Silicosis prevalence and exposure-response relations in South African goldminers

Abstract

Aims: To measure the prevalence of silicosis among black migrant contract workers on a South African goldmine and to investigate exposure-response relations with silica dust. Methods: In a cross sectional study, 520 black goldminers (aged .37 years) were interviewed and had chest radiographs taken. Silicosis was defined as International Labour Organisation Classification radiological profusion of 1/1 or greater. Results: Mean length of service was 21.8 years (range 6.3-34.5). The mean intensity of respirable dust exposure was 0.37 mg/m 3 (range 0-0.70) and of quartz 0.053 mg/m 3 (range 0-0.095). The prevalence of silicosis was 18.3-19.9% depending on reader. Significant trends were found between the prevalence of silicosis and length of service, mean intensity of exposure, and cumulative exposure. Conclusion: Results confirm a large burden of silicosis among older black workers in the South African goldmining industry, which is likely to worsen as such miners spend longer periods in continuous employment in dusty jobs. An urgent need for improved dust control in the industry is indicated. If the assumption of stability of average dust concentrations on this mine over the working life of this group of workers is correct, these workers developed silicosis while exposed to a quartz concentration below the recommended occupational exposure limit (OEL) of 0.1 mg/m 3 . This accords with a mounting body of evidence that an OEL of 0.1 mg/m 3 is not protective against silicosis.

Hazards identified and the need for health risk assessment in the South African mining industry

“…However, a prevalence and exposure-response study among gold workers shows that this value is insufficiently protective. 17 The study, showing a mean respirable crystalline silica (quartz) concentration of 0.053 mg/m 3 , demonstrated a prevalence of silicosis affecting 18.3-19.9% of workers in a gold mine. A similar study in the United States of America 66 showing a similar average respirable silica exposure concentration of 0.05 mg/m 3 , indicated a prevalence of silicosis of less than 1%.…”

“…10,16 A study on the prevalence of silicosis among black migrant contract workers on a South African goldmine indicated prevalence levels of 18.3-19.9%. 17 The prevalence of CWP has been determined to be 7.3%. 12 At the same time, the prevalence of tuberculosis and HIV among miners is said to be high.…”

Continued exposure to silica after diagnosis of silicosis in Brazilian gold miners

“…Nevertheless, from the exposure assessment parameters utilized, it can be inferred that blacks were more intensely exposed than non-blacks, which would explain the occurrence of more severe forms of the disease. It is emphasized that, as already described in other studies [Rosenman, 1996;Churchyard et al, 2004], it is possible that the blacks may have performed tasks with higher risk of exposure and that this may not have been detected by the elements utilized for devising the present index. Although this question was not quantified, the patients did report this subjectively when their histories were being taken.…”

Controlled fire use in early humans might have triggered the evolutionary emergence of tuberculosis

“…Individuals exposed to aerosolized silica, even without silicosis, have a dramatically increased risk of mycobacterial infection (59). The individual-level relative risk for silicosis and silica-associated TB also persists after exposure has ceased and is dose-dependent (60,66). Although biomass burning is not predominantly silica exposure, these principles may apply to other inorganic inhaled particles.…”