Inhaled ambient-level traffic-derived particulates decrease cardiac vagal influence and baroreflexes and increase arrhythmia in a rat model of metabolic syndrome.

BACKGROUND: Epidemiological studies have linked exposures to ambient fine particulate matter (PM2.5) and traffic with autonomic nervous system imbalance (ANS) and cardiac pathophysiology, especially in individuals with preexisting disease. It is unclear whether metabolic syndrome (MetS) increases susceptibility to the effects of PM2.5. We hypothesized that exposure to traffic-derived primary and secondary organic aerosols (P + SOA) at ambient levels would cause autonomic and cardiovascular dysfunction in rats exhibiting features of MetS. Male Sprague Dawley (SD) rats were fed a high-fructose diet (HFrD) to induce MetS, and exposed to P + SOA (20.4 ± 0.9 µg/m3) for 12 days with time-matched comparison to filtered-air (FA) exposed MetS rats; normal diet (ND) SD rats were separately exposed to FA or P + SOA (56.3 ± 1.2 µg/m3). RESULTS: In MetS rats, P + SOA exposure decreased HRV, QTc, PR, and expiratory time overall (mean effect across the entirety of exposure), increased breathing rate overall, decreased baroreflex sensitivity (BRS) on three exposure days, and increased spontaneous atrioventricular (AV) block Mobitz Type II arrhythmia on exposure day 4 relative to FA-exposed animals receiving the same diet. Among ND rats, P + SOA decreased HRV only on day 1 and did not significantly alter BRS despite overall hypertensive responses relative to FA. Correlations between HRV, ECG, BRS, and breathing parameters suggested a role for autonomic imbalance in the pathophysiologic effects of P + SOA among MetS rats. Autonomic cardiovascular responses to P + SOA at ambient PM2.5 levels were pronounced among MetS rats and indicated blunted vagal influence over cardiovascular physiology. CONCLUSIONS: Results support epidemiologic findings that MetS increases susceptibility to the adverse cardiac effects of ambient-level PM2.5, potentially through ANS imbalance.

Development and evaluation of a countercurrent parallel-plate membrane diffusion denuder for the removal of gas-phase compounds from vehicular emissions.

Diffusion denuders have been commonly used to remove trace gases from an aerosol (mixture of gases and particles), while allowing the particles to remain suspended in air. We present the design and evaluation of a high-flow (16.7 L min⁻¹) countercurrent parallel-plate membrane diffusion denuder that has high removal efficiencies for both non-reactive gases such as carbon monoxide (89%), as well as volatile organic compounds (80-85%) from an automobile exhaust. Particle losses were approximately 15% for particles around 100 nm in diameter. This denuder is suitable for toxicological tests involving both human and animal exposures to combustion aerosols. The denuder may also be used for other applications, for example, to reduce the effect of gas-phase sampling artifacts on particle composition.

Laboratory evaluation of a prototype photochemical chamber designed to investigate the health effects of fresh and aged vehicular exhaust emissions.

Laboratory experiments simulating atmospheric aging of motor vehicle exhaust emissions were conducted using a single vehicle and a photochemical chamber. A compact automobile was used as a source of emissions. The vehicle exhaust was diluted with ambient air to achieve carbon monoxide (CO) concentrations similar to those observed in an urban highway tunnel. With the car engine idling, it is expected that the CO concentration is a reasonable surrogate for volatile organic compounds (VOCs) emissions. Varying the amount of dilution of the exhaust gas to produce different CO concentrations, allowed adjustment of the concentrations of VOCs in the chamber to optimize production of secondary organic aerosol (SOA) needed for animal toxicological exposures. Photochemical reactions in the chamber resulted in nitric oxide (NO) depletion, nitrogen dioxide (NO2) formation, ozone (O3) accumulation, and SOA formation. A stable SOA concentration of approximately 40 µg m⁻³ at a chamber mean residence time of 30 min was achieved. This relatively short mean residence time provided adequate chamber flow output for both particle characterization and animal exposures. The chamber was operated as a continuous flow reactor for animal toxicological tests. SOA mass generated from the car exhaust diluted with ambient air was almost entirely in the ultrafine mode. Chamber performance was improved by using different types of seed aerosol to provide a surface for condensation of semivolatile reaction products, thus increasing the yield of SOA. Toxicological studies using Sprague-Dawley rats found significant increases of in vivo chemiluminescence in lungs following exposure to SOA.

