Analyzing terephthalate metabolites in human urine as biomarkers of exposure: Importance of selection of metabolites and deconjugation enzyme

Comprehensive assessment of the UV-filter 2-ethylhexyl salicylate and its phase I/II metabolites in urine by extended enzymatic hydrolysis and on-line SPE LC-MS/MS

2-ethylhexyl salicylate (EHS) is used as a UV filter in personal-care products, such as sunscreen, to prevent skin damage through UV radiation. The application of EHS-containing products leads to systemic EHS absorption, metabolization and excretion. To measure EHS and its corresponding metabolite levels in urine, a comprehensive analytical procedure based on an extended enzymatic hydrolysis, on-line-SPE, and UPLC-MS/MS was developed. The method covers a large profile of seven metabolites (including isomeric structures) as well as EHS itself in a run time only of 18 min. Easy sample preparation, consisting of a 2-h hydrolysis step, followed by on-line enrichment and purification, add to the efficiency of the method. An update, compared to a previous method for the determination of EHS and metabolites in urine, is that, during hydrolysis, both glucuronide and sulfate conjugates are considered. The method was furthermore applied to urine samples after a real-life exposure scenario to EHS-containing sunscreen. The method is highly sensitive with limits of detection ranging from 6 to 65 ng/L. Moreover, it is characterized by good precision data, accuracy, and robustness to matrix influences. Application of the method to urine samples following dermal exposure to an EHS-containing sunscreen revealed EHS as the main biomarker after dermal exposure, followed by the major biomarkers 5OH-EHS, 5cx-EPS, 4OH-EHS and 5oxo-EHS. The expansion and optimization of this method decisively contributes to the research on the dermal metabolism of EHS and can be applied in exposure studies and for human biomonitoring.

Medical devices used in NICU: The main source of plasticisers' exposure of newborns

Phthalates and other plasticisers are extensively used in medical devices (MD) from which they can leach out and lead to potential multiple problems for the patients. This exposure is a major issue because it is associated with reproductive and neurodevelopment disorders. The Neonatal Intensive Care Units (NICU) population is at high risk due to the daily intensive medical interventions, the reduced ability of newborns to remove these contaminants and their higher sensitivity to endocrine disruptors. We conducted a multicentric biomonitoring study to assess and compare the urinary levels of DEHP (di-(2-ethylhexyl)phthalate), DEHTP (di-(2-ethylhexyl)terephthalate) and TEHTM (tri-(2-ethylhexyl)trimellitate) metabolites as biomarkers of this exposure during and after the newborns' stay in NICU. Daily urinary samples were collected in NICU and at discharge from the hospital for each patient. MD sources and exposure factors were also investigated. 508 urinary samples from 97 patients enrolled in centres 1 and 2 (C1/C2) were collected. The exposure of newborns to DEHP was greater than that of DEHTP and TEHTM, with a median concentration of DEHP metabolites (C1:195.63 ng/mL;C2:450.87 ng/mL) respectively 5 to 10 times higher and 57 to 228 times higher than the median concentrations of DEHTP and TEHTM metabolites. The urinary concentrations of DEHP and TEHTM metabolites were significantly lower at discharge than in NICU, with a 18-and 35-fold decrease for DEHP and a 4 and 8-fold decrease for TEHTM, respectively for C1 and C2, but were similar for DEHTP metabolites. MD used for respiratory assistance, infusion therapy,enteral nutrition and transfusion were the main sources of exposure. Smaller gestational age and body weight significantly increased the newborns' exposure. The elevated levels of DEHP metabolites in NICU patients are still alarming. Additional efforts are necessary to promote its substitution in MD by possibly safer alternatives such as TEHTM and DEHTP, particularly when used for the care of newborns.

