Integrating effect-based monitoring tools into PM10 assessment: insights from an air quality network in the Po Valley (Northern Italy), a major European air pollution hotspot

: Airborne particulate matter (PM) is a complex mixture whose health effects depend not only on mass concentration but also on chemical composition and toxicological properties. This study investigated the mutagenicity, cytotoxicity, oxidative stress, and DNA damage of organic extracts of PM10 collected at an urban background and a suburban background site in the Po Valley (Piedmont Region, Northern Italy) during summer 2023 and winter 2024. Chemical characterization of the corresponding PM10 samples was performed to explore associations between biological responses and PM constituents. Winter samples exhibited significantly higher PM10 mass concentrations and elevated levels of combustion-related components, including polycyclic aromatic hydocarbons (PAHs), levoglucosan, and anthropogenic components. Consistently, all toxicological endpoints showed markedly stronger effects during winter, with clear dose-dependent responses for cytotoxicity, oxidative stress and DNA damage, and widespread mutagenicity across S. typhimurium strains (±S9). In contrast, summer samples induced low or negligible biological effects. Multivariate analyses (PCA and hierarchical clustering) revealed a clear seasonal separation of PM10 samples, with winter extracts characterized by higher loadings of combustion-related markers (PAHs, levoglucosan) and associations with mutagenicity, oxidative stress, and DNA damage, while PM10 mass showed no clear relationship with most biological endpoints. These findings highlight the importance of integrating effect-based assays into air quality assessment frameworks, as they capture the biological reactivity of PM mixtures and seasonal differences not evident from conventional metrics. Such approaches may support the evaluation of health risks in the context of the revised European air quality directive, which calls for the inclusion of emerging pollutants and toxicity-related metrics.