Paired Serum and Urine Concentrations of Biomarkers of Diethyl Phthalate, Methyl Paraben, and Triclosan in Rats

BACKGROUND: Exposure to environmental chemicals, including phthalates and phenols such as parabens and triclosan, is ubiquitous within the U.S. general population. Objective: This proof-of-concept rodent study examined the relationship between oral doses of three widely used personal care product ingredients [diethyl phthalate (DEP), methyl paraben (MPB), and triclosan] and urine and serum concentrations of their respective biomarkers. METHODS: Using female Sprague-Dawley rats, we carried out two rounds of experiments with oral gavage doses selected in accordance with no observed adverse effect levels (NOAELs) derived from previous studies: 1,735 (DEP), 1,050 (MPB), 50 (triclosan) mg/kg/day. Administered doses ranged from 0.005 to 173 mg/kg/day, 10-100,000 times below the NOAEL for each chemical. Controls for the MPB and triclosan experiments were animals treated with olive oil (vehicle) only; controls for the DEP serum experiments were animals treated with the lowest doses of MPB and triclosan. Doses were administered for 5 days with five rats in each treatment group. Urine and blood serum, collected on the last day of exposure, were analyzed for biomarkers. Relationships between oral dose and biomarker concentrations were assessed using linear regression. RESULTS: Biomarkers were detected in all control urine samples at parts-per-billion levels, suggesting a low endemic environmental exposure to the three chemicals that could not be controlled even with all of the precautionary measures undertaken. Among the exposed animals, urinary concentrations of all three biomarkers were orders of magnitude higher than those in serum. A consistently positive linear relationship between oral dose and urinary concentration was observed (R-2 > 0.80); this relationship was inconsistent in serum. CONCLUSIONS: Our study highlights the importance of carefully considering the oral dose used in animal experiments and provides useful information in selecting doses for future studies.