Within-person variability in urinary phthalate metabolite concentrations: Measurements from specimens after long-term frozen storage

Epidemiology Branch, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA.
Journal of Exposure Science and Environmental Epidemiology (Impact Factor: 3.19). 04/2009; 20(2):169-75. DOI: 10.1038/jes.2009.17
Source: PubMed


Laboratory studies show that exposure to phthalates during development can cause adverse effects, especially for males. Studies in humans would be facilitated by collection of urine during pregnancy, long-term storage, and measurement of phthalate metabolites at the time that offspring health is assessed. Our aims were to measure urinary phthalate metabolites after long-term freezer storage, to use those measurements to evaluate within-woman variability over 2- and 4-week intervals, and to determine whether the phases of the menstrual cycle affect metabolite levels. Samples were selected from daily first-morning urine specimens collected by 60 women and stored frozen since 1983-1985. Three specimens per woman were selected at approximately 2-week intervals to include both follicular and luteal phase samples. Seven metabolites of five phthalates were measured by mass spectrometry. Statistical analyses were conducted with correlation, mixed model regression, and the Wilcoxon signed rank test. Creatinine-corrected urinary phthalate metabolite concentrations measured in samples after long-term storage tended to have a similar right-skewed distribution, though with somewhat higher concentrations than those reported for recently collected US samples. The concentrations of three metabolites of di(2-ethylhexyl)phthalate in the same specimen were very highly correlated (Pearson r=0.85-0.97). Reproducibility over a 4-week interval was moderate for the metabolites of diethyl phthalate and benzylbutyl phthalate (intraclass correlation coefficients, ICCs, 0.48 and 0.53, respectively), whereas five other metabolites had lower ICCs (0.21-0.37). Menstrual phase was not related to metabolite concentrations. Although the same samples have not been measured both before and after long-term storage, results suggest that the measurement of phthalate metabolites after long-term sample storage yield generally similar distributions and temporal reliability as those reported for recently collected specimens. These findings support the use of stored urine specimens collected during the relevant stage of human pregnancy to investigate the influence of phthalate exposures on later outcomes.

