Dust from the Sahara in the Caribbean

A Reminder of Global Effects on Small Islands Far, Far Away

It may be a matter of days, of weeks, or maybe months, but someday soon we’re going to look out our windows and instead of seeing glorious blue sky, we’ll see a veil of haze instead. It may last for days, coating our screens with rust-colored dust, draining our sunsets of color, and leaving many of us with a sense of malaise.
It is dust from the Sahara desert and bordering Sahel of Africa, making its way thousands of miles across the Atlantic, through the Caribbean, all the way to Mainland, USA. Its many effects are not well understood, but Ginger Garrison, who recently retired as a research marine ecologist with the U.S. Geological Survey, has been trying to find out.
Garrison and other scientists recently completed a 15-year study which is summarized in a video: (http://coastal.er.usgs.gov/ african_dust/documentary.html).
They were trying to determine if African dust has played any role in the decline in live coral on Caribbean reefs over the past few decades.
Although they were unable to show any direct effects of African dust on living coral reefs, they found that the dust does transport living bacteria and fungi, as well as chemicals that are known carcinogens, toxic to humans, or endocrine disruptors, including pesticides, metals, polyaromatic hydrocarbons (PAHS), and polychlorinated biphenyls (PCBs).
Garrison first became interested in researching the connection between “Sahara Sand” (as the dust is known locally) and the decline in coral reefs when she moved to
the Virgin Islands with her husband John in 1983 to run a dive charter business.
“With a white boat, the dust was obvious,” said Garrison, who started to wonder if the dust contained some nutrient input.
When she took a job as a researcher with the Virgin Islands National Park several years later, the question loomed larger.
“We kept finding diseases among corals and the growth of algae around populated and unpopulated islands,” Garrison said. “We wondered what regional-scale event could affect both.”
The question led to a study that began on St. John, then included Mali (West Africa), a known source of dust, where scientists took air samples. They compared these samples to those from the Cape Verde Islands (off the West Coast of Africa,) in the U.S. Virgin Islands (in the northeast Caribbean,) and in Trinidad and Tobago (in the southeast Caribbean.)
“We were able to use the ‘fingerprint’ of the metals to determine where the dust was from, and we confirmed it was from the Sahara and Sahel of Africa and not from local sources,” said Garrison. “In the Virgin Islands during dust periods, there were three to eight times more living organisms than in normal, clear air.”
It’s not just metals, manmade compounds, and microorganisms that travel in the dust. Two-inch long African desert locusts “arrived alive” on Windward Islands in 1988.
Although scientists have not yet been able to prove a direct link between African dust and coral reef diseases, they did find low levels of a “suite of compounds that are known to be carcinogenic and toxic,” said Garrison.
“They always occurred together — in a ‘stew,’ and the toxicity of mixtures of these things has never been studied,” she said. “When you have an African dust event in the Caribbean, the amount of inhalable particles — smaller than two-and-a-half microns in diameter (PM2.5) exceeds U.S. Environmental Protection Agency limits, which in the U.S. are almost twice levels allowed in Europe.” And yes, Garrison confirmed, Europe also experiences African dust events.
It’s not only the composition of the African dust that makes it a health hazard, according to Garrison. It’s the particle size as well.
“Particles smaller than two-and-a-half microns in diameter (PM2.5) can be inhaled into the smallest areas of the lungs,” she said. “Increases of PM2.5 (and smaller) particles in the air are associated with increased mortality and hospital admissions for heart attack, strokes and pulmonary issues.”

When the researchers studied the metals in African dust (including iron, which gives the dust its rusty, reddish color,) they found changes occur during the trip from Africa to the Caribbean that make some metals more active biologically or toxic.

Some metals which are toxic in fine particles are not as toxic in larger particles mainly because they do not get deep into the lungs where they can cause inflammation, which may be one way they lead to heart attacks and strokes.

Garrison emphasized that there is no evidence that African dust causes asthma, which is a complex disease, but that dust can trigger or exacerbate the symptoms.
“Asthma sufferers, and anyone with chronic obstructive pulmonary disease (COPD) or heart issues, should stay inside during Saharan dust conditions,” she said.
Garrison further warned anyone from exercising outdoors when reddish dust is visible in the air.
“We all need iron to live, but it’s a matter of not wanting fine particles of it in your lungs,” she said.