Dust Storms Not Lethal, Experts Find Team Study Focuses On Smaller Combustion Particles

A study of 18 major dust storms in Spokane by a team of nationally known air-quality experts found no connection between blowing dust and increased respiratory deaths.

The same team also is continuing to study the link between smaller combustion particles and hospital admissions and unexpected deaths in Spokane.

The scientists want to know if Spokane’s pollution problems are consistent with a growing body of worldwide evidence that points to tiny combustion particles from factories, auto exhaust, wood stoves and agricultural burning - rather than the larger dust particles - as the main culprits causing death in susceptible people.

“We were asked to check out whether windblown dust could also be contributing to excess deaths,” said Jane Koenig, a University of Washington epidemiologist and one of the study’s six authors.

“When someone asks whether dust storms cause people to die, we can now say, `No, it doesn’t look like it,”’ Koenig said.

The study by a team of Harvard University, UW and and Washington State University scientists was supported by the U.S. Environmental Protection Agency and the Washington Department of Ecology.

Air pollution data for the project were collected by the Spokane County Air Pollution Control Authority.

The study appears next month in Environmental Health Perspectives, the peer-reviewed journal of the National Institute of Environmental Health, a branch of the National Institutes of Health.

The paper is already on the NIH Web site at www.nih.com. The lead author is epidemiologist Joel Schwartz of the Harvard School of Public Health, one of the nation’s leading experts on the links between pollution and respiratory problems.

The scientists looked at 18 major Spokane dust storms from 1989 to 1996. Most occurred in late summer and fall.

Average dust levels, also known as PM 10 levels, during the storms were 221 micrograms per cubic meter - exceeding the EPA’s 150 microgram 24-hour limit. During the storms, the gusty winds blew most small-particle pollutants out of the city.

If the dust particles had been as toxic as smaller particles, deaths should have risen 20 percent during the dust storms. But deaths were slightly fewer than normal during the storms, the study reports.

The study also notes “indirect evidence” from two other studies by Schwartz that fine combustion particles are causing health problems in Spokane.

Those studies, using data from the same time period as the dust study, report increased hospital admissions for respiratory and cardiovascular disease when dust storms aren’t raging and PM 10 levels are below 150 micrograms. On those days, much of the pollution in Spokane was from small combustion particles.

That finding is “consistent with the previous literature on air pollution and mortality,” the study notes.

The dust study results aren’t a surprise to local air-quality officials.

“I expected this. From a variety of other reports at the conferences I’ve been to, all the indications are that it’s small particles that are causing the problem,” said Ron Edgar, SCAPCA’s chief of technical services.

“We get a lot of windblown dust, and we haven’t seen a lot of people getting sick from it. It was nice to have this confirmed statistically,” Edgar said.

“Dust isn’t absolutely harmless, but it doesn’t seem to be anything more than an annoyance to most people,” Edgar said.

Much of the dust blown into Spokane is from agricultural areas in Central Washington and the Palouse.

Dust particles are about 10 microns in diameter - less than one-tenth the width of a human hair. Combustion particles are much smaller, from 1 to 1.5 microns.

The smaller particles can lodge in the alveolar area of the lung, where they carry toxins attached to them into the bloodstream. The toxins include sulfates, nitrates, organic compounds and heavy metals. Scientists still don’t know which combinations of these chemicals, and in which air pollution scenarios, cause the most deaths, Koenig said.

In 1997, the EPA revised its particulate standards in response to the studies that showed combustion particles were much more of a threat than windblown dust.

The EPA’s new regulation was based in part on Schwartz’s work. He found that fine particles, not coarse particles, were associated with daily deaths in six U.S. cities.

The Schwartz-Koenig team continues to study Spokane’s complex air pollution problems. The city sits in a bowl, which traps pollutants, and has distinct pollution episodes.

Autos and wood stoves are a problem during winter inversions. Road dust with chemicals from winter de-icing efforts can pollute the air in the spring. In the summer and fall, dust storms and agricultural burning add additional pollutants.

Spokane has far fewer sources of industrial pollution than most big cities the EPA studies.

With several years of new air pollution data from SCAPCA and a growing body of hospital records, “we now have the power, in the next two or three years, to answer some very important questions,” Koenig said.