The Health Impacts of Grass Seed Field Burning

Identifying the Problem

Eastern Washington and North Idaho are the nation's top producers of grass seed for growing Kentucky bluegrass, a popular grass for home lawns and recreation areas. Bluegrass growers have historically used fire to clear their fields of the stubble or straw left after harvest each year. Burning also controls weeds, pests, and plant diseases, and stimulates new growth.

The smoke produced by grass field burning is filled with air pollutants called particulates, also known as particulate matter (PM). In general, particulate matter includes carbon-based particles such as soot, ashes, dirt, soil dust, acid aerosols, and plant matter such as pollens. PM varies in size; larger particles tend to be the least threatening because they are more easily trapped in the nose or throat, while the smaller particles can be drawn into the smaller air passages and may get past the body's natural defenses to penetrate deep into the lungs.

Grass smoke emissions are primarily in the fine particulate range, measuring 2.5 microns in diameter. This fine particulate matter is recognized as most hazardous to human health, as compared to PM₁₀, particles 10 microns in diameter or larger, the size on which the current federal health standard is based.

During the 1995 season, the release of approximately 620 tons of particulates; 3,900 tons of carbon monoxide; and 750 tons of volatile organic compounds such as methane gas, formaldehyde, acrolein (which causes lung damage), and benzo-phyrene (a carcinogen) were a direct result of 11 days of grass field burning in Spokane County. Field burning contributes 17% of the particulate pollution and 8% of the volatile organic compounds present in Eastern Washington.

Though field burning takes place on a relatively few days of the year, the smoke produced is very intense due to the organic material burned and the number of acres torched. For example, during the 1995 burn season, 27,000 acres were burned within a three-day time period, creating smoke intrusion into surrounding communities.

Health Impacts

Research studies conducted within the last five years document a robust association between particulate matter air pollution and premature morbidity and mortality. Rates of illness and death rise in direct proportion to rising particulate levels.

Exposure to particulate air pollution can trigger asthma attacks and cause wheezing, coughing, and respiratory irritation in individuals with sensitive airways. Particulate matter air pollution is especially harmful to people with lung diseases such as asthma, emphysema, and chronic bronchitis. Respiratory distress from exposure to particulates can mean limited activities, increased visits to the doctor, increased use of medications, increased emergency room visits, increased calls to 911 for emergency care, and even premature death.

Those most at risk from exposure to particulates are the elderly, people with chronic respiratory or heart disorders, and children with asthma. Among Spokane County's nearly 400,000 residents, approximately 19,000 people have asthma, 20,000 have chronic bronchitis, and 3,000 have emphysema.

Even among otherwise healthy people, particulate matter air pollution can cause coughing; sneezing; irritation of the nose, mouth, and throat; and watery eyes. Children, who spend more time outdoors playing hard and breathing deeply than do adults, can be especially affected. Recent studies have documented increases in coughs and colds among healthy youngsters during high pollution periods.

Anecdotally, the Spokane County Air Pollution Control Authority receives hundreds of complaint calls about field burning each year, many of which report compromised health as a result of exposure to grass smoke. A number of Spokane physicians have written letters to oppose field burning because their patients' symptoms worsen, and in some cases their patients have to be hospitalized due to exposure to grass smoke.

There is no available method to protect individuals from inhaling the very fine particulates present in grass smoke. These microscopic particles readily penetrate buildings, which means taking refuge indoors does not guarantee protection. Indeed, it has been shown that air samples indoors may contain as much chemical particulate matter as is found outdoors in the same general area.

Grass seed growers maintain they can effectively manage smoke dispersion, but the very nature of smoke makes it impossible to completely manage, especially when that management relies only on prevailing wind patterns. Smoke intrusions into populated areas such as Newman Lake, Spokane, and Spokane Valley generated more than half of the complaints received by the Spokane County Air Pollution Control Authority in the 1995 burn season. Reports from local newspapers in dozens of small towns reflect the far-reaching effects of grass burning in Spokane County.

Federal Air Quality Standards for Particulates

Spokane County is a non-attainment area for particulates and carbon monoxide. In other words, the levels of those two pollutants in Spokane County exceeds what the federal government deems an acceptable level to protect human health.

The current federal air quality standard for particles 10 microns or less in diameter (PM₁₀) is 150 micrograms per cubic meter over a 24-hour period. Grass smoke does not typically violate this standard because the smoke disperses within that time frame. However, as Washington State Health Department Toxicologist Harriet Amman notes, "the current standard is based upon a 24-hour average, yet the greatest threat to health may be posed by peaks of pollution occurring for shorter periods."

Since 75% of grass smoke particulate is actually smaller than 2.5 microns in diameter, a new particulate standard proposed by the Environmental Protection Agency, based on a smaller particle size, will provide a more accurate measure. The EPA anticipates introducing this new standard in 1997.

Alternatives to Burning

There is no evidence that burning is required in order for a grass seed plant to flower. Rather it appears that an economical bluegrass yield depends on light and the temperature of the soil. Phoenix Industries in 1991 showed an increase in seed yields in fields manually dethatched rather than burned. The dethatching process produces dust, which is also a particulate, but of a larger size (PM₁₀).* The larger sized particulates are not as serious a health threat, as they may be moved out of the respiratory system by coughing or sneezing, or through the work of the macrophages in the lower respiratory tract.*

Another alternative, mobile field burning, a method that burns smaller areas at very high temperatures, was researched extensively by Washington State University from 1979 to 1992. It was deemed impractical except for burning ditches or small re-burn projects. Further expenditures on mobile field burning equipment would not be fiscally responsible.

*A report on this topic from Dr. Keith E. Saxton and Dr. Alan Busacca at Washington State University is forthcoming. Their data suggests that windblown soil and dust particulates on the Eastern Plateau are not a significant health or PM₁₀ problem due to the soil composition.