Comprehensive monitoring of a special mixture of prominent endocrine disrupting chemicals in human urine using a carefully adjusted hydrolysis of conjugates

Many xenobiotics were identified as possible endocrine disruptors during the last decades. Structural analogy of these substances to natural hormones may lead to agonists or antagonists of hormone receptors. For a comprehensive human biomonitoring of such substances, we developed a simple, reliable, and highly sensitive method for the simultaneous monitoring of the parameters bisphenol A, triclosan, methylparaben, ethylparaben, propylparaben, butylparaben, benzophenone-1, benzophenone-3, 3,5,6-trichloropyridin-2-ol, p-nitrophenol, genistein, and daidzein in urine. Thereby, optimization of the enzymatic hydrolysis and the use of β-glucuronidase from E. coli K12 as well as sulfatase from Aerobacter aerogenes ensures the acquisition of intact analytes without cleavage of ester bonds among parabens. Validation of the method revealed limits of detection between 0.02 and 0.25 µg/L as well as limits of quantification between 0.08 and 0.83 µg/L. Thereby, the use of analyte-free surrogate matrix for calibration and control material influenced the sensitivity of the procedure positively. Furthermore, excellent precision in and between series was observed. Good absolute and relative recoveries additionally proved the robustness of the multimethod. Thus, the procedure can be applied for exploring the exposome to these prominent endocrine disruptors in the general population.

Simultaneous and sensitive determination of the main metabolites of the plasticizer DEHP and its substitutes DEHTP, DINCH and TEHTM in human urine by coupling of on-line SPE, UHPLC and tandem mass spectrometry

With the prominent but toxicologically critical plasticizer di-(2-ethylhexyl) phthalate (DEHP) declining, alternative plasticizers are increasingly used leading to a continuously more diverse exposure situation of humans with multiple plasticizers. Therefore, an on-line SPE-LC-MS/MS method for the simultaneous determination of the most relevant urinary biomarkers of exposure to DEHP and the alternative plasticizers 1,2-cyclohexane dicarboxylic acid diisononyl ester (DINCH), di-(2-ethylhexyl) terephthalate (DEHTP) and tri-(2-ethylhexyl) trimellitate (TEHTM) was developed. The method is characterized by a high sensitivity with limits of detection ranging from 0.006 to 0.047 μg L^-1 combined with an easy and straightforward sample preparation procedure. The wide linear working range of the method enables a reliable determination of analyte background levels in the general population as well as its potential use for monitoring studies investigating elevated plasticizer exposure settings. The method was successfully applied to urine samples from ten volunteers without occupational exposure to plasticizers revealing ubiquitous background exposure levels of the common plasticizers DEHP, DEHTP and DINCH.

Validated single urinary assay designed for exposomic multi-class biomarkers of common environmental exposures

Epidemiological studies often call for analytical methods that use a small biospecimen volume to quantify trace level exposures to environmental chemical mixtures. Currently, as many as 150 polar metabolites of environmental chemicals have been found in urine. Therefore, we developed a multi-class method for quantitation of biomarkers in urine. A single sample preparation followed by three LC injections was optimized in a proof-of-approach for a multi-class method. The assay was validated to quantify 50 biomarkers of exposure in urine, belonging to 7 chemical classes and 16 sub-classes. The classes represent metabolites of 12 personal care and consumer product chemicals (PCPs), 5 polycyclic aromatic hydrocarbons (PAHs), 5 organophosphate flame retardants (OPFRs), 18 pesticides, 5 volatile organic compounds (VOCs), 4 tobacco alkaloids, and 1 drug of abuse. Human urine (0.2 mL) was spiked with isotope-labeled internal standards, enzymatically deconjugated, extracted by solid-phase extraction, and analyzed using high-performance liquid chromatography-tandem mass spectrometry. The methanol eluate from the cleanup was split in half and the first half analyzed for PCPs, PAH, and OPFR on a Betasil C18 column; and pesticides and VOC on a Hypersil Gold AQ column. The second half was analyzed for tobacco smoke metabolites and a drug of abuse on a Synergi Polar RP column. Limits of detection ranged from 0.01 to 1.0 ng/mL of urine, with the majority ≤0.5 ng/mL (42/50). Analytical precision, estimated as relative standard deviation of intra- and inter-batch uncertainty, variabilities, was <20%. Extraction recoveries ranged from 83 to 109%. Results from the optimized multi-class method were qualified in formal international proficiency testing programs. Further method customization options were explored and method expansion was demonstrated by inclusion of up to 101 analytes of endo- and exogenous chemicals. This exposome-scale assay is being used for population studies with savings of assay costs and biospecimens, providing both quantitative results and the discovery of unexpected exposures.

