold of OPEs exposure during gestation is especially scarce.

METHODS

Based on the Shanghai Minhang Birth Cohort Study, we measured maternal urine concentration of 8 OPE metabolites and THs levels in cord plasma and examined their associations using multiple linear regression and quantile g-computation (QGC) models. The benchmark dose (BMD) and its lower limit (BMDL) of urine OPE metabolites concentrations were further estimated via the Bayesian Benchmark Dose Analysis System (BBMD) to reflect the safety threshold of exposure in pregnant women. The corresponding daily intake (DI) of BMDL was then calculated and compared with the current oral reference dose (RfD).

RESULTS

A total of 309 mother-newborn pairs were included in this study. Gestational bis (2-butoxyethyl) phosphate (BBOEP) exposure was associated with higher total triiodothyronine (TT3), free triiodothyronine (FT3), total thyroxine (TT4), and free thyroxine (FT4) in cord plasma, while bis(1,3-dichloro-2-propyl) phosphate (BDCPP) was observed to be associated with lower TT3 and FT3/FT4 but higher thyroid stimulating hormone (TSH). In addition, sex-specific effects were observed for bis (2-chloroethyl) phosphate (BCEP), which was associated with lower TT3 in cord plasma of female newborns, and lower TT4 and FT4 in male newborns. Similar results were obtained through QGC model and BBOEP was identified as the main contributor to the higher levels of TT3 and FT3. With benchmark response (BMR) of 10% and background response (P0) of 97.5% for both TT3 and FT3, the BMDL10 of urine BBOEP concentration was 0.50 μg/L. Further, the corresponding DI of tris (2-butoxyethyl) phosphate (TBOEP), which is the precursor of BBOEP, was 2.53 μg/kg BW/d.

CONCLUSIONS

Our findings suggest associations between gestational exposure to OPEs and altered THs biomarkers. According to the estimated BMD10 (BMDL10) of BBOEP and the corresponding DI, the current RfD of 15 μg/kg BW/d for TBOEP may not protect pregnant women and their newborns from thyroid disruption.

Maternal organophosphate esters and sex steroid hormones in mid-pregnancy

BACKGROUND

/Aims: Organophosphate esters (OPEs) are synthetic chemicals used in consumer products as flame retardants and plasticizers. OPEs are potential endocrine disruptors, but little is known regarding gestational OPE exposure and maternal sex steroid hormones in human pregnancy.

METHODS

Understanding Pregnancy Signals and Infant Development (UPSIDE) cohort participants (n=265) provided biospecimens and completed questionnaires in each trimester. In second trimester samples, we measured urinary OPE metabolite concentrations using HPLC-MS/MS. In second and third trimester serum samples, we measured sex steroids (total testosterone [TT], free testosterone, estrone [E1], estradiol [E2], and estriol [E3]) using LC-MS/MS. We fitted linear regression and linear mixed models examining each log-transformed, specific gravity-adjusted OPE metabolite in relation to sex steroid concentrations, adjusting for covariates. Three OPEs with >70% detection were considered continuously; six less prevalent metabolites were dichotomized (above vs below lower limit of detection). Secondary models were fit for male and female fetuses, separately. Results are shown as % difference in hormone levels.

RESULTS

Percent detection of OPEs ranged from 26% to 100%. Diphenyl phosphate (DPHP) had the highest concentration (median 0.9ng/mL). Across trimesters 2 and 3, a log-unit increase in dibutyl phosphate/di-isobutyl phosphate (DBUP/DIBP) was associated with lower TT (%Δ= -6.6, 95%CI: -11.5, -1.5), E1 (%Δ= -5.6, 95%CI: -10.8, -0.1), and E2 (%Δ= -5.3, 95%CI: -8.2, -2.3). Compared to those with non-detectable levels, participants with detectable bis(methylphenyl) phosphate (BMPP) had lower E3 (%Δ= -45.9, 95%CI: -67.9, -8.9) and participants with detectable bis(2-chloroethyl) phosphate (BCETP) had lower E2 (%Δ= -1.4, 95%CI: -2.4, -0.4). Numerous associations were observed in trimesters 2 and 3, individually. We observed several differences by fetal sex that varied in magnitude and direction.

CONCLUSION

OPEs may act as endocrine disruptors by altering maternal sex steroid hormones during pregnancy, with some differences by fetal sex. Further research is needed to understand implications for maternal and child health.

Insight into natural attenuation of tributyl phosphate by indigenous anaerobic microbes in soils: Implication by stable carbon isotope fractionation and microbial community structures

Organophosphate esters (OPEs) are widespread in the environment, with high persistence and toxicity. However, the underlying mechanisms of anaerobic microbial degradation of OPEs remain elusive in the field environment. In this study, the natural attenuation mechanisms of tributyl phosphate (TnBP) by indigenous anaerobic microorganisms in soils were investigated by using compound-specific stable isotope analysis (CSIA) and characterization of microbial communities. The results indicated that dibutyl phosphate (DnBP) was the major degradation product of TnBP. Significant carbon isotope fractionation was observed for TnBP during the anaerobic microbial degradation, and the carbon isotope enrichment factor (εC) was determined to be -2.71 ± 0.13‰. Unlike aerobic degradation with P-O bond cleavage, C-O bond cleavage was verified as the mode to removal a butyl side chain for TnBP to generate DnBP during the anaerobic microbial degradation. Microbial community analysis indicated that Sphingomonans, Nocardioides and Streptomyces were the important contributors to microbial degradation of TnBP in anoxic soils. TnBP altered microbial metabolic functions in anoxic soils, mainly enhancing the biosynthesis of ansamycins, ketone bodies and amino acids, and flagellar assembly, which promoted microbial degradation of TnBP. This study provided a better method to characterize the chemical bond cleavage mode and effect of OPEs on microbial communities, which was a prerequisite for the bioremediation of OPE pollution in soils.

Presence of 1, 3-diphenylguanidine and its derivatives in human urine and their human exposure

Recent studies have demonstrated the widespread presence of 1,3-diphenylguanidine (DPG) and its derivatives in environmental matrices. While, the amount of human exposure to these rubber additives remains unclear. In this study, we collected human urine samples from healthy general adults (n = 221) living in Quzhou, China, and analyzed these samples for DPG and its five derivatives. DPG, 1,6-bis(cyano-guanidino)hexane (HCG), 1,3-di-o-tolylguanidine (DTG) and exhibited detection frequencies exceeding 50% in collected human urine. Presence of HCG, 1-(o-tolyl)biguanide (detection frequency 17%), and 1-(4-cyanophenyl)guanidine (6.0%) in human urine was also demonstrated for the first time. The highest mean human urinary concentration was found for DPG (0.89 ng/mL, < LOD-4.7 ng/mL), followed by DTG (0.57 ng/mL, < LOD-3.1 ng/mL) and HCG (0.34 ng/mL, < LOD-1.8 ng/mL). Male participants had consistently higher average human urinary levels of DPG, DTG, and HCG than female subjects, but none of these differences were significant (p > 0.10). DPG and DTQ consistently showed a decline in the human urinary concentrations as age of the participant increased. DPG (mean 170 ng/kg bw/day, median 137 ng/kg bw/day) had the highest human daily exposure amount, followed by DTG (106 ng/kg bw/day, 91 ng/kg bw/day) and HCG (58 ng/kg bw/day, 38 ng/kg bw/day). The study enhances our understanding of human exposure to these rubber additives, which is crucial for assessing their potential health risks.

A comparative study for organophosphate triesters and diesters in mice via oral gavage exposure: Tissue distribution, excreta elimination, metabolites and toxicity

Organophosphate triesters (tri-OPEs) and diesters (di-OPEs) may threaten human health through dietary intake, whereas little information is available about their fate in mammals. Herein, mice exposure experiments were carried out through gavage with six tri-OPEs and six di-OPEs, respectively. The residual levels of di-OPEs in mice were generally higher than those of tri-OPEs. The residual di-OPEs mainly distributed in the liver and blood while the most tri-OPEs remained in stomach, indicating easier transfer and lower metabolism levels of di-OPEs. The accumulation of tri- and di-OPEs with large octanol-water partition coefficients and long carbon chain were observed in tissues and feces, implying that the elimination of these OPEs through fecal excretion is an important elimination pathway. A total of 86 OPE metabolites were found in murine urine and feces, 57 of which were identified for the first time. For tri-OPEs, carboxylated OPEs had higher peak intensities and fewer interference factors among the metabolites, which could serve as ideal biomarkers. The predicted oral median lethal doses of OPEs and corresponding metabolites showed an increased toxicity of some hydroxylated OPEs and di-OPEs, needing further attention. These results provided new insights and evidence on the fates and biomarkers of OPEs exposure for mammals.

