114-4 Lead concentration and bioaccessibility decline with time after wildland-urban interface (WUI) fires

Session: Environmental Geochemistry and Health (Part I)

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Abstract:

The increasing frequency and severity of wildfires globally pose an emerging threat to the environment and human health. Wildfires occurring at the wildland-urban interface (WUI) can cause widespread damage to the built environment, mobilizing a wide range of toxic substances including metals such as lead (Pb), which can persist in the form of long-covered layers of lead-based paint in older (pre-1978) homes.

The 2025 Eaton Fire (Altadena, CA) destroyed 9000+ structures including 4300+ single-family homes, where the median timeframe of construction was 1945-1948. The release of Pb from the combustion of these structures resulted in substantial local surface deposition of Pb as ash and debris as well as downwind transport of Pb-enriched materials within the resulting smoke plumes. The distribution and bioaccessibility of Pb in ash-impacted soils immediately after the fires and in the subsequent months post-containment is largely unknown yet has significant importance due to the reconstruction and ongoing rehabitation of homes on these sites.

Soil sampling was conducted at 1, 6, 12, and 18 months post-containment of the 2025 Eaton Fire, sampling from ten burned residential sites located within the fire boundary and ten unburned sites within 3.5 km of the ash plume. Handheld X-ray fluorescence spectrometers were used to collect in situ measurements of a range of metals at multiple (n=40-50) locations at each site, measuring at both the soil surface and subsurface (5 cm depth). Soil samples were then collected from selected locations at each property at soil depths of 0–1 cm, 1–5 cm, and 5–10 cm. Samples were air-dried and sieved to recover potentially ingestible particles (≤250 µm), then underwent in vitro lead bioaccessibility analysis using simulated gastric fluid (SGF) extractions. Sampling was repeated at the same locations at each time point.

Key findings include: 1) [Pb] is initially elevated in surface soils of burned sites relative to unburned sites, with [Pb] progressively declining to background concentrations; 2) Pb bioaccessibility declines over time in soils from burned sites; and 3) soils from unburned lots show relatively constant [Pb] and Pb bioaccessibility as a function of both time and depth. This suggests progressive off-site transport of lead-enriched soils via weather events and remediation efforts.​ These findings provide critical insight into post-WUI fire metal contamination, informing future public health and soil remediation strategies

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