As I mentioned, during our trip to Egypt last year, I became very interested in the way people have used the Nile river to support civilization. I was especially interested in the damming of the river and its use as a source of hydroelectric power. It seems a few of you were as well, especially with regards to the environmental impact damming the river has had. But, I thought that before we began a discussion about something people seem to have a cursory knowledge of already, I would take the opportunity to highlight an environmental crisis that Egypt is facing that is not as commonly discussed:
Figure 1: The view flying out of Cairo. Cairo is down there, I promise. Somewhere.
The first and last stops on our trip were to Cairo and Giza. Cairo is the most populous city in Africa. Including the surrounding metropolitan area, it is home to more that 17 million Egyptians. While tourism is certainly a staple of the local economy, Cairo is also an important manufacturing and financial center. Over the last several decades, population growth in Cairo has far exceeded available resources, a phenomenon known as hyperurbanization. As a result, Cairo is a patchwork of middle to upper middles class neighborhoods and neighborhoods with with no running water or electricity. In some places people have sought shelter in the crypts of local, ancient cemeteries. The people of Cairo generate more than 10,000 tons of trash each day, but only half of it is picked up and disposed of.
- Lead from local, and frequently unregistered and unregulated, metal smelting plants
- Particulate matter from factory and automobile exhaust
- Oxidizing pollutants, like SO2, NO2, and O3, from factory and automobile exhaust
As a physiologist, my interest in Cairo's pollution problem was mainly related to my interest in its health effects. Lead exposure hinders neurological development in children and exposure to particulate matter and oxidizing pollutants alters pulmonary function, hinders lung growth in children, may be a direct cause of myocardial infarction, and is certainly related to an increased risk of infarction and stroke. The mechanisms by which these pollutants affect the vascualture are unclear, but vasoconstrictory effects may be mediated by the potent vasoconstrictor endothelin and vessel wall hypertrophy may be mediated by COX2. Then there are MAPK, angiotensin, and rho kinase, which may all play roles that people do not understand. All the end of the day, here's what we do understand.
Air pollution in Cairo is having another important, non-physiological effect. While many imagine the pyramids at Giza in the middle of an unoccupied desert, they are actually only about 30 meters from the city. There's a great picture here, illustrating the proximity to the city limits on a clear day.
Figure 3: The Great Pyramids at Giza in the haze. Right now, buses, trucks, and cars with tourists are allowed to drive to within meters of the bases of King Cheops (Khufu) and King Chephren (Khafre)'s pyramids. The haze was bad enough on the day that I took this picture that you are unable to see Cairo in the background.
Pollution around the pyramids that results from their proximity to the city and the regular automobile traffic that is allowed to approach them is eroding the pyramids.
Figure 4: King Cheops' pyramid at sunset. The black lines note the original height of the pyramid. The rate of erosion over the last 50 years is exponentially higher than the rate over the last several thousand years.
Egypt appreciates the effect pollution is having on its national treasures. For example, in 1995 it diverted a major eight lane highway away from the pyramids in an attempt to protect them . Still, the government of Egypt is faced with a major problem -- how to deal the industrial development needed to support its rapid population growth and still preserve the national landmarks that support its tourism-based economy.
Figure 5: The Sphinx.
Figure 6: The Sphinx and pyramid at night.
Environment
Physical Science
Comments
A major effect of inhaled particulates is to reduce the production of NO in the nasal passages. I suspect that this is the mechanism for inhaled particulates causing heart disease (and other things), and also the mechanism for the acute increase in heart attacks when the weather turns cold. Cold and dry air reduces NO production too.
Posted by: daedalus2u | April 15, 2009 12:45 PM
I think you mean 30 kilometers from the city, not 30 meters. Not that the Great Isis could be mistaken - probably Bill Gates's fault, right?
Posted by: Dave Gill | April 15, 2009 12:47 PM
No Bill, I mean 30 meters. When I visited I stayed at the Mena House in Cairo. If you visit the Mena House's website one of its major draws is that it is quite literally across the street from the pyramids.
Posted by: Isis the Scientist | April 15, 2009 1:29 PM
Wouldn't at least a substantial portion of this come from the NOX/VOCs/UV (i.e. photochemical smog), especially around urban areas? I'd imagine the UV component in Cairo is certainly not going to be limiting...
Which could help explain the 30m thing, as the location of reaction is not necessarily the same as the location of origin of individual components.
Thoughts?
Posted by: ScienceSealedDelivered | April 15, 2009 1:39 PM
yeah, the proximity of the city to the pyramids is pretty spectacular. when I was there 20 years ago, you could climb a ways up on the pyramids, and look both ways, one direction it was unending desert, the other was unending city and farms. the dividing line was amazing. the city just stopped. very much like something out of a sci-fi movie. at that point the distance was probably closer to a couple of hundred meters.
