In epidemiologic studies, classifying episodic exposures to chemicals with short half-lives, such as phthalates and phenols, is challenging. We assessed whether accounting for sources of variability unrelated to exposure pathways would improve the reproducibility of urine concentrations of select phthalate metabolites and phenols. In 2011, a subset of pregnant women (n = 19) enrolled in a prospective study provided first morning urine samples every 3–4 weeks between 16 and 36 weeks gestation. At the time of collection, we identified potential contributors to variations in urinary concentrations: weight gain, gestational age, time slept, time since awoke, time since last food/drink, and time since last void. We estimated intraclass correlation coefficients (ICCs) among repeat urine concentrations with and without adjustment for sources of variability using a random intercept linear mixed model. Concentrations of monoethyl phthalate, butyl, and propyl parabens were the most reproducible (ICCs: 0.68, 0.56, and 0.56, respectively). However, adjustment for potential sources of variability unrelated to exposure pathways did not materially improve reproducibility nor the ability of a single sample to predict exposure based on average biomarker concentrations across pregnancy. Future studies should carefully consider the exposure timeframe and the reliability of using biomarker concentrations from a single time point to represent exposures over pregnancy.
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We thank the study participants for their time and participation which made this work possible. We also thank Manori Silva, Prabha Dwivedi, Ella Samandar, Jim Preau, Xiaoliu Zhou, and Tao Jia for technical assistance in measuring the urinary concentrations of phenols and phthalate metabolites.
Support for this research was provided by the following grants: RD-83459301 and RD-835434010 from the U.S. Environmental Protection Agency; P20 ES018163, P20 ES018163-S1, P01 ES022848, and R01 ES014864 from the National Institute of Environmental Health Sciences (NIEHS/NIH). MMY was supported by NIEHS training grant T32 ES007069.
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The authors declare that they have no conflict of interest.
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Yazdy, M.M., Coull, B.A., Gardiner, J.C. et al. A possible approach to improving the reproducibility of urinary concentrations of phthalate metabolites and phenols during pregnancy. J Expo Sci Environ Epidemiol 28, 448–460 (2018). https://doi.org/10.1038/s41370-018-0050-0
- Child exposure/health
- Endocrine disruptors
- Prenatal exposure