Phthalate exposure in pregnant women and their children in central Taiwan

Abstract

Phthalate exposure was found to be associated with endocrine disruption, respiratory effects, reproductive and developmental toxicity. The intensive use of plastics may be increasing the exposure to phthalates in Taiwanese population, particularly for young children.

We studied phthalate metabolites in pregnant women and their newborns in a prospective cohort from a medical center in Central Taiwan. One hundred maternal urine samples and 30 paired cord blood and milk samples were randomly selected from all of participants (430 pregnant women). Eleven phthalate metabolites (MEHP, 5OH-MEHP, 2cx-MEHP, 5cx-MEPP, 5oxo-MEHP, MiBP, MnBP, MBzP, OH-MiNP, oxo-MiNP, and cx-MiNP) representing the exposure to five commonly used phthalates (DEHP, di-isobutyl phthalate (DiBP), DnBP, BBP, DiNP) were measured in urine of pregnant women, cord serum and breast milk after delivery, and in urine of their children. Exposure was estimated with excretion factors and correlation among metabolites of the same parent compound. Thirty and 59 urinary samples from 2 and 5 years-old children were randomly selected from 185 children successfully followed.

Total urinary phthalate metabolite concentration (geometric mean, μg L⁻¹) was found to be higher in 2-years-olds (398.6) and 5-years-olds (333.7) than pregnant women (205.2). Metabolites in urine are mainly from DEHP. The proportion of DiNP metabolites was higher in children urine (4.39 and 8.31%, ages 2 and 5) than in adults (0.83%) (p < 0.01). Compared to urinary levels, phthalate metabolite levels are low in cord blood (37.45) and milk (14.90). DEHP metabolite levels in women’s urine and their corresponding cord blood are significantly correlated. Compared to other populations in the world, DEHP derived metabolites in maternal urine were higher, while phthalate metabolite levels in milk and cord blood were similar. The level of phthalate metabolites in milk and cord blood were comparable to those found in other populations. Further studies of health effects related to DEHP and DiNP exposure are necessary for the children.

Introduction

Phthalates are chemicals widely used in commercial products, as plastic softeners and solvents in personal care products, lubricants and insect repellents (Fay et al., 1999, Koo and Lee, 2004, Lee et al., 2005). Potential sources of exposure for di(2-ethylhexyl)phthalate (DEHP) include polyvinylchloride containing medical devices, food packaging, plastic toys, furniture, and car upholstery. For instance, di-n-butyl phtalate (DnBP) are present in medicines, cosmetics, cellulose acetate plastics, latex adhesives, nail polish and other cosmetic products; butyl benzyl phthalate (BBP) are found in vinyl flooring, adhesives, sealants, food packaging, furniture upholstery, vinyl tile, carpet tiles, artificial leather, and di-isononyl phthalate (DiNP) are widely used in children’s toys (Sathyanarayana, 2008). Recent studies suggest that the intensive use of plastic material in Taiwan may be increasing the exposure of DEHP in Taiwanese population (Chen et al., 2008).

According to some epidemiological studies, phthalate exposure is associated with adverse health outcomes, including shorter ano-genital distances at birth (Swan, 2006), respiratory effects (Jaakkola et al., 1999, Jaakkola et al., 2000, Hoppin et al., 2004), increased waist circumference and insulin resistance (Stahlhut et al., 2007). Exposure to mono-n-butyl phthalate (MnBP), mono-benzyl phthalate (MBzP), and mono-2-ethylhexyl phthalate (MEHP) is associated to an overall pattern of decline in sperm motility parameters (Duty et al., 2004).

Pregnant and lactating women represent a population of special concern because of the potential impact of their exposures on the fetus and nursing infant. In general, exposure data for children under 6 years is scarce (NTP-CERHR, 2003a, McKee, 2004, Jahnke et al., 2005). Metabolites of DEHP, DnBP and BBP have been monitored in children aged 2–6 years old (Koch et al., 2004, Koch et al., 2005). Decrease in ano-genital distance in male infants has been found to be associated to phthalate exposure, particularly with urinary monoethyl phthalate (MEP), mono-butyl phthalate (MBP), MBzP and mono-isobutyl phthalate (MiBP) (Swan et al., 2005). In another study, MnBP in amniotic fluid has been found to be associated with shorter ano-genital distance only in female infants (Huang et al., 2009). In pregnant women, urinary MnBP is negatively correlated to thyroxine and free thyroxine (Huang et al., 2007).

