Association between Urinary Metabolite Levels of Organophosphorus Flame Retardants and Serum Sex Hormone Levels Measured in a Reference Sample of the US General Population

Associations between urinary phthalate metabolites and reproductive, adrenal, and gonadotropic hormones in peripubertal children: the Hokkaido study

Phthalates have raised concerns regarding the disruption of hormone synthesis and signaling. The purpose of this study was to investigate the associations between urinary phthalate metabolites and 18 hormones, including reproductive, adrenal, and gonadotropic hormones, in peripubertal children. The study comprised a cross-sectional analysis of participants in the Hokkaido Birth Cohort Study. We collected data from 429 school children aged 9-12 living in Sapporo, Japan. Ten phthalate metabolites and 14 steroid hormones were analyzed using LC-MS/MS, whereas four peptide hormones were detected using immunoassays. Multivariable linear regression, quantile-based g-computation (qg-computation), and Bayesian kernel machine regression (BKMR) were used to investigate the associations between the individual phthalate metabolites and the phthalate mixtures with hormone levels, as well as with puberty based on hormone levels. In girls, we found that higher phthalate metabolite levels, as well as phthalate mixtures, were significantly associated with lower dehydroepiandrostenedione-sulfate (DHEA-S) and higher (androstenedione + testosterone)/DHEA-S. The higher phthalate mixture showed lower levels of LH, FSH, and cortisol levels among girls, whereas higher 11-deoxycortisol levels. In boys, a higher phthalates mixture was significantly associated with a higher estradiol/testosterone ratio, whereas lower levels of insulin-like factor-3 (INSL3), testosterone, (androstenedione + testosterone)/DHEA-S, testosterone/androstenedione, and cortisol/cortisone. Higher phthalate mixtures were associated with lower prevalence of puberty in girls. These findings indicate that phthalate exposure may disrupt the hormones in children during puberty.

Association of organophosphate flame retardants exposure with liver function and the contrasting mediating roles of inflammatory and oxidative stress pathways

Organophosphate flame retardants (OPFRs) have been widely used as alternatives to traditional halogenated flame retardants, resulting in their pervasive environmental presence and significant human exposure. While animal studies using high doses of individual OPFRs have demonstrated hepatotoxicity, evidence of hepatic effects from chronic and low-dose exposure to OPFRs in humans is scarce, and the underlying mechanisms remain largely unknown. In this study, we evaluated the association between urinary metabolites of OPFRs (mOPFRs) and liver function biomarkers in a population aged 1-79 years from the Guangzhou Human Biomonitoring Program. Urinary concentrations of diphenyl phosphate exhibited a significant decreasing trend with increasing age across four age groups (≤12, 13-17, 17-59, ≥60 years), while bis(1-chloro-2-propyl) phosphate concentrations showed a significant positive association with age. Urinary mOPFRs were positively associated with alanine aminotransferase, gamma-glutamyl transferase, and aspartate aminotransferase, and negatively associated with indirect bilirubin levels. Urinary mOPFRs were significantly correlated with total bilirubin, which was consistent with that observed in the National Health and Nutrition Examination Survey database, while other associations were inconsistent. Moreover, we evaluated the roles of inflammatory and oxidative stress markers in the association between urinary mOPFRs and liver function biomarkers by mediation analysis. The results demonstrated that the mediation effects of inflammatory markers were consistent with the total and direct effects of mOPFRs on liver function biomarkers, whereas the mediation effects of oxidative stress markers were discrepant. Inflammation likely exacerbates the adverse effects of OPFRs on liver function, while oxidative stress may play a protective role. We further searched the comparative toxicogenomics database for genes associated with OPFRs and liver function biomarkers to understand the potential regulatory mechanisms.

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 0.9 ng/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.

