US EPA

In an effort to examine the absorption of a common chemical into the nasopharyngeal region in humans, a 57 year old male volunteer inhaled uniformly labeled 13C-acetone at 1.4 ppm for 30 min while performing different breathing maneuvers; nose inhale, nose exhale (NINE); mouth inhale, nose exhale (MINE); nose inhale, mouth exhale (NINE). Different respiration patterns reflecting conditions of rest and exercise were performed. Acetone concentrations were monitored in real time every 0.8 see during these maneuvers via the air-sampling probe of an ion-trap mass spectrometer inserted into the nasopharyngeal region. The breathing cycle of the volunteer was monitored so that acetone concentrations could be differentiated and correlated with inhalation (IN) & exhalation (EX). Preliminary results indicate the method can clearly differentiate acetone concentrations during IN & EX. Further results, recorded under normal respiration, show 13C-acetone concentrations in the nasopharyngeal region ranged mainly form 0-0.5 during NINE and 0-0.4 ppm during MINE maneuvers. Both of these maneuvers involve exhalation of air form the lungs past the probe. In the NIME maneuver were exhalation of air from the lungs past the probe was minimized, the concentrations in the nasopharyngeal area were markedly higher at 0.2-0.8 ppm. Overall, these results indicate the absorption in the nasal and lung regions can be estimated separately using this method. These data can help determine the differential absorption parameters of the various tissues that are in contact with chemicals of interest to the air pollution community. Information on human nasal absorption would also have extensive application in pharmacokinetic modeling of inhaled gases and vapors as well as use in risk assessment regarding regional dosimetry in the head and to the lungs in humans. (Funded by U.S. EPA 68-C-00-122).

Foureman, G. L., K. Thrall, C. Timchalk, R. E. Schwartz, AND J D. Prah. Nasopharyngeal Concentrations In The Human Volunteer Breathing Acetone. Presented at Society of Risk Analysis, New Orlean, LA, Dec. 8-11, 2002.