Dose-Response Assessment

Much of the scientific knowledge about the effects of fire on human health is created in medical experiments that isolate individual elements of smoke and study their effects in controlled laboratories. The results of such “pure” medical trials may be misleading since in “real” situations many substances interact with other substances and the combination of elements can have a different effect that a single element. In addition, it is difficult to duplicate dose-exposures for individuals in a diverse population and for variable fire events (Evans and Campbell 1983). Often, the high doses used in clinical trials are far greater than the doses humans would be exposed to from forest fires, particularly prescribed fires. Dose exposures among firefightersdiffer from those of the general population. Psychological issues among wildland firefightersalso differ from the general population. Psychosocial responses to fire differ from biophysical responses.

Dose Response to Air Pollutants

Exposure to smoke from fires has the potential to cause direct injuries and fatalities, suppressed immunity, and physical and cognitive impairments. The respiratory conditions that result from inhalation of biomass smoke include temporary, permanent, and progressive breathing problems (American Thoracic Society 2000). For most people, smoke is an irritant. Teary and burning eyes, a runny nose, and a scratchy and sore throat are the most common symptoms of exposure to smoke and its irritating components which are mainly organic acids, aldehydes, sulfur dioxide, and particulate matter.

Research shows that there is a link between elevated air pollution and decreases in lung functioning (Larson and Koenig 1994). Some common lung and heart problems caused by biomass smoke (Betchley and others 1997; Kane and Alarie 1977; Patz and others 2000; Tan and others 2000) are:

• decline in lung functioning
• decline in breathing rate
• breathing discomfort
• chest pain
• emphysema
• asthma
• allergies
• bronchitis
• angina
• myocardial infarction/heart attack
• pneumonia
• premature death

There are numerous components of smoke (Table:Heart and Lung Conditions Associated with Biomass Smoke)that cause declines in lung functioning, either individually or in combination. These include: particulate matter, carbon monoxide, ozone, and other substances.

Particulate Matter

Particulate matter is one of the most significant emissions from forest fires (EPA 1998; Ottmar 2001). Prescribed fires almost never produce enough particulate matter to damage human health. Very intense wildfires, however, may produce enough particulate matter to cause some health problems.

People who have pre-existing illnesses such as asthma and heart conditions may experience difficulties when particulate matter is very thick. When particulate matter is extremely dense, it can damage the lungs, cellular membranes and red blood cells (Dockery and Pope 1994; Eeden 2001; Larson and Koenig 1994; Osterman and Brauer 2000; Tan and others 2000). Coughing is the most common lung problem among people who are exposed to particulate matter in the air (Dockery and Pope 1994). People who inhale a lot of particulate matter may also experience discomfort from breathing, shortness of breath, asthma, wheezing, excess phlegm production, lung inflammation, systemic inflammation in the body, upper and lower respiratory tract infections, COPD (chronic obstructive pulmonary disease), and Ischemic Cardiomyopathy (Dost 1991; Eeden 2001; Health Research Working Group 2001; Larson and Koenig 1994). Exposure to extremely high levels of particulate matter is linked to cancer (Adami, Hunter, Trichopoulos 2002).

Irritants

Biomass smoke and some of its constituents are irritants. Smoke inhalation causes eye irritations and upper respiratory tract irritations. Symptoms from acute exposure to organic acids, aldehydes (e.g., acrolein and formaldehyde), and particulate matter include teary and burning eyes, runny nose, and scratchy and sore throat. Sulfur dioxide by itself irritates the lungs and in combination with particulate matter has even greater irritating effects (Evans and Campbell 1983). Acrolein is an irritant that is toxic to the cells in the upper respiratory tract (Dost 1991). When forest fires burn in areas where the soil contains crystalline silica, smoke inhalation can cause lung inflamation and scarring, thereby reducing the amount of oxygen the lungs are able to absorb (Ottmar and Reinhardt 2001).

