Reviewing the variability in urinary concentrations of non-persistent organic chemicals: evaluation across classes, sampling strategies and dilution corrections

Various biomonitoring studies have been carried out to investigate the exposure of populations by measuring non-persistent organic chemicals in urine. To accurately assess the exposure, study designs should be carefully developed to maximise reproducibility and achieve good characterization of the temporal variability. To test these parameters, the intraclass correlation coefficients (ICCs) are calculated from repeated measurements and range from poor (<0.4) to excellent (≥0.75). Several studies have reported ICCs based on diverse study designs, but an overview, including recommendations for future studies, was lacking. Therefore, this review aimed to collect studies describing ICCs of non-persistent organic chemicals, discuss variations due to study design and formulate recommendations for future studies. More than 60 studies were selected, considering various chemical classes: bisphenols, pyrethroids, parabens, phthalates, alternative plasticizers and phosphate flame retardants. The variation in ICCs for an individual chemical was high (e.g. ICC of propyl paraben = 0.28-0.91), showing the large impact of the study design and of the specific exposure sources. The highest ICCs were reported for parabens (median = 0.52), while lowest ICCs were for 3-phenoxybenzoic acid (median = 0.08) and bisphenol A (median = 0.20). Overall, chemicals that had an exposure source with high variation, such as the diet, showed lower ICCs than those with more stable exposure sources, such as indoor materials. Urine correction by specific gravity had an overall positive effect on reducing the variability of ICCs. However, this effect was mostly seen in the adult population, while specific compounds showed less variation with creatinine correction. Single samples might not accurately capture the exposure to most non-persistent organic chemicals, especially when small populations are sampled. Future studies that examine compounds with low ICCs should take adequate measures to improve accuracy, such as correcting dilution with specific gravity or collecting multiple samples for one participant.

Identification and characterization of quaternary ammonium compounds in Flemish indoor dust by ion-mobility high-resolution mass spectrometry

Quaternary ammonium compounds (QACs) are a class of surfactants commonly used in disinfecting and cleaning products. Their use has substantially increased during the COVID-19 pandemic leading to increasing human exposure. QACs have been associated with hypersensitivity reactions and an increased risk of asthma. This study introduces the first identification, characterization and semi-quantification of QACs in European indoor dust using ion-mobility high-resolution mass spectrometry (IM-HRMS), including the acquisition of collision cross section values (^DTCCS_N2) for targeted and suspect QACs. A total of 46 indoor dust samples collected in Belgium were analyzed using target and suspect screening. Targeted QACs (n = 21) were detected with detection frequencies ranging between 4.2 and 100 %, while 15 QACs showed detection frequencies > 90 %. Semi-quantified concentrations of individual QACs showed a maximum of 32.23 µg/g with a median ∑QAC concentration of 13.05 µg/g and allowed the calculation of Estimated Daily Intakes for adults and toddlers. Most abundant QACs matched the patterns reported in indoor dust collected in the United States. Suspect screening allowed the identification of 17 additional QACs. A dialkyl dimethyl ammonium compound with mixed chain lengths (C16:C18) was characterized as a major QAC homologue with a maximum semi-quantified concentration of 24.90 µg/g. The high detection frequencies and structural variabilities observed call for more European studies on potential human exposure to these compounds. For all targeted QACs, drift tube IM-HRMS derived collision cross section values (^DTCCS_N2) are reported. Reference ^DTCCS_N2 values allowed the characterization of CCS-m/z trendlines for each of the targeted QAC classes. Experimental CCS-m/z ratios of suspect QACs were compared with the CCS-m/z trendlines. The alignment between the two datasets served as an additional confirmation of the assigned suspect QACs. The use of the 4bit multiplexing acquisition mode with consecutive high-resolution demultiplexing confirmed the presence of isomers for two of the suspect QACs.

