Characterization of the exposure of underground miners to mixed aerosols

The exposure to airborne aerosols in any occupational environment can lead over time to debilitating respiratory diseases that can affect the health of workers. In several environments, the workers are exposed not to a single aerosol but to a combination of particulate substances of different composition and size. Miners in countries where diesel-powered equipment are employed, are exposed to elevated concentration of respirable mine dust and ultrafine diesel-generated particles. It is common scientific practice to characterize and investigate the exposure to a single aerosol. Few studies have been conducted on the characterization of the exposure to a mixture of aerosols. This study investigated the characteristic of the exposure to mine dust and DPM simultaneously present in a calm air exposure chamber. Different levels and types of dust and DPM were introduced in the chamber in controlled conditions for steady state and decay testing: the conditions simulated the mass concentration levels for dust and Diesel Particulate Matter (DPM) typically present in underground mines. Real time spectrometers were used to monitor the characteristics of the mixed aerosol. The data from each test were then processed for the determination of exposure in terms of lung deposited mass, surface, and number of the particles for each condition. Specific attention was given to accurately convert the data into activity median thermodynamic diameter that is used in the lung deposited models. The potential interaction of the two aerosols was also investigated. Electron microscope analysis of collected particles indicated a substantial presence of DPM particles aggregates on the surface of respirable mine dust. This indicates phenomena of absorption and deposition between micrometric dust particles and sub-micrometric diesel aggregates and the formation of a new hybrid type of particle.