I wondered at the time who had the unenviable job of sweeping up all that dust everyday.
check it out on google maps, the satellite view is pretty telling.
pyramids
as a side note, it was one of the earliest things that I remember showing me how important composition was in photographs. no one ever seems to take the shot facing back towards the city despite the amazing vista.
Posted by: peter | April 15, 2009 1:57 PM
Long-time lurker here, Dr. Isis. But imagine how excited I was to see your post about Cairo's air quality! That is my exact field of study and I am working to understand this problem at this very moment [or, em, I would be if I were not reading your blog]. Imagine how thrilled I am to know that you consider this topic worthy of your precious time. Could I even call it hot science?
Posted by: als | April 15, 2009 2:11 PM
It is tremendously hot science. ALS! This is exactly the kind of integrative science that thrills the domestic and laboratory goddess.
And you've got it, sciencesealeddelivered! There is no shortage of UV light to catalyze the formation of reactive pollutants. Also, the dry climate and lack of substantial air movement encourages them to stagnate right over Cairo.
Posted by: Isis the Scientist | April 15, 2009 2:19 PM
I've seen some data suggesting that inhaled fine particulate matter stimulates dendritic cell- and macrophage-mediated pulmonary inflammation within the context of asthma development. It isn't unreasonable to suppose that this could also be linked to dysregulation of blood pressure. If lung tidal volume is reduced by chronic asthma, blood oxygenation drops and the heart works harder to pump through more blood, thus raising blood pressure. I imagine it's a relatively tiny step from episodic events like these to chronic vascular and pulmonary stress in such air.
Dr. Isis, are you aware of any epidemiological data to support that? I mean, what are morbidity rates of emphysema, asthma, allergy, and COPD there?
Posted by: Toaster | April 15, 2009 9:45 PM
There is quite a substantial body of evidence that shows that exposure to ambient pollution causes/exacerbates all of those things. The risk of ending up in the hospital from one of those things is increased 0-4 days after exposure to pollution. Lilian Calderon-Garcidueñas has done beautiful work showing that children raised in Mexico City develop substantial lung pathology.
That said, I would rethink your mechanism. Sure, a decrease in tidal volume might decrease venous return in the short term, but I don't think you'd see any lasting increase in BP related purely to increased cardiac output. Think about the kinds of things can the body do to maintain systemic blood pressure.
Now, that doesn't mean there might not be effects on the heart. I would think more along the lines of the coronary circulation and the effect of pulmonary vasoconstriction on the right heart.
I love when you talk physiology to me.
Posted by: Isis the Scientist | April 15, 2009 9:55 PM
I see the Sphinx has taken your advice on the nose... ;-)
Posted by: Ed Yong | April 16, 2009 7:23 AM
I have never been to Cairo, but I have been to India, and I have to wonder how the air pollution compares. In Delhi, it often smells like a fire is burning (but there's no fire other than the one in your lungs). At times, it can be uncomfortable to breathe. The holy city of Varanasi was far worse. My snot and nose debris turned pitch black in these places, and it was clear that you could correlate the level of air pollution in any one place to the color of your boogers. Truly disturbing.
Posted by: Candid Engineer | April 16, 2009 11:00 AM
Interesting post, most lovely and knowledgeable Dr. Isis.
On a similar topic, as I get the impression you rock the world of respiratory physiology, I'm wondering if you could comment on the use of wood-burning stoves and if you know what their effect is on our respiratory health.
I ask because it's a hot topic where I am living, and there is talk of banning their use completely.
Posted by: x-ine | April 16, 2009 12:08 PM
It is really cool to hear about air pollution from the point of view of a physiologist. My intro class talks about air pollution a bit (a teeny-tiny bit), and I often wonder how good the discussion of biological impacts is. So thank you.
Posted by: Kim Hannula | April 16, 2009 1:01 PM
x-ine, I am a vascular physiologist to the extreme, but I also like to keep my knowledge base broad. Physiology is awesome!!!!
Without proper ventilation, which most places lack, wood stoves can be quite bad. Particulate matter and carbon monoxide are both important environmental toxins.
Posted by: Isis the Scientist | April 16, 2009 1:33 PM
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Posted by: Ken McClelland | April 16, 2009 1:36 PM
Dearest Dr. Isis- I just went to the hottest lecture on Nrf2 and COPD and innate immunity and cancer and... all I could think about was you. You've spoiled me for other scientists, Dr. Isis. I hope you're happy.
-love, your obsessive little muffin
Posted by: becca | April 16, 2009 2:32 PM