Comprehensive suspect screening for the identification of contaminants of emerging concern in urine of Flemish adolescents by liquid chromatography high-resolution mass spectrometry

The increasing human exposure to contaminants of emerging concern (CECs) cannot be fully assessed by targeted biomonitoring methods alone as these are limited to a subset of known analytes. On the contrary, suspect screening approaches based on liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS) allow the simultaneous detection of a high number of CECs and/or their (predicted) metabolites leading to a more comprehensive assessment of possible human exposure to these compounds. Within this study, 83 urine samples of Flemish adolescents (47 males, 36 females) collected in the frame of the 4th cycle of the Flemish Environment and Health Study (FLEHS IV) were selected with the aim of including a high and a low exposure group based on the overall exposure of 45 known contaminants. Samples were analyzed using a previously developed method involving a suspect screening approach to annotate CECs and their metabolites. The applied suspect list contained a total of >12,500 CECs and their known and predicted metabolites resulting from metabolization reactions, such as hydroxylation, glucuronidation and methylation. In total, 63 compounds were annotated at a confidence level of 3 or better, with most of the detected compounds not included in current biomonitoring programs. 5 out of the 63 compounds could be assigned with confidence level 2. Five compounds could unequivocally be identified (confidence level 1) through the comparison with reference standards. Personal care products were the main detected compound class (42% of detected compounds). Additionally, a detailed literature search indicated potential toxic effects for several of the detected CECs. Lastly, in the urine samples, a significantly higher number (p < 0.05) of compounds was detected in the high exposure group as opposed to the low exposure group. This difference could only be observed between high and low exposure load samples of female participants (p < 0.01).

Exposure to organophosphate flame retardants and plasticizers is positively associated with wheeze and FeNO and eosinophil levels among school-aged children: The Hokkaido study

Exposure to organophosphate flame retardants and plasticizers (PFRs) increases the risk of asthma and allergies. However, little is known about its association with type 2 inflammation (T2) biomarkers used in the management of allergies. The study investigated associations among urinary PFR metabolite concentrations, allergic symptoms, and T2 biomarkers. The data and samples were collected between 2017 and 2020, including school children (n = 427) aged 9-12 years living in Sapporo City, Japan, among the participants of "The Hokkaido Study on Environment and Children's Health." Thirteen urinary PFR metabolites were measured by LC-MS/MS. Allergic symptoms were assessed using the International Study of Asthma and Allergies in Childhood questionnaire. For T2 biomarkers, the peripheral blood eosinophil counts, fraction of exhaled nitric oxide level (FeNO), and serum total immunoglobulin E level were measured. Multiple logistic regression analysis, quantile-based g-computation (qg-computation), and Bayesian kernel machine regression (BKMR) were used to examine the associations between the health outcomes of the individual PFRs and the PFR mixtures. The highest concentration of PFR was Σtris(1-chloro-isopropyl) phosphates (ΣTCIPP) (Median:1.20 nmol/L). Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) was significantly associated with a high odds ratio (OR, 95%CI:1.36, 1.07-1.72) for wheeze. TDCIPP (OR, 95%CI:1.19, 1.02-1.38), Σtriphenyl phosphate (ΣTPHP) (OR, 95%CI:1.81, 1.40-2.37), and Σtris(2-butoxyethyl) phosphate (ΣTBOEP) (OR, 95%:1.40, 1.13-1.74) were significantly associated with increased odds of FeNO (≥35 ppb). ΣTPHP (OR, 95%CI:1.44, 1.15-1.83) was significantly associated with high eosinophil counts (≥300/μL). For the PFR mixtures, a one-quartile increase in all PFRs (OR, 95%CI:1.48, 1.18-1.86) was significantly associated with high FeNO (≥35 ppb) in the qg-computation model. The PFR mixture was positively associated with high FeNO (≥35 ppb) and eosinophil counts (≥300/μL) in the BKMR models. These results may suggest that exposure to PFRs increases the probability of asthma, allergies, and T2 inflammation.

Comprehensive investigation of persistent and mobile chemicals and per- and polyfluoroalkyl substances in urine of flemish adolescents using a suspect screening approach