Characterizing the Metabolism of Tire Rubber-Derived p-Phenylenediamine Quinones to Identify Potential Exposure Biomarkers in Humans

There is growing evidence of the frequent detection of tire rubber-derived contaminants p-phenylenediamine-derived quinones (PPD-Qs) (e.g., highly toxic N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-Q)) in the environment and biota and the adverse impact on organisms. Hence, a better understanding of their biotransformation/metabolism in humans is essential. However, relevant data are lacking owing to recent discoveries. Herein, the biotransformation patterns of 6PPD-Q and other five commonly detected PPD-Qs were characterized via combined in vitro assay and maternal cord blood screening monitoring. Rapid metabolism was found for each PPD-Q incubated with human liver S9 fraction and microsomes, resulting in the formation of abundant phase I and phase II metabolites. The subsequent screening for potential PPD-Q metabolites in blood samples showed the presence of suspect metabolites. Three detected metabolites were confirmed by matching the mass spectra and retention times of in vitro metabolites. N-Dealkylated, carboxy, carbonyl, and reductive metabolites and glucose, cysteine, and methionine conjugates were observed for the first time. The semiquantitative concentrations of metabolites were higher than those of the parent PPD-Qs, and several metabolites such as carboxy products were proposed as candidate biomarkers of PPD-Q exposure to humans. 6PPD-Q and N,N'-diphenyl-p-phenylenediamine quinone were detected in maternal and/or cord whole blood samples for the first time. This study holds great importance in elucidating the potential risks and health effects of PPD-Qs.

EHDPP induces proliferation inhibition and apoptosis to spermatocyte: Insights from transcriptomic and metabolomic profiles

BACKGROUND

2-ethylhexyldiphenyl phosphate (EHDPP) was used widespread in recent years and it was reported to impair reproductive behaviors and decrease fertility in male Japanese medaka. However, whether EHDPP causes spermatogenesis disturbance remains uncertain.

OBJECTIVES

We aimed to study the male reproductive toxicity of EHDPP and its related mechanism.

METHODS

Human spermatocyte cell line GC-2 was treated with 10 µM, 50 µM or 100 µM EHDPP for 24 h. Male CD-1 mice aged 6 weeks were given 1, 10, or 100 mg/kg/d EHDPP daily for 42 days and then euthanized to detect sperm count and motility. Proliferation, apoptosis, oxidative stress was detected in mice and cell lines. Metabolome and transcriptome were used to detect the related mechanism. Finally, anti-oxidative reagent N-Acetylcysteine was used to detect whether it could reverse the side-effect of EHDPP both in vivo and in vitro.

RESULTS

Our results showed that EHDPP inhibited proliferation and induced apoptosis in mice testes and spermatocyte cell line GC-2. Metabolome and transcriptome showed that nucleotide metabolism disturbance and DNA damage was potentially involved in EHDPP-induced reproductive toxicity. Finally, we found that excessive ROS production caused DNA damage and mitochondrial dysfunction; NAC supplement reversed the side effects of EHDPP such as DNA damage, proliferation inhibition, apoptosis and decline in sperm motility.

CONCLUSION

ROS-evoked DNA damage and nucleotide metabolism disturbance mediates EHDPP-induced germ cell proliferation inhibition and apoptosis, which finally induced decline of sperm motility.

Identification and quantification of acetyl tributyl citrate (ATBC) metabolites using human liver microsomes and human urine

Plasticizers are chemicals that make plastics flexible, and phthalates are commonly used. Due to the toxic effects of phthalates, there is increasing use of non-phthalate plasticizers like acetyl tributyl citrate (ATBC). ATBC has emerged as a safer alternative, yet concerns about its long-term safety persist due to its high leachability and potential endocrine-disrupting effects. This study aims to identify ATBC metabolites using human liver microsomes and suspect screening methods, and to explore potential urinary biomarkers for ATBC exposure. Using ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry, we identified ATBC metabolites, including acetyl dibutyl citrate (ADBC), tributyl citrate (TBC), and dibutyl citrate (DBC). Urine samples from 15 participants revealed the presence of ADBC in 5, TBC in 11, and DBC in all samples, with DBC concentrations pointedly higher than the other metabolites. These metabolites show promise as biomarkers for ATBC exposure, though further validation with human data is required. Our results underscore the need for comprehensive studies on ATBC metabolism, exposure pathways, and urinary excretion to accurately assess human exposure levels.

Exposure to organophosphate esters among Inuit adults of Nunavik, Canada

Halogenated organophosphate esters (OPEs) are increasingly used as flame retardants to replace polybrominated diphenyl ethers (PBDEs), which have been phased out due to their confirmed persistence, toxicity, and ability to undergo long range atmospheric transport. Non-halogenated OPEs are primarily used as plasticizers. While human exposure to PBDEs in the Canadian Arctic is well documented, it is not the case for OPEs. To assess the exposure to OPEs in Inuit living in Nunavik (northern Québec, Canada), we measured 16 metabolites of halogenated and non-halogenated OPEs in pooled urine samples from the last population health survey conducted in Nunavik, the Qanuilirpitaa? 2017 Inuit Health Survey (Q2017). Urine samples (n = 1266) were pooled into 30 pools by sex (female; male), age groups (16-19; 20-29; 30-39; 40-59; 60+ years old) and regions (Hudson Bay; Hudson Strait; Ungava Bay). Q2017 geometric means and 95 % confidence intervals were compared with data from the Canadian Health Measures Survey Cycle 6 (2018-2019) (CHMS). Halogenated OPEs were systematically detected and generally found at higher concentrations than non-halogenated OPEs in both Q2017 and CHMS. Furthermore, urinary levels of BCIPP and BDCIPP (halogenated) were lower in Q2017 compared to CHMS while concentrations of DPhP, DpCP and DoCP (non-halogenated) were similar between Q2017 and CHMS. Across the 16 metabolites measured in Q2017, BCIPHIPP (halogenated) had the highest levels (geometric mean: 1.40 μg/g creatinine). This metabolite was not measured in CHMS and should be included in future surveys. Overall, our results show that Inuit in Nunavik are exposed to lower or similar OPEs levels than the rest of the general Canadian population suggesting that the main current exposure to OPEs may be from consumer goods containing flame retardants and imported from the south rather than long-range atmospheric transport to the Arctic.

ExpoNano: A Strategy Based on Hyper-Cross-Linked Polymers Achieves Urinary Exposome Assessment for Biomonitoring

Urinary analysis of exogenous and endogenous molecules constitutes an efficient, noninvasive approach to evaluate human health status. However, the exposome characterization of urinary molecules remains extremely challenging with current techniques. Herein, we develop an ExpoNano strategy based on hyper-cross-linked polymers (HCPs) to achieve ultrahigh-throughput measurement of exo/endogenous molecules in urine. The strategy includes a simple trapping-detrapping procedure (15 min) with HCPs in enzymatically treated urine, followed by mass spectrometer determination. Molecules that can be determined by ExpoNano have a wide range of molecular weight (75-837 Da) and Log Kow (octanol-water partition coefficient; -9.86 to 10.56). The HCPs can be repeatedly used five times without decreasing the trapping efficiency. Application of ExpoNano in a biomonitoring study revealed a total of 63 environmental chemicals detected in >50% of the urine pools collected from Chinese adults living in 13 cities, with a median concentration of 0.026-47 ng/mL, while nontargeted analysis detected an additional 243 exogenous molecules. Targeted and nontargeted analysis also detected 926 endogenous molecules in pooled urine. Collectively, the ExpoNano strategy demonstrates unique advantages over traditional urine analysis approaches, including a wide range of analytes, satisfactory trapping efficiency, high simplicity and reusability, and extremely reduced time demand and financial cost.