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Available from: Pablo A Nepomnaschy,
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    • "Temporal variability in individual concentrations of urinary phthalate metabolites may be caused by changes in individual behaviors, such as dietary patterns or the use of personal care products, as well as by changes in the composition of commercial products, and consequently the presence of phthalates in indoor and outdoor environments. Previous studies have evaluated the intra-individual variability of urinary phthalate metabolite measurements, but have generally used repeated samples taken over a relatively short period of time, i.e. days or weeks to months (Baird et al., 2010; Frederiksen et al., 2013; Hoppin et al., 2002; Meeker et al., 2012; Peck et al., 2010; Preau et al., 2010). One recent study reported intra-individual variability in urinary phthalate metabolites over a 1 to 3 year period among U.S. women enrolled in the Nurses' Health Study (Townsend et al., 2013). "
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    ABSTRACT: Phthalate esters are man-made chemicals commonly used as plasticizers and solvents, and humans may be exposed through ingestion, inhalation, and dermal absorption. Little is known about predictors of phthalate exposure, particularly in Asian countries. Because phthalates are rapidly metabolized and excreted from the body following exposure, it is important to evaluate whether phthalate metabolites measured at a single point in time can reliably rank exposures to phthalates over a period of time. We examined the concentrations and predictors of phthalate metabolite concentrations among 50 middle-aged women and 50 men from two Shanghai cohorts, enrolled in 1997-2000 and 2002-2006, respectively. We assessed the reproducibility of urinary concentrations of phthalate metabolites in three spot samples per participant taken several years apart (mean interval between first and third sample was 7.5years [women] or 2.9years [men]), using Spearman's rank correlation coefficients and intra-class correlation coefficients. We detected ten phthalate metabolites in at least 50% of individuals for two or more samples. Participant sex, age, menopausal status, education, income, body mass index, consumption of bottled water, recent intake of medication, and time of day of collection of the urine sample were associated with concentrations of certain phthalate metabolites. The reproducibility of an individual's urinary concentration of phthalate metabolites across several years was low, with all intra-class correlation coefficients and most Spearman rank correlation coefficients ≤0.3. Only mono(2-ethylhexyl) phthalate, a metabolite of di(2-ethylhexyl) phthalate, had a Spearman rank correlation coefficient ≥0.4 among men, suggesting moderate reproducibility. These findings suggest that a single spot urine sample is not sufficient to rank exposures to phthalates over several years in an adult urban Chinese population. Published by Elsevier Ltd.
    Environment international 08/2015; 84:94-106. DOI:10.1016/j.envint.2015.07.003 · 5.56 Impact Factor
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    • "In fact, moderately high correlations were found for BPA measurements taken 2 weeks apart (Spearman correlation 0.5), as were levels of diethyl phthalate and benzylbutyl phthalate over several weeks, with intraclass correlation coefficients of 0.48 and 0.53, respectively (Nepomnaschy et al., 2009). No phthalates were observed to vary across the menstrual cycle (Baird et al., 2010). Categories of phthalate levels were reasonably consistent across one-month averages for all metabolites except DEHP (Peck et al., 2010). "
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    ABSTRACT: Bisphenol A, benzophenone-type UV filters, and phthalates are chemicals in high production and use including in a range of personal care products. Exposure of humans to these chemicals has been shown to affect endocrine function. Although short-lived, widespread exposure may lead to continual opportunity for these chemicals to elicit health effects in humans. The association of these chemicals with incident uterine leiomyoma, an estrogen sensitive disease, is not known. Urinary concentrations of bisphenol A (BPA), five benzophenone-type UV filters (2-hydroxy-4-methoxybenzophenone (2OH-4MeO-BP), 2,4-dihydroxybenzophenone (2,4OH-BP), 2,2׳-dihydroxybenzophenone (2,2׳OH-4MeO-BP), 2,2׳4,4׳-tetrahydroxybenzophenone (2,2׳4,4׳OH-BP), and 4-hydroxybenzophenone (4OH-BP), and 14 phthalate monoesters were quantified in 495 women who later underwent laparoscopy/laparotomy at 14 clinical sites for the diagnosis of fibroids. Significantly higher geometric mean creatinine-corrected concentrations of BPA, 2,4OH-BP, and 2OH-4MeO-BP were observed in women with than without fibroids [BPA: 2.09 µg/g vs. 1.46 µg/g p=0.004; 2,4OH-BP:11.10 µg/g vs. 6.71 µg/g p=0.01; 2OH-4MeO-BP: 11.31 µg/g vs. 6.10 µg/g p=0.01]. Mono-methyl phthalate levels were significantly lower in women with than without fibroids (1.78 µg/g vs. 2.40 µg/g). However, none of the exposures were associated with a significant odds ratio even when adjusting for relevant covariates. There was a lack of an association between select nonpersistent chemicals and the odds of a fibroid diagnosis.
    Environmental Research 02/2015; 137. DOI:10.1016/j.envres.2014.06.028 · 4.37 Impact Factor
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    • "Prior studies have most often used urine samples to evaluate exposure levels in population studies, because phthalate and BPA concentrations are about 20 to 100 times higher in urine than in blood [39,40]. Some evidence indicates low to moderate correlation between urinary BPA and phthalate measures taken a month or more apart, with observed intraclass correlation coefficients of approximately 0.1 to 0.3 for BPA and 0.3 to 0.5 for mono-ethyl phthalate [46-50]. Misclassification of subject exposure levels would tend to bias our results toward a null association and would thus not appear to explain the observed positive associations. "
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    ABSTRACT: Introduction Humans are widely exposed to estrogenically active phthalates, parabens, and phenols, raising concerns about potential effects on breast tissue and breast cancer risk. We sought to determine the association of circulating serum levels of these chemicals (reflecting recent exposure) with mammographic breast density (a marker of breast cancer risk). Methods We recruited postmenopausal women aged 55 to 70 years from mammography clinics in Madison, Wisconsin (N = 264). Subjects completed a questionnaire and provided a blood sample that was analyzed for mono-ethyl phthalate, mono-butyl phthalate, mono-benzyl phthalate, butyl paraben, propyl paraben, octylphenol, nonylphenol, and bisphenol A (BPA). Percentage breast density was measured from mammograms by using a computer-assisted thresholding method. Results Serum BPA was positively associated with mammographic breast density after adjusting for age, body mass index, and other potentially confounding factors. Mean percentage density was 12.6% (95% confidence interval (CI), 11.4 to 14.0) among the 193 women with nondetectable BPA levels, 13.7% (95% CI, 10.7 to 17.1) among the 35 women with detectable levels below the median (<0.55 ng/ml), and 17.6% (95% CI, 14.1 to 21.5) among the 34 women with detectable levels above the median (>0.55 ng/ml; Ptrend = 0.01). Percentage breast density was also elevated (18.2%; 95% CI, 13.4 to 23.7) among the 18 women with serum mono-ethyl phthalate above the median detected level (>3.77 ng/ml) compared with women with nondetectable BPA levels (13.1%; 95% CI, 11.9 to 14.3; Ptrend = 0.07). No other chemicals demonstrated associations with percentage breast density. Conclusions Postmenopausal women with high serum levels of BPA and mono-ethyl phthalate had elevated breast density. Further investigation of the impact of BPA and mono-ethyl phthalate on breast cancer risk by using repeated serum measurements or other markers of xenoestrogen exposure are needed.
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