2013 Progress Report: Simulated Roadway Exposure Atmospheres for Laboratory Animal and Human Studies
EPA Grant Number:
Subproject: this is subproject number 002 , established and managed by the Center Director under
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
University of Washington Center for Clean Air Research
Simulated Roadway Exposure Atmospheres for Laboratory Animal and Human Studies
McDonald, Jacob D.
, Doyle-Eisele, Melanie
, Larson, Timothy V.
, Mauderly, Joe L.
McDonald, Jacob D.
Lovelace Respiratory Research Institute
EPA Project Officer:
December 1, 2010 through
November 30, 2015
(Extended to November 30, 2017)
Project Period Covered by this Report:
December 1, 2012 through November 30,2013
Clean Air Research Centers (2009)
Objectives/Hypothesis: Traffic-related emissions are associated with the incidence and progression of acute and chronic cardiovascular sequelae in human population studies; however, the causal components, subsequent chemical transformation of these components, and their associated toxicity on the cardiovascular system have not yet been determined. Project #2 is in progress to develop atmospheres with the primary objective of simulating environments containing key components of roadway emissions and the products of environmental factors that transform them. Previous, current, and future exposures are designed to determine air contaminants (or components) that cause or potentiate the toxicity of roadway emissions or confound interpretations based on roadway proximity alone.
Approach: This project will generate and characterize multiple complex roadway mixtures for subsequent animal and human exposure-related toxicology studies. In Aim 1, we will develop and characterize laboratory-generated exposure atmospheres simulating the key components of near-roadway exposures, including transformed emissions and coexposures. In Aim 2, we will conduct inhalation exposures of laboratory animals (as described in Project 3). Lastly, in Aim 3, we will conduct inhalation exposures of human subjects in an effort to compare significant pathophysiological findings from our animal model exposures to responses in humans.
Expected Results: Results from these studies will identify key components, as well as the most potent combinations, of urban roadway and background co-pollutants that result in toxicological responses in the cardiovascular system of both rodents and humans.
This year we completed subchronic inhalation exposures to verify the impact of component/gas mixtures. Further, in collaboration with Project 3 we spent considerable effort focused on assay development for the bioassays. Finally, in consideration of the next round of experiments that are under consideration currently, we overcame some technical hurdles for the conduct of the irradiation chamber experiments and also considered the potential use of Project 1 data for design of additional test atmospheres.
Completion of Exposures and Analysis to Tease Out Components
We conducted 50-day exposure of Apo E -/- mice , on a high fat diet, to the following chemistries: (1) MVE, 300 μg PM/m3: 30 μg PM/m3 derived from a gasoline engine combined with 270 μg PM/m3 derived from a diesel engine; (2) MVE at the 300 μg PM/m3 concentration with PM filtered; (3) MVE at the 300 μg PM/m3 concentration with gases filtered, using a denuder; (4) MVE at the 300 μg PM/m3 concentration with NOx scrubbed out; and (5) filtered air (controls). Studies were conducted to evaluate atmospheres that would allow us to "tease" out the role of gases versus particles in novel ways, and that further evaluate the role of physical aging of motor vehicle exhaust. Studies were completed with test atmospheres to evaluate:
Mixed motor vehicle exhaust
Mixed motor vehicle exhaust minus particles
Mixed motor vehicle exhaust minus gases (includes particles)
Mixed motor vehicle exhaust minus NOx and ultrafines (simulates downwind)
These atmospheres were developed to address key CCAR questions related to transformation and multipolltant components that are most important for toxicity. To develop atmospheres minus particles, HEPA filters are used. The atmospheres remove 99% of the particles and permit the gases to pass through. The atmosphere with the gases removed was developed with the use of the HARVARD parallel plate denuder. The denuder was loaned to CCAR from the Harvard CLARC. This denuder allows the removal of 95% of all gases with only small (<5%) particle loss, mostly in the ultrafine range. A fourth condition uses the DRI cobalt oxide denuder (see below) to remove NOx and ultrafine particles. The NOx denuder removes 95% of the NOx and allows other gases to pass through. It also removes the smallest fraction of particles that may agglomerate and be removed in close proximity to roadways. Figures 4 and 5 illustrate the change in particle size resulting from the denuder.
The overall composition of major components from those test atmospheres are described in Figure 1 below. Atmosphere development and characterization activities included the development of test atmospheres that further characterized the gas:particle partitioning and atmospheric processing. The motivation for this work was driven by guidance from the oversight committee, which wanted us to further investigate previous findings of enhanced vascular response after exposure to the mixture of gasoline and diesel exhaust. The hypothesis was that the combination of particle enriched and highly sorptive diesel exhaust with the vapor hydrocarbons and inorganics enhanced the toxicity, perhaps through increase in the delivered dose of materials to the deep lung. Several atmospheres and atmospheric characterization experiments were conducted to better elucidate these findings. These were 50-day experiments and a number of molecular endpoints were evaluated. These are described in the Project 3 report.
