Investigation of the impact of atmospheric aging on aerosol toxicity using lung-cell model exposure at the air-liquid-interface (ALI)

Air pollution with inhalable particulate matter (PM) is one of largest environmental health risks. In addition to the directly emitted particles (e.g. soot, ashes, abrasive fine-dust etc.) also secondary particles are formed in the atmosphere from precursor gases during photochemical and dark atmospheric processing (aging). Albeit a large fraction of the atmospheric PM mass is of secondary origin, the effects of atmospheric aging on aerosol toxicity are still largely unknown. Within the framework of the German-Israeli Helmholtz International Laboratory aeroHEALTH, we aim to assess the impact of atmospheric processing of organic compounds on human health. In addition to method development (i.e. new mass spectrometric aerosol characterization techniques such as single particle mass spectrometry) and atmospheric aging studies (oxidation flow tube reactors/aerosol chambers), aeroHEALTH uses lung cell- and animal-based exposure studies to reveal the biological impact of the aging process. In a first interdisciplinary consortium-wide measurement campaign, the photochemical transformation of precursor compounds (naphthalene and ß-pinene as anthropogenic and biogenic model precursors, respectively) was simulated in an oxidation flow tube reactor. Secondary organic aerosol (SOA) was formed in the presence of freshly generated combustion soot as seed particles. This led to SOA coated soot particles. The produced aerosols were comprehensively characterized in terms of their physical and chemical composition. Furthermore, air-liquid-interface (ALI) cell exposure experiments were performed to assess different biological and toxicological endpoints. While the physical properties of the derived SOA aerosol from both model compounds were very similar, the ALI aerosol exposure of the in vitro lung cell model systems caused significant toxicological effects. Greater adverse biological responses were observed for the naphthalene-SOA coated soot in comparison to the ß-pinene-SOA coated soot. Note, that the nano-sized soot cores alone resulted only in very minor toxicological effects. At the functional level, we showed that naphthalene-based SOA augments cellular oxidative and inflammatory stress, induced primary and secondary genotoxicity in epithelial and endothelial cells, respectively, and enhanced the angiogenic potential with the respect to ß-pinene-based SOA. Additionally, RNA was extracted from exposed cells and subjected to transcriptome analysis (RANseq). To investigate the chemical composition of the two SOA types, we applied on- and off-line chemical analyses of the condensed particulate matter as well as of the gas phase by different mass spectrometric approaches. Distinct differences in the molecular composition of the two SOA types were observed. In naphthalene derived aerosols, the formation of naphthoquinones, naphthols and other ring-opening and ring-remaining products, induced by ozone and OH radical reactions, was observed. Photooxidation of ß-pinene resulted in an even larger number of different, predominately aliphatic oxidation products. The combined results from the comprehensive physicochemical analysis, the functional toxicological data and the transcriptome analysis underline the importance of the chemical composition of the formed SOA for aerosol-induced health effects.