Persistent and mobile chemicals (PMs) and per- and polyfluoroalkyl substances (PFAS) are groups of chemicals that have received recent global attention due to their potential health effects on the environment and humans. In this study, exposure to a broad range of PMs and PFAS was investigated in Flemish adolescents' urine samples (n = 83) using a suspect screening approach. For this purpose, three sample preparation methods were evaluated, and a basic liquid-liquid extraction was optimized for urine analysis based on the extraction efficiency of PMs (53-80%) and PFAS (>70%). In total, 9 PMs were identified in urine samples at confidence levels (CL) 1-3 and, among them, acetaminophen, 4-aminophenol, 2,2,6,6-tetramethyl-4-piperidone, trifluoroacetic acid (TFAA), sulisobenzone, ethyl sulfate, and 1,2-benzisothiazol-3(2H)-one 1,1-dioxide were confirmed at CL 1 and 2. In addition, the detection and identification of 2,2,6,6-tetramethyl-4-piperidone, 4-aminophenol, TFAA, and m-(2,3-epoxypropoxy)-N,N-bis(2,3-epoxypropyl) aniline (CL 3), has been reported for the first time in human urine in this study. For PFAS, only 2 compounds were identified at CL 4, implying that urine is not a suitable matrix for suspect screening of such compounds. A significant difference between sexes was observed in the detection rate of identified PMs, in particular for acetaminophen, 4-aminophenol, and sulisobenzone. The findings of this study can be used in future human biomonitoring programs, such as by including the newly identified compounds in quantitative methods or monitoring in other human matrices (e.g., serum).

In Vitro Metabolism of Quaternary Ammonium Compounds and Confirmation in Human Urine by Liquid Chromatography Ion-Mobility High-Resolution Mass Spectrometry

Quaternary ammonium compounds (QACs) are high-production chemicals used as cleaning and disinfecting agents. Due to their ubiquitous presence in the environment and several toxic effects described, human exposure to these chemicals gained increasing attention in recent years. However, very limited data on the biotransformation of QACs is available, hampering exposure assessment. In this study, three QACs (dimethyl dodecyl ammonium, C10-DDAC; benzyldimethyl dodecylammonium, C12-BAC; cetyltrimethylammonium, C16-ATMAC) commonly detected in indoor microenvironments were incubated with human liver microsomes and cytosol (HLM/HLC) simulating Phase I and II metabolism. Thirty-one Phase I metabolites were annotated originating from 19 biotransformation reactions. Four metabolites of C10-DDAC were described for the first time. A detailed assessment of experimental fragmentation spectra allowed to characterize potential oxidation sites. For each annotated metabolite, drift-tube ion-mobility derived collision cross section (DTCCSN2) values were reported, serving as an additional identification parameter and allowing the characterization of changes in DTCCSN2 values following metabolism. Lastly, eight metabolites, including four metabolites of both C12-BAC and C10-DDAC, were confirmed in human urine samples showing high oxidation states through introduction of up to four oxygen atoms. This is the first report of higher oxidized C10-DDAC metabolites in human urine facilitating future biomonitoring studies on QACs.

Cognitive Performance and Exposure to Organophosphate Flame Retardants in Children: Evidence from a Cross-Sectional Analysis of Two European Mother-Child Cohorts

The knowledge of the effects of organophosphate flame retardants on children's neurodevelopment is limited. The purpose of the present research is to evaluate the association between exposure to organophosphate flame retardants and children's neurodevelopment in two European cohorts involved in the Human Biomonitoring Initiative Aligned Studies. The participants were school-aged children belonging to the Odense Child Cohort (Denmark) and the PCB cohort (Slovakia). In each cohort, the children's neurodevelopment was assessed through the Full-Scale Intelligence Quotient score of the Wechsler Intelligence Scale for Children, using two different editions. The children's urine samples, collected at one point in time, were analyzed for several metabolites of organophosphate flame retardants. The association between neurodevelopment and each organophosphate flame retardant metabolite was explored by applying separate multiple linear regressions based on the approach of MM-estimation in each cohort. In the Danish cohort, the mean ± standard deviation for the neurodevelopment score was 98 ± 12; the geometric mean (95% confidence interval (95% CI)) of bis(1,3-dichloro-2-propyl) phosphate (BDCIPP) standardized by creatinine (crt) was 0.52 µg/g crt (95% CI = 0.49; 0.60), while that of diphenyl phosphate (DPHP) standardized by crt was 1.44 µg/g crt (95% CI = 1.31; 1.58). The neurodevelopment score showed a small, negative, statistically imprecise trend with BDCIPP standardized by crt (β = -1.30; 95%CI = -2.72; 0.11; p-value = 0.07) and no clear association with DPHP standardized by crt (β = -0.98; 95%CI = -2.96; 0.99; p-value = 0.33). The neurodevelopment score showed a negative trend with BDCIPP (β = -1.42; 95% CI = -2.70; -0.06; p-value = 0.04) and no clear association with DPHP (β = -1.09; 95% CI = -2.87; 0.68; p-value = 0.23). In the Slovakian cohort, the mean ± standard deviation for the neurodevelopment score was 81 ± 15; the geometric mean of BDCIPP standardized by crt was 0.18 µg/g crt (95% CI = 0.16; 0.20), while that of DPHP standardized by crt was 2.24 µg/g crt (95% CI = 2.00; 3.52). The association of the neurodevelopment score with BDCIPP standardized by crt was -0.49 (95%CI = -1.85; 0.87; p-value = 0.48), and with DPHP standardized by crt it was -0.35 (95%CI = -1.90; 1.20; p-value = 0.66). No clear associations were observed between the neurodevelopment score and BDCIPP/DPHP concentrations that were not standardized by crt. No clear associations were observed with bis(1-chloro-2-propyl) phosphate (BCIPP) in either cohort, due to the low detection frequency of this compound. In conclusion, this study provides only limited evidence of an inverse association between neurodevelopment and exposure to BDCIPP and DPHP. The timing of exposure and effect modification of other organophosphate flame retardant metabolites and other substances should be the subject of further investigations that address this scientific hypothesis.

