HEI releases research report on health effects of ultrafine particles
23 January 2013
A new report from the Health Effects Institute (HEI)—Understanding the Health Effects of Ambient Ultrafine Particles—concludes that while there have been a growing number of laboratory and field studies of the effects of ultrafine particles (UFPs), “toxicologic studies in animals, controlled human exposure studies, and epidemiologic studies to date have not provided consistent findings on the effects of exposures to ambient levels of UFPs, particularly in human populations. The current evidence does not support a conclusion that exposures to UFPs alone can account in substantial ways for the adverse effects that have been associated with other ambient pollutants such as PM2.5.”
“There is extensive evidence today that the complex mix of fine airborne particulate matter (known as PM2.5 or less than 2.5 microns in diameter) can contribute to a variety of cardiovascular, respiratory and other health effects,” said Dan Greenbaum, President of HEI. “But despite a large number of studies of the smallest particles (or particles less than 0.1 microns in size), our expert panel found that the evidence to date has not confirmed the hypothesis of some in the scientific community that these ultrafine particles are the principle reason for these broader PM2.5 health effects.”
Particulate matter emissions are a complex mixture, containing particles of a variety of sizes and composition, and there have been continuing questions from the scientific and policy communities about whether some components or characteristics of that mixture, or particles from some sources, are more toxic and deserving of priority efforts for control. The ultrafine particles—which are emitted from a variety of sources including traffic, industry, and cooking—have gained special attention, because of their potential for traveling deeper into the lungs, into the bloodstream, and into the brain. They are important as well because of a number of regulatory actions. A number of EU regulations, including Euro 5b and Euro VI, introduced particle number (PN) limits to control UFP emissions. US regulations, while not explicitly controlling UFP emissions, have triggered the introduction of particulate filters on new diesel engines that also reduce UFP emissions. At the same time, fuel economy rules are encouraging the use of more fuel efficient, direct injection gasoline engines (GDI) that may increase UFP emissions.
The report—the latest in a series of HEI Perspectives—was prepared by an HEI panel led by Dr. Mark Frampton (University of Rochester and member of the HEI Review Committee), and composed of six multidisciplinary scientific experts. At HEI, Senior Scientist Dr. Katherine Walker led the project. The team reviewed over 300 studies and syntheses of data to arrive at its conclusions, and its report was further peer reviewed by ten outside experts who had not participated in the preparation of the review.
The Panel found that despite the substantial number of studies completed to date, challenges and limitations remain. “The fact that the current database of experimental and epidemiologic studies does not support strong and consistent conclusions about the independent effects of UFPs on human health does not mean that such effects, as one part of the broader effects attributable to PM2.5, can be entirely ruled out,” said Mark Frampton. “There are limitations in the evidence base, including deficiencies in exposure data, and numerous challenges in comparing and synthesizing results of existing studies.”
The Panel’s major findings can be summarized as follows:
- Motor vehicles, especially diesel engines, have been important sources of emissions and exposures to UFPs but emissions are likely to change substantially in the years ahead.
- UFPs clearly differ from larger particles in their lung deposition, lung clearance, and potential for translocation to other parts of the body.
- Experimental and epidemiologic studies provide suggestive, but not consistent evidence of adverse effects of short-term exposures to ambient UFP.
- Currently, the Panel has no strong evidence that effects of short-term exposures to UFP are dramatically different from those of larger PM; information on long-term exposures is not available.
Source: Health Effects Insttute