We detected concentrations of free plus conjugated species of MP and PP in urine in > 92% of the samples examined; we detected EP and BP in about 50%. The high frequency of detection of MP and PP most likely resulted from their wide use in food products (Soni et al. 2005
) and in common personal care products (e.g., lotions, cosmetics, hair preparations) (Andersen 2008
). The range of urinary concentrations spanning up to three orders of magnitude (–) may be related to lifestyle factors, including diet, that result in exposure differences and/or to individual variations in bioavailability, distribution kinetics, or metabolism of the parabens. These factors are important in interpreting biomonitoring data for other chemicals found in personal care products, such as the bactericide triclosan (Calafat et al. 2008b
; Sandborgh-Englund et al. 2006
) and the sunscreen agent benzophenone-3 (Calafat et al. 2008a
). All these factors as well as the timing of sample collection will affect the urinary concentrations of parabens on an individual basis. On a population basis (e.g., NHANES), however, the wide range of concentrations observed would represent an average exposure scenario (i.e., a paraben urinary concentration in the upper percentiles resulting from the collection of the urine soon after a person’s paraben-related activity may be offset by a concentration in the lower percentiles of another person who provided a urine sample shortly before conducting the same activity).
We observed moderate correlations between the concentrations of EP and BP, and much weaker correlations between either of these parabens and MP or PP. These findings suggest a potential common source(s) of exposure for EP and BP, which was not the case for MP and PP. The concentrations of MP and PP were highly correlated, most likely because they are the two most common parabens (Soni et al. 2005
) and may be used in combination in many commercial applications, including food, pharmaceuticals, and personal care products.
We previously reported the urinary concentrations of free plus conjugated species of several parabens in a convenience sample of 100 adults during 2003–2005 (Ye et al. 2006a
). The frequencies of detection were comparable among the sample (MP, 99%; PP, 96%; EP, 58%; BP, 69%) and NHANES 2005–2006 (MP, 99.1%; PP, 92.7%; EP, 42%; BP, 47%). In addition, the median concentrations were practically the same for PP, slightly higher for MP, and lower for BP and EP in the NHANES 2005–2006 sample compared with the convenience population. Although exposure to these parabens (assessed by the urinary concentrations) may have changed, these two data sets are not directly comparable for establishing temporal exposure trends because of the small sample size and lack of national representativeness of the convenience sample. Nonetheless, both data sets confirm considerable human exposure to parabens and could potentially be used to derive internal dose exposure estimates. Of interest, the convenience biomonitoring samples have already been used to estimate internal dose of parabens (Cowan-Ellsberry and Robison 2009
). Unfortunately, data are lacking regarding human metabolism of parabens, particularly of the fraction of the paraben excreted in the urine as the parent paraben (free or conjugated) versus the fraction excreted as p
-hydroxybenzoic acid. This information, including a better understanding of the possible differences in metabolism by exposure route in humans, is needed to adequately link paraben urinary biomarker measurements to exposure and to internal dose.
We report here for the first time the concentrations of parabens among children and adolescents. Our data confirm that exposure occurs at these younger ages. Further, the apparent lower exposure among the younger segments of this NHANES 2005–2006 population (reflected in lower urinary concentrations than for adults) is likely associated with lifestyle. For example, in general, adults are more likely to use pharmaceuticals and personal care products than are children. We observed a similar age pattern for monoethyl phthalate (Silva et al. 2004
), a metabolite of diethyl phthalate (DEP) for which a primary source of exposure may be the routine use of personal care products (Duty et al. 2005
Although parabens are nonpersistent chemicals that are excreted from the body within hours after exposure (Janjua et al. 2008
), examination session used as a surrogate for the time of urine collection was not a significant factor in explaining the variance of the urinary concentrations of the parabens. In contrast, we observed important differences in concentrations on the basis of demographic characteristics. Specifically, the LSGM MP and PP concentrations were significantly greater among people in the high household income category than among those in the medium- and low-income categories (), suggesting that the use of pharmaceuticals and personal care products according to socioeconomic status may affect paraben exposure.
Of interest, we observed that LSGM concentrations of MP and PP were highly dependent upon sex, age, and race/ethnicity (, and ), as we have reported for other compounds (or their metabolites) found in personal care products, such as DEP (Silva et al. 2004
) and benzophenone-3 (Calafat et al. 2008a
). The higher concentrations of MP and PP found among women than among men were likely attributable to women’s increased use of personal care products, such as cosmetics and lotions. Non-Hispanic black children and adolescents had LSGM concentrations of MP and PP that were higher than or very similar to the concentrations in non-Hispanic black adults; non-Hispanic blacks had much higher MP and PP concentrations than did the other two race/ethnicity groups, particularly among children, adolescents, and adults 20–59 years old. These differences may result from increased, continuous, or prolonged use of beauty, hair, and/or skin care products specifically marketed to this population in whom the use often begins at a young age. The less dramatic differences by race/ethnicity among older adults may be explained by increased use of pharmaceuticals regardless of race/ethnicity that may compensate for differences in personal care products use. Because MP and PP are also used in food products, we cannot rule out that potential differences in diet, should they exist, may have also contributed to the differences in urinary concentrations of MP and PP among the various demographic groups examined.
Identifying populations in the highest exposure category (i.e., with concentrations above the 95th percentile) is an important consideration for public health. Our data suggest that females, non-Hispanic blacks, and, to a lesser extent, Mexican Americans have higher exposures to MP and PP than do other demographic segments of the general population. Specifically, females and non-Hispanic blacks were more likely to exhibit concentrations of MP and PP above the 95th percentile than were males, non-Hispanic whites, or Mexican Americans. In particular, females were 3.2 times more likely than males, and non-Hispanic blacks were about 5 times more likely than non-Hispanic whites and 2.5 times more likely than Mexican Americans, to have MP concentrations above the 95th percentile. Mexican Americans were about twice as likely as non-Hispanic whites to present MP concentrations above the 95th percentile. Similarly, for PP, females were 4.2 times more likely than males, and non-Hispanic whites were 3.6 times less likely than non-Hispanic blacks and 2.56 times less likely than Mexican Americans, to have MP concentrations above the 95th percentile. The likelihood of presenting PP concentrations above the 95th percentile did not differ (p = 0.13) between Mexican Americans and non-Hispanic blacks. Age was not significantly associated with having concentrations above the 95th percentile for either MP or PP.
In summary, we found significant differences in concentrations of parabens across demographic groups, particularly those associated with sex and race/ethnicity. These data can be used to establish a nationally representative baseline assessment of exposure—a baseline against which the concentrations of these parabens in future populations can be compared in order to identify exposure trends. These NHANES 2005–2006 data may also be useful in a risk assessment of parabens if warranted by toxicologic or epidemiologic studies.