Death Variability Induced by Different Clay Minerals: How A549 Epithelial Alveolar Cells Respond to Changes in Clay Particle Size and Composition

Dust storms are common meteorological phenomena in arid and semiarid areas where strong winds lift mineral dust particles into the air. Around 300 million people worldwide are exposed to these particles, which can travel long distances and remain suspended for long periods. The WHO has estimated that 4.2 million deaths per year are linked to poor air quality, in which mineral dust contributes up to 40 % of the particulate matter suspended in the air. Dust storms contain a mixture of mineral particles, including combinations of clay minerals whose composition and size distribution vary depending on the dust source. The effect of these particles on the respiratory system has been studied at multiple levels. In vitro, dust particles have been found to reduce cell viability, increase cytokine release, and damage DNA. However, what mechanisms lead to these adverse health outcomes is still unclear. Previous studies are limited by their temporal and special resolution: Most of them measure the effects of dust at only a few time points (usually 6, 24, or 48 hours) and in large populations of cells, which masks the interaction between each cell and the dust particles.

We analyzed the size distribution, composition, and concentration of heavy metals in five different clays (Na-rich Montmorillonite, Ca-rich Montmorillonite, Montmorillonite, Illite, and Kaolinite). We used the single-cell method to evaluate the impact of these clays in the human alveolar epithelial A549 cell line. This method used live cell imaging to monitor the cells every 15 minutes, following the outcome of each cell within a population, and quantify variables such as the number of times each cell divided, the number of particles it was in contact with, the exact time of death, and the type of death (apoptosis or necrosis). The composition of the clay was found to be a critical determinant of the sample’s toxicity after 48 hours of exposure. Cell death with increasing concentration was found to be non-monotonic for some clays, with more cells dying by necrosis. The impact of dust on cells that remained alive was also observed as they lowered their division rate and showed signs of cell arrest. These results will help clarify some of the current unknowns on why some dust storms are more toxic than others and help characterize the toxicity of the dust events per location based on their mineralogical composition.