Organophosphate flame retardants associated with increased oxidative stress biomarkers and elevated FeNO levels in general population of children: The Hokkaido study

Our previous study found that exposure to higher organophosphate flame retardants (PFRs) was associated with increased prevalence of wheeze and type 2 inflammation among school-aged children. It remains unclear whether PFR exposure elevates oxidative stress in these general pediatric population, thereby potentially contributing to the development of allergic diseases. This study examined the associations between individual and mixture exposure to PFRs and oxidative stress in children aged 9-12 years (n = 423). The oxidative stress biomarkers included 4-hydroxynonenal (4-HNE) and hexanoyl-lysine (HEL) for lipid peroxidation, and 8-hydroxy-2'-deoxyguanosine (8-OHdG) for DNA damage. We also examined the mediation effects of oxidative stress on the relationships between PFR exposure and health outcomes: wheeze and type 2 inflammation biomarkers, including fraction of exhaled nitric oxide (FeNO) and blood eosinophils. Higher concentrations of tris(1,3-dichloro-2-propyl) phosphate (TDCIPP), Σ triphenyl phosphate (ΣTPHP), Σ tris(2-butoxyethyl) phosphate (ΣTBOEP), and Σ 2-Ethylhexyldiphenyl phosphate (ΣEHDPHP) metabolites were significantly associated with higher levels of 4-HNE. Elevated concentrations of TDCIPP, ΣTPHP, and ΣTBOEP were positively associated with HEL. Higher ΣTPHP and ΣTBOEP were positively associated with 8-OHdG. The PFR mixture was positively associated with all three oxidative stress biomarkers according to the Quantile g-computation and Bayesian kernel machine regression models. Oxidative stress biomarkers mediated 11.4 % to 15.3 % of the association between PFRs and FeNO ≥35 ppb. PFR exposure was positively associated with oxidative stress markers of DNA damage and lipid peroxidation, which may contribute to elevated type 2 inflammation among school-aged children. These findings, identified in the general pediatric population at low exposure levels, highlight the need for ongoing attention to the allergic symptoms posed by PFR exposure.

In vitro biotransformation of 3-methylmethcathinone (3-MMC) through incubation with human liver microsomes and cytosol and application to in vivo samples

Synthetic cathinones are the second largest group of new psychoactive substances (NPS) monitored by the European Monitoring Centre for Drugs and Drug Addiction. Although 3-methylmethcathinone (3-MMC, C11H15NO) is legally banned in many countries, it is readily available for purchase online and on the street. Due to the scarcity of information regarding the pharmacokinetic and toxicological profile of 3-MMC, understanding its biotransformation pathways is crucial in determining its potential toxicity in humans and in the development of analytical methods for screening of human matrices. To gain more insight, Phase I and Phase II in vitro biotransformation of 3-MMC was investigated using human liver microsomes and human liver cytosol. Suspect and non-target screening approaches were employed to identify metabolites. To confirm in vitro results in an in vivo setting, human matrices (i.e., plasma, urine, saliva and hair) positive for 3-MMC (n=31) were screened. In total three biotransformation products were identified in vitro: C11H15NO2 (a hydroxylated derivate), C11H17NO (a keto-reduced derivate) and C10H13NO (an N-desmethyl derivate). All three were confirmed as human metabolites in respectively 16 %, 52 % and 42 % of the analysed human samples. In total, 61 % of the analysed samples were positive for at least one of the three metabolites. Interestingly, three urine samples were positive for all three metabolites. The presence of 3-MMC in saliva and hair indicates its potential applicability in specific settings, e.g., roadside testing or chronic consumption analysis. To our knowledge, C11H17NO was not detected before in vivo. Although some of these metabolites have been previously suggested in vitro or in a single post mortem case report, a wide in vivo confirmation including the screening of four different human matrices was performed for the first time. These metabolites could serve as potential human biomarkers to monitor human 3-MMC consumption effectively.

