Characterisation of dust emissions from machined engineered stones to understand the hazard for accelerated silicosis

Abstract

Engineered stones are novel construction materials associated with a recent upsurge in silicosis cases among workers in the stonemason industry. In order to understand the hazard for the short latency of lung disease among stonemasons, we simulated real-time dust exposure scenario by dry-machining engineered stones in controlled conditions, capturing and analysing the respirable dust generated for physical and chemical characteristics. Natural granite and marble were included for comparison. Cutting engineered stones generated high concentrations of very fine particles (< 1 µm) with > 80% respirable crystalline silica content, in the form of quartz and cristobalite. Engineered stones also contained 8-20% resin and 1-8% by weight metal elements. In comparison, natural stones had far lower respirable crystalline silica (4- 30%) and much higher metal content, 29-37%. Natural stone dust emissions also had a smaller surface area than engineered stone, as well as lower surface charge. This study highlighted the physical and chemical variability within engineered stone types as well as between engineered and natural stones. This information will ultimately help understand the unique hazard posed by engineered stone fabrication work and help guide the development of specific engineering control measures targeting lower exposure to respirable crystalline silica.

Figure 1

Representative cumulative plot for the particle size distribution of respirable dust generated from dry-cutting engineered (ES) (straight black lines) and natural stones, namely black granite, white granite and white marble (broken black lines). The reference quartz (Ref. Qu.; NIST 1878b) is illustrated as the black dotted line.

Figure 2

Representative SEM images of respirable dusts from machined engineered (a–f) and natural (g–i) stones, as well as reference quartz (j–k) under 40,000 and 20,000× magnification, which relate to 3 and 5 µm size fractions, respectively.

Figure 3

(a) Box-plot representation of the metal elemental composition (excluding Si) in twelve engineered stones. Centre line represents the median and whiskers represent the minimum and maximum values. (b) Variability of elements in the natural stones. The bracketed numbers in the pie charts show the abundance of elements as a percentage of the total elemental composition (reported in the chart titles). Elements not shown in the pie charts were below analytical detection limits.