Quantitative Identification of Unknown Exposure Pathways of Phthalates Based on Measuring Their Metabolites in Human Urine

Humans are exposed to ubiquitous phthalates via multiple pathways. Exposures to phthalates have been estimated in some previous risk assessments in Japan based on point-of-contact measurement or scenario evaluation approaches. While the Japanese national government has regulated the use of di(2-ethylhexyl)phthalate (DEHP) and excluded several other phthalates from its regulation based on some of them, it is unclear whether such past exposure assessment studies fully assessed total human exposure to phthalates. In the present study, we measured their urinary metabolites, which show direct evidence of human exposure to phthalates. We recruited voluntary participants (N = 36) who agreed to donate urine samples, and measured the urinary concentrations of phthalate metabolites using enzymatic deconjugation, solid-phase extraction, and high-performance liquid-chromatography isotope-dilution tandem mass spectrometry. We then derived the daily intakes of their respective phthalates based on steady state assumption and finally compared them with the corre sponding estimated daily intakes of each phthalate via diet and air derived from previous exposure or risk assessments in Japan. These comparisons showed that exposures to dimethyl phthalate, diethyl phthalate, and di-n-butyl phthalate via diet and air accounted for less than half of their respective total exposures. On the other hand, it appears that dietary intake was more predictive for the total exposure to n-butyl-benzyl phthalate and DEHP. The probabilities that the lognormal distribution of each phthalate daily intake estimated from the present study exceeds the corresponding tolerable daily intake were estimated to be less than 10^-4.