Triclosan has been detected in the aquatic environment and in some food sources (Lindstrom et al. 2002; Lopez-Avila and Hites 1980; McAvoy et al. 2002; Okumura and Nishikawa 1996; Singer et al. 2002), and has attracted interest as an environmental contaminant (Halden and Paull 2005). In frogs, triclosan can disrupt thyroid hormone-associated gene expression and induce changes in the thyroid hormone-mediated metamorphosis process (Veldhoen et al. 2006). Triclosan can also alter circulating serum concentrations of total thyroxine in rats (Crofton et al. 2007). Triclosan is not acutely toxic to mammals (Bhargava and Leonard 1996), but it can interact with cytochrome P450–dependent enzymes, UDP-glucuronosyltransferases, and the human pregnane X receptor (Hanioka et al. 1996; Jacobs et al. 2005; Wang et al. 2004). The relevance of these interactions is unknown.

Information about the known commercial uses of triclosan indicates that ingestion and dermal absorption are the most likely routes of exposure (Moss et al. 2000; Sandborgh-Englund et al. 2006). Radioactive triclosan is excreted in feces, and to a lesser extent in urine, after topical exposure in rats (Moss et al. 2000) and oral administration in mice (Kanetoshi et al. 1988). The extent of dermal absorption of triclosan was examined both in vitro and in vivo in rats and humans (Moss et al. 2000). In vitro, 24 hr after application, about 6.3% of triclosan had penetrated human skin compared with 23% for rat skin. These data suggest that dermal absorption of triclosan in humans is lower than in rats. In all cases, glucuronidation and to a lesser extent sulfation of triclosan occurred during passage through the skin. No oxidative metabolites were detected in the urine in vivo or after absorption through skin in vitro; the major urinary metabolites were triclosan glucuronide and sulfate (Moss et al. 2000). In another study, 10 healthy adult Swedish volunteers (50% males; median age, 28 years) were exposed to a single oral dose of 4 mg triclosan by swallowing an oral mouthwash solution, and the volunteers’ plasma and urinary concentrations of triclosan were determined (Sandborgh-Englund et al. 2006). Triclosan concentrations in plasma increased rapidly, with a maximum concentration within 1–3 hr; the estimated terminal plasma half-life was 21 hr. The major fraction of the triclosan dose was excreted in urine within the first 24 hr (calculated urinary excretion half-life was 11 hr), and approached baseline levels within 8 days after exposure. A median oral dose of 54% was excreted in urine within the first 4 days after exposure. The percentage of free triclosan in plasma was higher than in urine; in urine, triclosan was excreted mostly in its conjugated forms. These data suggest that the concentrations of triclosan in urine (conjugated and free species) can be used as biomarkers of exposure to triclosan.

The widespread use of triclosan has raised interest about assessing human exposure to this compound. Therefore, we measured the urinary concentration of triclosan in participants of the National Health and Nutrition Examination Survey (NHANES) 2003–2004 to obtain the first nationally representative concentration of triclosan in the United States.

A single spot urine sample per participant was collected during one of three daily examination session periods (i.e., morning, afternoon, evening). The samples were shipped on dry ice to CDC’s National Center for Environmental Health and stored at or below −20°C until analyzed. We measured the concentrations of free plus conjugated triclosan, in 100 μL of urine, by online solid-phase extraction coupled to high-performance liquid chromatography–isotope dilution–tandem mass spectrometry, as described in detail elsewhere (Ye et al. 2005). Briefly, the conjugated species of triclosan were hydrolyzed by use of 50 μL of a solution (4,000 μg/mL) of β-glucuronidase/sulfatase (Helix pomatia, 463,000U/g solid; Sigma Chemical Co., St. Louis, MO) in 1 M ammonium acetate pH 5 buffer (Sigma Chemical Co.). After hydrolysis, samples were acidified with 0.1M formic acid; triclosan was preconcentrated by online solid-phase extraction, separated from other urine components by reversed-phase high-performance liquid chromatography, and detected by atmospheric pressure chemical ionization–tandem mass spectrometry. The limit of detection (LOD)—calculated as 3 S₀, where S₀ is the standard deviation as the concentration approaches zero (Taylor 1987)—was 2.3 μg/L; the precision ranged from 14.3% to 23.2%. To minimize potential contamination with triclosan during the laboratory operations, we avoided the use of triclosan-containing soaps and detergents. In addition, low-concentration (~ 40 μg/L) and high-concentration (~ 230 μg/L) quality control materials, prepared with pooled human urine, and reagent blanks (to monitor and control for the potential contamination arising from the reagents and apparatus used) were analyzed with analytical standards and NHANES samples.

