Assessment of Ambient and Occupational Exposures to Air Contaminants from Wildland Fire Smoke
- Author(s): Navarro, Kathleen McGuire;
- Advisor(s): Balmes, John R;
- et al.
This dissertation combines traditional methods of exposure assessment with new approaches to evaluate exposures in community and occupational settings to air contaminants commonly emitted from wildland fires and found in the ambient environment.
Wildland fires emit large amounts of air pollutants known to cause adverse health effects. Past exposure assessments of wildland fires have measured levels of fine and respirable particulate matter (PM2.5-PM4), acrolein, benzene, carbon dioxide, carbon monoxide, formaldehyde, crystalline silica, total particulates, and polycyclic aromatic hydrocarbons (PAHs). I evaluated exposures to air pollutants associated with wildland fires, specifically PM2.5 and PAHs at different exposure receptor levels - in communities near a wildland fire, occupational exposures of wildland firefighters, and biomarkers of exposure in the US population.
First, I evaluated air quality impacts of PM2.5 from smoke from a mega wildland fire on receptor areas in California and Nevada. The 2013 Rim Fire was the third largest wildland fire in California history and burned 257,314 acres in the Sierra Nevada Mountains. This project employed two approaches to examine the air quality impacts, (1) an evaluation of PM2.5 concentration data collected by temporary and permanent air monitoring sites and (2) an estimation of intake fraction (iF) of PM2.5 from smoke. The Rim Fire impacted locations in the central Sierra nearest to the fire and extended to northern Sierra Nevada Mountains of California and Nevada monitoring sites. Daily 24-hr average PM2.5 concentrations measured at 22 air monitors had an average concentration of 20 μg/m3 and ranged from 0 to 450 μg/m3. iF for PM2.5 from smoke during the active fire period was 7.4 per million, which is slightly higher to representative iF for PM2.5 in rural areas and much lower than for urban areas. This study is a unique application of intake fraction to examine emissions-to-exposure for wildfires and emphasizes that air quality cannot only be localized to communities near large fires but can extend long distances and impact larger urban areas.
Next, I characterized exposures of wildland firefighters during wildland fire and prescribed fires to PAHs, explore associations between exposure and firefighting job tasks, and examine off-duty and community PAH and PM2.5 concentrations. Wildland firefighters working to control wildland fires work long shifts and are exposed to high levels of wood smoke with no respiratory protection. PAHs were measured on 21 wildland firefighters (N=28) while suppressing two wildland fires and 4 wildland firefighters conducting prescribed burns in California. Personal air samples were collected using actively sampled XAD-coated quartz fiber filters. Filters in cassette cases were attached to the back of each wildland firefighter’s backpack. Community-level PAH air samples were collected for the first 12 days of a wildland fire and were collocated with a PM2.5 sampler. Samples were analyzed for 17 individual PAHs through extraction with dichloromethane and analyzed on a gas chromatograph with a mass selective detector. I detected measurable concentrations of 17 PAHs in personal samples on firefighters at prescribed and wildland fires and in area samples at a community nearby a wildland fire. Naphthalene, retene, and phenanthrene were consistently the highest measured PAHs at all three sampling scenarios. PAH concentrations were higher at wildland fires compared to prescribed fires and were highest for firefighters during job tasks that involve the most direct contact with smoke near an actively burning wildland fire. Although concentrations do not exceed current occupational exposure limits, wildland firefighters are exposed to PAHs not only on the fire line at wildland fires, but also while working prescribed burns and while off-duty. It is important to characterize exposures from wildland fires to better understand any potential long-term health effects.
Lastly, I evaluated predictors of urinary PAH concentrations in 2001–2006 NHANES participants from a variety of sources including demographic information, food intake, housing characteristics, and modeled outdoor air pollutant exposures. Biomonitoring data provides a direct way to link human exposure to environmental contaminants. However, these data do not reveal how various exposure routes or media contribute to the body burden of a specific chemical. NHANES participants were linked to their census tract-level daily PM2.5 exposure estimate, outdoor temperature, and annual air toxics concentrations. Multivariate linear regression models were developed using the Deletion/Substitution/ Addition algorithm to predict urinary PAH levels using NHANES questionnaire data for model selection in all and non-smoking adult NHANES participants. Exposure parameters were then added to each model. Model fit was assessed by comparing the R2 for each model tested. Exposure to PM2.5 and air toxics emissions were not associated with levels of urinary PAH metabolites. In the analysis current smoking status was the strongest predictor of PAH biomarker concentration and was able to explain 10% - 47% of the variability of PAH biomarker concentrations. The DSA selected models did not improve prediction in the “all adults” analysis. They were able to explain 10% - 51% of the variability of PAH biomarker concentrations in all adults. Among non-smokers, the DSA selected variables only explained 2% - 5% of the variability in biomarker concentrations. Further studies of routes of exposure of PAHs should be completed to understand how PAHs in the environment are contributing to the body burden of PAH. This study demonstrated how a rich dataset of biomarkers with individual information on demographics, food intake, and air pollution exposures can be used to examine the contribution of each route of exposure on the body burden.
With the predicted increase of fire season in the western United States due to climate change resulting in more acres burned and smoke produced, it is important to quantify the air quality impacts from wildfires to develop effective strategies to protect public and wildland firefighter health. These methods outlined in this dissertation can be used to better estimate short-term and long-term health risks, so that public and occupational health practitioners, air quality regulators, and natural resource managers can develop mitigation strategies to reduce exposure to wildland fire smoke.