Development and application of simple pharmacokinetic models to study human exposure to di-n-butyl phthalate (DnBP) and diisobutyl phthalate (DiBP)

A systematic review of global distribution, sources and exposure risk of phthalate esters (PAEs) in indoor dust

Phthalate esters (PAEs) are a class of plasticizers that are readily released from plastic products, posing a potential exposure risk to human body. At present, much attention is paid on PAE concentrations in indoor dust with the understanding of PAEs toxicity. This study collected 8187 data on 10 PAEs concentrations in indoor dusts from 26 countries and comprehensively reviewed the worldwide distribution, influencing factors, and health risks of PAEs. Di-(2-ethylhexyl) phthalate (DEHP) is the predominant PAE with a median concentration of 316 μg·g-1 in indoor dust. Polyvinyl chloride wallpaper and flooring and personal care products are the main sources of PAEs indoor dust. The dust concentrations of DEHP show a downward trend over the past two decades, while high dust concentrations of DiNP are found from 2011 to 2016. The median dust contents of 8 PAEs in public places are higher than those in households. Moreover, the concentrations of 9 PAEs in indoor dusts from high-income countries are higher than those from upper-middle-income countries. DEHP in 69.8% and 77.8% of the dust samples may pose a potential carcinogenic risk for adults and children, respectively. Besides, DEHP in 16.9% of the dust samples may pose a non-carcinogenic risk to children. Nevertheless, a negligible risk was found for other PAEs in indoor dust worldwide. This review contributes to an in-depth understanding of the global distribution, sources and health risks of PAEs in indoor dust.

Associations between medication use and phthalate metabolites in urine and follicular fluid among women undergoing in vitro fertilization

BACKGROUND

Phthalates, which are used as excipients of drugs, have been related to adverse reproductive outcomes. However, the relationships between medication use and phthalate exposure among women undergoing in vitro fertilization (IVF) have not been studied.

OBJECTIVE

To investigate the associations between the medication intake and phthalate metabolites in urine and follicular fluid (FF).

METHOD

Eight phthalate metabolites were measured in urine and FF samples from 274 women undergoing IVF using liquid chromatography-tandem mass spectrometry. Information on recent medication intake was obtained via interview by trained staff. We constructed generalized linear regression models to examine the associations of medication intake with phthalate metabolite concentrations and dose-response relationships between the number of medicines used and metabolite concentrations in two matrices.

RESULTS

Four of 10 drugs were used by more than 10% of the participants, including vitamins (23.0%), traditional Chinese medicine (TCM, 22.3%), antioxidants (12.4%) and amoxicillin (10.2%). Participants who had used TCM had 26.0% (95% CI: 0.0, 58.8%), 32.6% (95% CI: 4.2, 68.8%) and 32.3% (95% CI: 2.6, 70.6%) higher urinary mono-n-butyl phthalate (MBP), mono(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP) and mono(2-ethyl-5-oxohexyl) phthalate (MEOHP) concentrations, respectively, than those who had not. Antioxidant intake was associated with a 30.6% (95% CI: -48.5, -6.6%) decrease in the urinary MBP concentration. Compared with non-users, women who reported the use of medicines had 53.2% (95% CI: 2.7, 128.5%) higher concentrations of MMP and a 37.7% (95% CI: -60.7, -1.5%) lower level of MBP in FF, respectively.

CONCLUSION

Our data suggest that the intake of some medications may increase phthalate exposure among women undergoing IVF.

