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Medicine for the Outdoors

Dr. Paul Auerbach is the world's leading outdoor health expert. His blog offers tips on outdoor safety and advice on how to handle wilderness emergencies.

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Ozone and the Outdoors

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Here's an interesting news item (within the quotation marks) that was recently brought to my attention:

"Content provided by Reuters on April 22, 2008
WASHINGTON (Reuters) - Even breathing in a little ozone at levels found in many areas is likely to kill some people prematurely, the National Research Council reported. The report recommends that the U.S. Environmental Protection Agency consider ozone-related mortality in any future ozone standards, and said local health authorities should keep this in mind when advising people to stay indoors on polluted days.

The report looks at ground-level ozone, a component of smog, as opposed to the ozone found in the high atmosphere, which protects the earth from ultraviolet rays. Ozone is a form of oxygen formed by the reaction of sunlight on air containing other pollutants such as hydrocarbons and nitrogen oxide. It is a powerful oxidizer, meaning it can damage cells in a process akin to rusting.

Ozone is known to cause respiratory problems and worsen heart disease. Children and the elderly are at special risk. The EPA asked the National Research Council, part of the advisory National Academies of Science, to analyze the link between ozone and early death.

A committee appointed by the council found that deaths related to ozone exposure are more likely among people with pre-existing diseases and other factors that could increase their susceptibility. But they said premature deaths are not limited to people who are already within a few days of dying. They looked at studies that linked deaths directly with variations in ozone levels, as well as animal studies that examined whether there was a biological explanation for ozone causing death.

The committee looked at studies done in several cities across the United States as well as in Canada and Europe. They took into account differences in temperature and humidity that may affect the ozone level. The EPA toughened standards for ozone pollution in March but outside experts complained its new requirements were more lax than the EPA's own scientists recommended. The new standards are 75 parts per billion in ambient air in the United States. The previous standard was 80 parts per billion. The EPA's Clean Air Scientific Advisory Committee recommended a standard of 60 to 70 parts per billion."

As it is difficult to conceive of wilderness medicine without the wilderness, I absolutely believe that environmental issues should be featured from time to time within this "Medicine for the Outdoors" blog. Indeed, it is well accepted that the outdoors is in need of the equivalent of medical attention. Certainly, for those of us who venture outdoors frequently, and who choose to exercise in urban locales in preparation for our wilderness excursions, air quality is a very high priority. It appears that accumulations of ozone at low altitude are increasing, and that they will have a deleterious effect upon human lungs, even in the absence of our immediate appreciation of pain, shortness of breath, or decreased exercise tolerance.

I was asked recently by Dr. Val Jones of Revolution Health to comment upon the ozone situation, and was happy to do so. John Briley, who is an excellent writer, prepared a report that featured useful information, and I provided elements of the following commentary in response to Mr. Briley's questions:

Knowledge about air quality on a day-to-day basis is becoming a necessity for persons who live, work, and play in the outdoors. It is crucial that these people, and those responsible for them, know what published ozone levels mean. The Environmental Protection Agency posts these data daily, with a U.S. map showing elevated-ozone areas, via http://airnow.gov/; these reports are also published on the weather pages of many daily newspapers. But how many of us look at them, and with what intensity are they reported? If people have access to this information, they can make informed choices about whether and how hard to exercise, how much time to spend outdoors, etc. Just as the heat index is a very useful guide for people to avoid being afflicted by heat illness during heat waves, the Air Quality Index (AQI) is essential for determining when it is safe to be exposed to atmospheric air. It is a sad fact of life, but a fact nonetheless, that AQI should be known and advertised to promote good health, and to avoid bad health.

EPA’s Air Quality Index runs from zero to 500; this covers a range of pollutants, but ozone is a leading factor in determining the AQI. Air pollutant levels above a value of 100 could be a concern for people with pre-existing respiratory conditions, and levels above 150 indicate potential for adverse health effects in anyone breathing that air. An air-quality from 201 to 300 is “very unhealthy” and anything above 300 is “hazardous.”

