Metal toxin threat in wildland fires determined by geology and fire severity

Catastrophic wildfires, exacerbated by climate change, pose a significant global public health risk due to smoke and dust inhalation. This study reveals a previously under-recognized threat: the release of toxic metals naturally present in soils and plants. High temperatures during California wildfires transformed chromium into its carcinogenic hexavalent form [Cr(VI)], particularly in metal-rich geological areas (e.g., serpentinite). Dangerous Cr(VI) levels (327–13,100 µg kg⁻¹) were found in wind-dispersible wildfire ash particles. Dry post-fire conditions led to persistent Cr(VI) in topsoil for up to ten months. The widespread distribution of metal-rich soils and fire incidents highlights the global risk of wildfire-borne metals, potentially explaining the higher hazard of wildfire smoke compared to other pollution sources.

Alandra Marie Lopez, Juan Lezama Pacheco, Scott Fendorf