Human risk assessment of di-isobutyl phthalate through the application of a developed physiologically based pharmacokinetic model of di-isobutyl phthalate and its major metabolite mono-isobutyl phthalate

Di-isobutyl phthalate (DiBP) is a substance used in the production of objects frequently used in human life. Mono-isobutyl phthalate (MiBP), a major in vivo metabolite of DiBP, is a biomarker for DiBP exposure assessment. Therefore, risk assessment studies on DiBP and MiBP, which have not yet been reported in detail, are needed. The aim of this study was to develop and evaluate a physiologically based pharmacokinetic (PBPK) model for DiBP and MiBP in rats and extend this to human risk assessment based on human exposure. Pharmacokinetic studies were performed in male rats following the administration of 5-100 mg/kg DiBP, and these results were used for the development and validation of the PBPK model. In addition, the previous pharmacokinetic results in female rats following DiBP administration and the pharmacokinetic results in both males and females according to multiple exposures to DiBP were used to develop and validate the PBPK model. The metabolism of DiBP to MiBP in the body was very significant and rapid, and the biodistribution of MiBP was broad and major. Furthermore, the amount of MiBP in the body showed a correlation with DiBP exposure, and from this, a PBPK model was developed to evaluate the external exposure of DiBP from the internal exposure of MiBP. The predicted rat plasma, urine, fecal, and tissue concentrations using the developed PBPK model fitted well with the observed values. The established PBPK model for rats was extrapolated to a human PBPK model of DiBP and MiBP based on human physiological parameters and allometric scaling. The reference dose of 0.512 mg/kg/day of DiBP and external doses of 6.14-280.90 μg/kg/day DiBP for human risk assessment were estimated using Korean biomonitoring values. Valuable insight and approaches to assessing human health risks associated with DiBP exposure were provided by this study.

Testicular dysgenesis syndrome and phthalate exposure: A review of literature

Endocrine disruptors are chemicals that interfere with the body's endocrine system and cause adverse effects in biological systems. Phthalates are a group of man-made chemicals which are mainly used as plasticizers and classified as endocrine disruptors. They are also used in cosmetic and personal care products as color or smell fixators. Moreover, phthalates are present in inks, adhesives, sealants, automobile parts, tools, toys, carpets, medical tubing and blood storage bags, and food packages. Pathological condition known as "testicular dysgenesis syndrome" (TDS) or "phthalate syndrome" is usually linked to phthalate exposure and is coined to describe the rise in alterations in reproductive health in men, such as reduced semen quality (decrease in sperm counts, sperm motility and increase in abnormal sperms), hypospadias, cryptorchidism, reduced anogenital distance and early-life testicular cancer. Phthalates are suggested to cause direct effect on gonadal and non-gonadal tissues, impair the differentiation and morphogenesis of seminiferous tubules and accessory sex organs and testicular cells (both Sertoli and Leydig cells), alter estradiol and/or testosterone levels, decrease insulin-like 3 (INSL3) peptide production, impair spermatogenesis and lead to epigenetic alterations, all of which may lead to TDS. This review will mainly focus on phthalates as causes of TDS and their mechanisms of action.

Modeling the bioaccessibility of inhaled semivolatile organic compounds in the human respiratory tract

The bioaccessibility of semivolatile organic compounds (SVOCs) via inhalation has rarely been studied, as indicated by the literature. There is no model to calculate the SVOC bioaccessibility following inhalation, and measurement data have focused on only a few polycyclic aromatic hydrocarbons (PAHs) in the particle phase. The present work developed a mechanistic model to address the mass transfer of inhaled SVOCs among the gas, particle and mucus phases in the human respiratory tract. The model considers (1) the SVOC partitioning between the gas and particle phases as well as between the gas and mucus phases and (2) the deposition of gas- and particle-phase SVOCs in the mucus of the respiratory tract. Based on the model, the inhalation bioaccessibility for 72 SVOCs was calculated. The SVOCs were measured in French dwellings at the nationwide scale, and their median concentrations in both the gas and particle phases were used for the bioaccessibility calculations. The results show that the inhalation bioaccessibility varies considerably from one compound to another, e.g., between 0.62 and 1.00 for phthalates, between 0.71 and 0.79 for polybrominated diphenyl ethers (PBDEs), between 0.48 and 0.56 for polychlorinated biphenyls (PCBs), between 0.48 and 1.00 for different chemical families of pesticides and between 0.48 and 0.90 for PAHs.

