1999 Progress Report: Human Health Effects of Exposure to Ultrafine ParticlesEPA Grant Number: R826781
Title: Human Health Effects of Exposure to Ultrafine Particles
Investigators: Frampton, Mark W. , Marder, Victor J. , Oberdörster, Günter , Utell, Mark J. , Zareba, Wojciech
Institution: University of Rochester
EPA Project Officer: Chung, Serena
Project Period: October 1, 1998 through September 30, 2001 (Extended to September 30, 2002)
Project Period Covered by this Report: October 1, 1998 through September 30, 1999
Project Amount: $736,260
RFA: Health Effects of Particulate Matter and Associated Air Pollutants (1998) RFA Text | Recipients Lists
Research Category: Air , Health Effects , Particulate Matter , Air Quality and Air Toxics
Ultrafine particles (UFP) may contribute to the health effects of ambient particle exposure because of their high number concentration and surface area, a high deposition efficiency in the pulmonary region, and a high propensity to penetrate the epithelium. Our objective is to initiate clinical studies of exposure to UFP in healthy human subjects and in subjects with asthma. These studies will determine the deposition efficiency of UFP in healthy and asthmatic humans, and will compare exposure to air, ultrafine carbon, and ultrafine iron oxide with regard to: (1) the induction of airway inflammation; (2) leukocyte and endothelial adhesion molecule expression in the blood; (3) activation and inflammatory cytokine profile of blood and airway T lymphocytes; (4) alterations in blood coagulability; and (5) alterations in cardiac electrical activity.
Ultrafine Particle Exposure Facility. We have developed a facility for experimental exposure of humans to ultrafine particles, which permits the quantitative determination of the exposure levels, respiratory intakes, and depositions of the aerosol. A detailed description of the facility has been presented at the Third Colloquium on Particle Matter and Human Health in Durham, NC, in June 1999 (1). Because our initial exposure mass concentrations are within the range of PM10 measurements outdoors, it was important to know numbers and mass concentrations of particles within the Clinical Research Center and the Environmental Chamber where the facility is located, as well as in the intake air for the exposure facility. These measurements were performed, and represent the first measurements of ultrafine particle number within an acute care hospital. These data have been published (2).
Ultrafine Particle Deposition. For our initial studies, exposures of healthy subjects were conducted at rest with a relatively low concentration of pure carbon UFP (~10 µg/m3, ~2 x 106 particles/cm3, count median diameter 26.4 nm, GSD 2.3). Twelve healthy nonsmoking subjects (6 female) inhaled either filtered air or UFP by mouthpiece for 2 hours at rest, with a 10 minute break after the first hour. Exposures were double blinded, randomized, and separated by at least 2 weeks. The total respiratory tract deposition fraction (DF) was determined for six different particle size fractions after correction for system losses, and the overall DF was calculated for both number and mass for each subject. Respiratory symptoms, spirometry, blood pressure, pulse-oximetry, and exhaled NO were assessed before and at intervals after the exposure. Sputum induction was performed 18 hours after exposure. Continuous 24-hour, 12-lead Holter monitoring was performed on the day of the exposure, and analyzed for changes in heart rate variability and repolarization phenomena.
The overall DF was 0.66 - 0.12 (mean - SD) by number, and 0.58 - 0.14 by mass. The number DFs during the first and second hours of exposure were similar within subjects, but the average overall DF varied from 0.43 to 0.79 among subjects. The DF decreased with increasing particle size in the UFP range, from 0.76 - 0.11 at 7.5 nm to 0.47 - 0.17 at 133.4 nm.
Health Effects of Carbonaceous Ultrafine Particles in Healthy Subjects. Preliminary analysis indicated no significant differences between particle and air exposure for respiratory symptoms, blood pressure, pulse-oximetry, spirometry, exhaled NO, blood markers of coagulation and endothelial activation, leukocyte activation, or sputum cell differential counts (3).