Degradation of organophosphate flame retardants by white-rot fungi: Degradation pathways and associated toxicity

The environmental persistence of organophosphate flame retardants (OPFRs) in water is becoming and environmental concern. White Rot Fungi (WRF) have proven its capability to degrade certain OPFRs such as tributyl phosphate (TBP), tris(2-butoxyethyl) phosphate (TBEP), tris(2-chloroethyl) phosphate (TCEP) and tris(2-chloroisopropyl) phosphate (TCPP). Despite this capability, there is limited knowledge about the specific pathways involved in the degradation. In this study, three different WRF were paired with individual OPFRs, and potential transformation products (TPs) were identified by UHPLC-HRMS. Some compounds structures were further validated by NMR. From these data degradation pathways were proposed. TBP was degraded by successive hydroxylation and hydrolysis reactions, with a novel dehydrogenation step suggested. Both TCEP and TCPP underwent oxidative dechlorination, with TCEP experiencing subsequent hydrolysis. Uncommon reductive dehalogenation was also observed. TCPP further underwent hydroxylation and environmentally relevant methylation. TBEP generated numerous TPs, mainly by successive dealkylations, along with hydroxylation. Notably, demethylation in TBEP degradation was proposed for the first time. Additional secondary products were formed through hydroxylation and oxidation of the initial metabolites. Finally, in vivo and in silico toxicity assessments were conducted, identifying certain TPs as potentially toxic.

Exposure to organophosphate esters and maternal-child health

Organophosphate esters (OPEs) are a class of chemicals now widely used as flame retardants and plasticizers after the phase-out of polybrominated diphenyl ethers (PBDEs). However, OPEs carry their own risk of developmental toxicity, which poses concern for recent birth cohorts as they have become ubiquitous in the environment. In this review, we summarize the literature evaluating the association between OPE exposure and maternal, perinatal, and child health outcomes. We included original articles investigating associations of OPE exposure with any health outcome on pregnant women, newborns, children, and adolescents. We found 48 articles on this topic. Of these, five addressed maternal health and pregnancy outcomes, 24 evaluated prenatal OPE exposure and child health, 18 evaluated childhood OPE exposure and child/adolescent health, and one article evaluated both prenatal and childhood OPE exposure. These studies suggest that OPE exposure is possibly associated with a wide range of adverse health outcomes, including pregnancy loss, altered gestational duration and smaller birthweight, maternal and neonatal thyroid dysfunction, child metabolic dysregulation and abnormal growth, impaired neurodevelopment, and changes in immune response. Many of the reported outcomes associated with OPE exposure varied by child sex. Findings also varied substantially by OPE metabolite and exposure time. The OPEs most frequently measured, detected, and found to be associated with health outcomes were triphenyl phosphate (TPHP, metabolized to DPHP) and tris(1,3-dichloro-2-propyl) phosphate (TDCIPP, metabolized to BDCIPP). The extensive range of health outcomes associated with OPEs raises concern about their growing use in consumer products; however, these findings should be interpreted considering the limitations of these epidemiological studies, such as possible exposure misclassification, lack of generalizability, insufficient adjustment for covariates, and failure to consider chemical exposures as a mixture.

Global environmental and toxicological impacts of polybrominated diphenyl ethers versus organophosphate esters: A comparative analysis and regrettable substitution dilemma

