Factors Affecting the Accuracy of Bisphenol A and Bisphenol A-Monoglucuronide Estimates in Mammalian Tissues and Urine Samples

Influence of Gut Microbiota on Metabolism of Bisphenol A, a Major Component of Polycarbonate Plastics

Bisphenol A (BPA) is a major component of polycarbonate plastics and epoxy resins. While many studies have investigated the effect BPA exposure has upon changes in gut microbial communities, the influence of gut microbiota on an organism's ability to metabolize BPA remains comparatively unexplored. To remedy this, in this study, Sprague Dawley rats were intermittently (i.e., at a 7-day interval) or continuously dosed with 500 μg BPA/kg bw/day for 28 days, via oral gavage. In the rats which underwent the 7-day interval BPA exposure, neither their metabolism of BPA nor their gut microbiota structure changed greatly with dosing time. In contrast, following continuous BPA exposure, the relative level of Firmicutes and Proteobacteria in the rats' guts significantly increased, and the alpha diversity of the rats' gut bacteria was greatly reduced. Meanwhile, the mean proportion of BPA sulfate to total BPA in rat blood was gradually decreased from 30 (on day 1) to 7.4% (by day 28). After 28 days of continuous exposure, the mean proportion of BPA glucuronide to total BPA in the rats' urine elevated from 70 to 81%, and in the rats' feces the mean proportion of BPA gradually decreased from 83 to 65%. Under continuous BPA exposure, the abundances of 27, 25, and 24 gut microbial genera were significantly correlated with the proportion of BPA or its metabolites in the rats' blood, urine, and feces, respectively. Overall, this study principally aimed to demonstrate that continuous BPA exposure disrupted the rats' gut microbiota communities, which in turn altered the rats' metabolism of BPA. These findings contribute to the better understanding of the metabolism of BPA in humans.

Human health risk assessment of bisphenol A (BPA) through meat products

Meat and meat products are often consumed in our daily diet, providing essential nutrients. Contamination by chemical hazards, including bisphenol A (BPA) in meat products, is a concern and is continuously monitored. BPA is well-known for its endocrine-disrupting properties, which may cause potential toxicological effects on reproductive, nervous, and immune systems. Dietary consumption is the main route of BPA exposure, and meat products are a major contributor. BPA exposure from meat consumption is the focus of this review. This review found that BPA has been widely detected in canned and non-canned meat products. BPA in canned meat is assumed to be predominantly from migration from can coatings. Relatively low levels are observed in non-canned products, and the source of contamination in these products has yet to be definitively identified. A recent European Food Safety Authority (EFSA) draft opinion has proposed to lower the tolerable daily intake of BPA from 4 μg kg body weight (bw)^-1 day^-1 to 0.04 ng kg body weight (bw)^-1 day^-1, therefore potential health risks need to be addressed. This review has investigated potential contamination at the farm, industrial processes, and retail levels. Data gaps in the literature are also identified to improve future food safety in the meat industry. Also, a unified risk assessment strategy has been proposed. Further understanding of BPA migration in meat products is needed as a part of the exposure assessment to reduce potential risk, and more data on the dose-response relationship will help comprehend potential adverse health effects of BPA on humans. This research will inform the public, meat producers and processing industry, and policymakers on potential exposure to BPA and risk reduction measures, thus, ensuring food safety.

Direct LC-MS/MS and indirect GC-MS/MS methods for measuring urinary bisphenol A concentrations are comparable

BACKGROUND

Bisphenol A (BPA) is typically measured in urine using an indirect method that involves enzymatic deconjugation and extraction. In contrast, the direct method measures free and conjugated BPA concurrently and sums them to estimate urinary BPA concentrations. Statistical comparison of total BPA results using the direct and indirect methods is necessary to accurately interpret biomonitoring data for risk assessments.

OBJECTIVES

To compare urinary BPA concentrations estimated from the indirect and direct methods in duplicate first trimester urine samples collected from 1879 pregnant women from the MIREC Study.

METHODS

For the indirect method, we measured urinary BPA concentrations using GC-MS/MS. For the direct method, we summed free and conjugated BPA concentrations measured using LC-MS/MS. We evaluated deviation between the two methods using the Bland-Altman analysis in the total sample and stratified (1) by specific gravity and (2) at the limit of quantification (LOQ).