Occurrence, spatial distribution and ecological risk assessment of Organophosphate Esters in surface water and sediments from the Ravi River and its tributaries

Organophosphate esters (OPEs) are widely used as substitutes for brominated flame retardants and characterized as emerging contaminants. Due to their toxicity and persistent nature, OPEs are becoming a matter of greater concern worldwide. However, information about the pollution profile of OPEs and associated ecological risks is still scarce in environmental matrices of the South Asian region, particularly Pakistan. Hence, the current study was conducted to investigate the occurrence, spatial distribution patterns, ecological risks and riverine flux of 10 organophosphate esters in surface water and sediments of Ravi River and its four tributaries. The concentrations of ∑10OPEs were in the range of 19.2 - 105 ng/L, with the dominance of chlorinated-OPEs (51 %) in surface water, whereas in case of sediments, the ∑10OPEs concentrations ranged from 20.7 to 149 ng/g dw, with high abundance of non - chlorinated alkyl-OPEs, which contributed about 56 % to total OPE concentration. The correlation analysis signified a strong positive relation of OPEs with TOC (p < 0.05, R = 0.76) in sediments; and in addition to this, field-based LogKoc values were estimated to be higher than predicted LogKoc. Moreover, a significantly positive correlation (p < 0.05, R = 0.88) was observed between LogKoc and LogKow, implying that hydrophobicity plays a significant role in OPE distribution in different environmental matrices. The global comparison revealed that contamination status of OPEs in the present study was comparatively lower than other regional findings, furthermore, principal component analysis suggested vehicular emissions, industrial discharges, household supplies and atmospheric deposition as main sources of OPEs occurrence in current study region. Furthermore, the riverine flux of ∑10OPEs was estimated to be 0.68 tons/yr and the ecological risk assessment indicated that all OPEs, except EHDPP and TCrP, showed negligible or insignificant ecological risks for aquatic organisms.

A new approach to monitoring typical organophosphorus compounds (OPs) in environmental media: From database building to suspect screening

Organophosphorus compounds (OPs) are widely used as flame retardants (FRs) and plasticizers, yet strategies for comprehensively screening of suspect OPs in environmental samples are still lacking. In this work, a neoteric, robust, and general suspect screening technique was developed to identify novel chemical exposures by use of ultra-high performance liquid chromatography-Q Exactive hybrid quadrupole-Orbitrap high resolution mass spectrometry (UHPLC-Q-Orbitrap HRMS). We firstly established a suspect chemical database which had 7,922 OPs with 4,686 molecular formulas, and then conducted suspect screening in n = 50 indoor dust samples, n = 76 sediment samples, and n = 111 water samples. By use of scoring criteria such as retention time prediction models, we successfully confirmed five compounds by comparison with their authentic standards, and prioritized three OPs candidates including a nitrogen/fluorine-containing compound, that is dimethyl {1H-indol-3-yl[3-(trifluoromethyl)anilino]methyl} phosphonate (DMITFMAMP). Given that the biodegradation half-life values in water (t1/2,w) of DMITFMAMP calculated by EPI Suite is 180 d, it is considered to be potentially persistent. This strategy shows promising potential in environmental pollution assessment, and can be expected to be widely used in future research.

Environmental exposures to organophosphorus flame retardants in early pregnancy and risks of gestational diabetes mellitus: a nested case-control study

OPFRs are emerging environmental pollutants with reproductive and endocrine toxicity. This study aimed to examine the association between environmental exposure to OPFRs during early pregnancy and GDM. This nested case-control study was based on a birth cohort that was constructed at a maternal and child health hospital, including 74 cases of GDM among 512 pregnant women. The OPFRs, including TBP, TBEP, TCEP, TDCPP, TMCP, TOCP, and TPHP during 10-14 weeks of pregnancy were determined using GC-MS. The association between the OPFRs and GDM was assessed using WQS and BKMR models. The levels of OPFRs were significantly elevated in GDM patients (60) compared with the controls (90). The WQS analysis showed that mixtures of the OPFRs were significantly associated with GDM (OR 1.370, 95% CI 1.036-1.810, P = 0.027), and TBP, TPHP, and TMCP were the major contributors to the mixed exposure effect. In the BKMR model, individual exposure to TBP, TPHP, and TMCP, and the interaction of TMCP with TBP and TPHP were significantly associated with GDM. Environmental exposure to OPFRs is positively associated with GDM. These findings provide evidence for the adverse effects of OPFR exposure on the health of pregnant women.

Occurrence, bioaccumulation and trophodynamics of organophosphate esters in the marine biota web of Laizhou Bay, Bohai Sea

The trophodynamic of organophosphate esters (OPEs) has not been known well despite their widespread occurrence in the aquatic environments. In this study, ten species of crustacean, seven species of mollusk, and 22 species of fish were collected in the Laizhou Bay (LZB) to examine the occurrence, bioaccumulation, and trophic transfer, and health risk of eight traditional OPEs and three emerging oligomeric OPEs. The results showed that total concentration of OPEs was 2.04 to 28.6 ng g-1 ww in the muscle of crustacean, mollusk, and fish and 2.62 to 60.6 ng g-1 ww in the fish gill. Chlorinated OPEs averagely contributed to over 85% of total OPEs while oligomeric OPEs averagely accounted for approximate 4%. The average log apparent bioaccumulation factor (ABAF) ranged from - 0.4 L kg-1 ww for triethyl phosphate to 2.4 L kg-1 ww for resorcinol-bis (diphenyl) phosphate. Apparent trophic magnification factors (ATMF) of individual OPE were generally less than 1, demonstrating the biodilution effect of the OPEs in the organism web of LZB. Additionally, the log ABAF and ATMF of OPEs were significantly positively correlated to their log Kow but negatively correlated to their biotransformation rate constant (BRC). Therefore, the OPEs with high Kow and low BRC tend to more accumulate in the marine organisms. The health risks associated with OPEs through the consumption of the seafood from the bay were low, even at high exposure scenario.

The neurotoxicity of organophosphorus flame retardant tris (1,3-dichloro-2-propyl) phosphate (TDCPP): Main effects and its underlying mechanisms

As a major alternative to the brominated flame retardants, the production and use of organophosphorus flame retardants (OPFRs) are increasing. And tris (1,3-dichloro-2-propyl) phosphate (TDCPP), one of the most widely used OPFRs, is now commonly found in a variety of products, such as building materials, furniture, bedding, electronic equipment, and baby products. TDCPP does not readily degrade in the water and tends to accumulate continuously in the environment. It has been detected in indoor dust, air, water, soil, and human samples. Considered as an emerging environmental pollutant, increasing studies have demonstrated its adverse effects on environmental organisms and human beings, with the nerve system identified as a sensitive target organ. This paper systematically summarized the progress of TDCPP application and its current exposure in the environment, with a focus on its neurotoxicity. In particular, we highlighted that TDCPP can be neurotoxic (including neurodevelopmentally toxic) to humans and animals, primarily through oxidative stress, neuroinflammation, mitochondrial damage, and epigenetic regulation. Additionally, this paper provided an outlook for further studies on neurotoxicity of TDCPP, as well as offered scientific evidence and clues for rational application of TDCPP in daily life and the prevention and control of its environmental impact in the future.

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.

Biotransformation of Organophosphate Diesters Characterized via In Vitro Metabolism and In Vivo Screening

Organophosphate diesters (di-OPEs), as additives in industrial applications and/or transformation products of emerging environmental pollutants, such as organophosphate triesters (tri-OPEs), have been found in the environment and biological matrices. The metabolic fate of di-OPEs in biological media is of great significance for tracing the inherent and precursor toxicity variations. This is the first study to investigate the metabolism of a suite of di-OPEs by liver microsomes and to identify any metabolite of metabolizable di-OPEs in in vitro and in vivo samples. Of the 14 di-OPEs, 5 are significantly metabolizable, and their abundant metabolites with hydroxyl, carboxyl, dealkylated, carbonyl, and/or epoxide groups are tentatively identified. More than half of the di-OPEs are detectable in human serum and/or wild fish tissues, and dibenzyl phosphate (DBzP), bis(2,3-dibromopropyl) phosphate (BDBPP), and isopropyl diphenyl phosphate (ip-DPHP) are first reported at a detectable level in humans and wildlife. Using an in vitro assay and a known biotransformation rule-based integrated screening strategy, 2 and 10 suspected metabolite peaks of DEHP are found in human serum and wild fish samples, respectively, and are then identified as phase I and phase II metabolites of DEHP. This study provides a novel insight into fate and persistence of di-OPE and confirms the presence of di-OPE metabolites in humans and wildlife.

