Unforeseen Metal Toxin Produced in Particulates of Wildland Fires

Abstract Accentuated by climate change, catastrophic wildfires are a growing, distributed global public health risk from inhalation of smoke and dust. An underrecognized health threat arises from altered naturally occurring metals originating in soils and plants. Here, we demonstrate that high temperatures during California wildfires catalyzed widespread transformation of chromium to its carcinogenic form in soil and ash, particularly in areas with metal-rich geologies. In wildfire ash, we observed dangerous levels of reactive hexavalent chromium in wind-dispersible particulates that persisted in surficial layers for up to a year post-fire. The geographic distribution of metal-rich soils and fire incidents illustrate the broad global threat of wildfire smoke- and dust-born metals to populations.