Aged particles derived from emissions of coal-fired power plants: the TERESA field results.

The Toxicological Evaluation of Realistic Emissions Source Aerosols (TERESA) study was carried out at three US coal-fired power plants to investigate the potential toxicological effects of primary and photochemically aged (secondary) particles using in situ stack emissions. The exposure system designed successfully simulated chemical reactions that power plant emissions undergo in a plume during transport from the stack to receptor areas (e.g., urban areas). Test atmospheres developed for toxicological experiments included scenarios to simulate a sequence of atmospheric reactions that can occur in a plume: (1) primary emissions only; (2) H(2)SO(4) aerosol from oxidation of SO(2); (3) H(2)SO(4) aerosol neutralized by gas-phase NH(3); (4) neutralized H(2)SO(4) with secondary organic aerosol (SOA) formed by the reaction of α-pinene with O(3); and (5) three control scenarios excluding primary particles. The aged particle mass concentrations varied significantly from 43.8 to 257.1 µg/m(3) with respect to scenario and power plant. The highest was found when oxidized aerosols were neutralized by gas-phase NH(3) with added SOA. The mass concentration depended primarily on the ratio of SO(2) to NO(x) (particularly NO) emissions, which was determined mainly by coal composition and emissions controls. Particulate sulfate (H(2)SO(4) + neutralized sulfate) and organic carbon (OC) were major components of the aged particles with added SOA, whereas trace elements were present at very low concentrations. Physical and chemical properties of aged particles appear to be influenced by coal type, emissions controls and the particular atmospheric scenarios employed.

Development and evaluation of a photochemical chamber to examine the toxicity of coal-fired power plant emissions.

When investigating the toxicity of individual particle sources, it is important to consider the contribution of both primary and secondary particles. In this article, we present the design of a new photochemical chamber that can be used to form secondary sulfuric acid particles from diluted coal-fired power plant emissions. The chamber is a relatively small, well-mixed flow reactor that can fit in a mobile reaction laboratory. It produces high concentrations of hydroxyl radical (OH) from the photolysis of ozone (O3) in the presence of water vapor. Two chambers were built and tested. A pilot chamber was tested in the laboratory, using mixtures of NO and SO2 in air, at concentrations that are approximately 100 times lower than those in power plant stack emissions. This chamber was able to oxidize about 20% of the SO2, thereby producing 1350 microg m(-3) of H2SO4 particles. Further tests showed that increasing O3 concentrations and residence time increased the H2SO4 production. A field chamber was built subsequently and used in a toxicological study. Diluted coal-fired power plant emissions were introduced in the chamber. Over 19 days of exposure, the chamber, on average, converted 17% of the supplied SO2 emissions and produced an average of 350 microg m(-3) of H2SO4 particles. Particle losses were determined for the pilot chamber, using artificial particles whose size ranged from 50 to 1000 nm. The determined losses ranged from 21 to 42%, with no trend between the amount of particle loss and particle size. Losses for the field chamber, estimated using model calculations, were found to be similar to those of the pilot chamber.

Development of an exposure system for the toxicological evaluation of particles derived from coal-fired power plants.