RESULTS

Median urinary BPA concentrations for the direct and indirect methods were 0.89 µg BPA equivalents/L and 0.81 µg/L respectively. Concentrations from the direct method were, on average, 8.6% (95% CI: 6.7%, 10.5%) higher than the indirect method in a Bland-Altman analysis. The percent differences between the two methods was 4.0% in urines with specific gravities < 1.02 (n = 1348, 72%) and 20.3% in urine with specific gravity ≥ 1.02. In values below the LOQ (n = 663, 35%), we observed smaller average percent deviation (4.8%) between the two methods but wider limits of agreement.

DISCUSSION

Results from this study, based on the largest statistically rigorous comparison of the direct and indirect methods of BPA measurement, contrast previous findings reporting that the indirect method underestimates total BPA exposure. The difference in urinary BPA concentrations we observed with the indirect and direct methods is unlikely to alter the interpretation of health outcome data.

Human biomonitoring initiative (HBM4EU): Human biomonitoring guidance values (HBM-GVs) derived for bisphenol A

The "European Human Biomonitoring Initiative" (HBM4EU) derives human biomonitoring guidance values (HBM-GVs) for the general population (HBM-GV_GenPop) and/or for occupationally exposed adults (HBM-GV_Worker) for several priority substances and substance groups as identified by policy makers, scientists and stakeholders at EU and national level, including bisphenol A (BPA). Human exposure to BPA is widespread and of particular concern because of its known endocrine-disrupting properties. Unlike the conjugated forms of BPA circulating in the body, free BPA is known to interact with the nuclear estrogen receptors. Because free BPA is considered to be more toxicologically active than the conjugated forms (e.g. BPA-glucuronide (BPA-G) and BPA-sulfate (BPA-S)), its measurement in blood provides the superior surrogate of the biologically effective dose. However, considering the difficulty of implementing blood sampling in large HBM cohorts, as well as the current analytical capacities complying with the quality assurance (QA)/quality control (QC) schemes, total BPA in urine (i.e. the sum of free and conjugated forms of BPA measured after an hydrolysis of phase II metabolites) was retained as the relevant exposure biomarker for BPA. HBM-GV_GenPop for total BPA in urine of 230 µg/L and 135 µg/L for adults and children, respectively, were developed on the basis of toxicological data. To derive these values, the concentrations of urinary total BPA consistent with a steady-state exposure to the temporary Tolerable Daily Intake (t-TDI) of 4 µg/kg bw/day set in 2015 by the European Food Safety Authority (EFSA) were estimated. The BPA human physiologically-based pharmacokinetic (PBPK) model developed by Karrer et al. (2018) was used, assuming an oral exposure to BPA at the t-TDI level averaged over 24 h. Dermal uptake of BPA is suspected to contribute substantially to the total BPA body burden, which in comparison with the oral route, is generating a higher ratio of free BPA to total BPA in blood. Therefore, an alternative approach for calculating the HBM-GV_GenPop according to the estimated relative contributions of both the oral and dermal routes to the global BPA exposure is also discussed. Regarding BPA exposure at the workplace, the steady-state concentration of urinary total BPA was estimated after a dermal uptake of BPA that would generate the same concentration of free BPA in plasma (considered as the bioactive form) as would a 24 h-averaged intake to the European Chemicals Agency (ECHA)'s oral DNEL of 8 µg BPA/kg bw/day set for workers. The predicted concentration of urinary total BPA at steady-state is equivalent to, or exceeds the 95th percentile of total BPA in urine measured in different European HBM studies conducted in the general population. Thus, no HBM-GV_Worker was proposed, as the high background level of BPA coming from environmental exposure - mostly through food intake - is making the discrimination with the occupational exposure to BPA difficult.

