Jun 17, 2001

Mobile Homes for Microbes




African dust that crosses the Atlantic and brings beautiful sunsets to Florida also carries potentially harmful bacteria and fungi, a new study shows.


Marshall Space Flight Center


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June 18, 2001 -- African dust has produced striking sunsets in south Florida for years. But it seems there is more to the dust clouds, which cross the Atlantic during north Africa's annual dry season, than meets the eye. NASA-funded researchers say motes of dust carry stowaway bacteria and fungi that could pose a health risk to people who inhale them.


Right: NASA's SeaWIFS satellite captured this image of Sahara Desert dust swirling westward across the Atlantic Ocean. Image courtesy NASA SeaWiFS Project and ORBIMAGE.

African dust plumes begin their trans-Atlantic journey with storm activity in the Sahara Desert region. The dust, originating from fine particles in the arid topsoil, is transported into the atmosphere by winds and may be carried more than 10,000 feet high. Dust clouds cross the Atlantic Ocean and reach the Caribbean and the Americas in about 5 to 7 days.




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"These dust events are cyclical," says Dale Griffin of the US Geological Survey (USGS), lead author of African Desert Dust in the Caribbean Atmosphere: Microbiology and Public Health, an article that appeared in the June 14th edition of the research journal Aerobiologia. "Studies by other researchers have shown that [each year] from February to April, winds bring an estimated 13 million tons [of dust] to the Northeastern Amazon Basin," he continued. "From June to October the winds shift and typically bring dust to North and Central America and the Caribbean."

During the peak of the dust season in July 2000, the USGS's Virginia Garrison collected daily samples of airborne pollutants and dust on the island of St. John in the Virgin Islands. She sent them to the USGS laboratory in St. Petersburg, FL, for microbial analysis by Griffin. At the same time NASA's space-based Total Ozone Mapping Spectrometer (TOMS) monitored dust moving across the Atlantic. Garrison and Griffin found that microbe levels were high in the air of the Virgin Islands just when TOMS observed dust sweeping in from Africa.

Below: Click on the strip to view a 1.9 MB Quicktime animation that begins with a close-up view of microbe-laden dust and zooms out to view a dust plume crossing the Atlantic Ocean. The strip below shows frames from the animation. The first is a microscopic image of microbes on a dust particle in a dust plume (top image). Each of the subsequent images show how the material looks from approximately factors of 10 farther away. The final frame shows how the plume looks from very high altitude above Earth, demonstrating a common transportation technique for microbes. Credit: NASA


"In the week it takes for North African dust to cross the Atlantic some of the microbes die because of exposure to ultraviolet (UV) rays of the Sun," explains Griffin. "However, microbes in the cracks and crevasses of dust particles may be shielded from UV. We also believe that the upper altitudes of the dust clouds deflect harmful UV rays, shielding microbes at lower altitudes. Additionally, when dust clouds move over open water in lower latitudes, the moderate temperatures and high humidity enhance microbial survival."

Florida receives more than 50 percent of all microbe-laden African dust that reaches the United States. Over the last 25 years, dust quantities reaching Miami have increased during periods of African drought. The U.S. Environmental Protection Agency says these tiny dust particles can penetrate deep into your airways and react with lung tissue.


Indeed, "the National Institute of Health's National Institute of Allergy and Infectious Diseases identifies airborne dust as the primary source of allergic stress worldwide," says Eugene Shinn of the USGS. In addition to the dust itself, even small concentrations of fungal spores can trigger allergic reactions. A study by M.E. Howitt of the Queen Elizabeth Hospital in Barbados documented a 17-fold increase in asthma attacks in Barbados between 1973 and 1996, corresponding with an increase in African dust transport to that region.


Above: Click to view a 0.8 MB Quicktime animation based on data from NASA's Total Ozone Mapping Spectrometer. The movie shows airborne dust traversing the Atlantic Ocean in July, 2000, at the same time Virginia Garrison (USGS) was monitoring air quality in the Caribbean Virgin Islands. Image Credit: NASA [more]

Not all dust-borne fungi and bacteria are disease producing, say researchers. Microbes that survive the trans-Atlantic journey are bound to be a mixture of harmless microorganisms and potentially troublesome ones. Finding out how many microbes cross the ocean unscathed and what they do when they reach the other side are important questions for future studies.



Dale Griffin, Virginia Garrison, and Eugene Shinn of the U.S. Geological Survey (USGS) and Jay Herman of NASA's Goddard Space Flight Center, Greenbelt, MD, outline their findings in a paper titled "African Desert Dust in the Caribbean Atmosphere: Microbiology and Public Health." The paper was published June 14 in the journal Aerobiologia.

NASA's Earth Science Enterprise Environment and Health Program at Goddard, a cooperative program with local, state, and federal and international institutions funded this research. The initiative uses NASA remote-sensing satellites and other data to investigate the connections between the world's environmental conditions and human health.

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More images and animations: from NASA's Goddard Space Flight Center.

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