Variability of Phthalate Monoester Levels in Daily First-Morning Urine from Adult Women: A Pilot Study

Phthalate exposure is ubiquitous and may affect child and adolescent health through both in utero exposure and direct exposure during childhood. Variability in exposure within women is not well documented. We analyzed 90 first-morning urine samples collected by ten reproductive-age women for phthalate metabolites and creatinine. Monoethyl [ 122 ng/mL (geometric mean concentration = 139 μg/g creatinine)], monobutyl [85.4 ng/mL (97.0 μg/g creatinine)], monobenzyl [37.2 ng/mL (42.2 μg/g creatinine)], and mono-2-ethylhexyl phthalate [9.4 ng/mL (10.7 μg/g creatinine)] were detected in most (94.4%) samples. The concentrations ranged from 23.8-1090 ng/mL, 43-437 ng/mL, 12.4-186 ng/mL, and 1.3-31.1 ng/mL, respectively. We observed considerable variation in phthalate concentrations by day for individual women. The intraclass correlation coefficient, indicating the proportion of variance explained by differences between subjects, ranged from 0.40 (monobutyl) to 0.68 (monoethyl). Monobenzyl and monoethyl phthalates showed higher levels on weekends as compared with weekdays (p = .01 for both). We found no significant difference between monoester levels from different menstrual cycles. Phthalate concentrations vary considerably for an individual and may require multiple samples for accurate assessment.