Variations of phthalate exposure and metabolism over three trimesters

Maternal exposure to phthalates may cause some adverse health effects on both mother and fetus, but variations of phthalate exposure and metabolism during pregnancy have not been thoroughly characterized. A total of 946 participants were selected from a cohort study conducted in Wuhan between 2014 and 2015 through which they had provided a complete set of urine samples at three trimesters. Eight phthalate metabolites were analyzed in 2838 urine samples. Based on urinary concentrations, various parameters (i.e. phthalate metabolite concentrations, ratios of metabolites of bis(2-ethylhexyl) phthalate (DEHP) in DEHP, and percentages of individual metabolites in total phthalates) were compared over three visits. We observed that levels of phthalate metabolites showed a U-shaped trend across three trimesters. The significant variations in the ratios of DEHP metabolites indicated that the efficiency in metabolizing DEHP declined during pregnancy and less recent exposure occurred in mid-pregnancy. The changes of percentages of individual compound in total phthalates suggested the inconsistent pattern over trimesters. This longitudinal study found that the exposure pattern, exposure timing and metabolic susceptibility varied by trimesters, which suggests that urine samples should be collected at multiple time points and mothers should be especially careful in the early pregnancy.

Temporal Trends in Exposures to Six Phthalates from Biomonitoring Data: Implications for Cumulative Risk

Phthalates are used in a wide range of consumer goods, resulting in exposures to specific phthalates that vary over time in accordance with changes in product use and how phthalates are utilized. We investigated trends in estimates of daily intake dose and several cumulative risk metrics, including the Hazard Quotient (HQ), Hazard Index (HI), and Maximum Cumulative Ratio (MCR) for six phthalates from 2005 to 2014 using metabolite biomonitoring data collected from spot urine samples under the National Health and Nutrition Examination Survey (NHANES). Over this period, there was a 2.2-fold decrease in the mean HI (0.34 to 0.15) and a 7.2-fold decrease in the percentage of participants with an HI > 1 (5.7% to 0.8%), indicating an overall decrease in combined exposure to these phthalates. Children (aged 6-11 years) had higher mean HI values than either adolescents (aged 12-19 years) or adults (aged 20+ years) during this period. MCR values were generally low and inversely correlated with HI. This indicated that a single phthalate usually drove the hazards for highly exposed individuals. However, the average value of MCR increased 1.2-fold (1.7-2.1) over this period indicating an increasing need to consider exposures to multiple phthalates in this group.

Multi-pathway human exposure assessment of phthalate esters and DINCH

Phthalate esters are substances mainly used as plasticizers in various applications. Some have been restricted and phased out due to their adverse health effects and ubiquitous presence, leading to the introduction of alternative plasticizers, such as DINCH. Using a comprehensive dataset from a Norwegian study population, human exposure to DMP, DEP, DnBP, DiBP, BBzP, DEHP, DINP, DIDP, DPHP and DINCH was assessed by measuring their presence in external exposure media, allowing an estimation of the total intake, as well as the relative importance of different uptake pathways. Intake via different uptake routes, in particular inhalation, dermal absorption, and oral uptake was estimated and total intake based on all uptake pathways was compared to the calculated intake from biomonitoring data. Hand wipe results were used to determine dermal uptake and compared to other exposure sources such as air, dust and personal care products. Results showed that the calculated total intakes were similar, but slightly higher than those based on biomonitoring methods by 1.1 to 3 times (median), indicating a good understanding of important uptake pathways. The relative importance of different uptake pathways was comparable to other studies, where inhalation was important for lower molecular weight phthalates, and negligible for the higher molecular weight phthalates and DINCH. Dietary intake was the predominant exposure route for all analyzed substances. Dermal uptake based on hand wipes was much lower (median up to 2000 times) than the total dermal uptake via air, dust and personal care products. Still, dermal uptake is not a well-studied exposure pathway and several research gaps (e.g. absorption fractions) remain. Based on calculated intakes, the exposure for the Norwegian participants to the phthalates and DINCH was lower than health based limit values. Nevertheless, exposure to alternative plasticizers, such as DPHP and DINCH, is expected to increase in the future and continuous monitoring is required.

