What Can We Learn About Thirdhand Smoke from Wildfires?

When scientists discuss thirdhand smoke, they mean the toxic residue left behind from smoking commercial tobacco products. The chemicals in the toxic residue can adsorb into and stick on surfaces, collect in dust, and off-gas into the air. The chemicals in the air can interact and create new, toxic chemicals. Some researchers are interested in how other types of smoke might leave similar residues, such as smoke from wildfires.

A recent study by Dr. Jienan Li at Colorado State University suggests that residue from wildfires is similar to thirdhand smoke. Like thirdhand smoke, wildfire smoke creates reservoirs on indoor surfaces and chemically changes overtime. Further, the researchers were interested in how wildfire residue could be cleaned from homes, which is known to be very difficult with thirdhand tobacco smoke.

Li observed how wildfire smoke residue impacts a home. He conducted his study in the National Institute of Standards and Technology’s Net-Zero Energy Residential Test Facility, which is a four-bedroom, three-bathroom unfurnished home used for research. The researchers injected smoke from one gram of wood chips into the home for two minutes to mimic wildfire smoke intruding into a home. They did this 23 times over two weeks. After the two weeks, they tested different ways to clean the home to see what best removes smoke residue.

The researchers found that compared to thirdhand smoke, wildfire residue may be easier to clean up. The most effective way was to clean surfaces, such as floors, walls, and furniture, by dusting, vacuuming, mopping, and other similar methods. Opening windows also helped reduce wildfire smoke chemicals in the air, but this was only temporary as once the windows were closed, the levels went back up.

One reason the researchers found wildfire smoke residue easier to clean may be because they studied the consequences of burning a relatively small amount of biomass. They burned just enough woodchips to make the air match what would be in a home during a wildfire. This was around 1 gram of woodchips each of the 23 times over two weeks.

In other studies, when researchers tried to clean up homes polluted with residue from tobacco smoke, they found it to be extremely difficult. In fact, professionally washing and wiping surfaces and deep-cleaning carpets only temporarily lowered pollutant levels before they increased again to baseline levels after only four weeks. 

Why is it so much harder to clean up residue from tobacco smoke? One reason is that when people smoke indoors over many months, they burn a much larger mass than 23 grams. One cigarette weighs about 1 gram.  If someone smokes one pack per week indoors over the course of a year, they have burned more than 1,000 grams of biomass. If someone smokes a pack of cigarettes a week for one year in a house, they create the same amount of indoor smoke pollution as 50 consecutive wildfires.

Another wildfire residue researcher is Dr. Stephan Koslitz at the Institute of the Ruhr University Bochum, who measured firefighters’ exposure to smoke via inhaling smoke and absorbing the residue. Specifically, Koslitz looked at the cancer-causing chemical polycyclic aromatic hydrocarbon (PAH), which is formed when things burn.

Just as the skin absorbs toxic chemicals when it comes into contact with things with thirdhand smoke on them, the skin absorbs wildfire smoke chemicals similarly. Firefighters are particularly at risk to absorb wildfire chemicals since they work closely to wildfires. While they wear protective gear, it is not completely smoke-proof.

The researchers took urine samples from firefighters before and after a training session inside a smoke-filled room. The firefighters had higher levels of 1-OHP, a PAH, after training – even though they wore protective gear.

This study suggests that firefighters swallow, inhale, and/or absorb wildfire smoke while working at wildfires as well as with objects that have been contaminated with wildfire smoke.

As wildfires become more and more common due to climate change, research on how to protect people from smoke is vital. Society has protection methods and recommendations for citizens and firefighters during wildfires, but there is little information on what to do after the fire. More studies on wildfire smoke residue are needed to gather and share that information.

Click here to read the first research study. Click here to read the second research study.

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