Developmental toxicity assessment of neonicotinoids and organophosphate esters with a human embryonic stem cell- and metabolism-based fast-screening model

In recent years, neonicotinoids (NEOs) and organophosphate esters (OPEs) have been widely used as substitutes for traditional pesticides and brominated flame-retardants, respectively. Previous studies have shown that those compounds can be frequently detected in environmental and human samples, are able to penetrate the placental barrier, and are toxic to animals. Thus, it is reasonable to speculate that NEOs and OPEs may have potential adverse effects in humans, especially during development. We employed a human embryonic stem cell differentiation- and liver S9 fraction metabolism-based fast screening model to assess the potential embryonic toxicity of those two types of chemicals. We show that four NEO and five OPE prototypes targeted mostly ectoderm specification, as neural ectoderm and neural crest genes were down-regulated, and surface ectoderm and placode markers up-regulated. Human liver S9 fraction's treatment could generally reduce the effects of the chemicals, except in a few specific instances, indicating the liver may detoxify NEOs and OPEs. Our findings suggest that NEOs and OPEs interfere with human early embryonic development.

Global patterns of human exposure to flame retardants indoors

To fill the knowledge gaps regarding the global patterns of human exposure to flame retardants (FRs) (i.e., brominated flame retardants (BFRs) and organophosphorus flame retardants (OPFRs)), data on the levels and distributions of FRs in external and internal exposure mediums, including indoor dust, indoor air, skin wipe, serum and urine, were summarized and analysed. Comparatively, FR levels were relatively higher in developed regions in all mediums, and significant positive correlations between FR contamination and economic development level were observed in indoor dust and air. Over time, the concentration of BFRs showed a slightly decreasing trend in all mediums worldwide, whereas OPFRs represented an upward tendency in some regions (e.g., the USA and China). The occurrence levels of FRs and their metabolites in all external and internal media were generally correlated, implying a mutual indicative role among them. Dermal absorption generally contributed >60% of the total exposure of most FR monomers, and dust ingestion was dominant for several low volatile compounds, while inhalation was found to be negligible. The high-risk FR monomers (BDE-47, BDE-99 and TCIPP) identified by external exposure assessment showed similarity to the major FRs or metabolites observed in internal exposure mediums, suggesting the feasibility of using these methods to characterize human exposure and the contribution of indoor exposure to the human burden of FRs. This review highlights the significant importance of exposure assessment based on multiple mediums for future studies.

Association between urinary organophosphate ester metabolite exposure and thyroid disease risk among US adults: National Health and Nutrition Examination Survey 2011-2014

Background

Organophosphate esters (OPEs) may interfere with thyroid function, but the relationship between OPEs and thyroid disease remains unclear. This study aims to elucidate the relationship between OPEs exposure and thyroid disease risk in the general population in the United States.

Method

Data were obtained from the 2011-2014 National Health and Nutrition Examination Survey cycle. All participants were tested for seven OPE metabolites in their urine and answered questions about whether they had thyroid disease through questionnaires. Logistic regression was employed to analyze the association between exposure to individual OPE metabolites and thyroid disease. Weighted Quantile Sum (WQS) regression modeling was utilized to assess exposure to mixed OPE metabolites and risk of thyroid disease. Bayesian kernel machine regression(BKMR) models to analyze the overall mixed effect of OPE metabolites.

Result

A total of 2,449 participants were included in the study, 228 of whom had a history of thyroid disease. Bis(1,3-dichloro-2-propyl) phos (BDCPP), Diphenyl phosphate (DPHP) and Bis(2-chloroethyl) phosphate (BCEP) were the top three metabolites with the highest detection rates of 91.75%, 90.77% and 86.57%, respectively. In multivariate logistic regression models, after adjustment for confounding variables, individuals with the highest tertile level of BCEP were significantly and positively associated with increased risk of thyroid disease (OR=1.57, 95% CI=1.04-2.36), using the lowest tertile level as reference. In the positive WQS regression model, after correcting for confounding variables, mixed exposure to OPE metabolites was significantly positively associated with increased risk of thyroid disease (OR=1.03, 95% CI=1.01-1.06), with BCEP and DPHP having high weights. In the BKMR model, the overall effect of mixed exposure to OPE metabolites was not statistically significant, but univariate exposure response trends showed that the risk of thyroid disease decreased and then increased as BCEP exposure levels increased.

Conclusion

The study revealed a significant association between exposure to OPE metabolites and an increased risk of thyroid disease, with BCEP emerging as the primary contributor. The risk of thyroid disease exhibits a J-shaped pattern, whereby the risk initially decreases and subsequently increases with rising levels of BCEP exposure. Additional studies are required to validate the association between OPEs and thyroid diseases.

Determinants of organophosphate esters exposure in pregnant women from East China

Organophosphate esters (OPEs) have been broadly used in various industrial and consumer products, resulting in global distribution and human exposure. Gestational exposure to OPEs may adversely affect the health of both pregnant women and their offspring. To better understand OPE exposure in pregnant women, our study determined eight urinary metabolites of major OPEs in pregnant women (n = 733) recruited at 12-16 weeks of gestation from Shanghai, China, and explored the determinants of OPE exposure among various sociodemographic characteristics, lifestyles, and dietary factors. Urinary metabolites of OPEs, including bis (1,3-dichloro-2-propyl) phosphate (BDCPP), bis (2-chloroethyl) phosphate (BCEP), bis (1-chloro-2-propyl) phosphate (BCIPP), dicresyl phosphate (DCP), diphenyl phosphate (DPP), dibutyl phosphate (DBP), bis (2-ethylhexyl) phosphate (BEHP), and bis (2-butoxyethyl) phosphate (BBOEP), exhibited a detection rate ranging from 69.30% to 99.32%. Multivariate linear regression models indicated that pregnant women who were multiparous, had a higher family income per capita, worked in white-collar jobs, and took nutritional supplements such as milk powder and fish oil tended to have higher urinary OPE metabolite concentrations. Besides, independent of sociodemographic characteristics and lifestyle factors, consumption of more aquatic products, soy products, pork, and puffed food, as well as drinking of purified tap water versus tap water, were associated with increased urinary OPEs metabolite concentrations. Our study demonstrated that OPE exposure was ubiquitous in pregnant women from Shanghai, and provided new insights into the potential factors influencing OPE exposure during pregnancy.

An overview of current knowledge on organophosphate di-esters in environment: Analytical methods, sources, occurrence, and behavior

Organophosphate di-esters (di-OPEs) are highly related to tri-OPEs. The presence of di-OPEs in the environment has gained global concerns, as some di-OPEs are more toxic than their respective tri-OPE compounds. In this study, current knowledge on the analytical methods, sources, environmental occurrence, and behavior of di-OPEs were symmetrically reviewed by compiling data published till March 2023. The determination of di-OPEs in environmental samples was exclusively achieved with liquid chromatography mass spectrometry operated in negative mode. There are several sources of di-OPEs, including industrial production, biotic and abiotic degradation from tri-OPEs under environmental conditions. A total of 14 di-OPE compounds were determined in various environments, including dust, sediment, sludge, water, and atmosphere. The widespread occurrence of di-OPEs suggested that human and ecology are generally exposed to di-OPEs. Among all environmental matrixes, more data were recorded for dust, with the highest concentration of di-OPEs up to 32,300 ng g-1. Sorption behavior, phase distribution, gas-particle partitioning behavior was investigated for certain di-OPEs. Suggestions on future studies in the perspective of human exposure to and environmental behavior of di-OPEs were proposed.

