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

Gestation Exposure to Organophosphate Esters: Structure-Dependent Transplacental Transfer Patterns, Mechanisms, and Toxicity

Organophosphate esters (OPEs), characterized by diverse chemical substituents, exhibit varying environmental exposure and toxicity profiles. Therefore, OPEs may have potential for placental transfer and could impact neonatal development. However, the structural-specific transplacental mechanisms and toxicity effects of the OPEs remain poorly understood. Herein, we develop an integrated evaluation system with human biomonitoring, uterine perfusion in pregnant rats, and placental cells. OPEs were frequently observed in maternal and cord whole blood, urine, and amniotic fluid samples (n = 41 sample sets) with median concentrations of 9.47, 9.31, 9.90, and 5.98 ng/mL, respectively. Rat uterine perfusion experiment suggested that chlor-OPEs exhibited relatively higher transplacental efficiency compared to alkyl- and aryl-OPEs. Passive diffusion dominated by lipophilicity (log Kow) and transporters dominated active transport may be involved in the transplacental transportation mechanisms. The results from exposure experiments to placenta BeWo cells indicated that organophosphate triesters (tri-OPEs) (IC50 values of 145 to 1464 μM) exhibited higher toxicity to the corresponding organophosphate diesters (di-OPEs) (IC50 values of 752 to 1794 μM). In addition, chlor-OPEs represented significantly greater cytotoxic potential to placenta cells in comparison to alkyl and aryl-OPEs. More attention should be paid for chlor-OPEs as its higher transplacental and toxicity potential compared to alkyl- and aryl-OPEs.

Do urinary metabolites reflect occupational exposure to organophosphate flame retardants? A case study in electronic waste recycling workers

Organophosphate esters (OPEs) are commonly used in electronic devices to meet safety standards, but electronic-waste recycling (e-recycling) workers may face significant exposure to those potentially hazardous compounds in their workplace. We examined the relationship between urinary OPE metabolites and their parent compounds in the air, in Canadian e-recycling facilities. We collected personal air samples and end-of-shift urine samples from workers at six e-recycling facilities. We employed linear and Tobit regression models to assess associations between air concentrations of triphenyl phosphate (TPhP) and three metabolites, of tris (2-chloroethyl) phosphate (TCEP) and two metabolites, of tris (2-chloroisopropyl) phosphate (TCPP) and two metabolites, of tris (1,3-dichloro-2-propyl) phosphate (TDCPP), and of tris (2-butoxyethyl) phosphate (TBOEP) and one metabolite each. The 85 participants, mostly male (78 %) and aged between 25 and 54, had concentrations of OPEs detected in 90-100 % of air samples, with geometric means of TPhP, TCEP, TBOEP and TDCPP, of 351, 404, 261 and 250 picomoles per cubic metre respectively. The proportion of detection of their corresponding metabolites varied between 32 % and 98 %. Regression models including the urinary flow rate as a covariate showed that a doubling of the air concentration of TCEP was associated with a 42-107 % increase in its metabolites, and a doubling of air concentration of TBOEP, with a 77 % increase. The paucity of data on the toxicokinetics of OPEs limits the determination of appropriate urinary metabolites to monitor OPE occupational exposure. Such additional data, in combination with workplace contextual information, may help clarify the major routes of exposure and the corresponding contributing sources.

An assessment of organophosphate ester mixtures and the placental transcriptome

Prenatal exposure to organophosphate ester (OPE) chemicals, commonly used as flame retardants and plasticizers, has been associated with adverse birth outcomes. The placenta is a critical fetal organ and therefore may be involved in pathogenesis of birth outcomes. The goal of this study was to evaluate associations of 10 maternal urinary OPE metabolites, individually and as a mixture, with the placental transcriptome at birth in the Conditions Affecting Neurocognitive Development and Learning in Early Childhood (CANDLE) study. Individual OPE metabolites were evaluated for associations with individual genes as well as co-expressed gene modules. Mixtures analysis was conducted using quantile g-computation. The analyses were performed with the entire data set (N = 737) as well as the sex-stratified subsets. Two genes (HAP1 and RAP1GAP) were associated with bis(1,3-dichloro-2-propyl) phosphate (BDCPP), and six genes were associated the mixture in the full data set. 3 genes were associated with diphenyl phosphate (DPHP) and 36 genes were associated with the mixture in a male stratified analysis. 2 genes were associated with DPHP, and 1 gene was associated with diethyl phosphate (DEP) in a female stratified analysis. Three gene modules were associated with BDCPP or diphenyl phosphate (DPHP) and one module was associated with the OPE mixture. 12 WGCNA modules were associated with individual OPE metabolites or the mixture in males, and 1 WGCNA module was associated with DEP in females. Five of the OPE-associated gene modules were enriched for a total of 17 KEGG pathways, and 11 modules were enriched with targets of 12 nuclear hormone receptor transcription factors. Overall, novel associations were identified between the placental transcriptome and OPE metabolites, individually and in mixture, including differences based on fetal sex. These findings highlight the need for additional research on mechanisms of OPE-associated gene expression changes in the placenta and associated health outcomes.

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.

Prenatal exposure to a mixture of organophosphate flame retardants and infant neurodevelopment: A prospective cohort study in Shandong, China

BACKGROUND

Previous studies have suggested that prenatal exposure to organophosphate flame retardants (OPFRs) may have adverse effect on early neurodevelopment, but limited data are available in China, and the overall effects of OPFRs mixture are still unclear.

OBJECTIVE

This study aimed to investigate the association between prenatal exposure to OPFR metabolites mixture and the neurodevelopment of 1-year-old infants.

METHODS

A total of 270 mother-infant pairs were recruited from the Laizhou Wan (Bay) Birth Cohort in China. Ten OPFR metabolites were measured in maternal urine. Neurodevelopment of 1-year-old infants was assessed using the Gesell Developmental Schedules (GDS) and presented by the developmental quotient (DQ) score. Multivariate linear regression and weighted quantile sum (WQS) regression models were conducted to estimate the association of prenatal exposure to seven individual OPFR metabolites and their mixture with infant neurodevelopment.

RESULTS

The positive rates of seven OPFR metabolites in the urine of pregnant women were greater than 70% with the median concentration ranged within 0.13-3.53 μg/g creatinine. The multivariate linear regression model showed significant negative associations between bis (1-chloro-2-propyl) phosphate (BCIPP), din-butyl phosphate (DnBP), and total OPFR metabolites exposure and neurodevelopment in all infants. Results from the WQS model consistently revealed that the OPFR metabolites mixture was inversely associated with infant neurodevelopment. Each quartile increased in the seven OPFR metabolites mixture was associated with a 1.59 decrease (95% CI: 2.96, -0.21) in gross motor DQ scores, a 1.41 decrease (95% CI: 2.38, -0.43) in adaptive DQ scores, and a 1.08 decrease (95% CI: 2.15, -0.02) in social DQ scores, among which BCIPP, bis (1, 3-dichloro-2-propyl) phosphate (BDCIPP) and DnBP were the main contributors.

CONCLUSION

Prenatal exposure to a mixture of OPFRs was negatively associated with early infant neurodevelopment, particularly in gross motor, adaptive, and social domains.

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.