Faculty Bibliography

The radiation dose to the sensitive cells of the bronchial epithelium from inhaled short-lived radon progeny depends critically on the efficiency with which the particles are deposited on the airway surfaces. Measurements of deposition for particles 50, 100, 180, and 400 nm in diameter have been carried out along three single pathways in full hollow airway casts of the human and canine tracheobronchial trees. The pathways are a major branch path, a minor branch path, and one which consists of alternating major and minor branches. The casts, prepared from whole lungs obtained at autopsy, extend to airways with diameters less than 1 mm. Monodisperse test aerosols were nebulized from either a 99mTc-ferric oxide or 99mTc-NaCl solution and size classified with an electrostatic classifier or formed by condensation of triphenyl phosphate onto 99mTc-salt nuclei. Measured deposition fractions (etaFs) form a family of curves with etaF being highest for the 50 nm particles and lowest for 400 nm. This agrees with expectations for this particle size range where diffusion is the dominant deposition mechanism. The etaF pattern is strongly influenced by the morphometry and resulting airflow distribution. Results of the experiments obtained in the human cast are compared with two predictive deposition models. The model, that is more explicit with respect to flow and geometric parameters, appears to be a marginally better predictor of the data

Expression of the metallothionein (MT) gene in frozen human lymphocytes has been developed as a new molecular biomarker of heavy metal exposure. Workers at a Polish battery factory with high exposure to cadmium were monitored for airborne exposure and blood cadmium levels. A novel quantitative reverse transcription-PCR (RT-PCR) technique, making use of a homologous internal standard, was used to assess the level of MT-specific mRNA in frozen stored aliquots of blood samples taken from exposed and control workers. Results from this assay showed a statistically significant 2.5-fold increase in MT mRNA in exposed compared to control workers. The RT-PCR results also showed significant correlation with airborne cadmium, as registered on personal monitors and with blood cadmium levels. The results suggest that gene induction measured by quantitative RT-PCR is a promising approach for application as a biomarker of biologically effective dose in small samples of frozen tissues or cells

The deposition of ultrafine (d less than or equal to 200 nm) particles on airway surfaces is an important determinant of the radiation dose that results from inhalation of radon progeny. Diffusion is the dominant deposition mechanism for radon progeny since most of the alpha particle activity is on ultrafine particles. Freshly formed Po-218 is rapidly neutralized but, there remains some charged fraction of each short-lived decay product. Theoretical predictions suggest that a measurable increase in airway deposition may result from particle charge. We have measured and compared the deposition (eta) of monodisperse singly charged, and charge neutralized, particles with diameters from 15 to 95 nm in simple tracheal models. Differences in deposition were detectable for particles < 30 nm in diameter in 10, 23 and 30 cm long tubes, and for particles up to 95 nm for the longest (30 cm) tube tested. Variations in the magnitude of electrostatic deposition with particle and flow parameters is consistent with theoretical predictions

A method for vapor-dosing of charcoal sorbent tubes (CST) that does not require the expense and effort of a test chamber was used to test the desorption efficiency (DE) of seven solvent vapors, representing six classes of solvents as follows: aromatic hydrocarbons (m-xylene); ether/alcohol (2-ethoxyethanol); vinyl monomers (styrene monomer, vinyl acetate); aliphatic hydrocarbons (n-hexane); aliphatic esters (n-butyl acetate); and aliphatic acrylic monomers (methyl methacrylate). The quantities of the solvents used in these experiments would represent eight-hour exposures to concentrations of approximately 0.2 to 10 ppm. The vapor-dosing experimental system consisted of a loaded filter cassette connected directly to a CST. Vapor was generated by injecting liquid solvent onto the glass fiber filter and drawing air through the system. The solvent was desorbed from the filter and charcoal for analysis. Vapor desorption efficiency was determined from the fraction of the injected solvent evaporated from the filter and the amount recovered from the charcoal. The measured DEs were similar to those reported for liquid dosed charcoal. Vapor dosing of sorbent tubes is more representative of samples collected for industrial hygiene exposure assessment. The system is simple to use and applicable for vapor dosing of any sorbent tube