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Dust Storms Overseas Carry Contaminants to U.S.
Scientists Study Whether Diseases Are Also Transported

By Doug Struck
Washington Post Staff Writer
Wednesday, February 6, 2008

Seventy-five years ago, aviator Charles Lindbergh turned the controls of his pontoon plane over to his co-pilot, wife Anne Morrow Lindbergh, while flying above Iceland. He thrust a makeshift metal arm holding a sticky glass plate from the cockpit. He wanted to see if the winds high aloft the Earth were as clean as they seemed.

They were not.

Now, with NASA satellites and sampling by researchers around the world, scientists know that great billowing clouds of dust waft over the oceans in the upper atmosphere, arriving in North America from deserts in Africa and Asia.

Researchers have also found that the dust clouds contain not only harmful minerals and industrial pollutants, but also living organisms: bacteria, fungus and viruses that may transmit diseases to humans. Some say an alarming increase in asthma in children in the Caribbean is the consequence of dust blown from Africa, and predict they will find similar connections in the Southeast and Northwest United States.

Scientists are beginning to look at these dust clouds as possible suspects in transcontinental movement of diseases such as influenza and SARS in humans, or foot-and-mouth disease in livestock. Until recently, epidemiologists had looked at people, animals and products as carriers of the diseases.

"We are just beginning to accumulate the evidence of airborne dust implications on human health," said William A. Sprigg, a climate expert at the University of Arizona. "Until now, it's been like the tree falling in the forest. Nobody heard, so nobody knew it was there."

The World Meteorological Organization, a science arm of the United Nations, is alarmed enough to set up a global warning system to track the moving clouds of dust and to alert those in the path. Sprigg is heading the project.

He foresees a system soon in which forecasters can predict "down to the Zip code" the arrival of dust clouds. That forecast could prompt schools and nursing homes to keep their wards inside, and help public health doctors predict a surge of respiratory complaints.

Analysis of soil samples has long shown that minerals picked up from barren deserts reach distant shores, for good or bad. The Amazon rain forest in South America, for example, gets phosphate nutrients from dust blown in from northern Africa's Sahara Desert.

Industrial development has added heavy metals and toxic chemicals to that airborne mix. Korea and Japan periodically chafe as storms of "Yellow Dust" wash over from China, bringing a caustic mix of sand and industrial pollutants.

Even natural minerals can be harmful to humans, and dust-borne particles have been linked to annual meningitis outbreaks in Africa and silicosis lung disease in Kazakhstan and North Africa. The Dust Bowl storms of the 1930s in the United States brought graphic descriptions of choking sediment getting into the lungs of people and felling livestock.

But the advent of satellite images gave scientists a sobering look at how even faraway storms can reach us.

Traveling for a week over the Pacific from the Gobi and Taklimakan deserts in Asia, clouds carrying hundreds of millions of tons of dust regularly reach the northwestern United States. From the Sahara and Sahel deserts in Africa and the East, they roll across the Atlantic to the Caribbean and reach the southeastern United States in three to five days.

Authorities in Los Angeles estimate that on some days, one-quarter of the city's smog comes from China.

"There is plenty of evidence from space observations of the Northern Hemisphere that there is a persistent ring of industrial emission dust and other pollutants in the air. You can actually see this bathtub ring around the Northern Hemisphere," said Stanley A. Morain, who heads the Earth Data Analysis Center at the University of New Mexico and collaborates with Sprigg.

"If something breaks out, it can move very quickly into other areas," he said.

Dust storms may be increasing as global warming and desertification expand arid areas. The dust swirls into the atmosphere containing plant pollens, fungal spores, dried animal feces, minerals, chemicals from fires and industry, and pesticide residues.

Asthma in the Caribbean increased just as an African drought increased the amount of dust washing over the islands. Asthma has increased in Barbados 17 times since 1973, when the African drought began, according to a national study there, and researchers have documented an increase in pediatric hospital admissions when the dust storms are worst.

Scientists previously had thought bacteria and viruses picked up by the dust storms would die on long flights, when they are exposed to ultraviolet radiation and extreme temperatures. But three-inch African locusts have been found alive in the Caribbean after dust storms.

In the late 1990s, Eugene Shinn, who was studying the widespread die-off of Caribbean coral reefs for the U.S. Geological Survey in Florida, began wondering if smaller living organisms came with the dust. He eventually linked live microbes brought from Africa to sea fan disease, which was infecting the coral.

Shinn enlisted USGS microbiologist Dale Griffin. They and other colleagues devised a method of collecting air samples, using a contraption built with a vacuum pump from Home Depot drawing air through a two-inch round sterile filter.

In the first test, collected during a dusty day in 2000 over the Virgin Islands, Griffin said he thought they might find evidence of four or five different microorganisms growing colonies on the filter. Instead, he found 30 colonies, each with billions of cells.

"I did not expect that many," he said. "And we know that whatever grows on the filter represents only about 1 percent of what's really there. People just don't think about microorganisms moving around the atmosphere, at least that far."

Griffin said that "in Florida in the summer, when the dust storms are pulsing across, if you walk outside and breathe, 50 percent of the particles you breathe come from Africa," more than 4,000 miles away. They contain mold spores and bacteria that increase allergies and respiratory diseases.

Shinn, who is now retired, said that there has not been enough response to these findings.

"No one in authority really wants to hear about this problem, even when it is known that African dust sporadically exceeds EPA air standards in places like Miami during the summer months," Shinn said in a letter recently. "No government agency wants to face this problem because no one knows what to do about it.

"In my opinion, nothing will change regarding either African or Asian dust until we have a catastrophe such as a large-scale avian flu, West Nile virus, or some other deadly outbreak that cannot be explained away by the usual suspects," he said. "Meanwhile we will continue to employ agents to check for fruit in baggage and dirt on tourists' shoes while hundreds of millions of tons of soil dust carrying live microbes continue to be transported unchecked overhead."

Unchecked, perhaps, but not unwatched. The early warning system being devised by Sprigg will track those storms, integrating the data with weather forecasts, so that local authorities have notice of one to three days to take precautions. Parts of the system have already been set up in China and Europe.

In addition to medical precautions, police can be warned about deteriorating driving visibility and airports can plan to reroute planes, Sprigg said. He said he hopes the next step will be more aggressive medical research to determine the composition and human health threats of what is in those dust clouds.

"I really see some practical applications here," he said. "We are just getting started."

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