Toxicological screening of PM_2.5 from wildfires involving different biomass fuels

Wildfires are becoming increasingly frequent and severe, particularly in Southern Europe. In addition to their immediate environmental and socioeconomic impacts, wildfires release significant amounts of particulate matter (PM), which poses serious health and ecological risks. Gaseous (CO and CO₂) and PM_2.5 samples were collected directly from smoke plumes, and the modified combustion efficiency (MCE) was calculated to characterise combustion conditions. This study aims to assess the cytotoxicity, mutagenicity and ecotoxicity of PM_2.5 collected during wildfires in Portugal, with a focus on how varying biomass types and combustion conditions impact these effects. Ecotoxicity assessments using Aliivibrio fischeri showed that PM_2.5 samples ranged from toxic to extremely toxic, with mixed vegetation burns (eucalyptus, acacia, ferns) exhibiting the highest toxicity levels. Cytotoxicity tests on human lung epithelial cells (A549) demonstrated a dose-dependent decrease in metabolic activity and no membrane damage, while mutagenicity assays identified direct-acting mutagens from smouldering acacia debris combustion, specifically inducing frameshift mutations in Salmonella typhimurium strain TA98. Root growth inhibition tests showed no toxicity, with some samples, instead, promoting growth probably due to nutrient content. Peroxidase activity responses indicated that, at higher concentrations, the enzyme function could be reduced if defence mechanisms are overwhelmed or stimulated due to high nutrient levels. These findings highlight the complex and varying toxicological profiles of wildfire PM, emphasising the need for further research.