To investigate the toxicity of particles originating from coal-fired power plants it is necessary to consider the effects of both primary particles and secondary components formed in the air through atmospheric reactions. This report describes a new exposure system that can be used to expose animals to both directly emitted particles and to secondary particles. The system consists of three main components. The first is a sampling system to continuously collect and dilute power plant stack emissions. The second is a reaction laboratory that contains reaction chambers to simulate atmospheric reactions. The following atmospheric reactions were simulated: (1) the oxidation of sulfur dioxide to form sulfuric acid, (2) the neutralization of sulfuric acid by ammonia, and (3) the reaction of alpha-pinene with ozone to form secondary organic aerosol. Using these chambers with the diluted emissions, different typical atmospheric scenarios can be simulated. The final component is a mobile toxicology laboratory where animals are exposed to the resulting test aerosols. We report here the characteristics of the test aerosol exposures obtained at a coal-fired electric power plant. Particle exposures were characterized for concentrations of mass, elements, elemental carbon, organic species, inorganic ions, strong acidity, particle number, and size distributions. Mass concentrations ranged from a few micrograms per cubic meter for a scenario of primary emissions only, to about 250 microg m(-3) for the most complex scenario. We show that the different scenarios produced a large variation in the composition of the test aerosol, thus potentially changing the toxicity of the emissions.

A counter-current parallel-plate membrane denuder for the non-specific removal of trace gases.

In this paper we present a counter-current parallel-plate membrane diffusion denuder for the non-specific removal of trace gases from an air flow. In this design, gaseous pollutants are removed by diffusing from a sample channel to two purge channels by crossing microporous membranes. In the laboratory, at a sample flow rate of 5 L/min and purge flow rates of 5 L/min each, gas removal efficiencies ranged from 84% for CO to 72% for SF6. Removal efficiencies increased with lower sample flow rate, a higher sample to purge flow rate ratio, a longer channel length, and using molecules with higher diffusion coefficient. Removal efficiencies were, however, not affected by the sample channel height. In addition, gas penetration was exponentially associated with the product of channel length, diffusion coefficient, and the inverse of sample flow rate. Particle losses were significant (10-25% losses) only for particles smaller than 50 nm. In a field evaluation, the denuder's performance was tested with an aerosol produced in a photochemical chamber. The denuder's performance was similar to that observed in the laboratory and was stable over time. Finally, the denuder was tested with a semivolatile organic aerosol. Particle mass losses due to volatilization were about 30%.

Inhalation of concentrated ambient air particles exacerbates myocardial ischemia in conscious dogs.

Short-term increases in ambient air pollution have been associated with an increased incidence of acute cardiac events. We assessed the effect of inhalation exposure to concentrated ambient particles (CAPs) on myocardial ischemia in a canine model of coronary artery occlusion. Six mongrel dogs underwent thoracotomy for implantation of a vascular occluder around the left anterior descending coronary artery and tracheostomy to facilitate particulate exposure. After recovery (5-13 weeks), pairs of subjects were exposed for 6 hr/day on 3 or 4 consecutive days. Within each pair, one subject was randomly assigned to breathe CAPs on the second exposure day and filtered air at other times. The second subject breathed CAPs on the third exposure day and filtered air at other times. Immediately after each exposure, subjects underwent 5-min coronary artery occlusion. We determined ST-segment elevation, a measure of myocardial ischemia heart rate, and arrhythmia incidence during occlusion from continuous electrocardiograms. Exposure to CAPs (median, 285.7; range, 161.3-957.3 microg/m3) significantly (p = 0.007) enhanced occlusion-induced peak ST-segment elevation in precordial leads V4 (9.4 +/- 1.7 vs. 6.2 +/- 0.9 mm, CAPs vs. filtered air, respectively) and V5 (9.2 +/- 1.3 vs. 7.5 +/- 0.9 mm). ST-segment elevation was significantly correlated with the silicon concentration of the particles and other crustal elements possibly associated with urban street dust (p = 0.003 for Si). No associations were found with CAPs mass or number concentrations. Heart rate was not affected by CAPs exposure. These results suggest that exacerbation of myocardial ischemia during coronary artery occlusion may be an important mechanism of environmentally related acute cardiac events.