Wildfire-driven geochemical transformations from soils to pyrogenic nanoparticles

Introduction Wildfires can substantially alter soil geochemistry in fire-prone environments, yet their influence on inorganic nanoparticles (NPs) remains poorly constrained. Methods This study investigated nanoparticle dynamics following a wildfire in the Cantillana Reserve (central Chile) by combining field sampling, controlled combustion experiments, bulk geochemical analyses, and single-particle ICP-TOFMS. Results Fire exposure caused a marked increase in nanoparticle number concentration, reaching up to 1.4 × 10 9 particles per gram in ash-enriched soils, together with a shift from predominantly monometallic to multimetallic particles (e.g., Fe–Mn–Ti and Fe–Zn). Comparable patterns were observed in laboratory heating experiments, supporting temperature as a key control on elemental redistribution, reduction, and volatilization. Fire-affected samples also contained smaller nanoparticles enriched in Pb and Zn, suggesting enhanced post-fire metal mobility and potential environmental exposure. In addition, bimetallic nanoparticle ratios such as Fe/Mn and Fe/Zn may serve as geochemical indicators of wildfire severity. Discussion Overall, the results show that wildfire can strongly modify nanoparticle abundance and composition, and that nanoscale characterization provides useful insight into post-fire geochemical transformations.