Indoor Air Pollution Zebras and Horses

Indoor Air Pollution and the Role of Zebras and Horses

 

Due to family illness, Kirk Smith, Professor of Global Environmental Health, University of California, Berkeley, U.S.A. (krksmith@berkeley.edu) was unable to attend the symposium. Allan Smith presented Kirk Smith's slides on his behalf, although he has not participated in Kirk Smith's work.


Dr. Smith referenced “zebras and horses” in the title of the presentation because in the presentation itself he drew an analogy between zebras and rare health issues and between horses and common health issues. Zebras are relatively rare in most societies, while horses are much more common globally.

 

Dr. Smith made the point that there has been much more emphasis in journals and conferences on rare diseases and applications of sophisticated measurement methods, whereas we hear much less about the environment and other common, pervasive risks that affect global health (Figure 1.1)

 

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The oldest and, in Dr. Smith's opinion, the most serious form of pollution is that caused by burning biofuel (wood, dung, coal) in homes with inadequate ventilation (Figure 1.2). Solid fuel, or biofuel, is used in millions of homes throughout the world (Figure 1.3) and there is a significant release of “products of incomplete combustion” when wood burns (Figures 1.4, 1.5, 1.6).

 

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Exposure to such toxic pollutants in the home has been monitored using systems devised by Dr. Smith (Figure 1.7). The results are outlined in Figure 1.8 which shows that in homes in India, using typical woodfired cookstoves, benzene, a carcinogenic agent, exists in concentrations 800 times higher then health-based standard levels.

 

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Many diseases (including cancer, cataracts, low birth weight, asthma, and tuberculosis) are likely linked to indoor air pollution, but more work is needed to prove these relationships (Figure 1.9). Diseases proven to be caused by indoor air pollution are listed in Figure 1.10.

 

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Indoor air pollution is a major cause of global death (Figure 1.11) causing an estimated 1.6 million premature deaths per year, certainly far more than the current number due to urban outdoor air pollution

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Definitive proof of the effect of indoor air pollution requires careful studies of which randomized controlled trials are the most powerful (Figure 1.12). Such studies on the effect of environmental pollutants on health are rare. However, Dr. Smith described a study that he performed in a community in the highlands of Guatemala (Figure 1.13). It was a controlled trial in which one arm of the study had chimneys to vent cooking exhaust, while the control group did not (Figure 1.14). Details of the study are shown in Figure 1.15. The results of this simple, remarkable study are shown in Figure 1.16.


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Dr. Smith returned to the zebra/horse analogy with a figure showing the most significant diseases in the world (as assessed by “disability adjusted life years [DALYs]) (the “global disease horses”) which represent the greatest burden to humanity. Many of these have important environmental causes (Figure 1.17), but more studies are needed.

 

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Dr. Smith's publications can be found at http://ehs.sph.berkeley.edu/krsmith/