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

Abstract

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 two and four-week intervals, and to determine if 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 two-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 U.S. 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), while five other metabolites had lower ICCs (0.21 – 0.37). Menstrual phase was not related to metabolite concentrations. Though the same samples have not been measured both before and after long-term storage, results suggest that 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.

Temporal variability of urinary concentrations of phthalate metabolites, parabens and benzophenone-3 in a Belgian adult population

“…Nevertheless, results should be interpreted with caution because the creatinine correction is still debated since its production and elimination are influenced by several physiological and pathological factors potentially found inside a population aged from 1 to 85 years, as previously discussed (Dewalque et al, 2014a). (Hauser et al, 2004;Smith et al, 2012;Frederiksen et al, 2013;Koch et al, 2014;Fromme et al, 2007;Suzuki et al, 2009;Braun et al, 2012;Kranich et al, 2014;Peck et al, 2010;Townsend et al, 2013;Adibi et al, 2008;Fisher et al, 2015;Hoppin et al, 2002;Marcus et al, 2010;Preau et al, 2010;Baird et al, 2010;Meeker et al, 2011;Meeker et al, 2012;Philippat et al, 2013;Watkins et al, 2014;Meeker et al, 2013;Cantonwine et al, 2014;Engel et al, 2014). Lines are the ICC obtained in this study and whiskers are their 95% confidence interval.…”

“…First of all, the majority of the available studies investigating the intra-individual variability of phthalate, paraben and BP3 biomarkers have been carried out in some US populations (Hauser et al, 2004;Smith et al, 2012;Teitelbaum et al, 2008;Braun et al, 2012;Peck et al, 2010;Townsend et al, 2013;Adibi et al, 2008;Hoppin et al, 2002;Marcus et al, 2010;Preau et al, 2010;Baird et al, 2010;Meeker et al, 2011;Meeker et al, 2012;Philippat et al, 2013;Ferguson et al, 2014;Watkins et al, 2014) and only very few were performed outside the USA, for instance in Puerto Rico (Meeker et al, 2013;Cantonwine et al, 2014), Canada (Fisher et al, 2015), Asia (Suzuki et al, 2009;Engel et al, 2014) or in the European Union Koch et al, 2014;Fromme et al, 2007). The level of exposure, the distribution and the correlations between pollutants have already been demonstrated to vary from one country to another, highlighting the dependence of local commercial applications or the legislations in force on the sources and pathways of exposure to these pollutants (Dewalque et al, 2014a;Suzuki et al, 2009;Shirai et al, 2013).…”

Variability and predictors of urinary phthalate metabolites in Spanish pregnant women

“…Urine levels of monoester and oxidized metabolites are commonly used for human biomonitoring of phthalate exposure and may reflect only recent exposure to phthalates (few hours or days) (Monfort et al, 2010(Monfort et al, , 2012Wittassek et al, 2011). High withinperson variability in phthalate metabolites has been observed in previous studies where more than one spot urine samples were analyzed and reproducibility of the measurements has been shown to vary (intraclass correlation coefficients (ICCs) range from 0.06 to 0.91) depending on the phthalate metabolite measured and the study population (Adibi et al, 2008;Baird et al, 2010;Braun et al, 2012;Cantonwine et al, 2014;Ferguson et al, 2014;Fisher et al, 2014;Frederiksen et al, 2013;Hoppin et al, 2002;Meeker et al, 2012;Peck et al, 2010;Preau et al, 2010). Within-person variability could be further enhanced during the period of pregnancy because of changes in maternal diet, in the use of personal-care products, changes in the time spent in the different indoor environments (e.g.…”

Prenatal phthalate exposure and reproductive function in young men

“…The limited size of our study may have reduced the power of the analyses and underestimated any true effects (Hodgson et al, 2010). Simultaneously, levels of DEHP-and DiNP metabolites vary considerably within individuals (Baird et al, 2010;Frederiksen et al, 2013;Fromme et al, 2007;Peck et al, 2010), including in pregnant women (Adibi et al, 2008;Cantonwine et al, 2014;Irvin et al, 2010), which might have decreased the power even further (Frederiksen et al, 2013). Still, these secondary metabolites are considered as the best available exposure markers (Calafat et al, 2013;Wittassek et al, 2011), and have been reported fairly reproducible by others (Kim et al, 2014;Townsend et al, 2013), also during pregnancy (Suzuki et al, 2009).…”