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December 09, 2011

Fine particle health risks calculated for roughly city size areas in California

Three new studies released today by the California Air Resources Board reveal that exposure to airborne fine-particulate matter significantly elevates the risk for premature deaths from heart disease in older adults and elevates incidence of strokes among post-menopausal women. Heart disease is the number one killer in California and is responsible for approximately 35% of annual deaths.

“We’ve long known particulate matter is a major component of California’s air pollution problem,” said ARB Chairman Mary D. Nichols. “These new studies underscore the need to eliminate the threat from California’s air.”

Particulate matter is a complex blend of substances ranging from dry solid fragments, solid-core fragments with liquid coatings, and small droplets of liquid. These particles vary in shape, size and chemical composition, and can contain metals, soot, nitrates, sulfates and very fine dust. One source of particulate matter, including PM2.5 or fine-particulate –matter, is exhaust from vehicles, especially from diesel engines. PM 2.5 is particulate matter smaller than 2.5 microns in diameter - a human hair is about 60 microns in diameter.




Michael Jerrett, Ph.D., of the University of California, Berkeley, found that exposure to fine particulate matter significantly elevated the risks for premature death from heart disease. The most frequent cause of death associated with PM2.5 in this study was ischemic heart disease, which can lead to heart attacks and heart failure. The findings of this study are based on the California participants in a large study sponsored by the American Cancer Society, which tracked 76,000 adults from 1982 to 2000.

In another study, Michael Lipsett, M.D., of the California Department of Public Health, led a team that examined the effects of chronic air pollution exposure on heart disease in women. The project tracked over 100,000 current and former female public school teachers and administrators in California. Like the University of California, Berkeley study, Dr. Lipsett found that exposure to PM2.5 elevated the risks for premature mortality from ischemic heart disease. In addition, this study found an increased risk of stroke among women who had never had one before, particularly among those who were post-menopausal.

These two studies demonstrate a relationship between long-term PM2.5 exposure and cardiovascular effects, such as heart attacks and strokes.

The third study, by Fern Tablin, V.M.D., Ph.D., and Dennis Wilson, D.V.M., Ph.D., of the University of California, Davis, investigated how inhaled PM2.5 could contribute to heart attacks and strokes. A common cause of heart attacks and strokes is development of clots in the blood stream. One suggested explanation is that PM2.5 exposure activates platelets, the key cells involved in blood clotting, so that they form clots and then trigger heart attacks and strokes. Drs. Tablin and Wilson examined the platelets of mice exposed to PM2.5 from the San Joaquin Valley Air Basin, and found that mice exposed to fine particulate matter showed platelet activation in both winter and summer, which could promote clotting and lead to stroke and heart attacks.

These new studies add to the existing scientific literature indicating that microscopic airborne particles pose a threat to public health. California Air Resources Board calculations of combined cardiovascular and respiratory (i.e., cardiopulmonary) deaths associated with PM2.5 exposure are based on the results of the national American Cancer Society study. Annually, 7,300 to 11,000 premature cardiopulmonary deaths in California are estimated to be associated with exposures to fine particulate matter.

Estimate of Premature Deaths Associated with Fine Particle Pollution (PM2.5) in California Using a U.S. Environmental Protection Agency Methodology (39 pages)

The U.S. EPA’s reports were peer reviewed in a public process by the Clean Air Scientific Advisory Committee (CASAC) Particulate Matter Review Panel, an
independent peer review body of national scientists.

There are a large number of published health studies that estimate the
additional risk of mortality due to long-term exposure to PM2.5. U.S. EPA’s new
quantitative health risk assessment for particulate matter uses a 2009 study
(Krewski et al., 2009) for the core analysis. This study is an extension of a 2002
study (Pope et al., 2002) used in the previous PM2.5 NAAQS risk assessment.
This report estimates premature death from PM2.5 in California based on the
2009 Krewski study.

Using U.S. EPA’s methodology, the estimated number of annual PM2.5-related
premature deaths in California is 9,200 with an uncertainty range of 7,300 –
11,000. This estimate of premature deaths is based on the latest exposure
period in the 2009 Krewski study with data from 116 U.S. cities and about
500,000 people.

The results of the national scale assessment are shown above. In U.S. EPA’s table the bolded figures indicate the estimate that corresponds with the lowest measured level in the epidemiological study. The bolded estimates in the Krewski et al. (2009) column were calculated using the same risk coefficients as the urban case study. U.S. EPA indicates a greater emphasis is placed on the results calculated using the lowest measured level reported in the epidemiological studies. The estimated total PM2.5-related premature mortality ranges from 63,000 – 80,000 for the two time periods in the Krewski et al. (2009) study to the lowest measured level of 5.8 μg/m3. For the Laden et al. (2006) study the estimate is 88,000 with a lowest measured level of 10 μg/m3. The 90% percent confidence intervals are shown in each case. The U.S. EPA national assessment is based on 2005 PM2.5 levels. This report provides a California estimate based on air quality data from the years 2006-2008.

Links to the studies:

Michael Jerrett: http://www.arb.ca.gov/research/single-project.php?row_id=64805
Michael Lipsett: http://www.arb.ca.gov/research/single-project.php?row_id=64806
Fern Tablin: http://www.arb.ca.gov/research/single-project.php?row_id=64824

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