Analysis of heart rate variability (HRV) showed exposure-related increases for both air and UFP in the RR interval, the standard deviation of the RR intervals in the 24-hour period (SDNN, an overall time-domain measure of HRV), and in the square root of the mean sum of squares of differences between adjacent N-N intervals (rMSSD, a short-term time-domain measure of HRV). There was a small, but significant, elevation of the ST segment, in V5 only, associated with UFP versus air.
We conclude that exposure to 10 µg/m3 pure carbon UFP at rest does not cause significant respiratory or cardiac effects in healthy nonsmokers. These results were presented at the American Thoracic Society (ATS) International Conference in Toronto (4,5).
We now have completed a study with healthy subjects incorporating exercise and two concentrations of ultrafine carbonaceous particles in order to examine concentration-response relationships. In this protocol, 12 healthy subjects were exposed for 2 hours to air and to two concentrations of carbon UFP, 10 µg/m3 and 25 µg/m3, with intermittent exercise. Each of the three exposures was separated by at least 2 weeks.
Analysis of variance is currently in progress by Dr. Cox, our biostatistician. Preliminary analyses indicated that exercise further increased the relatively high resting deposition of UFP (number deposition fraction at rest: 0.63 - 0.04; exercise: 0.76 - 0.06; means - SD). There were no obvious particle-related effects on symptoms, spirometry, pulse oximetry, airway nitric oxide production, sputum cell differential counts, or blood concentrations of fibrinogen, von Willbrandt factor, or clotting factor VII. Heart rate variability data from this study are currently being analyzed. Interestingly, preliminary results suggested small but significant particle effects on circulating leukocyte expression of several adhesion molecules and activation markers, with differing effects in women and men. For example, we found a statistically significant increase in the percentage of circulating T lymphocytes from females, but not males, expressing CD25 (part of the IL-2 receptor) 3.5 hours after exposure to 25 µg/m3 UFP (ANOVA particle X gender interaction, p = 0.0024). This suggests that UFP exposure may transiently activate circulating lymphocytes in healthy subjects. An abstract has been accepted for presentation at the ATS International Conference in San Francisco, CA, May 20, 2001 (6).
Generation of Particles Containing Trace Metals. An important goal of these studies is to compare the effects, in healthy and asthmatic subjects, of exposure to ultrafine carbonation particles with particles containing trace amounts of iron oxide, to more closely reflect the composition of ambient air particles. Our approach is to first initiate exposures to particles containing trace metals in animal studies (in Dr. Oberdorster's laboratory) and then extend these studies to human exposures. We have been successful in generating particles containing iron oxide. Carbon black powder was mixed with metallic iron powder, adding glucose and distilled water to form a paste. This was extruded into a cylinder, dried, and then graphitized by slowly raising the temperature to 2300°C. These graphitized cylinders were then used in the PALAS generator for the generation of ultrafine particles. Particle size distribution was approximately 25 nm with a GSD of 1.7. These particles exhibited very high biological activity, with 370 nmol of bioavailable iron/mg of particle (performed by Dr. Aust, Utah State University). Analyses by Dr. Castronova (NIOSH, Morgantown, WV) revealed that addition of iron to the particles resulted in generation of OH radicals in the presence of H2O2. Six hour exposures to these iron-containing particles have been initiated in aged and young mice at concentrations of 100 µg/m3.
Future studies planned in the remaining months of this project are to complete exposures to ultrafine carbonaceous particles in subjects with asthma. We plan to study a total of 16 asthmatic subjects, 8 female and 8 male. This larger number of subjects will provide additional statistical power, in view of the expected increased variability among asthmatic subjects compared to healthy subjects. Following studies in asthmatic subjects, in conjunction with continued funding for human studies from the University of Rochester EPA PM Center, we will begin studying inhalation of carbon particles containing trace metals, including iron oxide, in healthy and asthmatic subjects.