Post-fire mobilization of metals and polycyclic aromatic hydrocarbons in a recently burnt eucalypt stand in North-Central Portugal

Wildfires constitute a diffuse source of contamination to aquatic ecosystems. In burnt areas, the increase in surface runoff and associated sediment losses after fire, promotes the mobilization of hazardous substances, such as metals and polycyclic aromatic hydrocarbons (PAHs), posing a risk for the adjacent water bodies. In the present study, post-fire metals and PAHs export by surface runoff was evaluated in 16 m² bounded plots in a eucalypt stand in Albergaria-a-Velha (Aveiro district, North-Central Portugal) burnt in September 2019. Runoff samples were collected on a weekly to bi-weekly basis, depending on the occurrence of rainfall, during the first 6 months after fire. The metals analyzed in this study were, vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd) and lead (Pb). As for PAHs, the analyses focused on the 16 compounds classified as priority pollutants by the United States Environmental Protection Agency. Both dissolved and particulate fractions of metals and PAHs in runoff waters were analysed in this work. Preliminary results suggest that metals are more likely to affect the water quality of fire-affected water bodies than PAHs, since low levels of PAHs were found in runoff waters. This work provides valuable information for water managers to minimize the risks of wildfires both to the environment and to public health.