Characterizing Particle Size Distributions of Crystalline Silica in Gold Mine Dust

Abstract

Dust containing crystalline silica is common in mining environments in the U.S. and around the world. The exposure to respirable crystalline silica remains an important occupational issue and it can lead to the development of silicosis and other respiratory diseases. Little has been done with regard to the characterization of the crystalline silica content of specific particle sizes of mine-generated dust. Such characterization could improve monitoring techniques and control technologies for crystalline silica, decreasing worker exposure to silica and preventing future incidence of silicosis.Three gold mine dust samples were aerosolized in a laboratory chamber. Particle size-specific samples were collected for gravimetric analysis and for quantification of silica using the Microorifice Uniform Deposit Impactor (MOUDI). Dust size distributions were characterized via aerodynamic and scanning mobility particle sizers (APS, SMPS) and gravimetrically via the MOUDI. Silica size distributions were constructed using gravimetric data from the MOUDI and proportional silica content corresponding to each size range of particles collected by the MOUDI, as determined via X-ray diffraction and infrared spectroscopic quantification of silica.Results indicate that silica does not comprise a uniform proportion of total dust across all particle sizes and that the size distributions of a given dust and its silica component are similar but not equivalent. Additional research characterizing the silica content of dusts from a variety of mine types and other occupational environments is necessary in order to ascertain trends that could be beneficial in developing better monitoring and control strategies.

Can the South African Milestones for Reducing Exposure to Respirable Crystalline Silica and Silicosis be Achieved and Reliably Monitored?

“…Characterization of the particle size distribution, either as aerosols or as particles deposited on collection filters by laser light scattering, has been introduced in South Africa only recently. Direct measurement of the lung deposited surface area (LDSA) dose is currently not performed; the appropriate devices were introduced a few years ago and only recently deployed in the USA to assess exposure in mining operations (58). Since the contribution of submicron particles to the respirable mass concentration is relatively small (59), the relevance of the smaller silica particles may be underestimated.…”

Perspective: The Lung, Particles, Fibers, Nanomaterials, and Autoimmunity

“…Significantly, when silica exposure and smoking occur together it results in a synergistic interaction which, for example, greatly increases the risk of ACPA-positive RA in Asian (40) and Caucasian (41) populations. Silica dust exposure is most often via occupational inhalation with deposition of respirable particles [<10mm (42)] in the alveoli of the lungs leading to chronic inflammation and development of fibrotic nodules (36). Although the mechanistic aspects of the pathogenic process of silicosis have not been completely defined, a number of important checkpoints have been identified (36,43,44).…”

Case Report: Exposure to Respirable Crystalline Silica and Respiratory Health Among Australian Mine Workers

“…During mechanical processes such as crushing, cutting, drilling, or grinding of natural stone, or man-made products that contain silica, workers generate silica dust commonly referred to as respirable crystalline silica (RCS) ( 1 ). Silica dust particles with size from 0.01 to 100 μm in diameter are a significant health concern ( 2 ). When inhaled, RCS can penetrate deep into the lungs and cause irreversible lung damage including chronic bronchitis, chronic obstructive pulmonary disease (COPD), emphysema, silicosis, and silico-tuberculosis ( 3 , 4 ).…”