A new LC/MS method for specific determination of human systemic exposure to bisphenol A, F and S through their metabolites: Application to cord blood samples

Due to restriction of the use of BPA, several structural analogues such as BPS and BPF have been proposed for its replacement in many consumer products. This has increased the prevalence of BPS and BPF in urine from tested cohorts. However, these substitutes have similar endocrine disrupting properties to BPA, particularly on reproductive and metabolic functions, which suggests that fetal exposure to these analogues could be of concern for human health. Bisphenols (BPs) are mainly metabolized to glucuronides (BP-Gs), which are considered as inactive but provide a relevant marker of fetal exposure during pregnancy. In most instances, these metabolites are indirectly quantified after hydrolysis and measurement of the corresponding native BPs, which may lead to bias due to spurious BPs contamination during blood collection and/or analyses. We have developed a new method for direct quantification of BP-Gs, which has the advantage of not being affected by errors related to the presence of BPs. First, BP-Gs were extracted from plasma by anion exchange solid phase extraction. They were then labelled with dansyl chloride, using experimentally-optimized incubation conditions, after which the dansyl derivatives were injected into an on-line SPE-UHPLC/MS/MS system. The performance of the method, in terms of sensitivity, precision and accuracy, was evaluated in plasma over a concentration range of 0.05-5 ng/mL. The intra- and inter-day CV% precision were lower than 20% with accuracies ranging from 93% to 115%. The limit of quantification was set at 0.05 ng/mL. The method was then applied to measure BP-Gs in forty-four cord plasma samples. Although no BPF-G was found, BPA-G and BPS-G was determined in almost half of the cord plasma samples with concentration ranges nd-0.089 ng/mL and nd-0.586 ng/mL, respectively.

Bisphenol A and Metabolites in Meat and Meat Products: Occurrence, Toxicity, and Recent Development in Analytical Methods

Bisphenol A (BPA) is a commonly used compound in many industries and has versatile applications in polycarbonate plastics and epoxy resins production. BPA is classified as endocrine-disrupting chemical which can hamper fetal development during pregnancy and may have long term negative health outcomes in humans. Dietary sources, main route of BPA exposure, can be contaminated by the migration of BPA into food during processing. The global regulatory framework for using this compound in food contact materials is currently not harmonized. This review aims to outline, survey, and critically evaluate BPA contamination in meat products, including level of BPA and/or metabolites present, exposure route, and recent advancements in the analytical procedures of these compounds from meat and meat products. The contribution of meat and meat products to the total dietary exposure of BPA ranges between 10 and 50% depending on the country and exposure scenario considered. From can lining materials of meat products, BPA migrates towards the solid phase resulting higher BPA concentration in solid phase than the liquid phase of the same can. The analytical procedure is comprised of meat sample pre-treatment, followed by cleaning with solid phase extraction (SPE), and chromatographic analysis. Considering several potential sources of BPA in industrial and home culinary practices, BPA can also accumulate in non-canned or raw meat products. Very few scientific studies have been conducted to identify the amount in raw meat products. Similarly, analysis of metabolites and identification of the origin of BPA contamination in meat products is still a challenge to overcome.

Urinary Bisphenol A (BPA) Concentrations among Workers in Industries that Manufacture and Use BPA in the USA

Background

Bisphenol A (BPA) toxicity and exposure risk to humans has been the subject of considerable scientific debate; however, published occupational exposure data for BPA are limited.

Methods

In 2013-2014, 77 workers at six US companies making BPA, BPA-based resins, or BPA-filled wax provided seven urine samples over two consecutive work days (151 worker-days, 525 samples). Participant information included industry, job, tasks, personal protective equipment used, hygiene behaviors, and canned food/beverage consumption. Total (free plus conjugated) BPA, quantified in urine by mass spectrometry, was detected in all samples.

Results

The geometric mean (GM) creatinine-adjusted total BPA (total BPACR) concentration was 88.0 µg g-1 (range 0.78-18900 µg g-1), ~70 times higher than in US adults in 2013-2014 (1.27 µg g-1). GM total BPACR increased during Day 1 (26.6-127 µg g-1), decreased by pre-shift Day 2 (84.4 µg g-1) then increased during Day 2 to 178 µg g-1. By industry, baseline and post-baseline total BPACR was highest in BPA-filled wax manufacturing/reclaim (GM = 111 µg g-1) and lowest in phenolic resin manufacturing (GM = 6.56 µg g-1). By job, total BPACR was highest at baseline in maintenance workers (GM = 157 µg g-1) and post-baseline in those working with molten BPA-filled wax (GM = 441 µg g-1). Workers in the job of flaking a BPA-based resin had the lowest concentrations at baseline (GM = 4.81 µg g-1) and post-baseline (GM = 23.2 µg g-1). In multiple regression models, at baseline, industry significantly predicted increased total BPACR (P = 0.0248); post-baseline, handling BPA containers (P = 0.0035), taking ≥3 process/bulk samples with BPA (P = 0.0002) and wearing a Tyvek® coverall (P = 0.0042) significantly predicted increased total BPACR (after adjusting for total BPACR at baseline, time point, and body mass index).