On days with unhealthy ozone levels, one should try to limit exposure by staying in environments that are protected from the ozone-laden air. This might be indoors in a location with central air conditioning. If the air is toxic, you should avoid outdoor exercise, unless you are willing to suffer a burning sensation in your throat and eyes, difficulty breathing, triggering of incipient reactive airway disease (such as asthma), a general ill feeling, and the potential for lung irritation and inflammation that may contribute to permanent lung injury. Even casual exposure to high ozone levels is toxic. That toxicity rises when you exercise because you’re breathing more rapidly and deeply, thus assaulting your lungs and your immune system, and likely shuttling more of the atmospheric pollutants into your bloodstream and your tissues. So, if you walk outside and there’s a visible haze and your eyes burn and your throat is irritated, something’s not right. If you’re exercising in those conditions, you should cease the activity immediately.

On high-ozone days, exercising in the early morning or after dusk should not be relied upon to necessarily reduce exposure to ozone to an acceptable level. Ozone levels do not automatically correspond to temperature, so just because it is cooler outside doesn’t mean the ozone level is safe. Even though the EPA notes that ozone levels tend to peak in late afternoon and early evening, because levels build throughout the day on hot, sunny days, they still could be unsafe before dawn or after dusk. That’s why awareness of the levels via something like the AQI is key.

The press release above confirms that low level, chronic exposure to ozone can cause long-term damage. Even if the acute exposures are undetectable, the cumulative toxicity can lead to increased morbidity – and perhaps even mortality. This is not an alarmist perspective, as studies looking at ozone exposure and lung disorders confirm the links.

Many reversible conditions can become irreversible over time. Whether it’s cigarette smoking, or ozone, or toxicity from contaminated food products, the body can often repair itself to a certain extent, but in the case of ozone, chronic exposure may eventually cause sufficient persistent inflammation to lead to permanent scarring and inflammation of tissue.

Precisely when that permanent damage might occurs varies from person to person, so we can’t say definitively that, for example, someone who jogged three times a week at noon all summer long in a high-ozone area will develop lung disease. But we can say that, generally, chronic exposure to ozone will eventually become a contributor to lung irritation and injury.

I harken back to my youth in the summer of 1968, when the summer Olympics were held in Mexico City. There were ahtletes seeking to perform well who trained by running at altitude and by exercising behind buses, in order to acclimatize themselves, or so they thought, to the polluted air they expected to encounter during competition. They wanted to adapt to toxic particulate matter, vehicle exhaust, and ozone, but undoubtedly had no idea that in the process, they were assaulting their lungs. Today, from an ozone perspective, if you live in the following cities, you had best be careful:

25 Most Ozone-Polluted Cities (2007)

1 Los Angeles-Long Beach-Riverside, CA
2 Bakersfield, CA
3 Visalia-Porterville, CA
4 Fresno-Madera, CA
5 Houston-Baytown-Huntsville, TX
6 Merced, CA
7 Dallas-Fort Worth, TX
8 Sacramento--Arden-Arcade--Truckee, CA-NV
9 Baton Rouge-Pierre Part, LA
10 New York-Newark-Bridgeport, NY-NJ-CT-PA
11 Washington-Baltimore-Northern Virginia, DC-MD-VA-WV
12 Philadelphia-Camden-Vineland, PA-NJ-DE-MD
13 Hanford-Corcoran, CA
13 Modesto, CA
15 Phoenix-Mesa-Scottsdale, AZ
16 Charlotte-Gastonia-Salisbury, NC-SC
17 Las Vegas-Paradise-Pahrump, NV
17 Milwaukee-Racine-Waukesha, WI
19 St. Louis-St. Charles-Farmington, MO-IL
20 El Centro, CA
20 Kansas City-Overland Park-Kansas City, MO-KS
20 Beaumont-Port Arthur, TX
20 Chicago-Naperville-Michigan City, IL-IN-WI
24 Grand Rapids-Muskegon-Holland, MI
25 Atlanta-Sandy Springs-Gainesville, GA-AL
25 Cleveland-Akron-Elyria, OH

We are running out of time to mend our environmental ways. Air quality would be a reasonable place to begin.

opening image courtesy of the U.S. Environmental Protection Agency

Preview the 25th Anniversary & Annual Meeting of the Wilderness Medical Society, which will be held in Snowmass, Colorado July 25-30, 2008.

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Dr. Paul S. Auerbach is the world’s leading authority on wilderness medicine.

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