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A study confirms that dust crossing the Atlantic carries particles that pose a health risk.
By DAVID BALLINGRUD
© St. Petersburg Times, published June 14, 2001
Bacteria, fungi and probably viruses are crossing the Atlantic Ocean to Florida in clouds of dust from drought-stricken areas of Africa.
Photos taken by NASA satellites and on-the-ground air samples confirm the trans-Atlantic movement of tiny, potentially hazardous particles, according to an article published today in the scientific journal Aerobiologia.
The danger posed by the global movement of dust clouds to the United States is uncertain. Further study is needed, said Eugene Shinn of the U.S. Geological Survey office in St. Petersburg, one of the article's authors.
"The identification of microbes in transported dust is important. . . . They may be a source of disease above and beyond that caused by exposure (to dust)," Shinn said.
Ongoing tests have not identified a particle -- bacteria, fungi or virus -- that by itself is a human disease threat, said Dale Griffin, a USGS microbiologist and another author of the Aerobiologia article.
But about 10 percent of the particles found are considered "opportunistic," Griffin said, meaning they could cause illness in a person whose immune system was already compromised by illness or age.
About 25 percent of the particles threaten only plants, and the remainder, thus far, appear specific to soil and do not constitute a health threat.
"That's what we've seen so far, but it's a numbers game and we're still testing," he said. Shinn and Griffin were joined on the paper by Virginia Garrison of the USGS and Jay Herman of NASA's Goddard Space Flight Center in Maryland.
Garrison, who has gathered dust samples in the Virgin Islands National Park, said the dust is sometimes visible as a reddish haze as it approaches from the east. After a sample of air is collected, it is drawn through a filter and the filter is examined.
Shinn and other scientists have struggled to get the scientific establishment to recognize that African dust is a health hazard. With continued NASA funding for the study, and with publication of the Aerobiologia article, Shinn said he is hopeful more money will be forthcoming.
"The level of interest is spiraling upward," he said. "I've been asked to brief U.S. Sen. Mary Landrieu (D-La.) and I'm hopeful other federal agencies will have interest, too." A workshop on the subject will be in the USGS St. Petersburg offices in August, he said.
There is nothing new about clouds of dust blowing westward across the Atlantic. African dust has produced red-tinged sunsets in south Florida for years.
The dust comes every year during northern Africa's dry season, when storms in the Sahara Desert and Sahel grassland region generate vast clouds of dust. These clouds then are pushed westward by the same easterly "trade winds" that drive hurricanes toward U.S. and Caribbean shorelines every year. Typically, it takes five to seven days for the dust clouds to cross the Atlantic.
So much dirt makes the journey that air plants in the Amazon depend on nutrients derived from the airborne soil. Florida receives more than 50 percent of all microbe-laden African dust that reaches the United States, according to a statement released jointly by the USGS and NASA.
A long-term drought in North Africa has caused larger and more frequent dust storms in recent years. And, thanks to a new generation of Earth-observing satellites, the dust clouds can be seen and tracked as never before.
Last year, in February, a NASA satellite photographed one of the largest dust storms ever observed. About as big as Spain, the brown cloud was seen leaving Africa, heading west across the Atlantic toward the Caribbean and the United States. Smaller clouds make the trip more frequently.
But there's more than just dirt in the dust. Bacteria and fungi are confirmed hitchhikers, and viruses are almost certainly present, too, although confirmation of those extremely small particles is about a month away, Griffin said.
"At this point we don't know how serious the health concerns are," he said. "We're just trying to lay down a baseline of data, to show what's there."