Health Hazards of Smoke Spring 2001
Fire Storm 2000 (continued)
Health Hazards of Smoke
The health effects of exposure to smoke from burning vegetation have been studied in a variety of populations, ranging from children to wildland firefighters. This section will focus on the health effects of smoke exposure, including lung function, cardiopulmonary disease, and lung cancer.
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| Cilia Tiny hairlike projections called cilia sweep particles up and out of the respiratory passages. Days or weeks of smoke exposure, as in cigarette smoking, can deaden the ciliary action and suppress the immune system, setting the stage for particle buildup and bronchitis. The ciliary action recovers when the smoke exposure ends. |
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Acute Health Effects—Studies of smoke exposure indicate a relationship between exposure, respiratory symptoms, and respiratory illness. Respiratory symptoms (coughing, wheezing, shortness of breath) increased in a portion of the population exposed to smoke from agricultural burning. Women and people with asthma and chronic bronchitis were more likely to be affected. Although the prolonged Southeast Asian haze episodes (1997 to 1998) were associated with increased hospital visits and asthma symptoms in children, studies of smoke from bushfires in Australia did not detect an increase in emergency hospital visits for asthma during the episodes. Large forest fires in California (1987) led to increased emergency room visits for asthma and chronic obstructive pulmonary disease.
Wildland firefighters may be exposed to particulate levels several times higher than those observed in exposed communities (PM10 exposure averaged 690 µg/m3 on wildfires). Surveys of medical records (1989, 1994, and 2000) indicated that 30 to 50 percent of firefighter visits to medical tents are for upper respiratory problems, including coughs, colds, and sore throats. A number of factors in the firefighting environment influence immune function and the body's susceptibility to respiratory problems and other illnesses. Upper respiratory problems can be caused by fatigue, stress, sleep deprivation, poor nutrition, rapid weight loss, exposure to smoke, or a combination of stressors.
Lung Function—Studies of children and firefighters document the effect of smoke exposure on lung (pulmonary) function. When third-, fourth-, and fifth-grade school children were studied in Missoula, MT, elevated levels of suspended particulate were associated with a slight decrease in lung function. The adverse effects of particulate on children's lung function were small, acute, and reversible, with values returning to normal after 2 months with clean air. Studies of wildland firefighters show small but statistically significant decreases in lung function after a day or a season of firefighting. As with the children, the values returned to preexposure levels after the firefighters were able to breathe clean air. A 4-year study showed that wildland firefighters have above-average lung function and that occupational exposure to smoke has little effect on the decline in lung function that normally occurs with age.
The respiratory system is overbuilt for its duties. Its capacity is one-and-one-half times that needed at maximal effort (for instance 180 L/min compared to 120 L/min at maximal aerobic capacity). So a slight temporary decline in lung function is not noticeable and it does not decrease work performance. The human lung has a remarkable capacity to cleanse itself when given an opportunity. In one study, decreased lung function persisted 16 days-but not 25 days-after exposure to smoke. The significance of transient and apparently reversible effects on lung function, and their possible contribution to permanent functional or structural changes, has not been established.
Chronic Health Effects—Urban pollution has been linked to increased rates of mortality and morbidity. A recent study of five major cities in the United States found that the level of PM10 is associated with the rate of death from all causes and from cardiovascular and respiratory causes. The estimated increase in the relative rate of death from cardiovascular and respiratory causes was 0.68 percent for each 10 µg/m3 increase in PM10. These results suggest a long-term risk of exposure to fine particulate and strengthen the rationale for controlling the levels of respirable particles.
Lung Cancer—According to the World Health Organization, the data on exposure to vegetative smoke do not support an increase in the risk for lung cancer, even at exposure levels well above those experienced by firefighters. Studies of women in developing countries who cook over unvented stoves indicate that exposure to wood smoke with PM10 levels of 850 to 1,400 µg/m3 can be associated with chronic lung disease, but not with cancer. Cigarette smokers are subject to a variety of diseases and disorders (such as lung cancer, heart disease, emphysema, and chronic bronchitis) after many years of daily exposure to smoke. However, these exposures are much higher and last longer than exposures to biomass smoke from vegetative fires. The smoker's risk of lung cancer is 7 to 14 times higher than the risk associated with long-term exposure to second-hand tobacco smoke. An assessment of chronic smoke exposure for wildland firefighters indicated little increased risk for the average firefighter, even though exposure can be several times higher than that experienced by residents of communities exposed to smoke. While biomass smoke may be a potential carcinogen, it is much less of a cancer risk than motor vehicle exhaust or other known carcinogens. University of Montana chemist Garon Smith analyzed the smoke in the Missoula Valley during the fires of 2000. Smith's studies did not reveal a wildfire-related increase in cancer-causing polycyclic aromatic hydrocarbons.
Oncologists estimate that genetics is a factor in 60 to 90 percent of all cancers. Bad habits, such as tobacco, poor nutrition, and pollution are responsible for the remaining cancers. Cancer risks of less than 1 in 1 million pose a negligible addition to the overall cancer risk in the United States of about 1 in 3 (table 1).
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