Targeted household cleaning can reduce toxic chemicals after wildfire, study finds

Once the last embers of a campfire have died down, the musky smell of smoke remains. Distinct smoke odors may serve as a pleasant reminder of the night before, but in the aftermath of a wildfire, this smell carries ongoing health risks.

Wildfire smoke is certainly more widespread than a small campfire, and remnants can linger for days, weeks, and months inside homes and businesses. Recent research led by Elliott Gall, Portland State associate professor of mechanical and materials engineering, examined how long harmful chemicals in wildfire smoke persist and the most effective ways to remove them with daily household cleaning products.

Wildfires create compounds called polycyclic aromatic hydrocarbons (PAHs), which form during the high-temperature combustion process. These compounds are highly toxic.

“They are associated with a wide variety of long-term adverse health consequences, such as cancer, potential pregnancy complications and lung disease,” Gall said. “So if these compounds settle or stick to surfaces, there are different exposure pathways that people should be aware of. Right now, most Portlanders are probably thinking about how to clean their air when of a wildfire, but they may not think about other routes of exposure once the air clears.”

Public messages are fairly consistent about what to do during a fire to reduce exposure to smoke (close windows and doors, run an air purifier, and consider wearing a mask), but messages are limited on what to do after a wildfire. Gall’s study published in Environmental science and technology studied the accumulation and retention of PAHs over a four-month period on three different interior materials: glass, cotton, and air filters.

“We looked at a limited number of materials and intentionally included some that are common in indoor environments,” Gall said.

Initial results showed that PAH levels remained elevated for weeks after exposure. Once materials were laden with PAHs from wildfire smoke, it took 37 days for PAHs to decrease by 74% for air filters, 81% for cotton, and 88% for glass. This reduction is significant, but it takes time and results in increased health risks from prolonged exposure. However, washing cotton fabrics just once after exposure to smoke reduced PAHs on the fabric by 80%. Using a commercial window cleaner on glass materials like windows and mugs reduced PAHs by between 60% and 70%.

Unlike glass and cotton, air filters cannot be cleaned and must be replaced after an extreme smoke event.

“Even though they potentially contain a little more life, over time the PAHs can separate the filter and be re-emitted into your space,” Gall said. “Although it is a slow process, our study shows that the separation of PAHs from filters and other smoke-laden materials can result in concentrations of concern in the air. And while this separation is occurring , skin contact and ingestion of PAHs from materials can be significant. An example might be holding and drinking from a glass that has been exposed to wildfire smoke.

Gall said it’s important to consider the effect of cleaning solutions available to the average person. Although the results also open the door to additional questions. How do materials like drywall or ceramic tile respond to cleaning, for example? What if a person had access to a washer but not a dryer, would PAHs still be reduced to non-toxic levels?

The good news is that although toxic compounds from a wildfire can survive for a long time in palpable smoke, simple household cleaning techniques are effective in significantly reducing exposure. Gall said future studies on this topic will focus on additional common indoor surfaces and cleaning techniques to reduce PAHs, as well as work to understand the extent of possible health impacts related at the exhibition.