The inhalation of some plant compounds in smoke can cause skin and respiratory irritations. Some botanical species that cause skin irritations in people who have direct contact with the whole plant can cause even worse reactions in people who inhale the smoke that is emitted from the burning plant. One example of this sort is poison ivy (Toxicodendron radicans). Other plants that do not necessarily cause adverse reactions in their whole, living form may have severe consequences for people who inhale the smoke from the burning plant.

Carbon Monoxide

Carbon monoxide is a major constituent of biomass smoke. Inhalation of carbon monoxide increases production of carboxyhemoglobin (COHb) above the body’s normal amounts. Carboxyhemoglobin are bonds of carbon monoxide and hemoglobin that form when carbon monoxide displaces blood oxygen. In excessive amounts, carboxyhemoglobin:

• causes oxygen deprivation
• damages body tissue
• coughing and cold-like symptoms
• complicates atherosclerosis
• complicates coronary heart disease

Ozone

The following conditions can result from exposure to ozone (Evans and Campbell 1983; Patz, Engelberg, and Last 2000):

• chest pain
• pulmonary edema
• headaches
• aggravation of pre-existing edema
• aggravation of pre-existing arrhythmia

Cancer-causing Agents in Smoke

A number of the individual components of forest fire smoke have demonstrated carcinogenic effects which can lead to cancer. These include: particulate matter(Ostermann and Brauer 2000), dioxins, including the dioxin TCDD- a component of herbicides (Mukerjee 1997), nitrogen oxides(Adami, Hunter, Trichopoulos 2002), ozone, free radicals, over thirty polynuclear aromatic hydrocarbons (PAHs) and hundreds of PAH derivatives(Fang and others 1999; Adami, Hunter, Trichopoulos 2002), formaldehyde(Therriault 2001; Ottmar and Reinhardt 2001), other aldehydes, elemental carbon, and traces metals(Partanen 1993).

Experimental field and laboratory burns show that forest fires could increase the risk of human exposure to radionuclides(e.g., iodine-129, cesium-137, and chlorine-36) in areas contaminated with radioactive elements (Amiro and others 1996). Human exposure may occur through inhalation of smoke containing radionuclides or ingestion of plants growing in soil and ash containing radionuclides. In these cases, radionuclides can have immediate and/or delayed carcinogenic effects for the exposed population. Some claim that the wildland fire that burned through the Idaho National Engineering and Environmental Laboratory in Idaho in 2000 may have exposed people to harmful byproducts from the combustion of radioactive substances (Machlis 2002). However, no such examples have been found in the South.

Suppressed Immunity

The inhalation of wood smoke decreases resistance to lung infections and increases the possibility of acquiring respiratory infections (Brauer 1999; Dost 1991; Ward 1999). Aldehydes–namely acrolein–in wood smoke inhibit the ability of scavenger cells in the lungs to kill bacteria, thus increasing the possibility of respiratory infection (Ward 1999). The dioxins that are sometimes present in forest fire smoke decrease the ability of the body’s immune system to resist infections and diseases (Mukerjee 1997).

Physical and Cognitive Impairments

Trace gases in air pollution are associated with weight loss, weakness, and fatigue. Carboxyhemoglobin, from breathing excessive amounts of carbon monoxide, causes deficiency of blood oxygen leading to slower reaction times, slower reflexes, drowsiness, disorientation, fatigue, diminished work capacity, reduced manual skills, and impaired mental abilities (Betchley and others 1997; Evans and Campbell 1983). Inhalation of excessive amounts of carbon monoxide reduces maximal aerobic capacity but not sub-maximal capacity in “young, healthy males” (Evans and Campbell 1983:148). The physical discomforts and psychological stress that accompany exposure to forest fire smoke can also contribute to decreases in physical performance (Evans and Campbell 1983). Air pollution causes an assortment of other physical and cognitive impairments including the following: inability to distinguish letters, colors, and brightness; inability to calculate time intervals; and interferes with peripheral vision and ability to respond to peripheral stimuli (Evans and Campbell 1983).