Silica exposures and silicosis incidence in the Western Australia mining industry

Abstract

Background: Silicosis has historically been an issue in the Western Australian mining industry.

Aims: To determine the magnitude of exposures to atmospheric respirable crystalline silica (RCS) in mine workers recorded between 1986 and 2023 and if those exposures risk health effects.

Methods: We used descriptive statistics to compare RCS exposures in mining job types. We identified high exposure occupations and modelled their resulting lung silica burden using known toxicokinetic parameters. These were compared with critical lung silica burdens for alveolar inflammation, soft macules, fibrosis and progressive massive fibrosis. We compared the miners' RCS exposures with historical silicosis cases in Western Australia's mine workers.

Results: The geometric mean of more than 130 000 RCS results between 1986 and 2023 was 0.008 mg/m3. Exposures in exploration jobs were higher than in jobs on established mine operations (0.013 vs 0.007 mg/m3). Overall, exploration drilling assistant jobs and laboratory work were the two highest exposed cohorts, and modelling of steady state lung burden predicted 7.5 and 5.7 mg/lung, respectively, values an order of magnitude less than that associated with inflammation, and two orders of magnitude less than that associated with fibrosis. There have been 4 confirmed and 3 other possible cases of silicosis in more than 2 million person-years of mine work in WA since 1986.

Conclusions: The low incidence of silicosis in the WA mining industry over the past 20 years is consistent with the estimated low silica lung burdens resulting from work-related exposures, which are significantly lower than the silica lung burdens typically associated with silicosis in the literature.

Figure 1.

Frequency distribution of RCS concentration results in WA mining workers for the period 1986–2023 (n = 131 454). Insert shows the upper range of results 0.21–1.0 mg/m³. X-axis values represent the concentration range including the indicated value. There were 93 486 results (72%) less than or equal to 0.01 mg/m³.

Figure 2.

Annual GM of RCS results in mine workers’ personal samples for years 1986–2023 in WA.