Overcoming Technical Challenges to Evaluate Irradiated Atmospheres:
One of the atmospheres that we have targeted is in consideration of the atmospheric aging of motor vehicle exhaust. This atmosphere helps to evaluate the potential for aging to alter the biological potency of motor vehicle emissions, and also correlates to the work that is conducted at Harvard and EPA to consider the impact of aging on biological response. The LRRI irradiation chamber has been characterized and used extensively for the evaluation of secondary organic aerosol produced from single component mixtures.
The challenge for motor vehicle exhaust is the large amounts of inorganic gases, especially NOx, that can titrate the chemistry of the test atmosphere is present in large amounts. An ideal ratio for the test gases in an irradiation chamber are approximately 10:1 hydrocarbon to NOx. Further, it is ideal that the concentration of hydrocarbon in these test atmospheres are no more than approximately 1-2 ppm as a starting concentration. Out of the tailpipe, there is an approximate 3:1 ratio of NOx:hydrocarbons. In order to overcome this problem, and to optimize the ratio of NOx to hydrocarbons, LRRI implemented a cobalt-oxide coated denuder (See image below). This device, developed at the Desert Research Institute, removes NOx while allowing the hydrocarbons and particles to pass through.
A second challenge was in modulating the flow/air balance requirements to move material from the exhaust, to a dilution tunnel, through the denuder and then to the irradiation chamber. There are significant differences in the flow requirements for each of these stages. The flow in the denuder requires approximately 150 liters per minute. Further, the flow through the irradiation chamber must be at 30 liters per minute in total, including the addition of flow for system humidification. We met this challenge by meeting the flow requirements of the denuder, and then subsequently by creating a bypass for the removed excess denuded aerosol. The denuded aerosol that would transit to the irradiation chamber was transited to the exposure chamber with a positive displacement roots blower. This allowed us to create the desired test atmosphere under all of these limitations.
Another challenge that occurred with the irradiation chamber is the potential time that it would take to conduct the experiments as originally designed versus the complications of (a) running an engine for 2 months consecutively and (b) maintaining the "charge" of the denuder during that time. The irradiation chamber requires that the hydrocarbons and NOx are supplied 24 hrs per day. This can be accomplished for a short amount of time, but would be expensive and not feasible for a long duration of time. In addition, the NOx denuder would get saturated with that much use, and without a break we would not be able to recharge it.
Because of these challenges, we considered the irradiation chamber experiments, as designed, would need to be conducted over a short duration (maximum 7 days). To meet this, we worked in collaboration with Project 3 to develop meaningful acute bioassays. These are in the process of being implemented for this atmosphere now.
Figure 2. NOx denuder used to remove NOx from motor vehicle exhaust.
Consideration of Project 1 Data for Test Atmosphere Design
Part of the design of the Center was to integrate projects to help design experiments. The initial design of test atmospheres considered an approach where a priori we would evaluate the potentially useful components of roadway emissions and their transport on the change in composition and toxicity that we could model in the laboratory. We have developed on combinations on several of the important urban gas mixtures to meet this a priori goal, and are considering those for studies currently.
We also considered some of the ambient data from Project 1 in the design of test atmospheres. Figure 3 below shows a transect through Albuquerque from a roadway and a representative set of data (PAH/NOx). As indicated, there were some interesting differences as one transected away from the road. However, it is unclear if these differences would provide enough of a contrast to truly elucidate biological differences in the magnitude of response. Because of this, we have considered the use of the ambient data for the design of toxicology experiments more as a tool in placing the results/atmospheres in context of what they model as opposed to determining how we approach the test atmospheres. This may be a topic of discussion for the annual meeting.
The next round of studies will utilize the new short-term bioassays to include the atmospheric reaction chamber and urban background studies.
on this Report
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Inhalation toxicology, diesel, gasoline engine
, Health, Scientific Discipline, Air, ENVIRONMENTAL MANAGEMENT, Air Quality, air toxics, Health Risk Assessment, Risk Assessments, mobile sources, Biochemistry, Environmental Monitoring, Risk Assessment, ambient air quality, atmospheric particulate matter, particulate matter, aerosol particles, air pollutants, motor vehicle emissions, vehicle emissions, air quality models, motor vehicle exhaust, airway disease, bioavailability, air pollution, particle exposure, atmospheric aerosols, ambient particle health effects, vascular dysfunction, cardiotoxicity, atmospheric chemistry, exposure assessment
Progress and Final Reports:
2011 Progress Report
2012 Progress Report
2015 Progress Report
Main Center Abstract and Reports:
University of Washington Center for Clean Air Research
Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R834796C001 Exposure Mapping – Characterization of Gases and Particles for ExposureAssessment in Health Effects and Laboratory Studies
R834796C002 Simulated Roadway Exposure Atmospheres for Laboratory Animal and Human Studies
R834796C003 Cardiovascular Consequences of Immune Modification by Traffic-Related Emissions
R834796C004 Vascular Response to Traffic-Derived Inhalation in Humans
R834796C005 Effects of Long-Term Exposure to Traffic-Derived Particles and Gases on Subclinical Measures of Cardiovascular Disease in a Multi-Ethnic Cohort