Characteristic Profiles of Urinary <i>p</i>-Hydroxybenzoic Acid and its Esters (Parabens) in Children and Adults from the United States and China

Hydroxybenzoic acid esters (parabens) are used as preservatives in foods, cosmetics, and pharmaceuticals, which results in the exposure of humans to these compounds. Parabens and its metabolite, p-hydroxybenzoic acid (p-HB) are excreted from urine in free and conjugated forms. In this study, free and total forms (free plus conjugated) of parabens and their common metabolite, p-HB, were measured in urine samples collected from U.S. children (n = 40), Chinese children (n = 70), and Chinese adults (n = 26). The median concentrations of the sum of 6 parabens (Σparabens) in urine from U.S. and Chinese children were 54.6 and 10.1 ng/mL, respectively. The median concentration of urinary parabens measured for Chinese adults was 33.2 ng/mL, which was lower than that reported for U.S. adults. Elevated concentrations of parabens (1000-10,000 ng/mL) were found in urine from some Chinese adult females. Parabens were present predominantly (>90%) as conjugated species in urine. Among the six parabens analyzed, methyl paraben (MeP) and propyl paraben (PrP) were the predominant compounds, which accounted for 57-98% and 1.4-12%, respectively, of the total concentrations. A significant positive correlation was found between the concentrations of MeP and PrP. The geometric mean (GM) concentration of p-HB was 1380 and 2370 ng/mL for Chinese children and adults, respectively. The GM concentrations of p-HB in urine from U.S. children were 752 ng/mL for girls and 628 ng/mL for boys, which were 2-3 times lower than the concentrations determined for Chinese children. There was a significant difference in the ratios of concentrations of Σparabens and p-HB between demographic groups, which suggested the existence of various exposure routes to parabens. Based on the concentrations of urinary parabens and p-HB, the daily intake (DI) of MeP and PrP was estimated. The GM DI(MeP) estimated for Chinese children was 0.5-0.7 mg/day, which was similar to those determined for U.S. children. The GM DI(PrP) (0.2-0.5 mg/day) estimated for Chinese children was 20- to 50-fold higher than the value determined for U.S. children (0.01 mg/day). The highest exposure to parabens was found for Chinese adult females, with GM DI(MeP) and DI(PrP) of 5.9 and 1.2 mg/day, respectively. Elevated exposure to PrP was found in some Chinese adult females (27 mg/day) and children (11 mg/day).