Phthalates Biomarker Identification and Exposure Estimates in a Population of Pregnant Women

Abstract

Phthalates are known reproductive and developmental toxicants in experimental animals. However, in humans, there are few data on the exposure of pregnant women that can be used to assess the potential developmental exposure experienced by the fetus. We measured several phthalate metabolites in maternal urine, maternal serum, and cord serum samples collected at the time of delivery from 150 pregnant women from central New Jersey. The urinary concentrations of most metabolites were comparable to or less than among the U.S. general population, except for mono(2-ethylhexyl) phthalate (MEHP), mono(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), and mono(2-ethyl-5-oxohexyl) phthalate (MEOHP), three metabolites of di(2-ethylhexyl) phthalate (DEHP). The median urinary concentrations of MEHHP (109 mug/l) and MEOHP (95.1 mug/l) were more than 5 times their population-based concentrations, whereas the median urinary concentration of MEHP was more than 20 times higher. High concentration of MEHP may indicate a recent exposure to the parent chemical DEHP in the hospital shortly before the collection of the samples. Calculation of daily intakes using the urinary biomarker data reveals that none of the pregnant women tested had integrated exposures to DEHP greater than the Agency for Toxic Substances and Disease Registry's minimal risk levels (MRLs chronic 60, intermediate 100 mug/kg/day). No abnormal birth outcomes (e .g., birth weight, Apgar Score, and gestational age) were noted in those newborns whose mothers had relatively greater exposure to DEHP during the perinatal period than others in this study. Significantly greater concentrations and detection frequencies in maternal urine than in maternal serum and cord serum suggest that the urinary concentrations of the phthalate metabolites may be more reliable biomarkers of exposure than their concentrations in other biological specimens.

Figure 1

Mean concentrations* of phthalate metabolites in cord serum, maternal serum, and maternal urine. Except for MMP, the phthalate metabolite concentrations in maternal urine are significantly greater than in maternal and cord serum concentrations (p < .05). *LOD/SQRT(2) was used for the mean calculations in cord and maternal serum when they were < LOD.

Figure 2

Relative cumulative frequency of DEHP daily intakes. MRL(c): ATSDR reproductive minimal risk level for chronic duration 60 μg/kg/day. MRL(i): ATSDR reproductive minimal risk level for intermediate duration 100 μg/kg/day.