African dust bringing toxic chemicals to U.S., Caribbean; is it killing corals? Hurting people?

It’s one of those increasingly frequent stories demonstrating that ecologically, the whole globe is connected — and why that’s not always a good thing:

Pesticides, polycyclic aromatic hydrocarbons and polychlorinated biphenyls are among the contaminants hitching an airborne ride to the United States and other parts of the Western Hemisphere on dust storms blowing out of West Africa. That’s according to new research presented at the just-completed annual meeting of the Society of Environmental Toxicology and Chemistry.

This image from Aug. 5, 2005 shows African dust spreading west, north and south as the green and yellow. Courtesy Dr. Douglas Westphal, Navy Research Lab, Monterey, CA

The findings are worrisome because some of the chemicals carried on the trade winds originating in Africa are persistent in the environment, they bioaccumulate, and they are known to be toxic at low concentrations, said U.S. Geological Survey researcher Ginger Garrison, who presented the findings at the SETAC conference in New Orleans.

It’s been known for some time now that dust storms blowing off North Africa make their way across the Atlantic and deposit fine particles of dust. I covered that in my Florida days, the Sunshine State being the U.S. region getting the highest concentrations of the superfine dust.

The dust travels as far west as the Rockies and as far north as New England, and tongues of it have reached out across Central America into the Pacific. It also blankets the Amazon and is a major source of nutrients there.

This finding of contaminants in the dust is a new twist on the story — one that might go on to help explain why coral reefs off Florida aren’t recovering after they are damaged. Research in Australia showed that low doses of individual pesticides caused coral larvae to fail to attach to reefs, meaning they don’t recover from various environmental insults, Garrison said:

 One of the things we’ve been wondering about is … why aren’t the reefs rebuilding? Because they’re not. This would explain one thing.

 And who knows what else the contaminants in dust might be doing to the health of humans and ecosystems? Among the pollutants are some known to cause cancer, disrupt the reproductive and nervous systems, suppress the immune system and act as liver toxins.  

The dust particles we’re talking about here are far smaller than the PM2.5 particulates that are small enough to have prompted special EPA emphasis (PDF) earlier this year. Garrison said the findings must be followed up:

 We need to be concerned and we need to do further examinations to see what affect it has on the ecosystem and human health.

 Along with the modern contaminants in the reddish-brown African dust are old-fashioned metals found in the Earth’s crust, including iron, which is known to have some inflammatory properties, Garrison said. Getting particles that small in the lungs is bad enough; what happens if there’s iron in there, too? Or copper, or cadmium? USGS researchers are trying to find out.

Niger River Valley. Courtesy Wikipedia via GNU Free Documentation License

And where are these contaminants coming from? Here’s where that notion of a connected globe really shows up: The Niger River valley in Africa  runs right past Timbuktu in Mali, the country where Garrison went on her own dime to check out conditions. It’s not a pretty sight:

It’s a flood plain and so once a year it overflows its banks. Everything is going into the river.

Farmers growing rice and cotton there use pesticides, as do farmers fending off locusts from food crops. DDT is still sprayed to control malaria-carrying mosquitoes. Pesticides wash into the river, then are deposited in the floodplain to be blown away after flood season.

And where the people once burned bushes for fuel, they now also burn garbage — including plastic and tires that give off a pretty good-sized dose of dioxin and polycyclic aromatic hydrocarbons when burned at relatively low temperatures. Air quality there is terrible, Garrison said, making breathing difficult.

This image from May 18, 2007 shows a large dust storm coming out of Africa and heading west, north and east. Meanwhile, dust from Asia's Taklimakan and Gobi deserts heads east across the north Pacific toward the Western United States, including Rain City, and makes it all the way to the north Atlantic. Source: Dr. Douglas Westphal, Navy Resarch Lab, Monterey, CA

What can be done to control the transport of these contaminants? Garrison stresses that she just does the science, not the policy. But if you want to keep the dust down, you’d do things that would help the Africans as well as anyone downwind:

Improved land use practices would mean less deforestation. Better management of soils and lighter use of pesticides would help. So would better sanitation, and doing something with garbage other than burning it.

As with almost any environmental story nowadays, this one includes a climate angle: This dust is blowing off the Sahara Desert as well as the Sahel region to its south, which appears to be turning more desert-like in the face of global warming, combined with deforestation. More desert would presumably mean more dust being blown toward the New World.

As Dateline Earth has discussed before, the continental United States, including Rain City, also gets hit from time to time by contaminant-laden dust blown out of Asia. And studying where these air masses move globally shows that we’re all living in the same snow globe. Said Garrison:

It’s almost looking as if we have  global burden, a background of these pollutants, these pestsicides, these PCBs and we get pulses added to the environment.

— Robert McClure