The prevalence of organophosphate esters (OPEs) in the global environment is increasing, which aligns with the decline in the usage of polybrominated diphenyl ethers (PBDEs). PBDEs, a category of flame retardants, were banned and classified as persistent organic pollutants (POPs) through the Stockholm Convention due to their toxic and persistent properties. Despite a lack of comprehensive understanding of their ecological and health consequences, OPEs were adopted as replacements for PBDEs. This research aims to offer a comparative assessment of PBDEs and OPEs in various domains, specifically focusing on their persistence, bioaccumulation, and toxicity (PBT) properties. This study explored physicochemical properties (such as molecular weight, octanol-water partition coefficient, octanol-air partition coefficient, Henry's law constant, and vapor pressures), environmental behaviors, global concentrations in environmental matrices (air, water, and soil), toxicities, bioaccumulation, and trophic transfer mechanisms of both groups of compounds. Based on the comparison and analysis of environmental and toxicological data, we evaluate whether OPEs represent another instance of regrettable substitution and global contamination as much as PBDEs. Our findings indicate that the physical and chemical characteristics, environmental behaviors, and global concentrations of PBDEs and OPEs, are similar and overlap in many instances. Notably, OPE concentrations have even surged by orders of several magnitude compared to PBDEs in certain pristine regions like the Arctic and Antarctic, implying long-range transport. In many instances, air and water concentrations of OPEs have been increased than PBDEs. While the bioaccumulation factors (BAFs) of PBDEs (ranging from 4.8 to 7.5) are slightly elevated compared to OPEs (-0.5 to 5.36) in aquatic environments, both groups of compounds exhibit BAF values beyond the threshold of 5000 L/kg (log10 BAF > 3.7). Similarly, the trophic magnification factors (TMFs) for PBDEs (ranging from 0.39 to 4.44) slightly surpass those for OPEs (ranging from 1.06 to 3.5) in all cases. Metabolic biotransformation rates (LogKM) and hydrophobicity are potentially major factors deciding their trophic magnification potential. However, many compounds of PBDEs and OPEs show TMF values higher than 1, indicating biomagnification potential. Collectively, all data suggest that PBDEs and OPEs have the potential to bioaccumulate and transfer through the food chain. OPEs and PBDEs present a myriad of toxicity endpoints, with notable overlaps encompassing reproductive issues, oxidative stress, developmental defects, liver dysfunction, DNA damage, neurological toxicity, reproductive anomalies, carcinogenic effects, and behavior changes. Based on our investigation and comparative analysis, we conclude that substituting PBDEs with OPEs is regrettable based on PBT properties, underscoring the urgency for policy reforms and effective management strategies. Addressing this predicament before an exacerbation of global contamination is imperative.

Role of inflammatory lipid and fatty acid metabolic abnormalities induced by plastic additives exposure in childhood asthma

Lipid metabolism play an essential role in occurrence and development of asthma, and it can be disturbed by phthalate esters (PAEs) and organophosphate flame retardants (OPFRs). As a chronic inflammatory respiratory disease, the occurrence risk of childhood asthma is increased by PAEs and OPFRs exposure, but it remains not entirely clear how PAEs and OPFRs contribute the onset and progress of the disease. We have profiled the serum levels of PAEs and OPFRs congeners by liquid chromatography coupled with mass spectrometry, and its relationships with the dysregulation of lipid metabolism in asthmatic, bronchitic (acute inflammation) and healthy (non-inflammation) children. Eight PAEs and nine OPFRs congeners were found in the serum of children (1 - 5 years old) from Shenzhen, and their total median levels were 615.16 ng/mL and 17.06 ng/mL, respectively. Moreover, the serum levels of mono-methyl phthalate (MMP), tri-propyl phosphate (TPP) and tri-n-butyl phosphate (TNBP) were significant higher in asthmatic children than in healthy and bronchitic children as control. Thirty-one characteristic lipids and fatty acids of asthma were screened by machine-learning random forest model based on serum lipidome data, and the alterations of inflammatory characteristic lipids and fatty acids including palmitic acids, 12,13-DiHODE, 14,21-DiHDHA, prostaglandin D2 and LysoPA(18:2) showed significant correlated with high serum levels of MMP, TPP and TNBP. These results imply PAEs and OPFRs promote the occurrence of childhood asthma via disrupting inflammatory lipid and fatty acid metabolism, and provide a novel sight for better understanding the effects of plastic additives on childhood asthma.

