| Description |
The EPA's current vehicle emission regulations for particulate matter only consider mass emissions and do not consider other particle properties or their relationship to potential adverse health effects. This limits the development of strategies to address the health effects of combustion particles. Studies linking size have reported inconclusive results, and no studies have explored the effect of combustion particle morphology on particle toxicity. Confounding factors, including fuel type, use of additives, combustion conditions, particle collection methods, also affect particle properties, making it difficult to compare previous studies. The use of different in vitro exposure methods and dosimetry also complicates the comparison of previous studies. The first section of the study focused on the evaluation and development of methods to conduct size-based and shape-based studies. A method was developed to generate particles with consistent properties by combusting a jet-fuel surrogate at constant combustion conditions. The particles generated were collected in three ways to evaluate the effect of collection methods on particle properties and on the cellular responses in macrophage-like cells. The particles were also exposed to co-culture of human lung epithelial and macrophage-like cells using three different exposure methods (submerged in vitro, air-liquid interface (ALI), and pseudo-ALI). Both the particle collection and exposure methods resulted in a significant difference in some biological responses. Next, a quartz crystal microbalance (QCM) method was developed to accurately estimate mass iv concentration of nanoparticle suspensions in DI water, required to determine the administered dose in submerged in vitro exposure. A QCM method was also developed to measure real-time mass deposition of nanoparticles, needed to estimate the delivered dose in ALI exposures. Lastly, the effect of particle size and shape on cell response was explored. The methods used to obtain size fractions faced limitations rendering an inconclusive result regarding the effect of particle size. The particle morphology was changed from fiber-like to a more compact spherical shape (transformation observed during atmospheric aging). The more compact-spherical shaped particles induced high pro-inflammation and early apoptosis in lung cells compared to more fiber-like particles. This result highlights the role of morphology on cellular toxicity. |
