Airborne Hexavalent Chromium Nanoparticles Detected Around Cleanup Zones for the 2025 Los Angeles Wildfires

Abstract The 2025 Eaton and Palisades fires in Los Angeles exemplify destructive wildfires that increasingly threaten cities across the globe. The dangers during active burning are obvious, but the threats to public health during the post-burn cleanup phase are still being discovered. Here we report that airborne chrome (Cr) and silver (Ag) bearing nanoparticles (Dp<56 nm) were found in the debris cleanup zones around the Eaton and Palisades wildfires. These nanoparticles may have originated from corrosion inhibitors added to aerial fire suppressants dropped over the region which reacted under high temperatures during the fire, but further studies are required to test this hypothesis. The airborne chrome was predominantly in the carcinogenic +6 oxidation state (hexavalent chromium). The hexavalent chromium concentrations averaged 13.7 ± 6.2 ng / m3, below the NIOSH workplace exposure limit of 200 ng / m3 but above the US EPA screening levels for indoor air (0.1 ng / m3 for cancer; 3 ng / m3 for non-cancer effects). Outdoor nanoparticles can infiltrate indoors, and simple transport calculations indicate that hexavalent chromium-containing nanoparticles could travel several km downwind from the cleanup zone. Although the health effects from inhaled hexavalent chromium nanoparticles are uncertain, caution is warranted given that nanoparticles can easily cross cell membranes and circulate throughout the body. Residents near the cleanup zones should be aware of the potential risk so that they can take steps to reduce exposure and healthcare providers should monitor for possible health effects in these regions.