We performed statistical analyses using SAS (version 9.1.3; SAS Institute Inc., Cary, NC) and SUDAAN (version 9.0.1; RTI International, Research Triangle Park, NC). SUDAAN incorporates sample weights and design variables to account for the complex sample design of NHANES. We calculated the percentage of detection, the geometric mean, and distribution percentiles for both the volume-based (in micrograms per liter) and creatinine-corrected (in micrograms per gram creatinine) concentrations. For concentrations below the LOD, as recommended for the analysis of NHANES data (CDC 2006b), we used a value equal to the LOD divided by the square root of 2 (Hornung and Reed 1990).

We used analysis of covariance to examine the influence of several variables, selected on the basis of statistical, demographic, and biologic considerations, on the concentrations of triclosan. For the multiple regression models, we used the variables described below and all possible two-way interactions to calculate the adjusted least square geometric mean (LSGM) concentrations (in micrograms per liter), which provide geometric mean estimates for a variable after adjustment for the model covariates. Because the distribution of the triclosan concentrations was skewed, triclosan concentrations were log-transformed. A variable based on self-reported data defined three major racial/ethnic groups: non-Hispanic black, non-Hispanic white, and Mexican American. Self-reported annual household income was available in $5,000 increments (ranging from < $5,000 to > $75,000). To obtain comparable numbers of participants in each income group, we categorized income as < $20,000, $20,000–$45,000, and > $45,000. Those participants who had serum cotinine concentrations (the biomarker used to define smoking status) > 10 μg/L were classified as smokers. Creatinine concentrations were log-transformed for the data analysis because of their skewed distribution. Age was reported in years at the previous birthday. Because body mass index (BMI) is age- and sex-specific for people < 19 years of age, CDC recommends for children and teens the use of BMI-for-age percentile (BMIPCT) instead of BMI (Kuczmarski et al. 2002). Therefore, we conducted two separate models: one for adults (≥ 20 years of age) and one for children and teenagers (6–19 years of age). We could not include only children (6–11 years of age) in the model because of the small sample size for some strata. We considered age (continuous), sex, race/ethnicity, creatinine concentration (Barr et al. 2005), and income for both models. Additionally, for the adult model, we included smoking status and BMI, and for the children and teens model, we included BMIPCT. When both age and age-squared were in the model, to avoid multicollinearity we centered age by subtracting the mean age from each participant’s age (Bradley and Srivastava 1979). To evaluate the relation between the log-transformed concentration of triclosan and age, we estimated the weighted geometric mean and LSGM concentrations after adjusting by the other covariates in the model, and we generated a bar chart of triclosan concentrations by age group.

The children and adolescents model included age (p = 0.4), age-squared (p = 0.04), income, log-transformed creatinine, race/ethnicity, and interaction terms between race/ethnicity and income (p = 0.04) and log-transformed creatinine and income (p = 0.02). However, the relatively low frequency of detection of triclosan (55%) in one of the combination groups (non-Hispanic whites with $20,000–$45,000 household income), although with sufficient sample size, resulted in a biased low LSGM and hence in the significant interaction term between race/ethnicity and income. Therefore, we repeated the multiple regression analyses without these interaction terms. The final model included income (p = 0.0014), log-transformed creatinine (p < 0.001), age (p = 0.12), and age-squared (p = 0.014) (Table 2). We observed both an accelerated increasing relationship between the log-transformed triclosan concentration and age (β coefficient for age-squared = 0.006), and a linear increasing relationship between the log-transformed triclosan and creatinine concentrations (β coefficient = 0.0002). People in the < $20,000 income group had lower LSGM [95% confidence interval (CI)] triclosan concentrations [9.3 μg/L (6.8–12.7 μg/L)] than those in the > $45,000 income group [15.7 μg/L (11.8–20.8 μg/L)]. People in the $20,000–$45,000 income group had the lowest LSGM concentrations [7.7 μg/L (5.6–10.8 μg/L)]. The frequency of detection of triclosan varied by income group [63.7% ($20,000–$45,000); 78.7% (< $20,000); and 76.8% (> $45,000)].