Association of blood metals with serum sex hormones in adults: A cross-sectional study

Heavy metals such as lead, mercury, and cadmium have been identified to have negative impacts on human health. Although the individual effects of these metals have been extensively researched, the present study aims to explore their combined effects and their association with serum sex hormones among adults. Data for this study were obtained from the general adult population of the 2013-2016 National Health and Nutrition Survey (NHANES) and included five metal (mercury, cadmium, manganese, lead, and selenium) exposures and three sex hormones (total testosterone [TT], estradiol [E2], and sex hormone-binding globulin [SHBG]) levels. The free androgen index (FAI) and TT/E2 ratio were also calculated. The relationships between blood metals and serum sex hormones were analysed using linear regression and restricted cubic spline regression. The effect of blood metal mixtures on sex hormone levels was examined using the quantile g-computation (qgcomp) model. There were 3,499 participants in this study, including 1,940 males and 1,559 females. In males, positive relationships between blood cadmium and serum SHBG (β=0.049 [0.006, 0.093]), lead and SHBG (β=0.040 [0.002, 0.079]), manganese and FAI (β=0.080 [0.016, 0.144]), and selenium and FAI (β=0.278 [0.054, 0.502]) were observed. In contrast, manganese and SHBG (β=-0.137 [-0.237, -0.037]), selenium and SHBG (β=-0.281 [-0.533, -0.028]), and manganese and TT/E2 ratio (β=-0.094 [-0.158, -0.029]) were negative associations. In females, blood cadmium and serum TT (β=0.082 [0.023, 0.141]), manganese and E2 (β=0.282 [0.072, 0.493]), cadmium and SHBG (β=0.146 [0.089, 0.203]), lead and SHBG (β=0.163 [0.095, 0.231]), and lead and TT/E2 ratio (β=0.174 [0.056, 0.292]) were positive relationships, while lead and E2 (β=-0.168 [-0.315, -0.021]) and FAI (β=-0.157 [-0.228, -0.086]) were negative associations. This correlation was stronger among elderly women (>50 years old). The qgcomp analysis revealed that the positive effect of mixed metals on SHBG was mainly driven by cadmium, while the negative effect of mixed metals on FAI was mainly driven by lead. Our findings indicate that exposure to heavy metals may disrupt hormonal homeostasis in adults, particularly in older women.

Organophosphorus insecticides exposure and sex hormones in general U.S. population: A cross-sectional study

BACKGROUND

Evidence showed organophosphorus (OPs) insecticide exposure is common in general population with endocrine-disrupting effects. However, the association between OPs metabolites and sex hormones remains unclear.

OBJECTIVE

To investigate the association between OPs metabolites and sex hormones.

METHODS

Data of 1438 participants from NHANES 2015-2016 was applied. Urinary OPs metabolites, dialkyl phosphates (DAPs), and serum sex hormones (total testosterone (TT), estradiol (E₂), and sex hormone-binding globulin (SHBG)) were measured. Free androgen index (FAI) and TT/E₂ ratio were also calculated. The generalized linear regression model and restricted cubic spline (RCS) model were employed to evaluate the association and exposure-response curve of DAPs and sex hormones in males and females. The modulation effect of age on their associations in female participants was also explored.

RESULTS

After adjusting for confounding factors, DETP was negatively associated with E₂ (β = -0.03; 95% CI: -0.05, -0.01) and FAI (β = -0.03; 95% CI: -0.06, -0.001) in males. In females, all the four DAP metabolites (DMP, DEP, DMTP, and DETP) were negatively associated with FAI (DMP: β = -0.06, 95% CI: -0.11, -0.01; DEP: β = -0.06, 95% CI: -0.12, -0.01; DMTP: -0.05, 95% CI: -0.09, -0.02; DETP: -0.09, 95% CI: -0.14, -0.04). DETP was also found negatively associated with TT and TT/E₂ ratio in females. The associations between DETP and TT, FAI, and TT/E₂ ratio were modified by gender (P_interaction<0.05). RCS analysis found these associations were in linear decreased exposure-response curves. For females of different age groups, the inverse associations of DETP with TT and FAI remained stable. Decreased FAI with DMP and DMTP was also found in females ≤50 years old.