Phosphate Flame Retardants and Plasticizers and Their Association with Reproductive and Steroid Hormone Levels among Peripubertal-Aged Children: The Hokkaido Birth Cohort Study

This cross-sectional study investigated associations between exposure to organophosphate flame retardants and plasticizers (PFRs) and reproductive and steroid hormones in peripubertal children from the Hokkaido Birth Cohort (429 children aged 9-12 years; between September 2017 and March 2020). Thirteen urinary PFR metabolites and 14 plasma steroid hormones were investigated using LC-MS/MS and four reproductive hormones were investigated using immunoassays. Linear regression for single PFR, quantile g-computation, and Bayesian machine kernel regression (BKMR) models for the PFR mixtures were used to examine the association between hormones and PFRs. Among boys, significant positive associations were observed between estradiol and ΣTCIPP and ΣTBOEP, and inverse associations were identified between insulin-like factor-3 (INSL3) and ΣTCIPP, and between luteinizing hormone (LH) and ΣEHDPHP. The PFR mixture was associated with the trends of increasing estradiol and androstenedione, and decreasing cortisol, cortisone, LH, inhibin B, and INSL3. Among girls, androstenedione and ΣTCIPP, testosterone and ΣEHDPHP, (androstenedione + testosterone)/DHEA-S and ΣTCIPP, and ΣEHDPHP and ΣTPHP were significantly correlated. The PFR mixture showed trends of increasing testosterone, androstenedione, and inhibin B, and decreasing cortisol, cortisone, and INSL3. Individual PFRs and PFR mixtures altered steroids and reproductive hormones in peripubertal children.

Identification, semi-quantification and risk assessment of contaminants of emerging concern in Flemish indoor dust through high-resolution mass spectrometry

Indoor dust can contribute substantially to human exposure to known and contaminants of emerging concern (CECs). Novel compounds with high structural variability and different homologues are frequently discovered through screening of the indoor environment, implying that constant monitoring is required. The present study aimed at the identification and semi-quantification of CECs in 46 indoor dust samples collected in Belgium by liquid chromatography high-resolution mass spectrometry. Samples were analyzed applying a targeted and suspect screening approach; the latter based on a suspect list containing >4000 CECs. This allowed the detection of a total of 55 CECs, 34 and 21 of which were identified with confidence level (CL) 1/2 or CL 3, respectively. Besides numerous known contaminants such as di(2-ethylhexyl) phthalate (DEHP), di(2-ethylhexyl) adipate (DEHA) or tris(2-butoxyethyl) phosphate (TBOEP) which were reported with detection frequencies (DFs) > 90%, several novel CECs were annotated. These included phthalates with differing side chains, such as decyl nonyl and decyl undecyl phthalate detected with DFs >80% and identified through the observation of characteristic neutral losses. Additionally, two novel organophosphate flame retardants not previously described in indoor dust, i.e. didecyl butoxyethoxyethyl phosphate (DDeBEEP) and bis(butoxyethyl) butyl phosphate (BBEBP), were identified. The implementation of a dedicated workflow provided semi-quantitative concentrations for a set of suspects. Such data obtained for novel phthalates were in the same order of magnitude as the concentrations observed for legacy phthalates indicating their high relevance for human exposure. From the semi-quantitative data, estimated daily intakes and resulting hazard quotients (HQs) were calculated to estimate the exposure and potential health effects. Neither of the obtained HQ values exceeded the risk threshold, indicating no expected adverse health effects.