In the adult model, log-transformed creatinine, income, and age were significant (Table 2). Triclosan LSGM concentrations (95% CI) increased with household income and were significantly lower for people in the low household income category [10.2 μg/L (8.5–12.2 μg/L)] than for people in the medium [13.8 μg/L (10.9–17.4 μg/L); p = 0.02] and high [15.5 μg/L (13.7–17.5 μg/L); p = 0.01] income categories; the differences in LSGM concentrations between people in the medium and high household income categories were not statistically significant (p = 0.38). Triclosan concentrations decreased as age increased (β coefficient = −0.004) and increased as creatinine (log-transformed) increased (β coefficient = 0.58).

Because BMI or BMIPCT and smoking status were not significantly associated with the triclosan concentration in the models above, we combined the two models for all ages without including these variables. In the final all-ages model, log-transformed creatinine, household income, age, and age-squared were significant (Table 2). The LSGM urinary triclosan concentration (in micrograms per liter) increased as income increased: Participants in the high household income category had significantly higher LSGM (95% CI) triclosan concentrations [15.3 (13.7–17.3)] than participants in the low-[10.3 (9.1–11.6); p < 0.01] and medium-[12.2 (10–14.9); p = 0.04] income categories. However, differences in LSGM concentrations between people in the medium and lowest household income categories were not statistically significant (p = 0.13). The triclosan concentrations increased as creatinine (log-transformed) increased (β coefficient = 0.63). Figure 1 shows the relationship of triclosan concentrations with age.

The range of urinary concentrations of triclosan in the NHANES 2003–2004 sample was wide, with 25% of persons examined having concentrations < 2.3 μg/L, and 5% of the participants having concentrations > 363.8 μg/g creatinine (Table 1). A wide distribution of concentrations of triclosan has also been reported for 10 healthy Swedish volunteers, five of whom related using personal-hygiene products that contained triclosan (Sandborgh-Englund et al. 2006). In the Swedish study, the baseline urinary excretion of triclosan (determined from 24-hr urine samples) was 0.1–743 μg/day among people not using triclosan-containing products, and 21–218 μg/day among users of triclosan-containing products. In another Swedish study involving a group of 36 nursing women, triclosan concentrations were higher in both plasma and milk among the women who used personal care products containing triclosan than in the women who did not (Allmyr et al. 2006). These data suggest that personal care products may be a principal source of exposure to triclosan in humans. The wide range of concentrations of triclosan may be attributable to differences in exposure, as well as to individual variations in distribution kinetics and metabolism (Sandborgh-Englund et al. 2006).

Data are limited on the urinary concentrations of triclosan in human populations. In a pilot study, triclosan was detected in 67.8% of 90 prepubertal girls, with mean age of 7.77 years, from New York City, New York; Cincinnati, Ohio; and Northern California (Wolff et al. 2007). The median concentration (5.9 μg/L) was comparable to the median concentration of triclosan for the 341 children 6–11 years of age in this NHANES 2003–2004 population (7.2 μg/L).

As is true for other nonpersistent chemicals (Fenske et al. 2005; Hauser et al. 2004; Hoppin et al. 2002; Meeker et al. 2005), within-person variability in urinary concentrations of triclosan exists. Despite this variability, results from one recent study suggest that triclosan concentrations in a single urine sample can be used to categorize the 6-month average exposure to triclosan among a group of 35 children (Teitelbaum et al. 2007). More important, concentrations based on one spot sample per person can be useful in calculating mean population concentration estimates in cross-sectional studies such as NHANES.

We observed a curvilinear-increased relation between age and triclosan LSGM concentration for people ≥ 6 years of age. For people ≥ 20 years of age, concentrations appeared to decline as age increases (Figure 1 and Table 2). These data suggest that the concentrations of urinary species of triclosan peak around the third decade of life and then slowly decrease. This relation between age and triclosan concentration is not clearly understood, and these differences might reflect differences in lifestyle choices affecting exposure and/or pharmacokinetic factors based on age.

We did not observe differences in the adjusted LSGM concentrations of triclosan based on race/ethnicity or sex. LSGM triclosan concentrations were significantly higher among people in the high household income category than among people in the medium (p = 0.04) and low (p < 0.01) income categories. These differences might reflect differences in lifestyle choices (e.g., use of personal care products) that affect exposure to triclosan.