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Welcome to PSR's Environmental Health Policy Institute, where we ask questions -- then we ask the experts to answer them. Join us as physicians, health professionals, and environmental health experts share their ideas, inspiration, and analysis about toxic chemicals and environmental health policy.


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Hidden Health Costs of Forest Fires and Control Burns

By Marsha Honn, PhD

In response to: Particulate Matter: Widespread and Deadly

Increasing fire activity is occurring across large parts of the planet. Whether due to wildfires or managed “control burns,” fires result in increased release of particulate matter (PM) that has a negative impact on human health.  In addition, fires release greenhouse gases that make for a vicious cycle of rising temperatures and increasing wildfires. This problem is particularly severe in the Southwest, which is experiencing warming conditions greater than anywhere in the United States except Alaska. Tree mortality, dying vegetation and reduced moisture conditions are all likely scenarios in the future (1).

Currently, the U. S. Forest Service in Arizona is developing a forest restoration initiative that calls for substantially increasing prescribed burns of up to a million acres over a 20-year period in just four forests in Arizona. This increase in prescribed burns is significant, as the project will be used as a template for other U.S. forests. The following information will reinforce the importance to health of finding safer alternatives for forest management.

New modeling efforts by the National Oceanic and Atmospheric Administration indicate that each year, wildfires emit a total of 1.5 to 2.5 million tons of particulate matter.  This is more than is emitted by better-known sources of PM such as fuel combustion, industrial processes and transportation.  This smoke poses a danger for everyone, but is particularly hazardous to children and the elderly. Approximately 80 to 90 percent of wood smoke particles are 2.5 microns or smaller, and EPA studies show that the tiny dagger-shaped particles are particularly harmful to children since they are able to go deep into a child’s lungs. Other particles pass through the lungs into the blood stream, attacking vital organs (2).  

An article by the American Thoracic Society found that with an increase of 10 micrograms per cubic meter of particles over two years, the risk of dying was increased by 32% for people with diabetes, 28% for people with COPD, asthma and pneumonia, 27% for people with congestive heart failure and 22% for people with inflammatory diseases (3).

PM is not only emitted at higher levels during wildfire episodes, but is also much more toxic to the lungs, according to a 2008 study by University of California’s department of pulmonary and critical care medicine (4).  It noted, “The lungs of mice when exposed to the wildfire PM 10-2.5 or PM 2.5 showed significant damage, as measured by histologic evaluation of inflammatory cell influx or by relative europhile or total protein count of lung lavage fluid” and that “toxicity was manifested as increased europhiles and protein in lung lavage and by histologic indicators of increased cell influx and edema in the lung.”  (4) The study concluded that wildfire PM contains chemical substances toxic to the lungs, even causing cell death. 

A California study measured cellular toxicity with two standard tests of oxidative stress, dithiothreitil (DDT) assay and a macrophage reactive oxygen species (ROS) assay. The particles collected during a wildfire showed nearly five times more DDT activity compared to a non-wildfire time period (5).

Besides fine particulate matter, smoke from wildfires and prescribed burns contains volatile organic compounds, carbon monoxide, ozone, numerous other toxins and literally thousands of chemicals.  One particularly troubling toxin released in forest fire smoke is mercury. Scientists estimate that fires in the continental U.S. and Alaska release 44 metric tons of mercury into the atmosphere every year (6).  In a 2001 study, researchers collected foliage and ground litter samples from seven forests across the continental United States (7). These samples were set alight at a U.S. Forest Service fires laboratory, where sensors detected large amounts of mercury. The samples released 94 to 99% of all the mercury stored in the foliage, and “All the coniferous and deciduous samples contained mercury at levels ranging from 14 to 71 nanograms per gram of fuel.”

Mercury is dangerous when it ends up in waterways, where it can transform into methyl mercury and move up the food chain, becoming more concentrated. Mercury causes its greatest damages to unborn fetuses and newborns, including developmental defects, reduced IQ, mental retardation, learning disabilities, behavioral problems and chronic neurological diseases. Already, Arizona lakes such as Roosevelt, Tonto Creek, Soldier Lake and Upper and Lower Lake Mary post  mercury warnings that fish are not safe for consumption. A study found that forest fires near Durango, Colorado could be responsible for unlocking the mercury trapped beneath the soil in the San Juan National Forest and allowing it to wash into the Vallecito Reservoir (8).

Based on the increasing likelihood of wildfires, increasing temperatures and drought, and given the hazards from PM and other substances released during a prescribed burn or a forest fire, alternatives to prescribed burns need to be sought and implemented by the Forest Service. Safer alternatives include logging for fire breaks, chipping, thinning, and goat or cattle grazing.  Implementation of these techniques will help provide cleaner air and also reduce the carbon contribution to global warming.


1 Droughts, Megadroughts, and More: A Conversation with Johnathan Overpeck, Southwest Climate Change by Zack Guido, June 15, 2012.

2 Center for Disease Control: A Review of Factors Affecting the Human Health Impacts of Air Pollutants From Forest Fires. Division of Environmental Hazards and Health Effects National Center for Environmental Health.

3 Am. J. Respir. Crit. Care Med. March 15, 2006, Vol. 173 (6): Reduction in Fine Particulate Air Pollution and Mortality, Extended Follow-Up of the Harvard Six Cities Study.

4 Environmental Health Perspectives, California Wildfires of 2008: Coarse and Fine Particulate Matter Toxicity, 2009, Vol. 117 (6):893-897.

5 Environmental Health Perspectives: Oxidative Punch of Wildfires, 117:A58, February,


6 National Science Foundation, Scientists Estimate Mercury Emissions from U.S. Forest Fires, October 17, 2007.

7 Hans Friedli and Larry Radke, Wildfires and Mercury Pollution: A Smoking Gun? UCAR, July 2001.

8 Joseph Ryan, CU-Boulder Awarded NSF Grant to Study Effect of Forest Fires on Mercury in Durango, July 15, 2010.


Darryl Templer said ..

I wish everyone exposed to the smoke and drinking water contaminated by forest fires read this outstanding article. The alternate solutions to controlled burns must by used to limit these dangers to the public's health. This factual, well-supported article exposes multiple health dangers of forest fires that can be limited instead of increased.

September 13, 2012
Mary Templer said ..

Thank you for informing us of the multiple health dangers of forest fires and suggestions for alternate solutions to controlled burns. Your article is powerful, well organized, and well documented in the specific harmful releases of forest fires. The research cited validating the harmful effects is impressive. I hope bringing these valid concerns to awareness result in changes to prevent major health problems affecting many people with resulting great costs of health care.

September 12, 2012
Barbara Warren said ..

Important connection to mercury in our environment from coal ash! We can get exposed a second time around.

September 4, 2012
Mary LeGrand said ..

This is a great article, very informative.

September 1, 2012
greg conradf said ..

well stated. These control burns in AZ are choking us out! Such burns are truly unacceptable, highly toxic and dangerous practices.

August 26, 2012

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