Exposure to 15 phthalates and two substitutes (DEHTP and DINCH) assessed in trios of infants and their parents as well as longitudinally in infants exclusively breastfed and after the introduction of a mixed diet

OBJECTIVE

Several phthalates have been restricted/banned due to their adverse endocrine disrupting properties. The use of other phthalates and substitutes has increased. Here we examine the current exposure to phthalates in family trios comprised of infants and their parents and in infants exclusive breastfed and following introduction to a mixed diet.

METHODS

Metabolites of 15 phthalates and two substitutes, di(2-ethylhexyl)-teraphthalate (DEHTP) and diisononyl-cyclohexane-1,2-dicarboxylate (DINCH), were measured in urine samples collected from >100 infants and their parents and in paired urine samples collected from 67 infants, while they were exclusively breastfed and when they got mixed diet.

RESULTS

Among infants and their parents, metabolites of nine out of 15 phthalates and both substitutes were detected in >74% of all samples. Estimated daily intake (DI) calculated as µg/kg/day, showed similar exposure levels among infants and their parents for several of the substances, and infants were more exposed to DEHTP than their mothers. Significantly higher estimated DIs were observed for some low-molecular phthalates in infants exclusively breastfed. In contrast, comparable estimated DIs were observed for many other phthalates and DEHTP regardless of feeding status. For most of the substances, the within-family variation, was lower than the between-family variation. Likewise, the within-infant variation on exclusively breast vs. mixed diet was lower than the between-infant variation. Independent of food status, some infants were concurrently exposed to almost all the measured phthalates and substitutes in higher amounts than others.

CONCLUSION

Surprisingly, irrespective of diet status infants were exposed to several phthalates and substitutes some of which have been regulated for years. Exposure patterns and levels were similar in infants and their parents. Importantly, risk assessment based on new refined reference doses (RfD-AA) exceeded the safety level for anti-androgenic effects in a number of infants and parents, which is of concern.

Proficiency and Interlaboratory Variability in the Determination of Phthalate and DINCH Biomarkers in Human Urine: Results from the HBM4EU Project

A quality assurance/quality control program was implemented in the framework of the EU project HBM4EU to assess and improve the comparability of biomarker analysis and to build a network of competent laboratories. Four rounds of proficiency tests were organized for 15 phthalate and two DINCH urinary biomarkers (0.2–138 ng/mL) over a period of 18 months, with the involvement of 28 laboratories. A substantial improvement in performance was observed after the first round in particular, and by the end of the program, an average satisfactory performance rate of 90% was achieved. The interlaboratory reproducibility as derived from the participants’ results varied for the various biomarkers and rounds, with an average of 24% for the biomarkers of eight single-isomer phthalates (e.g., DnBP and DEHP) and 43% for the more challenging biomarkers of the mixed-isomer phthalates (DiNP, DiDP) and DINCH. When the reproducibility was based only on the laboratories that consistently achieved a satisfactory performance, this improved to 17% and 26%, respectively, clearly demonstrating the success of the QA/QC efforts. The program thus aided in building capacity and the establishment of a network of competent laboratories able to generate comparable and accurate HBM data for phthalate and DINCH biomarkers in 14 EU countries. In addition, global comparability was ensured by including external expert laboratories.

Determination of urinary metabolites of the UV filter homosalate by online-SPE-LC-MS/MS

Homosalate (HMS) is an organic UV filter used in sunscreens and personal care products worldwide. It has been detected in various environmental matrices and in humans after application of HMS-containing products. However, sufficient data on the internal HMS exposure in humans is currently not available. Thus, we aimed at providing an analytical method for the sensitive determination of specific HMS metabolites in human urine. We describe the synthesis of analytical standards for the four oxidative HMS metabolites included in this method: 5-((2-hydroxybenzoyl)oxy)-3,3-dimethylcyclohexane-1-carboxylic acid (HMS-CA) and 3-hydroxy-3,5,5-trimethylcyclohexyl 2-hydroxybenzoate (3OH-HMS), as cis- and trans-isomers, respectively. After enzymatic hydrolysis, urine samples were analyzed using liquid chromatography-electrospray ionization-triple quadrupole-tandem mass spectrometry, including turbulent flow chromatography for online sample cleanup and analyte enrichment (online-SPE-LC-MS/MS). Quantification was performed by stable isotope dilution analysis, using deuterium-labeled HMS-CA as internal standards (cis and trans). Limits of quantification of 0.02-0.04 μg L^-1 were sufficiently low to quantify the HMS metabolites for up to 96 h (trans-HMS-CA), 48 h (cis-HMS-CA and 3OH-trans-HMS), and 24 h (3OH-cis-HMS) after a pilot dermal application of a commercially available sunscreen in one human volunteer, showing clear elimination kinetics. Furthermore, in a German pilot population (n = 35), HMS metabolites were above the LOQ precisely in those three individuals who had applied sunscreen within the previous five days, thus corroborating the specificity of the identified metabolites as biomarkers of HMS exposure. The method is currently used in a human metabolism study and will be applied in future population-scale human biomonitoring studies.

