UC Irvine study finds organic constituents of UFP play important role in heart disease; suggestions for more effective emission control
|Particle scale. Inset: 4 polydisperse modes of traffic-related ambient particulate matter span approximately 4 orders of magnitude from below 1 nm to above 10 μm. Source: Kleinman presentation. Click to enlarge.|
Results of a study funded and released by the California Air Resources Board (ARB) suggest that the organic constituents of ultrafine PM (UFP, particles ≤ 0.18 μm aerodynamic diameter) resulting from internal-combustion engine exhaust and from chemical reactions in the air play an important role in the progression of heart disease, the leading cause of death in the US. The findings thus suggest a direction for mor effective emission control measures—i.e., technology for the removal of the organic constituents as well as the reduction of the number of particles.
Led by Dr. Michael T. Kleinman of the University of California Irvine, the new study used a novel approach to determine whether or not the toxicity of UFP particles depends on the concentration and composition of semi-volatile and non-volatile fractions of the PM.
PM comprises solid, liquid, and semi-volatile organic components. Traffic-related particulate matter spans approximately 4 orders of magnitude from below 1 nm to above 10 μm and is formed by a number of different mechanisms.
Numerous studies have found that exposure to PM air pollution may contribute to both disease and death. Other work at UC Irvine has shown that Ultrafine PM is more effective than Fine PM in promoting atherosclerosis, and that the large surface area of UFP may act as a “carrier” that brings chemicals into areas that they couldn’t ordinarily reach.
The observed associations between PM exposure and human heart disease and death may be related to PM-induced oxidative stress and/or inflammation in the body; however, the specific mechanisms by which PM exposure worsens heart function and cardiovascular disease are not well understood.
Preliminary studies have shown that if most of the organic components were removed from the particles, the particles would become much less chemically reactive. This new study thus tested the hypothesis that adverse effects of exposure to UFP, which are highly enriched in semi-volatile components, would be significantly attenuated by removal of those semi-volatile components from the aerosol. Dr. Kleinman used a novel mobile in vivo rodent exposure system in combination with a particle concentrator and thermal denuder—a heating method to remove organic compounds from the particles—to study the cardiopulmonary effects of UFP, before and after the removal of the semi-volatile components.
The thermal denuder removed more than 60% of the particle-associated organic compounds (OC) but did not remove the non-volatile components such as elemental carbon (EC) or trace metals.
Genetically modified mice with impaired lipid metabolism and predisposed to the development of atherosclerotic-like plaques were exposed to UFP 6 hr/day, 4 days per week for 8 weeks; the experiments were conducted near the University of Southern California campus in central Los Angeles.
The study found that mice exposed to either fully intact particles or just the organic components of the particles had more rapid development of atherosclerotic plaques, compared to mice exposed to particles without the organics. The intact particles also had other negative effects on heart health. Atherosclerosis is hardening of the arteries, a factor contributing to heart attacks.
We therefore conclude that the organic constituents of UFP contribute to the accelerated development of atherosclerotic plaque in arteries, lipid oxidation is an important mechanism of action in PM-induced coronary artery disease, and that removal of the organic compounds from PM greatly ameliorates plaque development associated with air pollutant exposure.
These findings suggest that emission control measures that remove and sequester or destroy organic constituents of combustion generated aerosols could benefit public health because coronary artery disease is a leading contributor to heart-related deaths, which represents about 50% of deaths, annually, in California and other states as well.—Dr. Kleinman
Such emission control measures might include thermal denuding technology such as afterburner emission controls not only to reduce pollution but also to reduce the toxicity of the residual particles, Dr. Kleinman suggested.
Dr. Kleinman presented his findings at a seminar on 9 October at the Cal/EPA Headquarters Building in Sacramento.
Michael Kleinman (2013) “Cardiopulmonary Health Effects: Toxicity of Semi-Volatile and Non-Volatile Components of PM” (Final Report Agreement No. 07-307)