Detection of phthalate metabolites in human saliva

In assessment of exposure to environmental contaminants, the use of unconventional matrices is becoming an increasingly important area of research. Saliva is one of the most promising alternative matrices because its collection is easy, noninvasive, and inexpensive. In this study, we measured the salivary concentrations of 14 phthalate metabolites in 39 anonymous adult volunteers using isotope-dilution, automated solid phase extraction-high performance liquid chromatography-tandem mass spectrometry. Seven phthalate metabolites were detected at the concentrations ranging from below the limit of detection (< 1 ng/mL) to 10.6 ng/mL for phthalic acid, 3.1 ng/mL for monomethyl phthalate (MMP), 91.4 ng/mL for monoethyl phthalate (MEP), 65.8 ng/mL for mono-n-butyl phthalate (MBP), 17.9 ng/mL for mono-iso-butyl phthalate, 353.6 ng/mL for monobenzyl phthalate, and 6.8 ng/mL for mono-2-ethylhexyl phthalate (MEHP). The frequency of detection was highest for MBP (85%) and lowest for MMP (8%). The median salivary MBP level in this group of adults was higher than the median serum MBP level in another non-occupationally exposed human adult population in the United States, whereas, the median salivary levels of MEP and MEHP were lower than the corresponding median serum levels. The frequency of detection and the salivary levels of each phthalate monoester in this study population were lower than the frequency of detection and urinary level of the same monoester in the general US population. Although urine is preferred for exposure assessment to non-persistent chemicals such as phthalates, the similar levels in serum and saliva suggest that saliva could be used as a surrogate matrix for measuring the bioavailable dose of phthalates in biomonitoring studies.