Conclusion

Several work-related factors, including industry, job, and certain tasks performed, were associated with increased urinary total BPACR concentrations in this group of manufacturing workers. The potential for BPA-related health effects among these workers is unknown.

Recent advances in simultaneous analysis of bisphenol A and its conjugates in human matrices: Exposure biomarker perspectives

Human exposures to bisphenol A (BPA) has attained considerable global health attention and represents one of the leading environmental contaminants with potential adverse health effects including endocrine disruption. Current practice of measuring of exposure to BPA includes the measurement of unconjugated BPA (aglycone) and total (both conjugated and unconjugated) BPA; the difference between the two measurements leads to estimation of conjugated forms. However, the measurement of BPA as the end analyte leads to inaccurate estimates from potential interferences from background sources during sample collection and analysis. BPA glucuronides (BPAG) and sulfates (BPAS) represent better candidates for biomarkers of BPA exposure, since they require in vivo metabolism and are not prone to external contamination. In this work, the primary focus was to review the current state of the art in analytical methods available to quantitate BPA conjugates. The entire analytical procedure for the simultaneous extraction and detection of aglycone BPA and conjugates is covered, from sample pre-treatment, extraction, separation, ionization, and detection. Solid phase extraction coupled with liquid chromatograph and tandem mass spectrometer analysis provides the most sensitive detection and quantification of BPA conjugates. Discussed herein are the applications of BPA conjugates analysis in human exposure assessment studies. Measuring these potential biomarkers of BPA exposure has only recently become analytically feasible and there are limitations and challenges to overcome in biomonitoring studies.

Contemporary Issues in Exposure Assessment Using Biomonitoring

In environmental epidemiology, use of biomonitoring (i.e., trace-level measurement of environmental chemicals or their metabolites in biospecimens) for exposure assessment has increased considerably in past decades. Although exposure biomarkers should reflect a person's exposure to the target chemicals (or their precursors) within a specific timeframe, timing, duration, and intensity of exposures are normally unknown and likely vary within the study period. Therefore, evaluating exposure beyond a single time point may require collecting more than one biospecimen. Of note, collection and sample processing procedures will impact integrity and usefulness of biospecimens. All of the above factors are fundamental to properly interpret biomonitoring data. We will discuss the relevance of the exposure assessment study protocol design to (a) ensure that biomonitoring specimens reflect the intended exposure, (b) consider the temporal variability of concentrations of the target biomarkers, and

Measurement of Total and Free Urinary Phenol and Paraben Concentrations over the Course of Pregnancy: Assessing Reliability and Contamination of Specimens in the Norwegian Mother and Child Cohort Study

BACKGROUND

Exposures to environmental phenols and parabens may be harmful, especially in utero. Prior studies have demonstrated high within-person variability of urinary concentrations across pregnancy.

OBJECTIVES

We sought to measure phenol and paraben biomarker concentrations for the Norwegian Mother and Child Cohort (MoBa) study, assess within-person variability, and investigate any possible external phenol or paraben contamination of specimens.

METHODS

We collected three spot urine samples at approximately 17, 23, and 29 weeks gestation in a hospital setting and added a preservative containing ethyl paraben. We measured urinary concentrations and within-person variability for phenols and parabens in a MoBa sample (n = 45), including a subgroup of 15 participants previously randomly selected for a bisphenol A (BPA) exposure study who had unusually high total BPA concentrations. Additionally, we compared reliability results for total, conjugated, and free concentrations of phenolic compounds.

