2000 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. , Utell, Mark J. , Zareba, Wojciech
Current 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, 1999 through September 30, 2000
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
Objective: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. 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 (Riesenfeld et al., 2000).
Particle Characterization. During the previous year, we found that the method of generating ultrafine carbon particles using electric spark discharge between two pure graphite electrodes in an argon atmosphere delivers particles that also contain organic carbon components. Indeed, analysis in the laboratory found that between 24 and 32 percent of the generated carbon particles collected on a filter consisted of organic carbon. This finding is consistent with findings from other institutions (National Research Center for Environment and Health (GSF), Munich, Germany; Lovelace Respiratory Research Institute (LRRI), Albuquerque, NM) that are using the same particle generation system. Diverting the particles through an aging tube with a residence time of approximately 4 minutes did not change this contamination with organic material.
We considered the following possible sources for the organic material: (1) adsorption of organic materials from the air after collection of the particles; (2) trace impurities within the argon gas supply (the argon is 99.998 percent pure); and (3) contaminating sources within the generation system. The graphite rods used to generate the particles are heated to a very high temperature prior to use, which would eliminate any contaminating organic materials. Before initiating the study of subjects with asthma, we attempted to identify and eliminate any potential sources of organic material in the exposure system itself.
Closer examination of the generation system made by the PALAS Company, Germany, indicated several potential sources that could contribute to the organic carbon material on the particles. One possibility was the internal combustion chamber, which is made of black plastic material; another was the collars holding the graphite electrodes, which also come into contact with the argon flow perfusing the combustion chamber. They are made of the same black plastic material. In addition, there are several flexible plastic tubes inside the generator that transport the incoming argon flow and dilute air to the inner combustion chamber or to the exit of that chamber, respectively. We replaced these parts one-by-one with either Teflon® (inner combustion chamber), ceramic (collar piece), or corrugated stainless steel tubing (inner plastic tubing conduits). A further potential source for the off-gassing of organic components was the plastic tubing between the argon tank and the generator, which initially consisted of polyethylene terephthalate (PET) tubing. This too was replaced by metal tubing (copper). Essentially, the whole exposure system was rebuilt to eliminate any potential sources of organic contamination.
We have performed a number of re-analyses during the process of improving the generation system that occurred over a time-course of several months. Prior to rebuilding the generator, we had samples analyzed for specific organic composition by scientists at the LRRI, and a variety of organic compounds were identified. Unfortunately, the small amount of mass available with even prolonged filter collections of UFP precludes a quantitative analysis of specific organic species. Removal of all plastic material from the generator did not result in an overall reduction in the amount of organic carbon present in the particles. Because we have eliminated potential sources of organic compounds from the generator itself, we are left with the conclusion that the major source of the organic material may be adsorption from the air after particle generation.
Because ambient air particles contain organic as well as elemental carbon, our laboratory-generated particles are relevant to those found in ambient air. We performed validation and characterization studies confirming that the operating characteristics of the generator and size distribution of the particles generated were not altered by the modifications made to the generator.
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, and count median diameter 26.4 nm, GSD 2.3). Twelve healthy non-smoking 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 6 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 nitric oxide, blood markers of coagulation and endothelial activation, leukocyte activation, or sputum cell differential counts.
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 (see Table 1).
|Table 1. Changes from Baseline for Heart Rate Variability and ST Segment Position|
|RR (ms)||Air||20 ± 42||169 ± 34||-4 ± 25||-32 ± 35|
|UFP||16 ± 40||140 ± 31||-37 ± 45||34 ± 27|
|Air||29 ± 12||16 ± 17||-7 ± 8||-6 ± 10|
|UFP||34 ± 13||26 ± 8||13 ± 12||34 ± 11*|
|Air||19 ± 15||20 ± 21||10 ± 9||-12 ± 11|
|UFP||30 ± 19||27 ± 9||2 ± 11||27 ± 12|
|Air||9030 ± 2447||3505 ± 3705||-1714 ± 1405||-1425 ± 2122|
|UFP||8720 ± 3155||3556 ± 1554||2026 ± 2092||4923 ± 1775|
|Air||-1 ± 4||-3 ± 3||-16 ± 6||-10 ± 7|
|UFP||7 ± 2*||4 ± 2*||-7 ± 2||4 ± 4|
|p<0.05, Air compared with UFP|
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 International Conference in Toronto.
We have now completed a study with healthy subjects incorporating exercise and 2 concentrations of ultrafine carbonaceous particles to examine concentration-response relationships. In this protocol, 12 healthy subjects were exposed for 2 hours to air and to 2 concentrations of carbon UFP, 10 µg/m3 and 25 µg/m3, with intermittent exercise. Each of the 3 exposures was separated by at least 2 weeks. Detailed subject evaluation and testing was completed prior to each exposure, immediately after, 3.5 hours after, and approximately 21 hours after exposure. These measurements included symptoms, spirometry, vital signs, oximetry, phlebotomy, measurement of airway production of nitric oxide, and a resting Holter heart recording for detailed analysis of heart rate variability. Sputum induction was performed at 21 hours after each exposure.
No subject withdrew from the study because of exposure-related effects. Analysis of variance is currently in progress. 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. HRV 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.
Health Effects of Carbonaceous Ultrafine Particles in Asthmatic Subjects. We have now initiated studies of exposure to carbonaceous particles in subjects with asthma. To assure that there is no carry-over of effects from one exposure to the next in this crossover study design, the minimum interval between exposures has been extended to 3 weeks for this study. In addition, we have added an additional time point for evaluating subjects at 48 hours after exposure, to detect the unlikely possibility of delayed or persistent effects in subjects with asthma.
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 first approach is to initiate exposures to particles containing trace metals in animal studies, 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 2,300°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 geometric standard deviation (GSD) of 1.7. These particles exhibited very high biological activity, with 370 nmol of bioavailable iron/mg of particle. 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 Activities: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 Environmental Protection Agency Particulate Matter Center (EPA PM Center), we will begin studying inhalation of carbon particles containing trace metals, including iron oxide, in healthy and asthmatic subjects.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
|Other project views:||All 28 publications||16 publications in selected types||All 13 journal articles|
||Riesenfeld E, Chalupa D, Gibb FR, Oberdo G, Gelein R, Morrow PE, Utell MJ, Frampton MW. Ultrafine particle concentrations in a hospital. Inhalation Toxicology 2000;12(Suppl 2):83-94.||