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Public Radio's Environmental News Magazine (follow us on Google News)


Air Date: Week of

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Millions of tons of dust cross the oceans to distant continents, and new research shows the dust may bring along some toxic guests. Janet Raloff, senior editor of Science News, discusses this issue with host Steve Curwood.


CURWOOD: This is Living on Earth. I'm Steve Curwood. To most of us, dust is a local nuisance. We find it on the countertop and underneath the bed. Maybe a bit of it blows across the road as we walk or drive along. What we don't realize though is that a lot the dust we see comes from far away--hundreds of millions of tons of it blow across the Atlantic from Africa to the Americas. From Asia, tons of dust cross the Pacific. Some of the dust that we generate winds up in far away places as well.

Now, new research, highlighted in the latest edition of Science News, shows that this dust may bring along some unwanted hitchhikers. Science News Editor Janet Raloff joins me now. Hi Janet.

RALOFF: Hi Steve.

CURWOOD: So, Janet, what evidence is there that dust can transport unwanted disease across the oceans?

RALOFF: Well, some scientists, federal scientists, just cultured some dust that had been falling out in the Caribbean. It had originally come from Africa, and they could track it through satellite photos to know that it made those movements. And they're finding lots of bacteria, fungi and viruses in the dust that comes from Africa. And not only is it there but--this is pretty surprising--they found out that the stuff can grow. They can culture it and it blossoms in a petri dish. Looks pretty awful.

CURWOOD: Any diseases, specifically, they link to this dust?

RALOFF: Well, they haven't identified many of the germs yet, but the ones they have tend to be plant pathogens, and that's particularly interesting because in the late seventies there had been an epidemic of sugar cane rust in the Caribbean that seemed to come out of nowhere. And when an analysis was done about a year after the epidemic broke, they noticed that it seemed to be occurring in areas downwind of an area in Africa where the disease was also an epidemic. And now this would seem to give strong support to the idea that the germs that set off that epidemic in the Caribbean actually came from Africa.

CURWOOD: What about diseases in animals?

RALOFF: Well, there are fewer that have been tied at this point, but again, there's this nice, intriguing little episode, back about 20 years ago, where some British scientists looked at outbreaks of foot and mouth disease throughout Britain and Europe. And there are lots of cases that seem to, again, come out of nowhere, but they would show up on different sides of bodies of water, like the English Channel or the Baltic Sea. And at that time they said there was, at least, circumstantial support for foot and mouth disease having traveled by air, across water.

CURWOOD: What about us humans? What kind of risk do we run from dust-borne disease?

RALOFF: Well, one of the big concerns right now is asthma. There's a big asthma epidemic in Barbados and that's one of the eastern most islands in the Caribbean, one of those that gets the first dustfall from Africa. And they're finding that emergency room admissions for asthma for peaking at times when African dust is in the atmosphere. And they think they have linked it now to a particular bacterium that's present in that dust; when the bacterium isn't there, the asthma epidemic doesn't peak in emergency rooms.

CURWOOD: We've had dust forever. Why are we just noticing this now?

RALOFF: Well, part of it is that we have better monitoring, more air sampling stations, and more chemical analyses that can sort of finger print where dust is coming from. They can match it up with soils and tell that it's not like where it's landing. But there's also probably more dust just because of changing land use practices, which often leaves ground uncovered during dry seasons, making it very vulnerable to erosion. And there's, in addition, a lot of diversion of water bodies right now, to try and irrigate soils for crops and also to feed populations that are getting thirsty, like Los Angeles.

CURWOOD: What's going on in Los Angeles?

RALOFF: Actually, the situation there developed beginning around 1900. They could see that Los Angeles was growing fast and didn't have sufficient water, so they started tapping rivers that fed Owens Lake, in the mountains, several hundred miles to the east of Los Angeles. They took so much water that the lake totally dried up within ten years. And since then, the lake bed has been eroding and throwing lots of dust into the atmosphere and totally inundating several of the towns right next to it--to the extent that there's now lawsuits over that, and the city of Los Angeles is going to have to pay for re-mediation of Owens Lake.

CURWOOD: What's in this dust?

RALOFF: The thing of primary concern is a lot of arsenic, from 19th century gold mining operations upstream. There's sufficient arsenic, they think, that exposed individuals in the nearby towns can increase their life time cancer risk to about 1 in 40,000. And usually anything above one in a million is considered very serious cancer risk.

CURWOOD: Anything that we can do, in general, about dust?

RALOFF: Well, we do usually a fairly good job in this country of controlling erosion. Many people in the developing world don't have the money and resources to do the same, and I think a lot of people in North America figured, well, that's their problem, not ours. Now that we see that their dust and any of the wastes in it can end up in our back yard, it might turn out to be in our vested interest to help them out with some kind of agricultural aid, so they can also practice good soil conservation techniques.

CURWOOD: Janet Raloff's article on the disease carrying components of dust is in this week's edition of Science News. Thanks, Janet.

RALOFF: Thank you, Steve.



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