66 Not just a particulate matter: chemistry trumps particle metrics in driving toxicity from exhaust emissions—results from the ULTRHAS project

Abstract Current mass-based regulation of ambient air particulate matter (PM) does not encompass source dependent variation in PM toxicity, the high numbers of ultrafine particles, or the impact of volatile and semi-volatile organic compounds (VOC/SVOC) from combustion emissions which contributes significantly to primary particle growth through condensation and secondary organic particle formation by atmospheric ageing. Therefore, fresh and photochemically aged exhaust emissions from Euro 6d-compliant cars (gasoline, diesel, and compressed natural gas), ship engines (heavy fuel oil and marine gas oil), and a jet combustor rig (JP-8 fuel), as well as model particles, were studied to better understand the properties driving toxicity. Effects (cytotoxicity, genotoxicity, cytokines, transcriptomics) were assessed in a 3D lung tissue model at air liquid interphase, and in vitro models of secondary tissues. Exhaust emissions from different transport modes varied considerably both in physicochemical characteristics and toxicological effects. This was further altered by photochemical ageing. Chemical composition appears to be a main driver of toxicity, while particle metrics (PM mass, number concentrations, and surface area) was poorly correlated with observed effects. The majority of biological responses induced by exhaust emissions were likely due to organic chemicals in the gas phase or adsorbed to particles species. The implications of this will be discussed in context of regulatory needs as well as the challenges this poses for in vitro toxicity testing, especially for the understanding of effects beyond the lung.