Probing the relationship between external and internal human exposure of organophosphate flame retardants using pharmacokinetic modelling

Human external exposure (i.e. intake) of organophosphate flame retardants (PFRs) has recently been quantified, but no link has yet been established between external and internal exposure. In this study, we used a pharmacokinetic (PK) model to probe the relationship between external and internal exposure data for three PFRs (EHDPHP, TNBP and TPHP) available for a Norwegian cohort of 61 individuals from 61 different households. Using current literature on metabolism of PFRs, we predicted the metabolite serum/urine concentrations and compared it to measured data from the study population. Unavailable parameters were estimated using a model fitting approach (least squares method) after assigning reasonable constraints on the ranges of fitted parameters. Results showed an acceptable comparison between PK model estimates and measurements (<10-fold deviation) for EHDPHP. However, a deviation of 10-1000 was observed between PK model estimates and measurements for TNBP and TPHP. Sensitivity and uncertainty analysis on the PK model revealed that EHDPHP results showed higher uncertainty than TNBP or TPHP. However, there are indications that (1) current biomarkers of exposure (i.e. assumed metabolites) for TNBP and TPHP chemicals might not be specific and ultimately affecting the outcome of the modelling and (2) some exposure pathways might be missing. Further research, such as in vivo laboratory metabolism experiments of PFRs including identification of better biomarkers will reduce uncertainties in human exposure assessment.

Linking a dermal permeation and an inhalation model to a simple pharmacokinetic model to study airborne exposure to di(n-butyl) phthalate

Six males clad only in shorts were exposed to high levels of airborne di(n-butyl) phthalate (DnBP) and diethyl phthalate (DEP) in chamber experiments conducted in 2014. In two 6 h sessions, the subjects were exposed only dermally while breathing clean air from a hood, and both dermally and via inhalation when exposed without a hood. Full urine samples were taken before, during, and for 48 h after leaving the chamber and measured for key DnBP and DEP metabolites. The data clearly demonstrated high levels of DnBP and DEP metabolite excretions while in the chamber and during the first 24 h once leaving the chamber under both conditions. The data for DnBP were used in a modeling exercise linking dose models for inhalation and transdermal permeation with a simple pharmacokinetic model that predicted timing and mass of metabolite excretions. These models were developed and calibrated independent of these experiments. Tests included modeling of the "hood-on" (transdermal penetration only), "hood-off" (both inhalation and transdermal) scenarios, and a derived "inhalation-only" scenario. Results showed that the linked model tended to duplicate the pattern of excretion with regard to timing of peaks, decline of concentrations over time, and the ratio of DnBP metabolites. However, the transdermal model tended to overpredict penetration of DnBP such that predictions of metabolite excretions were between 1.1 and 4.5 times higher than the cumulative excretion of DnBP metabolites over the 54 h of the simulation. A similar overprediction was not seen for the "inhalation-only" simulations. Possible explanations and model refinements for these overpredictions are discussed. In a demonstration of the linked model designed to characterize general population exposures to typical airborne indoor concentrations of DnBP in the United States, it was estimated that up to one-quarter of total exposures could be due to inhalation and dermal uptake.

Urinary concentrations of 25 phthalate metabolites in Brazilian children and their association with oxidative DNA damage

