CHANGES IN THE BIOACCESSIBILITY OF METALS IN SOILS AT A RECOVERING WILDFIRE SITE

Wildfires are increasing with climate change, making the human health implications of exposure to burned soils an essential area of research. Metals associated with fire-impacted soils can be inhaled or accidentally ingested by surrounding communities, causing health risks that may complement risks from particles that cause physical respiratory irritation. This study explores metal changes in burned soils over time as a site naturally recovers from wildfire. The Border 32 fire burned 4,456 acres near the US-Mexico border in Aug-Sept, 2022. Soil samples were collected from the burned area at 0, 3, 6, 9, and 12 months after the fire. Grain size, total metals, soil color, and bioaccessibility experiments characterized the physical and geochemical nature of the site. Over the course of 12 months as the site naturally recovered and revegetated, soil Cr exhibited a weak increase (29 +/- 9 mg kg-1 at 12 months post-fire compared with 18 +/- 5 mg kg-1 in unburned soil controls) and Zn concentrations appeared enriched immediately after the fire (207 +/- 131 mg kg-1 at 0 months post-fire) but steadily declined (89 +/- 23 mg kg-1 at 12 months). Trends in lung fluid bioaccessibility were different. No Zn or Cr were detected in lung fluid though Mn was found to steadily increase from 2-35 mg kg-1 bioaccessibility as the site recovered, approaching the background average bioaccessibility of 44 mg kg-1 Mn. These results suggest that metal biogeochemistry is complex as soils recover from wildfire and though some metals were not detected in lung fluid for these soils at this site, they were detected in more acidic gastric fluid. These results highlight the importance of assessing burned soils chemically at specific sites, particularly where trace elements of health concern like Cr and Mn may be naturally elevated. This project adds to the growing literature that focuses on inhalation risk from particulate matter exposure after fires.