Many experimental studies using different laboratory animals (mainly rats) examined the reproductive toxicity, developmental toxicity, endocrine disruption, and genotoxicity that might be induced by phthalic acid esters. For example, anti-androgenic effects including delayed puberty in F₀, decreased sperm production and fecundity in F₁, malformations in F₁ reproductive organs, and decreased F₂ litter size, were reported for DnBP (NTP-CERHR, 2003b). Its metabolite, MnBP, is responsible for the toxicity effects associated with DnBP exposure, including increased prenatal mortality, decreased fetal weight, cleft palate, fused sternebrae, reduced ano-genital distance in male, cryptorchidism, hypospadias, agenesis of epididymides or seminal vesicles (NTP-CERHR, 2003b). High doses of DiNP caused increase in liver weight, peroxisomal proliferation, skeletal variations and renal toxicity were observed in a one-generation and a two-generation toxicity study (Moorman et al., 2000, NTP-CERHR, 2003a). In rats, BBP was associated with decreased testis weight, reduced ano-genital distance, increased incidence of nipple retention and decreased birth weight in both sexes of the first filial generation (Gray et al., 2000, Parks et al., 2000). Treatment with DEHP was also associated to altered ano-genital distance and nipple retention (NTP-CERHR, 2006). In general, phthalic acid ester exposure was related to anti-androgenic endpoints.

In vitro studies help understanding the possible mechanisms of toxicity. Phthalates and their metabolites can bind to several nuclear receptors and act as endocrine disruptors or metabolic disruptors (Desvergne et al., 2009). In a series of reporter gene assays, DnBP, MnBP and DEHP have been found to have both anti-androgenic and androgenic activities at different concentrations. These compounds also showed thyroid receptor (TR) antagonistic activity. Only DnBP reported estrogenic activity (Shen et al., 2009). BBP has a binding affinity for estrogen receptor (ER) (Zacharewski et al., 1998, Blair et al., 2000, Hashimoto et al., 2000, Matthews et al., 2000), activates ER-mediated transcription (Zacharewski et al., 1998, Coldham et al., 1997, Harris et al., 1997, Hashimoto et al., 2000, Nishihara et al., 2000). DEHP has weak agonistic activity for aryl hydrocarbon receptor (AhR) (Kruger et al., 2008), constitutive androstane receptor (CAR, Nr1i3) (Eveillard et al., 2009), and Pregnane X nuclear receptor (PXR, Nr1i2) (Hurst and Waxman, 2004, Cooper et al., 2008). The interference of phthalates with steroid production, namely estradiol production and aromatase expression, is most affected by MEHP. A possible mechanism of this interference is through peroxisome proliferator-activated receptors (PPAR) mediation (Lovekamp and Davis, 2001, Lovekamp-Swan et al., 2003). MEHP is a true ligand for all three PPAR isotypes and a selective modulator of PPAR gamma (Desvergne et al., 2009). BBP does not activate progesterone receptor-mediated transcription (Tran et al., 1996) or AR-mediated transcription (Sohoni and Sumpter, 1998). Whereas BBP alone does not show significant agonistic AhR effect, it enhanced the TCDD induced AhR activity in a dose-dependent manner (Kruger et al., 2008). BBP exposure of female rats is also associated with a significant increase in liver Ethoxyresorufin-O-deethylation (EROD) activity (Singletary et al., 1997). BBP also induces human breast cancer cell proliferation (Harris et al., 1997, Soto et al., 1997, Korner et al., 1998).

We have monitored eleven phthalate metabolites (Mono-2-ethylhexyl phthalate (MEHP), 5-mono hydroxyl isononyl phthalate (5OH-MEHP), 2-mono carboxyl isononyl phthalate (2cx-MEHP), 2-ethyl-5-carboxypentyl phthalate (5cx-MEPP), 2-ethyl-5-oxylhexyl phthalate (5oxo-MEHP), MiBP, MnBP, MBzP, mono hydroxyl isononyl phthalate (OH-MiNP), mono oxo isononyl phthalate (oxo-MiNP), and mono carboxyl isononyl phthalate (cx-MiNP)) in pregnant women (urine, serum and milk), their newborns (cord blood) and prospectively in their children aged 2–3 years and 5–6 years (urine) from a medical center in Central Taiwan. These eleven metabolites are derived from the exposure to five commonly used phthalates: DEHP (MEHP, 5OH-MEHP, 2cx-MEHP, 5cx-MEPP, and 5oxo-MEHP), DiBP (MiBP), DnBP (MnBP), BBP (MnBP and MBzP), and DiNP (OH-MiNP, oxo-MiNP, and cx-MiNP). Exposures to phthalic acid esters were estimated based on the geometric mean and 95% confidence interval of each measured urinary metabolite level, and excretion fraction published in literature. Correlation among metabolites of the same parent compounds and among different types of samples from pregnant women and their corresponding children were also tested.