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Background: Human exposure to bisphenol A (BPA) is widespread. After exposure, BPA is rapidly metabolized and eliminated in urine. Therefore, there is considerable within-person and between-person variability of BPA concentrations in spot urine samples. However, no information exists on the within-day variability of urinary BPA concentrations. Objectives: We examined the between-person and within-person and between-day and within-day variability in the urinary BPA concentrations of eight adults who collected all voids for 1 week to investigate the impact of sampling strategy in the exposure assessment of BPA using spot, first morning, or 24-hr urine collections. Methods: We determined the urinary concentrations of BPA using on-line solid-phase extraction coupled to isotope dilution high-performance liquid chromatography/tandem mass spectrometry. Results: The between-day and within-person variability was the primary contributor to the total variance both for first morning voids (77%) and 24-hr urine collections (88%). For the spot collections, we observed considerable within-day variance (70%), which outweighed the between-person (9%) and between-day and within-person (21%) variances. Conclusions: Regardless of the type of void (spot, first morning, 24-hr collection), urinary BPA concentrations for a given adult changed considerably—both within a day and for the 7 days of the study period. Single 24-hr urine collections accurately reflect daily exposure but can misrepresent variability in daily exposures over time. Of interest, when the population investigated is sufficiently large and samples are randomly collected relative to meal ingestion times and bladder emptying times, the single spot–sampling approach may adequately reflect the average exposure of the population to BPA.

Background Parabens are widely used as antimicrobial preservatives in cosmetics, pharmaceuticals, and food and beverage processing. Objectives We assessed exposure to methyl, ethyl, propyl, and butyl parabens in a representative sample of persons ≥ 6 years of age in the U.S. general population from the 2005–2006 National Health and Nutrition Examination Survey. Methods We analyzed 2,548 urine samples by using online solid-phase extraction coupled to isotope dilution–high-performance liquid chromatography/tandem mass spectrometry. Results We detected methyl paraben (MP) and propyl paraben (PP) in 99.1% and 92.7% of the samples, respectively. We detected ethyl (42.4%) and butyl (47%) parabens less frequently and at median concentrations at least one order of magnitude lower than MP (63.5 μg/L) and PP (8.7 μg/L). Least-square geometric mean (LSGM) concentrations of MP were significantly higher (p ≤ 0.01) among non-Hispanic blacks than among non-Hispanic whites except at older ages (≥ 60 years). Adolescent and adult females had significantly higher (p < 0.01) LSGM concentrations of MP and PP than did adolescent and adult males. Females were more likely than males [adjusted odds ratios (ORs) and 95% confidence intervals (CIs): MP, 3.2 (2.99–5.27); PP, 4.19 (2.34–7.49)] and non-Hispanic blacks were more likely than non-Hispanic whites [MP, 4.99 (2.62–9.50); PP, 3.6 (1.86–7.05)] to have concentrations above the 95th percentile. Conclusions The general U.S. population was exposed to several parabens during 2005–2006. Differences in the urinary concentrations of MP and PP by sex and race/ethnicity likely reflect the use of personal care products containing these compounds.

Nonylphenol (NP) has been widely used for more than 50 years in the synthesis of NP ethoxylates, which are important nonionic surfactants. NP is considered an endocrine disruptor based on in vitro and in vivo animal studies. However, the toxic effects of NP in humans are unknown. Information regarding the metabolic fate of 4-t-nonylphenol (4-tNP), a mixture of commercial NP branched isomers, in mammalian species is limited. This information is critical for the identification of adequate biomarkers of exposure to NP that could be used for exposure and risk assessment. We identified metabolites of one 4-tNP isomer, namely, 4-(3',6'-dimethyl-3'-heptyl) phenol (P363-NP), using rat and human liver microsomes. The P363-NP metabolites were extracted by on-line solid-phase extraction and then separated and detected using high-performance liquid chromatography/tandem mass spectrometry. Using the genuine standard, we unambiguously identified 4-(3',6'-dimethyl-3'-heptyl) catechol (P363-NC) as the main P363-NP metabolite when using human liver microsomes. Based on their chromatographic behavior and mass spectral fragmentation patterns, several other metabolites were tentatively identified, including a hydroxylated P363-NP with the alcohol functional group on the branched alkyl chain and its oxidative metabolite, a catechol with a hydroxylated alkyl side chain. Furthermore, the metabolite profile of P363-NP using rat and human enzymes was compared. Our findings suggest that P363-NC could be used as a biomarker to assess exposure to 4-tNP, although additional research to evaluate its suitability as a biomarker is warranted.

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.

Parabens (esters of p-hydroxybenzoic acid) and triclosan are widely used as preservatives and antimicrobial agents, respectively, in personal care products, pharmaceuticals, and food processing. Because of their widespread use and potential risk to human health, assessing human exposure to these compounds in breastfed infants is of interest. We developed a sensitive method, using a unique on-line solid-phase extraction-high performance liquid chromatography-tandem mass spectrometry system with peak focusing feature, to measure in human milk the concentrations of five parabens (methyl-, ethyl-, propyl-, butyl-, and benzyl parabens), triclosan, and six other environmental phenols: bisphenol A (BPA); ortho-phenylphenol (OPP); 2,4-dichlorophenol; 2,5-dichlorophenol; 2,4,5-trichlorophenol; and 2-hydroxy-4-methoxybenzophenone (BP-3). The method, validated by use of breast milk pooled samples, shows good reproducibility (inter-day coefficient of variations ranging from 3.5% to 16.3%) and accuracy (spiked recoveries ranging from 84% to 119% at four spiking levels). The detection limits for most of the analytes are below 1 ng mL(-1) in 100 microL of milk. We tested the usefulness of the method by measuring the concentrations of these twelve compounds in four human milk samples. We detected methyl paraben, propyl paraben, triclosan, BPA, OPP, and BP-3 in some of the samples tested. The free species of these compounds appear to be the most prevalent in milk. Nevertheless, to demonstrate the utility of these measures for exposure and risk assessment purposes, additional data about sampling and storage of the milk, and on the stability of the analytes in milk, are needed.