RESULTS

We detected total and free BPA, butyl paraben, propyl paraben, and methyl paraben in 100% of samples, total benzophenone-3 in 95% of samples, and infrequently detected free benzophenone-3 and total and free 2,4-dichlorophenol and 2,5-dichlorophenol. Intraclass correlation coefficients (ICCs) for total, conjugated, and free concentrations ranged from relatively low for BPA to moderate for propyl paraben. ICCs were generally similar overall and by subgroup.

CONCLUSIONS

Using conjugated concentrations improved reliability estimates only for BPA. Measuring total and free concentrations, an approach that may be useful for future studies, allowed us to identify likely BPA and butyl paraben contamination of archived MoBa urine specimens.

Presence and bioavailability of bisphenol A in the uterus of rats and mice following single and repeated dietary administration at low doses

This research examined the distribution of low dietary doses of bisphenol A (BPA). When female rats received 50μg/kg (14)C-BPA orally, radioactivity was distributed throughout the body, with especial presence in the uterus. Pre-treatment with estradiol or the estrogen antagonist ICI 182,780 significantly reduced radioactivity in the uterus. The majority of BPA at the uterus was determined to be aglycone (receptor-active) via GC-MS. Subsequently, mice given 0.5, 5, or 50μg/kg (14)C-BPA showed more radioactivity in the uterus than in other non-metabolic tissues. When female mice received 1, 7, or 28 daily doses of 50μg/kg (14)C-BPA, then were measured 24h after the last dose, significantly more radioactivity was detected in the uterus, liver, and kidney following repeated doses. Collectively, these data provide evidence for the in vivo interaction of BPA with estrogen receptors. They also indicate elevated presence of BPA in reproductive tissues after repeated low doses.

Biomonitoring of human fetal exposure to environmental chemicals in early pregnancy

The first trimester of human fetal life, a period of extremely rapid development of physiological systems, represents the most rapid growth phase in human life. Interference in the establishment of organ systems may result in abnormal development that may be manifest immediately or programmed for later abnormal function. Exposure to environmental chemicals may be affecting development at these early stages, and yet there is limited knowledge of the quantities and identities of the chemicals to which the fetus is exposed during early pregnancy. Clearly, opportunities for assessing fetal chemical exposure directly are extremely limited. Hence, this review describes indirect means of assessing fetal exposure in early pregnancy to chemicals that are considered disrupters of development. Consideration is given to such matrices as maternal hair, fingernails, urine, saliva, sweat, breast milk, amniotic fluid and blood, and fetal matrices such as cord blood, cord tissue, meconium, placenta, and fetal liver. More than 150 articles that presented data from chemical analysis of human maternal and fetal tissues and fluids were reviewed. Priority was given to articles where chemical analysis was conducted in more than one matrix. Where correlations between maternal and fetal matrices were determined, these articles were included and are highlighted, as these may provide the basis for future investigations of early fetal exposure. The determination of fetal chemical exposure, at the time of rapid human growth and development, will greatly assist regulatory agencies in risk assessments and establishment of advisories for risk management concerning environmental chemicals.

Concentrations of bisphenol A and seven other phenols in pooled sera from 3-11 year old children: 2001-2002 National Health and Nutrition Examination Survey

Concerns exist regarding children's exposure to bisphenol A (BPA) and other phenols because of the higher sensitivity, compared to adults, of children's developing organs to endocrine disruptors. Several studies reported the urinary concentrations of these phenols in children, but data on levels of these compounds in children's serum are limited. We present here the total (free plus conjugated) and free concentrations of BPA and seven other phenols in 24 pooled serum samples prepared from individual specimens collected from 936 children 3-11 years old who participated in the 2001-2002 National Health and Nutrition Examination Survey. We detected benzophenone-3, triclosan, 2,4-dichlorophenol, 2,5- dichlorophenol, and three parabens in at least 60% of the pools suggesting children's exposure to these compounds or their precursors. Conjugated phenols were the major species. However, although many previous studies have shown widespread detection of BPA in children's urine, we only detected total or free BPA in 3 and 2 pooled serum samples, respectively, at concentrations of 0.1-0.2 μg/L. The nonpersistent nature of BPA and the phenols examined and the likely episodic nature of the exposures to these compounds (or their precursors) suggest that for general population biomonitoring of these nonpersistent phenols, urine, not serum or plasma, is the preferred matrix.

