Identifying The Key Drivers Of The Lung Response To Inhaled Geogenic Dusts

Background: The current guidelines for acceptable levels of ambient PM (< 10 µm diameter particulate matter) are 10 primarily based on the relative concentrations of anthropogenic particles in urban areas. However, there are many communities where the total suspended particulates are dominated by particles of crustal (geogenic) origin. There is evidence to suggest that such communities are exposed to higher concentrations of PM 10 than urban populations and that geogenic 10 dusts generate a more pronounced inflammatory response in the lung than anthropogenic particles. This study aimed to determine the key characteristics of inhaled geogenic PM that have the greatest impact on the lung.

Methods: The PM fraction was extracted from surface soil samples from 4 communities across Western Australia. BALB/c 10 mice were intranasally exposed to 100 µg of PM . Control mice received 100 µg of polystyrene beads (2.5 µm) or vehicle 10 alone. Mice were assessed for inflammation (cellular influx, MIP-2, IL-6 and IL-1β), lung volume (plethysmography) and lung mechanics (forced oscillation technique) 6, 24 or 168 hours post-exposure. The physical and chemical characteristics of the particles were assessed by cascade impactor and ICP-MS/OES respectively. Principal component analysis of the outcome measures were used to construct lung impairment scores. Multivariate linear regression models were then used to identify the characteristics of the particles driving the lung responses.

Results: Exposure to geogenic particles caused an acute inflammatory response (6 hours post-exposure), an acute impairment in lung mechanics (24 hours post-exposure) and a long term deficit in lung volume (168 hours post-exposure). Both the inflammatory response and long term deficits in lung volume were associated with the concentration of Fe and variability in particle size (GSD) while the impairment in lung mechanics was associated with Fe and particle size (MMAD).

Conclusions: Despite the complex physico-chemical characteristics of geogenic dusts we were able to identify the concentration of Fe and physical dimensions of the particles as the key drivers of lung responses. Using these data we may be able to predict which communities are at greatest risk of adverse respiratory health due to high geogenic particle loads.