CONCLUSIONS

Our study indicates OPs metabolites had negative associations with androgen indicators, which was characterized as decreased FAI and E₂ in males and decreased TT, FAI, and TT/E₂ ratio in females, particularly among females ≤50 years old. Further studies are warranted in larger-scale populations.

E-Cigarettes Reexamined: Product Toxicity

The introduction of e-cigarettes, or electronic nicotine delivery systems (ENDS), has been accompanied by controversy regarding their safety and effectiveness as a cessation aid and by an explosion in their use by youth. Their use does not involve the combustion of tobacco and the creation of harmful combustion products; they have been seen as a "harm reduction" tool that may be of assistance in promoting smoking cessation. Recognition that ENDS can deliver an array of chemicals and materials with known adverse consequences has spurred more careful examination of these products. Nicotine, nitrosamines, carbonyl compounds, heavy metals, free radicals, reactive oxygen species, particulate matter, and "emerging chemicals of concern" are among the constituents of the heated chemical aerosol that is inhaled when ENDS are used. They raise concerns for cardiovascular and respiratory health that merit the attention of clinicians and regulatory agencies. Frequently cited concerns include evidence of disordered respiratory function, altered hemodynamics, endothelial dysfunction, vascular reactivity, and enhanced thrombogenesis. The absence of evidence of the consequences of their long-term use is of additional concern. Their effectiveness as cessation aids and beneficial impact on health outcomes continue to be examined. It is important to ensure that their production and availability are thoughtfully regulated to optimise their safety and permit their use as harm reduction devices and potentially as smoking-cessation aids. It is equally vital to effectively prevent them from becoming ubiquitous consumer products with the potential to rapidly induce nicotine addiction among large numbers of youth. Clinicians should understand the nature of these products and the implications of their use.

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

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

Emerging Chemicals of Health Concern in Electronic Nicotine Delivery Systems

Electronic nicotine delivery systems (ENDS), by virtue of their highly engineered construction (plastics, glass, e-liquids), may contain a number of emerging chemicals of concern (ECCs), including phthalates, phenolic compounds, and flame retardants. Current knowledge regarding the safety of ENDS may underestimate the health risks from ECCs. In this study, we examined the types and levels of those three groups of chemicals in the components and parts of ENDS devices, including refill liquids, tanks/cartridges, atomizers, drip tips/mouthpieces, and sealing materials. Our results suggest that phthalates were the most prevalent chemicals in all tested samples, followed by parabens and organophosphate flame retardants (OPFRs). Particularly, all measured chemicals had significantly higher detection rates in cartridges/tanks, drip tips/mouthpieces, and sealing materials in contrast to e-liquids and coil samples. Among all those three types of ENDS components, phthalates generally had the highest concentrations (0.279-3790 ng/unit) in the drip tip/mouthpiece samples, followed by the sealing materials (0.380-508.8 ng/unit) and the empty tank/cartridge samples (up to 761.7 ng/unit). For parabens, highest concentrations were observed in drip tip/mouthpiece samples (1.152-130.1 ng/unit), followed by sealing materials (0.220-30.08 ng/unit) and the tank/cartridge samples (1.794-34.24 ng/unit). For OPFRs, tris(1,3-dichloro-2-propyl) phosphate had the highest concentrations (39.40-774.1 ng/unit) in all component samples. High concentrations (20.25-260.4 ng/unit) were also observed for several OPFRs in sealing materials and drip tip/mouthpiece samples. These findings will contribute to addressing the information gaps pertinent to the presence of ECCs in ENDS and will warrant further studies for understanding the potential negative health effects and to what extent those chemicals may cause potential negative health effects when using the ENDS. The findings will also contribute to developing evidence-based standards for the regulatory control of the types and levels of ECCs in ENDS products.