Dust busters gather. (NIEHS News).

Researchers have long known that occupational dust can pose health hazards--coal miners, construction workers, and others exposed regularly to dust on the job have a greater risk of developing respiratory disease than those who are not. But what about the dust-filled air the general public breathes on any given day? Might the increased severity of dust storms born in Africa and Asia take a toll on public health downwind in communities across the globe?

In 2001 a monster dust storm originating in the Mongolian Gobi touched countries that were oceans away, including the United States and Canada, and got North American researchers more acutely interested in examining this source of long-range pollution transport. Such Asian storms were the focus of the Sino-U.S. Workshop on Dust Storms and Their Effects on Human Health, held 25-26 November 2002 in Raleigh, North Carolina. If there was one consensus among the 80 participants at the workshop, it's that people will have to unite across national boundaries to fully understand, study, and combat this threat; every nation is an involuntary importer and exporter of dust.

The workshop included presentations on government program overviews, observations on Asian dust and its transport (including satellite imagery and remote sensing), modeling and forecasting of dust storms, effects of aerosols on the climate, properties of dust, and effects of dust on ecosystems and human health. Funding was provided by the National Aeronautic and Space Administration, the U.S. Environmental Protection Agency (EPA), the U.S. Department of Agriculture's Forest Service, the National Oceanic and Atmospheric Administration, and the NIEHS. The workshop was organized mainly by Chinese-American scientists, through the North Carolina Chapter of the Chinese Association for Science and Technology.

Lian Xie, an associate professor of marine and atmospheric sciences at North Carolina State University and cochair of the workshop, said the initiative of the Chinese-American scientists was fueled by both personal and professional interest. "Many of us lived through dust storms in China," he said. "We are also very concerned about the environmental consequences of the rapid economic development in China if land, water, and natural resource uses are not properly managed. We all want to see a sustainable development in China and the world."

Not Just Dust

Dust transported by storms is known to contribute to a range of problems, including effects on marine ecosystems (such as a proliferation of "red tides" and coral reef decline) and interference with high-tech military instruments. It is further suspected as an aggravating factor in respiratory diseases (such as asthma), cardiovascular disease, and global climate change. Dust in clouds can suppress rainfall, exacerbating drought conditions in and regions on a local scale. And because of its influence on radiative forcing, particulate matter in the atmosphere (including dust) may soon rival greenhouse gases in their contribution to global warming, said Carey Jang, project manager at the EPA's Office of Air Quality Planning and Standards.

But there's more to dust clouds than just dust--bacteria, fungi, viruses, and other microorganisms are carried with the clouds. The list of potential microbial hitchhikers includes Aspergillis sydowii, a soilborne fungus implicated in deaths of Caribbean sea fans, and insidious human pathogens such as those responsible for plague, hantavirus, bacterial meningitis, and tuberculosis. These microbes particularly threaten the compromised immune systems of more sensitive populations, including the elderly and young children. Dale Griffin, a microbiologist with the U.S. Geological Survey's Center for Coastal and Watershed Studies in St. Petersburg, Florida, estimated conservatively that a quintillion or more bacteria move through the atmosphere via dust transport each year. Griffin said research suggests that about 30% of culturable microorganisms in atmospheric dust are capable of causing disease in plants, trees, and animals.

Microorganisms aren't the only toxic hitchhikers in dust clouds. Chemicals from pesticides, herbicides, pharmaceuticals, toxic outputs from waste burning (such as dioxins and plasticizers, which are known carcinogens and endocrine disruptors), and industrial emissions also can be transported with the dust. The mineral structure of the dust itself also poses threats. For example, the fine iron particles that are the source of the reddish color of African dust can cause lung inflammation and, over time, scarring. The Asian dust storm season also coincides with the North American spring/summer, when pollution concentrations are already high.

Approaching an Evolving Phenomenon

Dust storms are not a new phenomenon. Pierre Biscaye, a research scientist at Columbia University's Lamont-Doherty Earth Observatory, said his research teams have provided a 100,000-year record of atmospheric dust transport from Asia to Greenland through ice core analyses. What has changed appears to be the intensity, rather than the frequency, of storms. Xie said that in analyzing the past decade of dust storms in China, the total number of storms per year decreased overall, but there was an increase in more intense storms.

Thomas Gill, a research assistant professor at Texas Tech University's Wind Science and Engineering Research Center, likened the scenario to the escalating worldwide frequency of such weather-related events as hurricanes and tornadoes. "Perhaps it's an indicator that there may be a larger global climatic-scale phenomenon driving events that go beyond the threshold of our control," he said.

Dust storms result from weather phenomena such as wind, but also have human-influenced sources, such as improper land use in desert regions resulting in desertification. The extent to which humans contribute to the occurrence of dust storms is still unknown. This is just one of the questions that participants hope will be answered through a systematic "end-to-end" approach--starting with identifying the sources of dust and continuing to include transport, climate interaction, prediction, impacts on terrestrial and marine ecosystems, economy, society and human health, mitigation, and policy issues. According to Xie, one major accomplishment of the meeting was that representatives from five U.S. agencies, each responsible for a specific aspect of the dust problem, sat together at the workshop to discuss ways to solve the dust problem using this integrative, end-to-end approach.

"We should be cautious to parse the problem to manageable scales," said Joseph Prospero, a long-time researcher of African dust and director of the University of Miami's Cooperative Institute for Marine and Atmospheric Studies. "There are so many different aspects of dust generation and transport that one could look into, that we could end up with a `shopping list' that's very long and would be rather chaotic." Prospero suggested choosing focus areas, and as one example proposed that a team of scientists with multiple perspectives and disciplines examine areas with repeated large-scale dust activity.

Ken Wilkening, an international environmental policy specialist and assistant professor at the University of Northern British Columbia, urged that Canada and the United States hold another conference, specifically on desertification and long-range transport of dust in the Pacific region, as soon as possible. He reiterated the current conference's goal of forming a trans-Pacific network of dust experts to share information and develop a consensus understanding of the state of the science of those topic areas. He also called for an international meeting within the next year or two that would include scientists and policy makers, although he noted that researchers should synthesize, summarize, and evaluate current knowledge before requesting policy action.