Asthma and air pollution

Lianne Sheppard

The Clean Air Act specifies that National Ambient Air Quality Standards must be set to protect the most sensitive members of the population. Without doubt individuals with asthma fall into that category. Because of this and because of our longtime relationship with an asthma and allergy clinic, investigators at the University of Washington have specialized in the study of the health effects of air pollution on people with asthma. We have published extensively on the topic.

One recent publication, led by Lianne Sheppard, PhD, an investigator in the EPA NW Particulate Matter Center, reported that symptoms of asthma aggravation in children were associated with particulate matter (PM) air pollution in Seattle (http://ehpnet1.niehs.nih.gov/docs/2000/108p1209-1214yu/abstract.html ). Researchers observed a panel of 133 children with asthma enrolled in the Childhood Asthma Management Program (CAMP) funded by the National Institutes of Health. Daily self-reports of asthma symptoms were obtained from study diaries and compared with daily air pollution levels during 1994 and 1995. The statistical analysis was restricted to effects within a single subject. We found a 30% increase in symptoms for a 10 mg/m³ increase in nephelometer light scattering (PM_1.0) and an 18% increase for a 10 mg/m³ increase in PM₁₀. Carbon monoxide levels were also significantly associated with symptoms. The authors assume that CO is serving as a marker for vehicle exhaust rather than directly affecting asthma. These results agree well with earlier studies by our group that showed lung function decrements, emergency department visits for asthma, and hospital admissions for asthma in Seattle, all associated with PM air pollution. Taken together, these studies suggest that the health effects among persons with asthma from short-term changes in air pollution levels are an important public health problem.

Mortality and PM air pollution

The year 2000 saw the publication of further evidence that tiny particles can kill. Attempts by US Environmental Protection Agency to regulate PM_2.5as well as PM₁₀ has been contentious; industry took EPA to court. The newly published results from the National Morbidity, Mortality and Air Pollution Study (NMMAPS) solidly back the EPA's decision on proposing regulation of finer particles, namely PM_2.5. NMMAPS was funded by the Health Effects Institute, Cambridge, MA. This study of daily PM and daily deaths in 90 of the largest cities in the US found a 0.5% increase in daily death for each 10 mg/m³increase in PM₁₀. Seattle and Spokane were two of the 90 cities studied.

Two Seattle scientists have joined the national debate. Surresh Moolgavkar, PhD, Fred Hutch-inson Cancer Research Cancer, expressed his opinion is Science magazine that NMMAPS did not evaluate associations between daily deaths and other air pollutants sufficiently and also used an untested statistical model. In support of the NMMAPS study, Gerald van Belle, PhD, a biostatistician at UW and a member of the Health Effects Institute review committee, was quoted in Science as follows: " Whatever concern there was about a single-city idiosyncratic effect is no longer tenable."

An example of PM₁₀ levels at four monitoring stations in Idaho on September 18, 1995, a day of field burning

Animal model

One of the goals of the EPA NW PM Center is to identify individual constituents of PM that can explain its lethal effects and to develop an animal model of susceptible individuals that can test the effects of these constituents. Dan Luchtel, PhD, an investigator in the center, implants cardiac and respiratory monitoring devices in mice chosen to be susceptible to cardiac disease. He now is ready to embark on a series of exposures in the mice to a variety of sizes and chemical compositions. Preliminary results of these studies should be available for the next newsletter.

A regional smoke modeling system

Every fall, when farmers burn their field stubble in Eastern Washington and Northern Idaho, smoke from tens of thousands of acres can drift into neighboring towns, drawing complaints from residents. These episodes are hard to measure because of variations in space and time, and the area's limited number of air quality monitoring stations.

For example, one September afternoon, field burning took place in the Spokane and Coeur d'Alene region. Afternoon concentrations of particulate matter increased to short-term, very high levels at three of the four regional monitors in Post Falls, Coeur d'Alene, and Rathdrum Prairie. The fourth monitoring station, in Sandpoint, ID, showed no significant impact.

Good predictions are needed to economically manage the region's agricultural resources while minimizing air quality impacts. They would help determine the location and number of acres that could be burned on a given day. These predictions rely on information on pollutant emission factors, the time and type of fire, and locations and number of acres burned.

Candis Claiborn, PhD, of Washington State University is leading the Center's research in eastern Washington. Her study involves modeling the transport and dispersion of particulate matter from grass field burning, and measuring both the particulate concentrations and chemical composition of smoke sampled immediately downwind of a wheat stubble burn. These preliminary studies will provide the basis for a regional smoke measurement and modeling program for eastern Washington and northern Idaho. Program sponsors include the US Environmental Protection Agency, the Washington Department of Ecology, and the Idaho Department of Environmental Quality.

A complementary research project funded by the Washington Wheatgrowers Association seeks to reduce air quality impacts while limiting the economic impact to the farming community.

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