Human metabolism and urinary excretion kinetics of di-n-butyl adipate (DnBA) after oral and dermal administration in three volunteers

Di-n-butyl adipate (DnBA) is used as a plasticizer and in various consumer products (e.g. personal care products) replacing, in part, the endocrine disruptor di-n-butyl phthalate (DnBP). We provide quantitative in vivo data on human DnBA metabolism and excretion after oral dose (105-185 μg/kg bw) and dermal application to three volunteers each as a tool for exposure and risk assessment. Complete and consecutive urine samples were collected for two (oral) and four days (dermal), respectively, and analyzed for the metabolites mono-n-butyl adipate (MnBA), 3- and tentative 4-hydroxy-mono-n-butyl adipate (3OH-MnBA, 4OH-MnBA), and 3-carboxy-mono-n-propyl adipate (3cx-MnPrA), as well as the hydrolysis product adipic acid (AA) using stable isotope dilution quantification. Metabolites were excreted within 24 h after oral dose with one or two concentration maxima at 0.8-3.0 h (n = 3) and 4.8-6.3 h (n = 2). AA was the major but unspecific metabolite with urinary excretion fractions (F_UEs) of 14-26 %. Mean F_UEs (range) of 3cx-MnPrA, MnBA, 3OH-MnBA, and tentative 4OH-MnBA were low, but consistent between volunteers (0.47 % (0.35-0.63 %), 0.079 % (0.065-0.091 %), 0.012 % (0.006-0.016 %), and 0.005 % (0.002-0.009 %), respectively). MnBA and 3OH-MnBA seem to be suitable, specific exposure biomarkers for DnBA, whereas 3cx-MnPrA and 4OH-MnBA seem to originate also from other, unknown sources not related to DnBA. Compared to the oral study, metabolite excretion in the dermal study was delayed and MnBA excretion was somewhat higher compared to the oxidized metabolites. Based on urinary concentrations and the above excretion fractions, calculated uptakes in the dermal study did not exceed the adipate ester ADI of 5 mg/(kg bw*day).

Biomarkers, matrices and analytical methods targeting human exposure to chemicals selected for a European human biomonitoring initiative

The major purpose of human biomonitoring is the mapping and assessment of human exposure to chemicals. The European initiative HBM4EU has prioritized seven substance groups and two metals relevant for human exposure: Phthalates and substitutes (1,2-cyclohexane dicarboxylic acid diisononyl ester, DINCH), bisphenols, per- and polyfluoroalkyl substances (PFASs), halogenated and organophosphorous flame retardants (HFRs and OPFRs), polycyclic aromatic hydrocarbons (PAHs), arylamines, cadmium and chromium. As a first step towards comparable European-wide data, the most suitable biomarkers, human matrices and analytical methods for each substance group or metal were selected from the scientific literature, based on a set of selection criteria. The biomarkers included parent compounds of PFASs and HFRs in serum, of bisphenols and arylamines in urine, metabolites of phthalates, DINCH, OPFRs and PAHs in urine as well as metals in blood and urine, with a preference to measure Cr in erythrocytes representing Cr (VI) exposure. High performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) was the method of choice for bisphenols, PFASs, the HFR hexabromocyclododecane (HBCDD), phenolic HFRs as well as the metabolites of phthalates, DINCH, OPFRs and PAHs in urine. Gas chromatographic (GC) methods were selected for the remaining compounds, e.g. GC-low resolution MS with electron capture negative ionization (ECNI) for HFRs. Both GC-MS and LC-MS/MS were suitable for arylamines. New developments towards increased applications of GC-MS/MS may offer alternatives to GC-MS or LC-MS/MS approaches, e.g. for bisphenols. The metals were best determined by inductively coupled plasma (ICP)-MS, with the particular challenge of avoiding interferences in the Cd determination in urine. The evaluation process revealed research needs towards higher sensitivity and non-invasive sampling as well as a need for more stringent quality assurance/quality control applications and assessments.