Indirect Emissions from Organophosphite Antioxidants Result in Significant Organophosphate Ester Contamination in China

Organophosphite antioxidants (OPAs) have been seriously neglected as potential sources of organophosphate esters (OPEs) in environments. This study utilizes a modeling approach to quantify for the first time national emissions and multimedia distributions of triphenyl phosphate (TPHP)─a well-known flame retardant─and three novel OPEs: tris(2,4-ditert-butylphenyl) phosphate (AO168═O), bis(2,4-ditert-butylphenyl) pentaerythritol diphosphate (AO626═O2), and trisnonylphenol phosphate (TNPP). Emphasis is on the quantitative assessment of OPA source in China. TPHP has 1.1-9.7 times higher emission (300 Mg/year in 2019 with half from OPA sources) than AO168═O (278 Mg/year), AO626═O2 (53 Mg/year), and TNPP (32 Mg/year), but AO168═O is predominant in environments (63-79%) except freshwaters. About 72-99% of the studied OPEs are emitted via air, with 88-99% ultimately distributed into soils as the major sink. OPA-source emissions contribute 9.5-57% and 4.7-56% of TPHP masses and concentrations (except in sediments) in different media, respectively. Both AO168═O and AO626═O2 exhibit high overall persistence ranging between 2 and 11 years. Source emissions and environmental concentrations are elevated in economically developed areas, while persistence is higher in northern areas, where precipitation and temperature are lower. This study shows the significance of the sources of OPA to OPE contamination, which supports chemical management of these substances.

Organophosphorus flame retardants and their metabolites in paired human blood and urine

Organophosphorus flame retardants (OPFRs) have been shown to be carcinogenic, neurotoxic, and endocrine disruptive, so it is important to understand the levels of OPFRs in human body as well as the modes of external exposure. In this study, we investigated the levels of 13 OPFRs and 7 phosphodiester metabolites in paired human blood and urine, as well as the influencing factors (region, age and gender), and studied the relationship between OPFRs and oxidative stress by urinary metabolites. We found that the concentrations of triphenyl phosphate (TPhP) and tris-(2-ethylhexyl) phosphate (TEHP) in the blood of urban populations were higher than those of rural populations, and that younger populations suffered higher TPhP and 2-ethylhexyl diphenyl phosphate (EHDPP) exposures than older populations. In addition, we found that tris-(2-chloroethyl) phosphate (TCEP), tributyl phosphate (TnBP), TPhP and EHDPP exposure induced oxidative stress. The results of the internal load principal component analysis indicated that dust ingestion, skin exposure, respiration and dietary intake may be the most important sources of TCEP, tris(2-butoxyethyl) phosphate (TBOEP), tri(2-chloroisopropyl) phosphate (TCIPP) and TEHP, respectively, and dust ingestion and skin exposure may be the main sources of TPhP for humans.

Review on typical organophosphate diesters (di-OPEs) requiring priority attention: Formation, occurrence, toxicological, and epidemiological studies

The impact of primary metabolites of organophosphate triesters (tri-OPEs), namely, organophosphate diesters (di-OPEs), on the ecology, environment, and humans cannot be ignored. While extensive studies have been conducted on tri-OPEs, research on the environmental occurrence, toxicity, and health risks of di-OPEs is still in the preliminary stage. Understanding the current research status of di-OPEs is crucial for directing future investigations on the production, distribution, and risks associated with environmental organophosphate esters (OPEs). This paper specifically reviews the metabolization process from tri-OPEs to di-OPEs and the occurrence of di-OPEs in environmental media and organisms, proposes typical di-OPEs in different media, and classifies their toxicological and epidemiological findings. Through a comprehensive analysis, six di-OPEs were identified as typical di-OPEs that require prioritized research. These include di-n-butyl phosphate (DNBP), bis(2-butoxyethyl) phosphate (BBOEP), bis(1,3-dichloro-2-propyl) phosphate (BDCIPP), bis(2-chloroethyl) phosphate (BCEP), bis(1-chloro-2-propyl) phosphate (BCIPP), and diphenyl phosphate (DPHP). This review provides new insights for subsequent toxicological studies on these typical di-OPEs, aiming to improve our understanding of their current status and provide guidance and ideas for research on the toxicity and health risks of di-OPEs. Ultimately, this review aims to enhance the risk warning system of environmental OPEs.

Maternal exposure to organophosphate flame retardants and neonatal anthropometric measures

BACKGROUND

Organophosphate flame retardants (OPFRs) are widely used as flame retardants and plasticizers. Laboratory evidence has suggested that maternal OPFR exposure may adversely affect fetal growth, but the epidemiological data are limited.

OBJECTIVES

To investigate the association of maternal OPFR exposure with neonatal anthropometric measures.

METHODS

This study included 354 mother-newborn pairs from the Laizhou Wan Birth Cohort (LWBC), China. Ten OPFR metabolites were measured in maternal urine samples collected before delivery. Neonatal anthropometric data was collected from medical records and standardized into z-scores using the WHO standards (2007), including the weight-for-age (WAZ), length-for-age (LAZ), body mass index-for-age (BMIZ), weight-for-length (WLZ), and head circumference-for-age z-score (HCZ). Multiple linear regression and weighted quantile sum (WQS) regression were used to estimate the associations of individual OPFR metabolites and their mixtures with neonatal anthropometrics, respectively. Stratified analysis by sex was performed.

RESULTS

The detection rates of BCEP, DPHP, BCIPP, BDCIPP, BBOEP, DnBP and DiBP were above 60%, with median concentrations ranging from 0.14 to 3.60 μg/g creatinine. Most OPFR metabolites (i.e., BCIPP, BDCIPP, DiBP, DnBP, or BBOEP) were associated with decreased offspring WAZ and HCZ. When using WQS analysis, the OPFR metabolite mixture was inversely associated with the WAZ, BMIZ and HCZ, whereas DnBP had the highest weights. After stratified by gender, the negative associations were more pronounced among males.

CONCLUSIONS

Maternal OPFR exposure was negatively associated with offspring WAZ, BMIZ, and HCZ, and males seemed to be more vulnerable to the developmental toxicity of certain OPFRs.

First insight into the sex-dependent accumulation, tissue distribution and potential toxicities of 2-ethylhexyl diphenyl phosphate and its metabolites in adult zebrafish

The 2-ethylhexyl diphenyl phosphate (EHDPHP), a primary organophosphorus flame retardant used in various industrial products, is prone to biotransformation. However, there is a knowledge gap on the sex- and tissue-specific accumulation and potential toxicities of EHDPHP (M1) and its metabolites (M2-M16). In this study, adult zebrafish (Danio rerio) were exposed to EHDPHP (0, 5, 35 and 245 µg/L) for 21-day, which was followed by 7-day depuration. The bioconcentration factor (BCF) of EHDPHP in female zebrafish was 26.2 ± 7.7% lower than in males due to the lower uptake rate (k_u) while higher depuration rate (k_d) in the females. The regular ovulation and higher metabolic efficiency promoted elimination from female zebrafish, thus leading to much less (28-44%) accumulation of ∑(M1-M16) in female zebrafish. They exhibited the highest accumulation in the liver and intestine in both sexes, which might be regulated by tissue-specific transporters and histones evidenced by molecular docking results. Intestine microbiota analysis further revealed that female zebrafish were more susceptible to EHDPHP exposure, with more significant changes in phenotype number and KEGG pathways in female than male fish. Disease prediction results suggested that EHDPHP exposure might cause cancers, cardiovascular diseases as well as endocrine disorders in both sexes. These results provide a comprehensive understanding of the sex-dependent accumulation and toxicity of EHDPHP and its metabolites.

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.

