Relative roles of convection and chemical reaction for the disposition of formaldehyde and ozone in nasal mucus.
The mucociliary apparatus is an important respiratory-tract defense system that may provide significant protection of the underlying epithelium from gases and vapors. Limiting-case calculations were performed to determine the significance of convective mucus transport and chemical reaction for formaldehyde (HCHO) and ozone (O(3)) in rat nasal respiratory epithelial mucus. Less than 4.6% of absorbed HCHO can be bound to amino groups (serum albumin) after 20 min of exposure. Thus, at the slowest measured mucus flow rates in rats, approximately 1 mm/min, a fluid element of mucus could travel more than 2 cm before binding 5% of absorbed HCHO, by which time the element would probably leave the nose (the site of toxic responses). In other calculations, HCHO removed by chemical reaction from a volume of mucus exposed for longer times was determined to be less than 0.54% of that removed by mucus flow (convection). Given the solubility of HCHO in mucus (water) and estimates of total mucus flow, however, as much as 22-42% of inhaled HCHO may be removed by total mucus flow. Alternately, O(3) dissolved in mucus would react completely with unsaturated fatty acids in 8.3 x 10(-4) s, in which time the mucus could flow no more than approximately 0.42 microm at the maximum reported flow rate of 30 mm/min. Even if a volume of mucus is flushed by net flow in 1 s, the amount of O(3) removed by flow would only be 0.12% of that removed by chemical reaction. Finally, based on the solubility of ozone, less than 8.0 x 10(-5)% of inhaled material could be removed from the nose by mucus flow. These results indicate which mucociliary processes are significant in site-specific dosimetry modeling.
Schlosser
P M
PM
Chemical Industry Institute of Toxicology, PO Box 12137, Research Triangle Park, NC 27709, USA. schlosser@ciit.org
D000465:Algorithms; D000818:Animals; D018481:Convection; D005557:Formaldehyde / Q000737:chemistry* / Q000493:pharmacokinetics*; D008168:Lung / Q000378:metabolism; D009093:Mucus / Q000737:chemistry / Q000378:metabolism*; D009296:Nasal Cavity / Q000378:metabolism; D010083:Oxidants, Photochemical / Q000737:chemistry* / Q000493:pharmacokinetics*; D010084:Oxidation-Reduction; D010126:Ozone / Q000737:chemistry* / Q000493:pharmacokinetics*; D051381:Rats
D010083:Oxidants, Photochemical; D005557:Formaldehyde; D010126:Ozone