Exposure of humans to phthalates has received considerable attention due to the ubiquitous occurrence and potential adverse health effects of these chemicals. Nevertheless, little is known about the exposure of the Brazilian population to phthalates. In this study, concentrations of 25 phthalate metabolites were determined in urine samples collected from 300 Brazilian children (6-14years old). Further, the association between urinary phthalate concentrations and a biomarker of oxidative stress, 8-hydroxy-2'-deoxyguanosine (8OHDG), was examined. Overall, eleven phthalate metabolites were found in at least 95% of the samples analyzed. The highest median concentrations were found for monoethyl phthalate (mEP; 57.3ngmL^-1), mono-(2-ethyl-5-carboxypentyl) phthalate (mECPP; 52.8ngmL^-1), mono-isobutyl phthalate (mIBP; 43.8ngmL^-1), and mono-n-butyl phthalate (mBP; 42.4ngmL^-1). The secondary metabolites of di(2-ethylhexyl) phthalate (DEHP), and mEP, mIBP, and mBP were the most abundant compounds, accounting for >90% of the total concentrations. On the basis of the measured concentrations of urinary phthalate metabolites, we estimated daily intakes of the parent phthalates, which were 0.3, 1.7, 1.8, 2.1, and 7.2μg/kg-bw/day for dimethyl phthalate, di-n-butyl phthalate, diisobutyl phthalate, diethyl phthalate, and DEHP, respectively. Approximately one-quarter of the Brazilian children had a hazard index of >1 for phthalate exposures. Statistically significant positive associations were found between 8OHDG and the concentration of the sum of phthalate metabolites, sum of DEHP metabolites, mEP, mIBP, mBP, monomethyl phthalate, mono(3-carboxypropyl) phthalate, monobenzyl phthalate, monocarboxyoctyl phthalate, monocarboxynonyl phthalate, monoisopentyl phthalate, and mono-n-propyl phthalate. To the best of our knowledge, this is the first study to report the exposure of a Brazilian population to phthalates.

Estimating uptake of phthalate ester metabolites into the human nail plate using pharmacokinetic modelling

There is a lack of knowledge regarding uptake of phthalate esters (PEs) and other chemicals into the human nail plate and thus, clarity concerning the suitability of human nails as a valid alternative matrix for monitoring long-term exposure. In particular, the relative importance of internal uptake of phthalate metabolites (from e.g. blood) compared to external uptake pathways is unknown. This study provides first insights into the partitioning of phthalate-metabolites between blood and nail using pharmacokinetic (PK) modelling and biomonitoring data from a Norwegian cohort. A previously published PK model (Lorber PK model) was used in combination with measured urine data to predict serum concentrations of DEHP and DnBP/DiBP metabolites at steady state. Then, partitioning between blood and nail was assessed assuming equilibrium conditions and treating the nail plate as a tissue, assuming a fixed lipid and water content. Although calculated as a worst-case scenario at equilibrium, the predicted nail concentrations of metabolites were lower than the biomonitoring data by factors of 44 to 1300 depending on the metabolite. It is therefore concluded that internal uptake of phthalate metabolites from blood into nail is a negligible pathway and does not explain the observed nail concentrations. Instead, external uptake pathways are more likely to dominate, possibly through deposition of phthalates onto the skin/nail and subsequent metabolism. Modelling gaseous diffusive uptake of PEs from air to nail revealed that this pathway is unlikely to be important. Experimental quantification of internal and external uptake pathways of phthalates and their metabolites into the human nail plate is needed to verify these modelling results. However, based on this model, human nails are not a good indicator of internal human exposure for the phthalate esters studied.

Associations of urinary phthalate and phenol biomarkers with menarche in a multiethnic cohort of young girls

To study potential environmental influences on puberty in girls, we investigated urinary biomarkers in relation to age at menarche. Phenols and phthalates were measured at baseline (6-8 years of age). Menarche was ascertained over 11 years for 1051 girls with menarche and biomarkers. Hazards ratios were estimated from Cox models adjusted for race/ethnicity and caregiver education (aHR, 95% confidence intervals [CI] for 5th vs 1st quintile urinary biomarker concentrations). 2,5-Dichlorophenol was associated with earlier menarche (aHR 1.34 [1.06-1.71]); enterolactone was associated with later menarche (aHR 0.82 [0.66-1.03]), as was mono-3-carboxypropyl phthalate (MCPP) (aHR 0.73 [0.59-0.91]); the three p-trends were <0.05. Menarche differed by 4-7 months across this range. Enterolactone and MCPP associations were stronger in girls with below-median body mass index. These analytes were also associated with age at breast development in this cohort. Findings from this prospective study suggest that some childhood exposures are associated with pubertal timing.

