Skip to Navigation
Skip to Content
Share this page


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.


More Topics »

Hidden Health Costs of Forest Fires and Control Burns

Posted on August 20, 2012

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, 2009.

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.


Anonymous said ..

I live in a very forested area of Western Australia. I have noticed that it rains at my place but not in town .I assume that the rain clouds areattracted to the trees like a magnet We have had fires .However are extinguished by the dampness of the ground.and healthy trees drip all night .My point is by burning the forest many trees do die.Abetter way is to build your house undergroundor in the side of a hill with dirt on top.would you do this sort of construction.

November 23, 2016
Travis Daley said ..

Simon says it the best

July 1, 2016
Mark Donham said ..

It certainly is easy to tell the commenters that more than likely financially benefit from the prescribed burning industry in one way or another. Those folks are incapable of admitting the health and environmental impacts of forest fires, both wild and prescribed. The fact that the decisions of where and when or whether or not to burn are too often left to these biased opinions is dangerous and sad.

December 5, 2015
Evie Wilson said ..

In the California foothills, where I live, there used to be cattle grazing, logging, and mining, and this resource use helped keep forests healthy, especially around small towns. But then the so-called "environmentalists" took over our federal land management agencies, and most resource use was stopped. Now, because of being highly overgrown, the drought and beetles, we have huge stands of dead trees. Controlled burns would NOT BE SAFE IN THESE CONDITIONS, so logging MUST BE DONE before any controlled burns. However, lightening-caused wildfires cause enough burning in my book, along with logging and grazing, to keep forests healthy, and CB's should be done rarely. They often apparently emit more pollution than all the rest of the sources put together, and release mercury, one of our most toxic heavy metals.

November 4, 2015
T. Lee said ..

1,000,000 acres!?! Why not just call the logging/lumber companies and tell them "free lumber" (for housing/furniture construction, paper and paper products save the pollution, help the economy?

October 29, 2015
Jim Brenner said ..

WOW, the lack of peer reviewed information in this article is astounding. Where to begin? The author is equating wildfire with prescribed fire as if they are one and the same. The POINT in doing prescribed burns is to burn when the system can handle it in a much for efficient way to reduce the amount of aersols that get pumped into the atmosphere. This author clearly knows nothing about the subject and the number of errors stated as fact are of great concern. Another "expert" trying to make a name for themselves.

July 21, 2015
Clive Stott said ..

Thanks for the article. I fully support any efforts, no matter where we live in the world, to stop harmful prescribed burning. There has been so much misinformation spread about the need to burn, so much so that it has spread like wildfire! But, "There has got to be an understanding that people who complain about smoke have a legitimate case, the medical science is on their side now." - Professor David Bowman, Tasmania. ABC News Feb. 20, 2012. And you can not get higher than this from the leading cancer arm of the World Health Organisation when they say, "Outdoor air pollution a leading environmental cause of cancer deaths." - IRAC 17/10/2013. There are many alternatives to burning and some of these can be found here...

January 31, 2015
Shirley Brandie said ..

I, personally, don't see the great need for prescribed burns that cause such health problems for humans and animals and many times become out of control fires. We need trees in order to survive. I don't see how setting fires to prevent fires makes much sense.

January 1, 2015
Karin said ..

Another unfortunate consideration that we have faced in AZ and in other southwestern states, many prescribed/controlled burns have quickly become uncontrolled wildfires during the past 14 years I've been a resident. As in the recent excerpt... "WILDFIRES: Southwest struggles to adapt to year-round fire season Nathanael Massey, E&E reporter, ClimateWire: Monday, May 12, 2014; The Forest Service and Department of the Interior announced last week that they already anticipate breaking their firefighting budget by $470 million, citing climate change as one of the primary causes for the rising costs. "A firefighter from Edmond, Okla., watches an inferno rage in a mobile home park last week. A controlled burn, an attempt to prevent wildfires from spreading, got out of control."

June 8, 2014
gavin said ..

cool.. but scary

June 4, 2014
Simon said ..

Interesting that people are espousing how factual and well documented this information is when none of the referenced links can even be viewed due to certificate errors that cannot be trusted. How are you folks arriving at the conclusion that this information in the article is "a great article, very informative, well stated, etc.". You're all imposing very sweeping views that all prescribed burning is bad based on an article from which no back up information can be viewed to see of the data they are claiming supports their views. Prescribed burns are necessary if one wants to maintain a healthy ecosystem. They return nutrients to the ground, get rid of last year's duff, promote the germination of native plants and deter colonization of invasive species to the site. They also are useful to deter wildfires, contrary to what the first person commenting indicates. I'm a proponent of prescribed burns based on the benefit the earth derives. I know I may be in the minority but I tend to not impose an anthropocentric view on life.

April 1, 2014
Elizabeth O'Nan said ..

It must become public knowlege that forest fires are primarily caused by drought and man's activities and are NOT due to a lack of "prescribed burns", which have been shown to be of little use in preventing fires and pose a major health threat while contributing to Global Warming. These "prescribed burn" programs are plagued by fraud and abuse and are used to prop up an arrogant abusive bureaucracy that is directed toward unhealthy, below cost extractions such as: logging, drilling, mining, grazing, hunting, fracking, even raising GMO eucayliptus trees, but not preservation. At one time it may have been good to promote extraction, but no more. Today each tree is precious and we must preserve and protect remaining species. To this end we should expand our National Parks System to include all of the US Forest Service lands with a mandate to manage these lands for true preservation without harmful human interference. It is time we defended our public lands and stopped subsidizing the wealthy 1% with our forests.

September 28, 2013
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

Comments closed.