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Impacts of wildfire activity in the wildland-urban interface on environmental mobilization and bioaccessibility of nanoscale trace metals, The
Villarruel, Carmen M.
Villarruel, Carmen M.
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2025
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Abstract
Global wildfire activity is increasing in frequency and severity, driven by anthropogenic climate change. Wildfires at the Wildland-Urban Interface (WUI), regions where structures are intermixed with vegetative fuel sources, are becoming increasingly common, impacting thousands of people worldwide. The biological and environmental health risks of forest wildfires are well documented, including mobilization of respirable particulate matter, water contamination, and trace metal enrichment. However, less is known about the biogeochemical impacts of WUI wildfires. Given that structures are concentrated sources of metals (wiring, paints, treated wood, electronics, etc.), there is a growing need to characterize ash generated from structure fires. This thesis investigates the environmental lability and pulmonary bioaccessibility of ash from structures burned in the Marshall Fire, a WUI wildfire that burned over 1000 structures in Boulder Country, Colorado.
Exposure to WUI ash impacts a range of people, including first responders and residents. In the first part of this work, the bulk environmental lability and respiratory bioaccessibility of toxic trace metals in structure ash were quantified using a water leach and a Simulated Epithelial Lung Fluid (SELF) leach as inhalation is a major vector for metal exposure. Ash samples were compared to soils, another exposure vector in urban areas. Metal concentrations and leachability were highly variable. Bioaccessibilities up to 15% were reported for ash-derived Ni, with elevated Cr, and Cu bioaccessabilities in ash compared to soils. single particle Inductively Coupled Plasma Mass Spectrometry was used to quantify nanoparticles (NPs, <100 nm) in ash, driven by concerns of NPs’ small size enabling crossing of biological membranes and organ translocation. Changes to ash derived NP populations in SELF were reported for the first time, providing insight into the impact of the pulmonary environment on metal uptake. Further, I characterized wildfire generated nanoparticles from Tire Crumb Rubber (TCR), an end-of-life tire product frequently used in children’s playgrounds. Increases in number and size of NPs were associated with burning TCR, including a unique enrichment of Cr in metal NPs. Together, this work rresents for the first time a quantification of nanoparticulate trace metal content in ash from structure fires.
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