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MEDICAL BIOLOGY: ON OZONE AND ASTHMA

The following points are made by J.F. Gent et al (J. Am. Med. Assoc. 2003 290:1859):

1) Children with asthma are particularly vulnerable to the adverse health effects of high levels of air pollution. Studies of children with asthma living in some of the most highly polluted regions of the world conclude that exposure to levels of ozone or particulate matter (especially particles 2.5 microns in diameter [PM2.5]) regularly in excess of US Environmental Protection Agency (EPA) air quality standards significantly enhances the risk of respiratory symptoms, asthma medication use, and reduced lung function.1-5.

2) Studies of children with asthma living in regions with levels of pollution within or near compliance with EPA air quality standards suggest that the current standards do not protect these more vulnerable members of the population. Asthma severity, as measured by symptoms, medication use, restrictions in activity, or use of medical services, has been shown to be affected by exposure to ozone or PM2.5.

3) Of interest in many recent studies of children with asthma are the simultaneous effects of ozone and particulates on asthma severity.(2,3) Simultaneous exposure to high levels of both ozone and PM2.5 (fine particles)(2) or PM10(coarse particles)(3) found in Mexico City, Mexico, contributed to increased respiratory symptoms among children with asthma. In a region of lower pollution, asthma symptoms were associated with both ozone and course particles.

4) The authors examined the simultaneous effects of ozone and fine particles on daily respiratory symptoms and rescue medication use of children with asthma residing in southern New England during spring and summer 2001. From their results, the authors conclude that after controlling for exposure to fine particles, asthmatic children using maintenance medication are particularly vulnerable to ozone at levels below EPA standards.

References (abridged):

1. Gold DR, Damokosh AI, Pope CA III, et al. Particulate and ozone pollutant effects on the respiratory function of children in southwest Mexico City. Epidemiology. 1999;10:8-16

2. Romieu I, Meneses F, Ruiz S, et al. Effects of air pollution on the respiratory health of asthmatic children living in Mexico City. Am J Respir Crit Care Med. 1996;154:300-307

3. Romieu I, Meneses F, Ruiz S, et al. Effects of intermittent ozone exposure on peak expiratory flow and respiratory symptoms among asthmatic children in Mexico City. Arch Environ Health. 1997;52:368-376

4. Peters A, Dockery DW, Heinrich J, Wichmann HE. Medication use modifies the health effects of particulate sulfate air pollution in children with asthma. Environ Health Perspect. 1997;105:430-435

5. Ostro BD, Lipsett MJ, Mann JK, Braxton-Owens H, White MC. Air pollution and asthma exacerbations among African-American children in Los Angeles. Inhal Toxicol. 1995;7:711-722

J. Am. Med. Assoc. http://www.jama.com

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HEALTH EFFECTS OF GROUND-LEVEL OZONE

Ozone is a blue gas and a blue-black solid and liquid, melting point -193 degrees centigrade, boiling point -112 degrees centigrade. Known pathological changes are caused by exposure to ozone, still the principal component of photochemical air pollution. Inflammatory injury as well as nervous system mediated changes in lung function are observed, perhaps as the result of the formation of free radicals. Individuals with pre-existing respiratory diseases are especially vulnerable to the high levels of ozone found in many urban areas. The authors recommend that people who live in high-ozone areas should not engage in outdoor sports or strenuous outdoor activities when ozone warnings are in effect.

The following points are made by K.J. Bransford and J.A. Lai (J. Am. Med. Assoc. 2002 287:2285):

1) Ground-level ozone, a by-product of fossil fuel combustion, is the major component of smog. Ozone is formed from the reaction of nitrogen oxides and volatile organic compounds, as from power plant emissions and automobile exhaust, in the presence of light and heat. This reaction occurs more rapidly at higher temperatures, explaining, in part, why smog is more marked during the summer months. Global warming would be expected to worsen this form of air pollution.(3)

2) Ozone has been linked to decreased pulmonary function in healthy adults, an effect that depends on exposure concentration and duration.(4) At low levels (0.3 ppm-0.5 ppm), ozone irritates mucous membranes of the eyes and throat and induces chest tightness. High-level exposure (5.0 ppm-10.0 ppm) for more than one hour can lead to pulmonary edema and death.(5) Long-term exposure (4 or more years in areas with summer ozone levels of 80 ppb or more for at least 1 h daily) has been associated with adult-onset asthma in otherwise healthy, nonsmoking individuals.(4)

3) More generally, elevated ozone levels have been found to lead to more frequent asthma attacks, emergency department visits, and hospitalizations; increased use of asthma medications; and greater morbidity and mortality in patients with pre-existing pulmonary or cardiovascular disease.(6,7) Children are at even greater risk because their respiratory systems are still developing, they spend significantly more time outdoors, and they breathe more air per pound body weight than adults. One study found that the relative risk of asthma developing in active children (three or more outdoor sports) living in high ozone environments is 3.3 times greater than those who did not play those sports.

References (abridged):

3. Spellman F, Whiting N. Environmental Science and Technology. Rockville, Md: Government Institutes; 1999.

4. GaliziaA, Kinney PL. Long-term residence in areas of high ozone: associations with respiratory health in a nationwide sample of non-smoking adults. Environ Health Perspect. 1999;107:675-679.

5. US Army Corps of Engineers. Occupational Exposure to Ozone. HQ Environmental Division Lessons, December 16,1996.

6. US Environmental Protection Agency. Health and environmental effects of ground-level ozone. Fact sheet: July 17, 1997.

7. Gong H Jr, Wong R, Sarma RJ, et al. Cardiovascular effects of ozone exposure in human volunteers. Am J Respir Crit Care Med. 1998:158:538-546.

J. Am. Med. Assoc. http://www.jama.com

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