Predicting dermal absorption of gas-phase chemicals: transient model development, evaluation, and application

Area of Science:

• Environmental Health
• Toxicology
• Chemical Exposure Assessment

Background:

• Dermal absorption of gas-phase chemicals directly from air is often overlooked in exposure assessments.
• Existing models typically assume steady-state conditions, which may not reflect real-world fluctuating exposures.
• Understanding non-steady-state dermal absorption is crucial for accurate risk evaluation.

Purpose of the Study:

• To develop and validate a transient model for predicting dermal absorption of gas-phase chemicals from air to blood.
• To compare the predictions of the transient model with a steady-state model under various exposure scenarios.
• To assess the dermal intake of specific phthalate esters under different exposure durations and conditions.

Main Methods:

• Development of a transient mathematical model incorporating convective mass-transfer resistance in the air boundary layer.
• Validation of the model against limited available experimental data.
• Application of the model to estimate dermal absorption of six phthalate esters in 24-hour and 7-day exposure scenarios.

Main Results:

• The transient model showed good agreement with experimental data.
• In a 24-hour scenario, the transient model predicted higher dermal absorption and lower blood absorption compared to a steady-state model.
• For a 7-day scenario, model predictions converged after 3-4 days, except for DEHP. Dermal intake was comparable to or greater than inhalation for several phthalates.

Conclusions:

• Dermal absorption of gas-phase chemicals directly from air is a significant exposure pathway, often comparable to or exceeding inhalation intake.
• The developed transient model is more appropriate than steady-state models for estimating dermal absorption under non-steady-state or changing exposure conditions.
• This pathway and the transient modeling approach should be incorporated into aggregate exposure and risk assessments for various organic chemicals.