Exposure Estimation for Risk Assessment of the Phthalate Incident in Taiwan

Background

In May 2011, di(2-ethylhexyl) phthalates (DEHP) and, to a lesser extent, di-iso-nonyl phthalate (DiNP) were found to have been illegally used for many years in Taiwan as clouding agents in foods including sports drinks, juice beverages, tea drinks, fruit jam/nectar/jelly, and health or nutrient supplements.

Objective

To estimate the DEHP exposure for the study participants for the follow-up epidemiological study and health risk assessment.

Methods

A total of 347 individuals possibly highly exposed to phthalate-tainted foods participated in the study. Exposure assessment was performed based on the participants' responses to a structured questionnaire, self-report of exposure history, urinary metabolite concentrations, and DEHP concentration information in 2449 food records. A Bayesian statistical approach using Markov chain Monte Carlo simulation was employed to deal with the uncertainties in the DEHP concentrations of the contaminated foods and the participants' likelihood of being exposed.

Results

An estimated 37% and 15% of children younger than 12 years old were exposed to DEHP at medium (20–50 μg / kg_bw / day) and high AvDIs (50–100 μg / kg_bw / day), respectively, prior to the episode (9% and 3% in adults, respectively). Moreover, 11% of children and 1% of adults were highly exposed (> 100 μg / kg_bw / day), with a maximum of 414.1 μg / kg_bw / day and 126.4 μg / kg_bw / day, respectively.

Conclusions

The phthalate exposure-associated adverse health effects for these participants warrant further investigation. The estimation procedure may be applied to other exposure assessment with various sources of uncertainties.

Development of a Highly Specific Fluorescence Immunoassay for Detection of Diisobutyl Phthalate in Edible Oil Samples

The diisobutyl phthalate (DiBP) hapten containing an amino group was synthesized successfully, and the polyclonal antibody against 4-amino phthalate-bovine serum albumin (BSA) was developed. On the basis of the polyclonal antibody, a rapid and sensitive indirect competitive fluorescence immunoassay (icFIA) has been established to detect DiBP in edible oil samples for the first time. Under the optimized conditions, the quantitative working range of the icFIA was from 10.47 to 357.06 ng/mL (R(2) = 0.991), exhibiting a detection limit of 5.82 ng/mL. In this assay, the specific results showed that other similar phthalates did not significantly interfere with the analysis, with the cross-reactivity less than 1.5%, except for that of DiBAP. Thereafter, DiBP contamination in edible oil samples was detected by icFIA, with the recovery being from 79 to 103%. Furthermore, the reliability of icFIA was validated by gas chromatography-mass spectrometry (GC-MS). Therefore, the developed icFIA is suitable for monitoring DiBP in some edible oil samples.

Development of a multi-compartment pharmacokinetic model to characterize the exposure to Hexamoll® DINCH®

We developed and calibrated a multi compartment pharmacokinetic (PK) model to predict urinary concentrations after oral exposure of four specific DINCH metabolites: MINCH, OH-MINCH, cx-MINCH, and oxo-MINCH. This descriptive model has 4 compartments: a "stomach" (SC) compartment, a "holding" (HC) compartment, a "blood" (BC) compartment and a "bladder" (BLC) compartment. DINCH is assumed to first deposit into the SC, with transfer split between the HC and the BC. Unmetabolized DINCH from the HC then transfers to the BC. The DINCH metabolism is assumed to occur in the BC before excretion via the BLC. At each urination event, all the metabolite mass in the BLC is excreted. The model was calibrated using published urine metabolite data from 3 different male volunteers, each orally dosed with 50mg DINCH. Full urine voids were taken for 48 h after dosage. The predicted values showed a good agreement with the observed urinary DINCH metabolite concentrations, with a Spearman correlation coefficient exceeding 0.7 for all oxidized metabolites. We showed the importance of a holding reservoir. Without it, a good agreement could not be found. We applied the model to a set of 24-h general population samples measured for DINCH metabolites. The model was unable to duplicate the ratio of metabolites seen in the 24-h samples. Two possibilities were offered to explain the difference: the exposure pattern in the general population did not match the oral exposure in the dosing experiments, or the long-term toxicokinetics of DINCH was not captured in the 48-h controlled dosing experiments.