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

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

Organophosphate Flame Retardants in Pregnant Women: Sources, Occurrence, and Potential Risks to Pregnancy Outcomes

Organophosphate flame retardants (OPFRs) are found in various environmental matrixes and human samples. Exposure to OPFRs during gestation may interfere with pregnancy, for example, inducing maternal oxidative stress and maternal hypertension during pregnancy, interfering maternal and fetal thyroid hormone secretion and fetal neurodevelopment, and causing fetal metabolic abnormalities. However, the consequences of OPFR exposure on pregnant women, impact on mother-to-child transmission of OPFRs, and harmful effects on fetal and pregnancy outcomes have not been evaluated. This review describes the exposure to OPFRs in pregnant women worldwide, based on metabolites of OPFRs (mOPs) in urine for prenatal exposure and OPFRs in breast milk for postnatal exposure. Predictors of maternal exposure to OPFRs and variability of mOPs in urine have been discussed. Mother-to-child transmission pathways of OPFRs have been scrutinized, considering the levels of OPFRs and their metabolites in amniotic fluid, placenta, deciduae, chorionic villi, and cord blood. The results showed that bis(1,3-dichloro-2-propyl) phosphate (BDCIPP) and diphenyl phosphate (DPHP) were the two predominant mOPs in urine, with detection frequencies of >90%. The estimated daily intake (EDI_M) indicates low risk when infants are exposed to OPFRs from breast milk. Furthermore, higher exposure levels of OPFRs in pregnant women may increase the risk of adverse pregnancy outcomes and influence the developmental behavior of infants. This review summarizes the knowledge gaps of OPFRs in pregnant women and highlights the crucial steps for assessing health risks in susceptible populations, such as pregnant women and fetuses.

Organophosphate Esters (OPEs) Flame Retardants in Water: A Review of Photocatalysis, Adsorption, and Biological Degradation

As a substitute for banned brominated flame retardants (BFRs), the use of organophosphate esters (OPEs) increased year by year with the increase in industrial production and living demand. It was inevitable that OPEs would be discharged into wastewater in excess, which posed a great threat to the health of human beings and aquatic organisms. In the past few decades, people used various methods to remove refractory OPEs. This paper reviewed the photocatalysis method, the adsorption method with wide applicability, and the biological method mainly relying on enzymolysis and hydrolysis to degrade OPEs in water. All three of these methods had the advantages of high removal efficiency and environmental protection for various organic pollutants. The degradation efficiency of OPEs, degradation mechanisms, and conversion products of OPEs by three methods were discussed and summarized. Finally, the development prospects and challenges of OPEs’ degradation technology were discussed.

Gestational exposure to organophosphate esters and adiposity measures of children up to 6 years: Effect modification by breastfeeding

Organophosphate esters (OPEs) are synthetic chemicals used in various commercial products. Accumulating evidence has shown that they may act as metabolic disruptors. However, no study has investigated the long-term effects of gestational OPEs exposure on childhood adiposity. Breast milk represents the optimal nutritional form of feeding for infants and may protect against the adverse effects of gestational OPEs exposure on offspring development. Using data from the Shanghai-Minhang birth cohort study, we investigated the associations of gestational OPEs exposure with adiposity measures in children up to 6 years of age, and whether breastfeeding could modify these associations. A total of 733 mother-child pairs with available data on OPE concentrations and child anthropometry were included. Eight OPE metabolites were assessed in maternal urine samples collected at 12-16 weeks of pregnancy. Information on children's weight, height, arm circumference, and waist circumference was collected at birth and 0.5, 1, 4, and 6 years of age. Weight-for-age and body mass index-for-age z scores were calculated. The duration of children's breastfeeding was categorized as ≤4 months or >4 months. The generalized estimate equation and Bayesian Kernel Machine Regression models were used to examine the associations of OPEs exposure with children's adiposity measures. Selected OPEs exposure was associated with higher children's adiposity measures. Particularly, we found stronger associations of bis(1-chloro-2-propyl) phosphate (BCIPP), bis(2-chloroethyl) phosphate (BCEP), bis(1,3-dichloro-2-propyl) phosphate (BDCPP), and di-o-cresyl phosphate and di-p-cresyl phosphate (DCP) with higher adiposity measures in children breastfed for ≤4 months, while little evidence of associations was found among those breastfed for >4 months. Our study suggested that gestational OPEs exposure could alter children's adiposity measures, but the potential effects were attenuated if children were breastfed for >4 months.

Fluorescence turn-off sensing strategy based on Al-based MOF for selective detection of tricresyl phosphate

Tricresyl phosphate (TCP), a notable emerging pollutant with a high bioconcentration factor and biotoxicity, is a typical representative of aryl-organophosphorus flame retardants. The electrochemical and chromatographic technologies used in conventional TCP detection have a variety of drawbacks. Hence, it is crucial to suggest an easy, accurate, and selective method for detecting TCP. In this study, we presented a brand-new method based on NH₂-MIL-53(Al) nanoprobe for the direct luminescence assay of TCP. NH₂-MIL-53(Al) possessed an excellent crystal structure and superior optical qualities. Notably, the introduction of TCP caused a considerable dampening of the photoluminescence signal of the nanoprobe. The fluorescence response based on static quenching was verified by fluorescence lifetime decay curves. The thermodynamic analysis further concluded that TCP and nanoprobe spontaneously produced non-fluorescent complexes due to hydrophobic interaction. The quenching efficiency (F₀-F)/F₀ of the nanoprobe and the TCP concentration displayed good linearity in the scope of 0.3-3.0 μM (R² = 0.996), and the LOD was 0.058 μM under the ideal detection conditions. More significantly, the technique was effectively used to identify TCP in lake and tap water (RSD ≤5.79%), which provided a fresh perspective on how to recognize OPFRs in environmental water.

Integrating Physiologically Based Pharmacokinetic Modeling-Based Forward Dosimetry and in Vitro Bioassays to Improve the Risk Assessment of Organophosphate Esters on Human Health

The ability to accurately assess the health risks of contaminants is limited by the shortcomings of toxicological standards. Using organophosphate esters (OPEs) as an example, this study attempted to integrate physiologically based pharmacokinetic (PBPK)-based forward dosimetry and in vitro bioassays to assess the likelihood of contaminants inducing biological effects in humans. The total exposure level of OPEs for Chinese residents was 19.5 ± 8.71 ng/kg/day with inhalation being the main exposure pathway. Then, human PBPK models were developed for individual OPEs to predict their steady-state concentrations in human tissues, and the predicted median levels in blood were close to the measurements. The reference doses (RfDs) of OPEs based on in vitro bioassays were comparable to in vivo animal-derived RfDs, demonstrating the reliability of in vitro bioassays. Therefore, the likelihood of OPEs inducing bioactivities in humans (RQ_in-vitro) was calculated using in vitro toxicity data and OPE levels in human tissues. The RQ_in-vitros of tris(2-chloroisopropyl) phosphate, tris(1,3-dichloropropyl) phosphate, and triphenyl phosphate (7.68 × 10^-5-3.18 × 10^-3) were comparable to the risks assessed using traditional RfDs (5.22 × 10^-5-1.94 × 10^-3), indicating the credibility of the method proposed in this study. This study establishes a new framework to improve the health risk assessment of contaminants without sufficient toxicity data and minimize the need for animal experimentation.

First Insight into the Formation of In Vivo Transformation Products of 2-Ethylhexyl diphenyl phosphate in Zebrafish and Prediction of Their Potential Toxicities

As a frequently detected organophosphorus flame retardant in the environment, 2-ethylhexyl diphenyl phosphate (EHDPHP) is vulnerable to biotransformation, while the transformation mechanisms and potential toxicities of its transformation products remain unclear. In the present study, in vivo transformation products of EHDPHP in exposed zebrafish for 21d were analyzed by suspect screening and identified by mass spectrometry. Fifteen metabolites were identified, including 10 phase I and 5 phase II products with monohydroxylated products being primary, among which 5-OH-EHDPHP was the most predominant. Two sulfation products and one terminal desaturation metabolite of EHDPHP were reported for the first time. A density functional calculation coupled with molecular docking disclosed that the specific conformation of EHDPHP docked in the protein pockets favored the primary formation of 5-OH-EHDPHP, which was fortified to be a more suitable biomarker of EHDPHP exposure. The in vitro tests suggested that EHDPHP transformation took place not only in liver but also in intestine, where gut microbes played an important role. Due to lack of standards, in silico toxicity prediction combined with molecular docking indicated that several metabolites potentially cause higher toxicities than EHDPHP. The results provide deep insight into the potential health risks due to specific in vivo transformation of EHDPHP.

