Effects of wildfire on soil properties and ecotoxicity: A short-term, site-specific remediation experiment (Cinigiano, Tuscany, Italy)

Global change is increasing the occurrence and extent of wildfires, with growing impacts on the environment and human health. As wildfires can alter soil microbial diversity and increase contaminant presence, bioremediation may support soil recovery. This study investigated the short-term direct and indirect effects of wildfire that occurred on July 24, 2022, in the village of Cinigiano (Tuscany, Italy). Three soil types were analyzed based on their fire exposure: a control soil not affected by the fire (CS), a soil located near the burned area but affected by ash and heat (NBS), and a soil within the burned area (BS). Soils were tested both in the solid phase and as elutriate, either untreated or treated for 15 days with effective microorganisms (EM), under short-term experimental conditions. Ecotoxicity assays were performed considering Lepidium sativum, Aliivibrio fischeri, Raphidocelis subcapitata and Daphnia magna; the quality index (TBI) was calculated for each condition (CS, NBS, BS, -EM/+EM). Biochemical stress responses in L. sativum were also assessed. Under the tested experimental conditions, the 15-day EM treatment was generally accompanied by a decrease in pH, while increased ecotoxicological hazard was observed in +EM-treated soils. Although long-term EM applications may support remediation over long time scales, these findings indicate that short-term EM application should also be carefully evaluated, given the potential increase in ecotoxicological hazard and the possible repercussions for organisms from different environmental compartments.