Bisphenol A in 24 h urine and plasma samples of the German Environmental Specimen Bank from 1995 to 2009: a retrospective exposure evaluation

Human exposure to Bisphenol A (BPA) is omnipresent. Both the extent of the exposure and its toxicological relevance are controversially discussed. We aim to reliably determine and evaluate the extent of BPA body burden in the German population from 1995 to 2009 based on 600 24 h urine samples and corresponding plasma samples from the Environmental Specimen Bank. We determined total and unconjugated BPA in urine and plasma using on-line solid-phase extraction high-performance liquid chromatography coupled to isotope dilution tandem mass spectrometry with a limit of quantification (LOQ) of 0.1 μg/l. In the stored urines, total BPA was quantifiable in >96% (median: 1.49 μg/l; 95th percentile: 7.37 μg/l), whereas unconjugated BPA was quantifiable only in <15% of the samples. Total BPA concentrations decreased over time, but 24 h urine volumes increased. Therefore, daily intakes calculated from the 24 h urines remained rather constant at a median of 0.037 and a 95th percentile of 0.171 μg BPA/kg body weight/day. In 60 corresponding plasma samples, total BPA levels were generally below the LOQ of 0.1 μg/l and, if quantifiable, most BPA was unconjugated, thus hinting to external contamination. We see total BPA in urine as the most appropriate and robust marker for BPA exposure assessment (if controlled for BPA contamination). Unconjugated BPA in urine and unconjugated or total BPA in plasma where contamination or breakdown of the glucuronide cannot be ruled out are of no value for human exposure assessment.

Distribution of bisphenol-A, triclosan and n-nonylphenol in human adipose tissue, liver and brain

In this study, an analytical method was optimized for the determination of bisphenol-A (BPA), triclosan (TCS) and 4-n-nonylphenol (4n-NP), environmental contaminants with potential endocrine disruptive activities, in human tissues. The method consisted of a liquid extraction step, derivatization with pentafluorobenzoylchloride followed by a clean-up on acidified silica and detection with gas chromatography coupled with mass spectrometry (GC-ECNI/MS). Recoveries ranged between 92% and 102% with a precision below 5%. Limits of quantification ranged between 0.3-0.4 ng g(-1), 0.045-0.06 ng g(-1) and 0.003-0.004 ng g(-1) for BPA, TCS and 4n-NP in different tissues, respectively. The method was applied for the determination of BPA, TCS and 4n-NP in paired adipose tissue, liver and brain samples from 11 individuals. BPA could be detected in almost all tissues, with the highest concentrations found in adipose tissue (mean 3.78 ng g(-1)), followed by liver (1.48 ng g(-1)) and brain (0.91 ng g(-1)). TCS showed the highest concentrations in liver (3.14 ng g(-1)), followed by adipose tissue (0.61 ng g(-1)), while it could be detected in only one brain sample. Levels of 4n-NP were much lower, mostly undetected, and therefore 4n-NP is considered of minor importance for human exposure. Despite the measurable concentrations in adipose tissue, these compounds seem to have a low bioaccumulation potential. The reported concentrations of free BPA in the various tissues are slight disagreement with pharmacokinetic models in humans and rats and therefore the possibility of external contamination with BPA during sample collection/storage cannot be ruled out.

Pharmacokinetics of bisphenol A in serum and adipose tissue following intravenous administration to adult female CD-1 mice

