Systematic review on the toxicity of wildfire emitted particulate matter: State of science, knowledge gaps and way...

The intensity and frequency of wildfires have increased worldwide. The health impact of wildfire emitted particulate matter (WFPM) has been considered an emerging field in air pollution research. This review presents the state of toxicological science related to WFPM for the 2005-2025 period. We found 46 peer-reviewed in vitro and in vivo studies, excluding clinical, epidemiological, and ecotoxicological studies. Environmental WFPM collected during active wildfires was used to model exposure in only 42% of in vitro and 27% of in vivo studies. Most in vitro studies investigate effects on the pulmonary system (50%) and on macrophages (17%), with all other biological systems corresponding to 33%. Mechanisms of toxicity focused mostly on inflammatory and stress response, and DNA damage/mutation. Inhalation studies evaluated lung (46%), cardiovascular (15%) and brain (15%) effects, with the remaining 24% addressing reproductive, genetic or immune effects. WFPM induced significant toxicity with distinct mechanisms as a function of concentration, particle-size, biomass type and burning conditions. Knowledge gaps included: lack of a comprehensive physicochemical characterization of WFPM to achieve robust structure-activity conclusions, use of realistic concentrations representing human exposure scenarios, chronic exposure studies, evaluation of systemic effects and toxicokinetic studies, potential synergistic effects with other anthropogenic air pollution sources.