Impact of forest fires on PAH level and distribution in soils

Surface (0-5 cm) and subsurface (-5 to 15 cm) soils from burned forest areas in South of France were analyzed to determine contents of 14 priority polycyclic aromatic hydrocarbons (PAHs) and their distribution profile. The sampling procedure allowed us to study the effect of the frequency of fire as well as the influence of the time elapsed since the last fire. The contribution of forest fires to the content of PAHs in soils was demonstrated, as well as the decrease of their total level with time. The hypothesis is that a natural remediation takes place a few years after the last fire event. The lowest molecular weight studied PAHs (naphthalene, acenaphtene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene) appear to be the major ones produced by forest fire. Naphtalene levels are remarkably high in burned soils (more than 70 μg kg(-1), i.e. more than 20 times higher than in the control soils) and still remain important years after the last fire event. The time elapsed since the last fire appears to be a more influencing factor than the fire frequency. The index defined from the PAH levels shows values reflecting the time elapsed since the last fire.