Development and validation of a liquid chromatography/tandem mass spectrometry method to quantify metabolites of phthalates, including di-2-ethylhexyl terephthalate (DEHTP) and bisphenol A, in human urine

RATIONALE

Several phthalates and bisphenol A are endocrine-disrupting chemicals (EDCs). Recently, their use has been partially restricted and less toxic compounds, such as di-2-ethylhexyl terephthalate (DEHTP), have been placed on the market. The aim of this work was to develop and validate a method for the simultaneous quantitation of bisphenol A and urinary metabolites of phthalates, including DEHTP.

METHODS

An isotopic dilution high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC/ESI-MS/MS) method for the determination of bisphenol A (BPA), monobenzyl phthalate (MBzP), mono-2-ethyl-5-carboxypentyl phthalate (MECPP), mono-2-ethyl-5-carboxypentyl terephthalate (MECPTP), mono-2-ethyl-5-hydroxyhexyl terephthalate (MEHHTP), monoethyl phthalate (MEP), and mono-n/i-butyl phthalates (MnBP/MiBP) in human urine was developed. A complete validation was carried out and the method was applied to 36 non-occupationally exposed adults.

RESULTS

Limits of quantitation ranged from 0.02 (MECPP) to 1 μg/L (MnBP and MiBP). Relative standard deviations below 10% indicated a suitable precision; accuracy, evaluated using a standard reference material, ranged from 74.3% to 117.5%; isotopically labelled internal standards were suitable for correcting the matrix effect. The accuracy was confirmed by the successful participation in an external verification exercise. However, for terephthalates, the validation was incomplete due to the lack of reference materials and external verification. Levels of the investigated chemicals in subjects were in line with those previously reported.

CONCLUSIONS

An LC/MS/MS assay for the simultaneous measurement of BPA and phthalate metabolites in human urine was developed and validated; it is useful to investigate exposure in epidemiological studies involving the general population.

German Environmental Specimen Bank: 24-hour urine samples from 1999 to 2017 reveal rapid increase in exposure to the para-phthalate plasticizer di(2-ethylhexyl) terephthalate (DEHTP)

The worldwide plasticizer markets are facing constant substitution processes. Many classic ortho-phthalate plasticizers like di(2-ethylhexyl) phthalate (DEHP) are phased out, due to their proven toxicity to reproduction. Assumedly less critical, less regulated plasticizers such as di(2-ethylhexyl) terephthalate (DEHTP) are increasingly applied in consumer near products like toys, food contact materials, and medical devices. With the increasing use of DEHTP, increasing exposures of the general population have to be expected likewise. Human biomonitoring is a well-established tool to determine population exposures. In the present study we investigate the time trend of exposure to DEHTP using 24-hour urine samples of the German Environmental Specimen Bank (ESB) collected from 1999 to 2017. In these samples (60 per odd-numbered year, 600 samples in total) collected from young German adults (20-29 years, equal gender distribution) we determined four specific urinary metabolites as biomarkers of DEHTP exposure. From 1999 to 2009, the main specific urinary metabolite 5cx-MEPTP was quantifiable in <10% of the samples. Thereafter, detection rates and levels constantly increased, in line with rapidly increasing DEHTP consumption volumes. In 2017, all samples had 5cx-MEPTP levels above the limit of quantification (LOQ) with a median concentration of 3.35 μg/L (95th percentile: 12.8 μg/L). The other metabolites were detected less frequently and at lower levels but correlated well with 5cx-MEPTP robustly confirming the increasing DEHTP exposure. All 5cx-MEPTP concentrations were well below the German health based guidance value (HBM-I) of 2800 μg/L for adults. Likewise, the median calculated daily intake, based on 5cx-MEPTP measured in 2017, was 0.74 μg/kg bw∗d (95th percentile: 3.86 μg/kg bw∗d), still well below the tolerable daily intake (TDI) of 1000 μg/kg bw∗d. Based on current toxicological knowledge we can hence conclude that for the population investigated, DEHTP exposure gives no reason for immediate concern. However, the steep ongoing increase of DEHTP exposure warrants further close monitoring in the future, preferably also in sub-populations with known higher exposures to plasticizers, especially children.