Presence of novel and legacy flame retardants and other pollutants in an e-waste site in China and associated risks

Electrical and Electronic Equipment (EEE) residues and their management have been widely identified as potential sources of plasticizers and flame retardants to the environment, especially in non-formal e-waste facilities. This study evaluates the distribution, partitioning and environmental and human impact of organophosphate esters (OPEs), legacy polychlorinated biphenyls (PCBs), polybromodiphenyl ethers (PBDEs) and organochlorine pesticides (OCPs) in the e-waste recycling area of Baihe Tang village, in the Qingyuan county, Guangdong province, China. A plastic debris lump accumulated in a small pond during years was identified as the main source of pollution with ∑pollutants of 8400 μg/g dw, being OPEs the main contaminants detected, followed by PBDEs. This lump produced the contamination of water, sediments, soils and hen eggs in the surrounding area at high concentrations. Plastic-water and water-sediment partitioning coefficients explained the migration of OPEs to the water body and accumulation in sediments, with a strong dependence according to the K_OW. Triphenyl phosphate (TPhP), tricresyl phosphate (TCPs) and high chlorination degree PCBs produced a risk in soils and sediments, considering the lowest predicted no effect concentration, while the presence of PCBs and PBDEs in free range hen eggs exceeded the acceptable daily intake. OCPs were detected at low concentrations in all samples. The presence of organic contaminants in e-waste facilities worldwide is discussed to highlight the need for a strict control of EEE management to minimize environmental and human risks.

Chlorinated Organophosphate Flame Retardants Impair the Lung Function via the IL-6/JAK/STAT Signaling Pathway

Toxicological studies have revealed the adverse impacts of organophosphate flame retardants (OPFRs) on the respiratory system, while there is a lack of epidemiological evidence, and information for risk assessment remains insufficient. Herein, we investigated the associations of urinary metabolites of OPFRs with the lung function in 987 adults participating in the U.S. National Health and Nutrition Examination Survey 2011-2012. The elevation of three primary metabolites of chlorinated OPFRs [bis(1,3-dichloro-2-propyl) phosphate (BDCIPP), bis(2-chloroethyl) phosphate (BCEP), and bis(1-chloro-2-propyl) phosphate (BCIPP)] was related to pulmonary dysfunction in a sample-weighted regression model. Each one-unit increase in the log-transformed levels of BDCIPP and BCEP was related to 91.52 and 79.34 mL reductions in the forced vital capacity (FVC). Each one-unit elevation in BCIPP was correlated with 130.86, 153.56, 302.26, and 148.24 mL reductions in forced expiratory volume 1st second (FEV₁), FVC, peak expiratory flow rate (PEF), and forced expiratory flow at 25-75% of FVC (FEF_25-75%), respectively. Then, an adverse outcome pathway (AOP) framework was constructed using the Comparative Toxicogenomics Database, the Toxicity Forecaster, and the GeneCards database. Based on the weight of the evidence, BDCIPP, BCEP, BCIPP, and their parent compounds (TDCIPP, TCEP, and TCIPP) may affect the IL-6/Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway, induce airway remodeling, and impair the lung function. Additionally, tobacco smoke exposure may modify the effects of BDCIPP on the lung function (P_int < 0.05) and affect the IL-6-mediated AOP. These results suggested that chlorinated OPFRs were associated with pulmonary dysfunction via the IL-6/JAK/STAT pathway.

The associations between renal disease severity and exposure to organophosphate flame retardants in patients with chronic kidney disease

Organophosphate flame retardants (OPFRs) are emerging and widespread environmental pollutants with potential health hazards, including nephrotoxicity. However, the exposure patterns and nephrotoxic potential of OPFRs are yet to be investigated in patients with chronic kidney disease (CKD). We conducted a cross-sectional study involving 166 patients with CKD stratified by estimated glomerular filtration rate (eGFR) and severity of proteinuria. The urinary concentrations of 10 OPFR compounds were measured to evaluate the exposure patterns. Clinical and urinary OPFR profiles were compared among subgroups to identify whether the OPFR compounds were independently correlated with eGFR and proteinuria. Additionally, lifestyle factors were compared among subgroups stratified by median concentrations of urinary OPFR compounds associated with renal disease severity. This study revealed universal exposure to OPFRs in the CKD population, with an overall urinary detection rate of 98.80 %. Furthermore, after adjusting for covariates, the urinary concentration of bis(2-chloroethyl) phosphate (BCEP) was identified as an independent predictor of lower eGFR (low vs high eGFR, odds ratio (OR) (95 % confidence interval (CI)), 1.761 (1.032-3.005) per log μg/g creatinine, p = 0.038), and the urinary concentration of bis(2-butoxyethyl) phosphate (BBOEP) was independently correlated with overt proteinuria in CKD patients (with vs without overt proteinuria, OR (95 % CI), 1.813 (1.065-3.086) per log μg/g creatinine, p = 0.028). Moreover, frequent seafood consumption was negatively correlated with urinary BCEP concentration (high vs low BCEP, OR (95 % CI), 0.455 (0.228-0.908), p = 0.025), and age was inversely associated with urinary BBOEP concentration (high vs low BBOEP, OR (95 % CI), 0.968 (0.937-0.999) per year, p = 0.048). In conclusion, our investigation highlights the extensive exposure to OPFRs and the independent association between renal disease severity and urinary BCEP/BBOEP concentrations in the CKD population, indicating the nephrotoxic potential of these pollutants.

An overview of organophosphate esters and their metabolites in humans: Analytical methods, occurrence, and biomonitoring

With the strict regulation of brominated flame retardants, organophosphate esters (OPEs) have been extensively used as replacements. Increasing concerns on OPEs have aroused due to their extensive distribution in the environment and humans, as well as their potential toxicities. Recent studies have demonstrated that some organophosphate di-esters are even more toxic than their respective tri-esters. This review summarized the current state of knowledge on the analytical methodologies (including sample collection and preparation, instrumental analysis, and the feasibility of each potential human matrix), as well as the occurrences of OPEs and/or their metabolites (m-OPEs) in various human matrices. Organophosphate esters are readily metabolized in human thus only limited studies reported their occurrences in blood and breast milk, whereas abundant studies are available regarding the occurrences of m-OPEs rather than OPEs in urine. Since none of the matrix is suitable all the time, appropriate matrix should be selected depending on the aims of biomonitoring studies, e.g., high throughput screening or body burden estimation. Biomonitoring with non-invasive matrices such as hair and/or nail is useful to screen specific populations that might be under high exposure risks while urine is more suitable to provide valuable information on body burden. In terms of urinary monitoring, specific biomarkers have been identified for some OPE compounds, including tri(2-butoxyethyl) phosphate, tri(1,3-dichloro-2-propyl) phosphate, tri(2-chloroethyl) phosphate and tri(1-chloro-2-propyl) phosphate. Further studies are required to identify suitable urinary biomarkers for other OPE compounds, especially the emerging ones.

Organophosphate tri-esters and di-esters in drinking water and surface water from the Pearl River Delta, South China: Implications for human exposure

Some organophosphate di-esters (di-OPEs) have been found to be more toxic than their respective tri-esters. The environmental occurrence of di-OPEs remains largely unclear. A total of 106 water samples, including 56 drinking water (bottled, barreled, and tap water) and 50 surface water (lake and river) samples were collected and analyzed for 10 organophosphate tri-esters (tri-OPEs) and 7 di-OPEs. The concentrations (range (median)) of ∑₇di-OPE were 2.8-22 (9.7), 1.1-5.8 (2.6), 3.7-250 (120), 13-410 (220), and 92-930 (210) ng/L in bottled water, barreled water, tap water, lake water, and river water, respectively. In all types of water samples, tris(1-chloro-2-propyl) phosphate was the dominant tri-OPE compound. Diphenyl phosphate was the predominant di-OPE compound in tap water and surface water, while di-n-butyl phosphate and bis(2-ethylhexyl) phosphate was the dominant compound in bottled water and barreled water, respectively. Source analysis suggested diverse sources of di-OPEs, including industrial applications, effluents of municipal wastewater treatment plants, degradation from tri-OPEs during production/usage and under natural environmental conditions. The non-carcinogenic and carcinogenic risks of OPEs were lower than the theoretical threshold of risk, indicating the human health risks to OPEs via drinking water consumption were negligible. More studies are needed to explore environmental behaviors of di-OPEs in the aquatic environment and to investigate ecological risks.

