Long-term inhalation exposure: A model for phthalate accumulation in the respiratory tract

Inhalation is a major pathway for phthalates (PAEs), an endocrine disruptor, to enter the human body. The actual internal exposure amount that participates in metabolism cannot be estimated by calculating total inhalation intake.

To estimate the accumulation in each region of the respiratory tract after long-term exposure to PAEs in different populations.

A mass transfer model was developed to simulate the long-term accumulation of PAEs in respiratory tract through inhalation. The model considered (1) mass transfer of PAEs in three phases across seven regions, (2) the effect of temperature differences on the mass transfer process. Based on this model, we simulated adult exposure to PAEs in a laboratory, identified key model parameters, and further simulated various scenarios for children, adults, and elders.

PAEs are not completely cleared from the respiratory tract after 16 hours, following 8 hours of daily exposure. Under regular laboratory environment, accumulation after 30 days is 3.8 times higher than that after the first day. The distribution of PAEs between the gas and mucus phases has a greater impact on the results than between the gas and particle phases. Children are at the highest risk to Diethyl phthalate (DEP) exposure compared with adults and elders. Nearly 80 % of DEP is exhaled, with 14 % accumulating in the alveolar region after an hour.

This model links indoor air PAEs to human internal exposure, showing that most PAEs are exhaled, while the remainder accumulates in the respiratory tract and may participate in human metabolism.