Bisphenol A (BPA) is an important industrial chemical used as the monomer for polycarbonate plastic and in epoxy resins for use in food can liners. Worldwide biomonitoring studies consistently find high prevalence of BPA conjugates in urine consistent with pervasive exposure at levels typically below 1 μg/kg bw/day. The current study used LC/MS/MS to measure serum pharmacokinetics of unconjugated (active) and conjugated (inactive) BPA in adult female CD-1 mice following intravenous (IV) injection, which produces higher serum levels by circumventing the processes of absorption from the GI tract and presystemic metabolism that occur after oral administration. Deuterated BPA (100 μg/kg bw) was used to avoid interference by background contamination from trace amounts of native BPA. Additionally, the pharmacokinetics of unconjugated BPA were determined in adipose tissue, a proposed site of action and "depot" for BPA. After IV injection, unconjugated BPA rapidly distributed out of the circulation (t(1/2)=0.2 h) and terminal elimination also proceeded rapidly (t(1/2)=0.8 h). Consistent with the degree of aqueous solubility, lipid/water solubility ratio, and partitioning from blood into adipose tissue in vivo, the levels of unconjugated BPA in mouse adipose tissue rapidly reached a maximal level (0.25 h) that did not exceed the serum maximum at the initial sampling time (0.08 h). Terminal elimination of unconjugated BPA from adipose tissue (t(1/2)=7.0 h) was similar to that for conjugated BPA in serum (t(1/2)=6.6 h) and <0.01% of the administered dose remained in adipose tissue after 24 h. These plasma and tissue kinetics are consistent with rapid equilibria and underscore the non-persistent nature of BPA, particularly when compared with slowly metabolized lipophilic organic pollutants like halogenated dibenzodioxins.

Distribution of bisphenol A into tissues of adult, neonatal, and fetal Sprague-Dawley rats

Bisphenol A (BPA) is an important industrial chemical used in the manufacture of polycarbonate plastic products and epoxy resin-based food can liners. The presence of BPA metabolites in urine of >90% of Americans aged 6-60 suggests ubiquitous and frequent exposure in the range of 0.02-0.2μg/kgbw/d (25th-95th percentiles). The current study used LC/MS/MS to measure placental transfer and concentrations of aglycone (receptor-active) and conjugated (inactive) BPA in tissues from Sprague-Dawley rats administered deuterated BPA (100μg/kg bw) by oral and IV routes. In adult female rat tissues, the tissue/serum concentration ratios for aglycone BPA ranged from 0.7 in liver to 5 in adipose tissue, reflecting differences in tissue perfusion, composition, and metabolic capacity. Following IV administration to dams, placental transfer was observed for aglycone BPA into fetuses at several gestational days (GD), with fetal/maternal serum ratios of 2.7 at GD 12, 1.2 at GD 16, and 0.4 at GD 20; the corresponding ratios for conjugated BPA were 0.43, 0.65, and 3.7. These ratios were within the ranges observed in adult tissues and were not indicative of preferential accumulation of aglycone BPA or hydrolysis of conjugates in fetal tissue in vivo. Concentrations of aglycone BPA in GD 20 fetal brain were higher than in liver or serum. Oral administration of the same dose did not produce measurable levels of aglycone BPA in fetal tissues. Amniotic fluid consistently contained levels of BPA at or below those in maternal serum. Concentrations of aglycone BPA in tissues of neonatal rats decreased with age in a manner consistent with the corresponding circulating levels. Phase II metabolism of BPA increased with fetal age such that near-term fetus was similar to early post-natal rats. These results show that concentrations of aglycone BPA in fetal tissues are similar to those in other maternal and neonatal tissues and that maternal Phase II metabolism, especially following oral administration, and fetal age are critical in reducing exposures to the fetus.

Critical evaluation of key evidence on the human health hazards of exposure to bisphenol A