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

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

Indoor exposure to selected flame retardants and quantifying importance of environmental, human behavioral and physiological parameters

Indoor exposure to organic flame retardants (FRs) has raised extensive concern due to associated adverse health effects. Indoor-exposure induced daily intakes of six widely used FRs individually ranged 0.002-611 ng/day and 0.02-463 ng/day, respectively, for adults and 2-6-year-old children; and resulting internal exposure levels ranged 0.1-159 and 2.1-4500 ng/g lipid, respectively. A proportion of 0.001-5.9% and 0.006-10.3% of individual FRs emitted into indoor air ultimately entered bodies of adults and children respectively. Tris(2-chloroisopropyl)phosphate dominated in emissions, whilst 2-ethylhexyl-2,3,4,5-tetrabromobenzoate dominated in human bodies. Hand-to-mouth contact was the most important exposure pathway for less volatile FRs including most brominated FRs, whilst inhalation was the predominant intake pathway of tris(2-chloroisopropyl)phosphate. Relative importance of 29 environmental, behavioral and physiological parameters was ranked to explore key drivers influencing exposure and accumulation of FRs in humans. Results suggested that frequent bathing and handwashing can reduce exposure effectively, especially for children. Bodyweight and lipid fraction were only positively related to internal accumulation and body-weight-normalized concentrations of compounds with low metabolic rates (half-lives ≥10³ h) in humans. Our findings help control indoor exposure to FRs and are supportive of human exposome studies in the future.

Simultaneous determination of 16 urinary metabolites of organophosphate flame retardants and organophosphate pesticides by solid phase extraction and ultra performance liquid chromatography coupled to tandem mass spectrometry

Organophosphate flame retardants (OPFRs) and organophosphate pesticides (OPPs), pertaining to organophosphate esters, are ubiquitous in environment and have been verified to pose noticeable risks to human health. To evaluate human exposures to OPFRs and OPPs, a fast and sensitive approach based on a solid phase extraction (SPE) followed by the ultra-high-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS) detection has been developed for the simultaneous analysis of multiple organophosphorus metabolites in urine. The method allows the identification and quantification of ten metabolites of the most common OPFRs and all six dialkylphosphates (DAPs) of OPPs concerning the population exposure characteristics. The method provided good linearities (R² = 0.998-0.999), satisfactory method detection limits (MDLs) (0.030-1.129 ng/mL) and only needed a small volume (200 μL) of urine. Recovery rates ranged 73.4-127.1% at three spiking levels (2, 10 and 25 ng/mL urine), with both intra- and inter-day precision less than 14%. The good correlations for DAPs in a cross-validation test with a previous gas chromatography-mass spectrometry (GC-MS) method and a good inter-laboratory agreement for several OPFR metabolites in a standard reference material (SRM 3673) re-enforced the precision and validity of our method. Finally, the established method was successfully applied to analyze 16 organophosphorus metabolites in 35 Chinese children's urine samples. Overall, by validating the method's sensitivity, accuracy, precision, reproducibility, etc., data reliability and robustness were ensured; and the satisfactory pilot application on real urine samples demonstrated feasibility and acceptability of this method for being implemented in large population-based studies.

Risk Assessment of Dietary Exposure to Organophosphorus Flame Retardants in Children by Using HBM-Data

Due to their extensive usage, organophosphorus flame retardants (OPFRs) have been detected in humans and in the environment. Human are exposed to OPFRs via inhalation of indoor air, dust uptake or dietary uptake through contaminated food and drinking water. Only recently, few studies addressing dietary exposure to OPFRs were published. In this study, we used human biomonitoring (HBM) data of OPFRs to estimate how much the dietary intake may contribute to the total exposure. We estimated by reverse dosimetry, the daily intake of tris (2-chloroethyl) phosphate (TCEP), tris (1-chloro-2-propyl) phosphate (TCIPP), tris (1,3-dichloro-2-propyl) phosphate (TDCIPP) for children using HBM data from studies with sampling sites in Belgium, Denmark, France, Germany, Slovenia and Slovakia. For estimating the dietary exposure, a deterministic approach was chosen. The occurrence data of selected food categories were used from a published Belgium food basket study. Since the occurrence data were left-censored, the Lower bound (LB)—Upper bound (UB) approach was used. The estimated daily intake (EDI) calculated on the basis of urine metabolite concentrations ranged from 0.03 to 0.18 µg/kg bw/d for TDCIPP, from 0.05 to 0.17 µg/kg bw/d for TCIPP and from 0.02 to 0.2 µg/kg bw/d for TCEP. Based on national food consumption data and occurrence data, the estimated dietary intake for TDCIPP ranged from 0.005 to 0.09 µg/kg bw/d, for TCIPP ranged from 0.037 to 0.2 µg/kg bw/d and for TCEP ranged from 0.007 to 0.018 µg/kg bw/d (summarized for all countries). The estimated dietary intake of TDCIPP contributes 11–173% to the EDI, depending on country and LB-UB scenario. The estimated dietary uptake of TCIPP was in all calculations, except in Belgium and France, above 100%. In the case of TCEP, it is assumed that the dietary intake ranges from 6 to 57%. The EDI and the estimated dietary intake contribute less than 3% to the reference dose (RfD). Therefore, the estimated exposure to OPFRs indicates a minimal health risk based on the current knowledge of available exposure, kinetic and toxicity data. We were able to show that the dietary exposure can have an impact on the general exposure based on our underlying exposure scenarios.

Semi-volatile organic compounds in fine particulate matter on a tropical island in the South China Sea

Measurements of hazardous semi-volatile organic compounds (SVOCs) in remote tropical regions are rare. In this study, polycyclic aromatic compounds (PACs) [including polycyclic aromatic hydrocarbons (PAHs), nitrated PAHs (NPAHs), and oxygenated PAHs (OPAHs)], organophosphate esters (OPEs), and phthalic acid esters (PAEs) were measured in fine particulate matter (PM_2.5) at Yongxing Island in the South China Sea (SCS). The concentrations of PACs (median = 53.5 pg/m³) were substantially low compared with previous measurements. The concentration weighted trajectory (CWT) model showed that the eastern and southern China was the main source region of PAC, occurring largely during the northeast (NE) monsoon. The PM_2.5 showed remarkably high concentrations of OPEs (median = 3231 pg/m³) and moderate concentrations of PAEs (13,013 pg/m³). Some Southeast Asian countries were largely responsible for their higher concentrations, driven by the tropical SCS monsoons. We found significant atmospheric loss of the SVOCs, which is an explanation for the low concentrations of PACs. Enhanced formation of N/OPAHs originated from tropical regions was also observed. The positive matrix factorization model was applied to apportion the SVOC sources. The results, as well as correlation analyses of the SVOC concentrations, further indicate insignificant local sources and enhanced atmospheric reactions on this island.

Dehalococcoides-Containing Enrichment Cultures Transform Two Chlorinated Organophosphate Esters

Although chlorinated organophosphate esters (Cl-OPEs) have been reported to be ubiquitously distributed in various anoxic environments, little information is available on their fate under anoxic conditions. In this study, we report two Dehalococcoides-containing enrichment cultures that transformed 3.88 ± 0.22 μmol tris(2-chloroethyl) phosphate (TCEP) and 2.61 ± 0.02 μmol tris(1-chloro-2-propyl) phosphate (TCPP) within 10 days. Based on the identification of the transformed products and deuteration experiments, we inferred that TCEP may be transformed to generate bis(2-chloroethyl) phosphate and ethene via one-electron transfer (radical mechanism), followed by C-O bond cleavage. Ethene was subsequently reduced to ethane. Similarly, TCPP was transformed to form bis(1-chloro-2-propyl) phosphate and propene. 16S rRNA gene amplicon sequencing and quantitative polymerase chain reaction analysis revealed that Dehalococcoides was the predominant contributor to the transformation of TCEP and TCPP. Two draft genomes of Dehalococcoides assembled from the metagenomes of the TCEP- and TCPP-transforming enrichment cultures contained 14 and 15 putative reductive dehalogenase (rdh) genes, respectively. Most of these rdh genes were actively transcribed, suggesting that they might contribute to the transformation of TCEP and TCPP. Taken together, this study provides insights into the role of Dehalococcoides during the transformation of representative Cl-OPEs.