Urinary concentrations of phthalates in couples planning pregnancy and its association with 8-hydroxy-2'-deoxyguanosine, a biomarker of oxidative stress: longitudinal investigation of fertility and the environment study

Abstract

Oxidative stress has been recognized as one of the most important contributors to infertility in both males and females. Exposure to many environmental chemicals, such as phthalates, has been shown to induce oxidative stress. In a longitudinal study designed to assess exposure to environmental chemicals and fecundity in couples who were planning pregnancy, 894 urine samples were collected from 469 couples from Michigan and Texas during 2005-2009. The concentrations of 14 phthalate metabolites and a marker of oxidative stress, 8-hydroxy-2'-deoxyguanosine (8-OHdG), were determined in these samples. Concentrations, profiles, and estimated daily intakes (DIs) of phthalates were positively associated with 8-OHdG. The median concentrations of monomethyl phthalate (mMP), monoethyl phthalate (mEP), mono(3-carboxypropyl) phthalate (mCPP), mono-n-butyl phthalate (mBP), mono(2-isobutyl) phthalate (miBP), monobenzyl phthalate (mBzP), Σ5mEHP (sum of five metabolites of di(2-ethylhexyl) phthalate (DEHP)) and Σ14phthalates (sum of 14 urinary phthalate metabolites) were 0.48, 85.2, 4.50, 7.66, 4.36, 3.80, 54.8, and 249 μg/g creatinine, respectively. The estimated DI values for DEHP in 39 individuals were above the U.S. Environmental Protection Agency's (EPA) reference dose (RfD) of 20 μg/kg-bw/day. The mean and median concentrations of 8-OHdG were 6.02 and 3.13 μg/g creatinine, respectively, which were significantly higher in females than in males. Statistically significant associations were found between 8-OHdG and urinary concentrations of mEP, and Σ5mEHP for females. Similarly, a significant association was found between 8-OHdG and DIs estimated for select phthalates. Our results suggested that phthalate exposure increases oxidative stress, which can be a mechanism for the diminished fertility observed in couples who were highly exposed to select phthalates.

Figure 1

Estimated daily intake (μg/kg-bw/day) of phthalates for males and females (from the urinary metabolite concentrations) in couples in Texas and Michigan planning pregnancy, 2005–2009. Horizontal lines represent the 10th, 50th, and 90th percentiles, and the boxes represent the 25th and 75th percentiles. Outliers are shown as individual points. The short horizontal line represents mean concentrations. DEHP1 and DEHP2 are DI of DEHP estimated from the concentrations of mEHHP and mEOHP, respectively. Legends with an asterisk indicate significant differences between females and males.