Despite the fact that more than 5000 safety-related studies have been published on bisphenol A (BPA), there seems to be no resolution of the apparently deadlocked controversy as to whether exposure of the general population to BPA causes adverse effects due to its estrogenicity. Therefore, the Advisory Committee of the German Society of Toxicology reviewed the background and cutting-edge topics of this BPA controversy. The current tolerable daily intake value (TDI) of 0.05 mg/kg body weight [bw]/day, derived by the European Food Safety Authority (EFSA), is mainly based on body weight changes in two- and three-generation studies in mice and rats. Recently, these studies and the derivation of the TDI have been criticized. After having carefully considered all arguments, the Committee had to conclude that the criticism was scientifically not justified; moreover, recently published additional data further support the reliability of the two- and three-generation studies demonstrating a lack of estrogen-dependent effects at and below doses on which the current TDI is based. A frequently discussed topic is whether doses below 5 mg/kg bw/day may cause adverse health effects in laboratory animals. Meanwhile, it has become clear that positive results from some explorative studies have not been confirmed in subsequent studies with higher numbers of animals or a priori defined hypotheses. Particularly relevant are some recent studies with negative outcomes that addressed effects of BPA on the brain, behavior, and the prostate in rodents for extrapolation to the human situation. The Committee came to the conclusion that rodent data can well be used as a basis for human risk evaluation. Currently published conjectures that rats are insensitive to estrogens compared to humans can be refuted. Data from toxicokinetics studies show that the half-life of BPA in adult human subjects is less than 2 hours and BPA is completely recovered in urine as BPA-conjugates. Tissue deconjugation of BPA-glucuronide and -sulfate may occur. Because of the extremely low quantities, it is only of minor relevance for BPA toxicity. Biomonitoring studies have been used to estimate human BPA exposure and show that the daily intake of BPA is far below the TDI for the general population. Further topics addressed in this article include reasons why some studies on BPA are not reproducible; the relevance of oral versus non-oral exposure routes; the degree to which newborns are at higher systemic BPA exposure; increased BPA exposure by infusions in intensive care units; mechanisms of action other than estrogen receptor activation; and the current regulatory status in Europe, as well as in the USA, Canada, Japan, New Zealand, and Australia. Overall, the Committee concluded that the current TDI for BPA is adequately justified and that the available evidence indicates that BPA exposure represents no noteworthy risk to the health of the human population, including newborns and babies.

Determination of total and free mono-n-butyl phthalate in human urine samples after medication of a di-n-butyl phthalate containing capsule

Phthalates like di-n-butyl phthalate (DnBP) and diisobutyl phthalate (DiBP) are commonly used as plasticisers, enteric coatings in medications and their metabolites (MnBP respectively MiBP) are suspect of adverse endocrine activities. The aim of this study was to determine kinetical data in humans after the application of a drug containing 3600 microg of DnBP and to quantify main metabolites of DnBP and DiBP with and without glucuronidase treatment. Since commonly glucuronides do not exhibit endocrine activity it is of interest to determine the potentially active metabolite like free MnBP and MiBP for a valid risk assessment. After the application of one capsule containing 3600 microg of DnBP to 17 volunteers 78% (median of 2248 microg of total MnBP) of administered DnBP was found within 24h in urine. After 24h the levels of MnBP in urine were comparable to concentrations before administration showing a fast elimination. In contrast to controls in all urine samples collected within 24h after the administration of the drug free MnBP was observed with a median of 4% of total MnBP. In controls total MnBP and MiBP were found in median concentration of 23 microg/24h and about 50 microg/24h, respectively and therefore environmental exposure to DnBP is only 1% compared to medication. Since an uptake of 3600 microg in only one capsule is already above the tolerable daily intake (TDI) for DnBP of 10 microg/kg b.w. from a preventive health protection DnBP should be replaced in medical drugs.

Temporal stability of the conjugated species of bisphenol A, parabens, and other environmental phenols in human urine

Human exposure to environmental phenols can be assessed by measuring the urinary concentrations of these compounds or their metabolites. Total concentrations, which include both free and conjugated (i.e., glucuronide and sulfated) species, are usually reported. Because conjugation may reduce the potential bioactivity of the compounds, measuring separately both the concentrations of free and conjugated species can be of interest. Data on the stability of these conjugated species in urine is critical if the concentrations of free and conjugated species are to be compared. Over a period of 6 months, we investigated the stability of the urinary conjugates of eight environmental phenols (bisphenol A, 2-hydroxy-4-metoxybenzophenone or benzophenone-3, triclosan, 2,5-dichlorophenol, methyl paraben, ethyl paraben, propyl paraben, and butyl paraben) at three storage conditions (room temperature, 4 degrees C, and -70 degrees C). After collection, conjugated species appeared to be stable for at least 7 days when the urine was stored at 4 degrees C, and for at least 180 days at -70 degrees C. By contrast, some of the environmental phenol conjugates commenced to degrade within 24 h after collection when the urine was stored at room temperature although the total concentrations remained relatively constant for at least 30 days. These results suggest that if the concentrations of free and conjugated species will be used for exposure assessment purposes, urine specimens collected for analysis of environmental phenols should be kept at room temperature for the shortest possible time after collection.