Elevated concentrations and temporal persistence of polycyclic aromatic hydrocarbons in soils after wildfires in different biogeoclimatic zones of British Columbia, Canada

Across North America the area burned by wildfire is steadily increasing, and these fires have significant impacts on terrestrial and aquatic ecosystems. Of particular concern are the contaminants that are produced during wildfires when biomass and structures burn. One class of contaminants of concern is polycyclic aromatic hydrocarbons (PAHs), which can be mutagenic, carcinogenic, and toxic for certain species. This study measured concentrations of PAHs in the burned topsoil and the burned organic layer in eight wildfires of varying ages across the interior of British Columbia, Canada. Samples were analysed for the 16 U.S. Environmental Protection Agency (EPA) Priority PAHs and for 30 alkylated PAHs, the latter of which are often more toxic and difficult to break down. Results showed that within three to six years after wildfire the concentrations of ΣPAHs returned to concentrations similar to reference sites. The year post-fire that the sample was collected showed a strong correlation to the ΣPAH concentrations, and comparisons across all samples showed that characteristics associated with the fire's biogeoclimatic zone explained most of the variability. Soil quality guidelines were not available for all compounds analysed, but concentrations for many of the samples exceeded available guidance. Coupling post-wildfire landscape susceptibility to erosion and the hydrophobicity of PAHs, the threat to water quality in burned areas is significant. More post-wildfire erosion mitigation on hillslopes should be undertaken to avoid negative impacts on the aquatic environment, particularly in the British Columbia interior where salmon are already under numerous anthropogenic and environmental pressures.