Radiologic abnormalities in South African mica millers: a survey of a mica milling plant in the Limpopo Province

Our plain-English summary of Radiologic abnormalities in South African mica millers: a survey of a mica milling plant in the Limpopo Province, by E. Venter, B. Nyantumbu, A. Solomon, et al (International Journal of Occupational and Environmental Health, 2004).

The study

• Authors: E. Venter, B. Nyantumbu, A. Solomon, D. Rees
• Journal: International Journal of Occupational and Environmental Health
• Published: 2004;10(3):278-83
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

All 73 workers at a South African mica milling plant were surveyed for radiographic evidence of abnormalities related to dust exposures at work. Chest x-rays were taken and questionnaires administered to determine occupational and environmental exposure histories. Dust levels to which workers were exposed were measured. All but one of 12 airborne inhalable and respirable dust levels were below the occupational exposure limits (OEL-RLs) of 10 mg/m3 and 5 mg/m3 respectively. The mica concentrations were below the OEL-RL of 1 mg/m3 for respirable mica. Mean age and service duration of the workers were 45 and 14 years, respectively. 19 workers (27%) had changes referable to their exposures to asbestos, mica, silica, or combinations. Of these, four showed additional radiographic changes in keeping with tuberculous lung scarring. Six had evidence of lung changes consistent with past tuberculosis alone. Rates of radiologic abnormalities were higher in older workers and those with longer service. An association between mica and radiologic changes could not be convincingly shown because of the nature of the survey and the co-exposure to other mineral dusts. Nevertheless, six workers had radiologic changes consistent with pneumoconiosis attributable to mica or the combination of mica and silica.

In plain English

This study was a survey of all 73 workers at a mica milling plant in the Limpopo Province, South Africa. Chest x-rays were available for 71 workers and were read by an experienced radiologist using the ILO classification. Questionnaires covered work history, asbestos exposure, smoking and tuberculosis. Twelve dust samples were taken. All mica dust levels were below the respirable mica limit of 1 mg/m3. One inhalable dust sample, from dry milling, measured 13.4 mg/m3, above the 10 mg/m3 nuisance dust limit. Nineteen of the 71 workers (27%) had lung or pleural changes considered related to asbestos, mica, silica or combinations: 16 had pleural changes and nine had parenchymal changes. The share with abnormalities rose with length of service, from 0 among workers with 0 to 9 years to 47% among those with 20 years or more. Eleven affected workers had asbestos and mica exposure or possible exposure. The authors said mixed exposures and limited exposure data prevented final conclusions. They concluded that mica could have contributed to the disease burden.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Cross-sectional radiographic and questionnaire survey of the workforce of one mica milling plant, with workplace dust measurements
• Who was studied: The 73 workers employed at a mica milling plant in the Limpopo Province, South Africa. Chest radiographs were available for 71 and results are reported for these 71. Mean age was 45 years (range 22 to 65), mean service 14 years (range eight months to 35 years), and ten were women. The survey date is not given.
• Exposure: Mica dust from milling, with co-exposures to silica, to asbestos (environmental or occupational, fiber type not specified), and to past mining dusts. Of 12 dust samples, all mica levels were below the respirable mica limit of 1 mg/m3. Inhalable dust was below 10 mg/m3 except for 13.4 mg/m3 in dry milling (one worker).
• Main results:
  • 19 of 71 workers (27%) had lung changes considered referable to asbestos, mica, silica or combinations. Four of these also had changes in keeping with tuberculous scarring, and six other workers had changes consistent with past tuberculosis only.
  • The proportion with radiologic abnormalities increased with service duration: 0 of 13 workers with 0 to 9 years, 12 of 43 (28%) with 10 to 19 years, and 7 of 15 (47%) with 20 years or more.
  • Pleural changes (hyaline plaques, pleural thickening, calcification) were recorded in 16 workers. Nine workers had parenchymal changes (s or t) of ILO category 1/0 or greater, and six had both pleural and parenchymal changes.
  • Eleven workers with abnormalities had some asbestos and mica exposure or possible exposure. Two workers with only pleural reactions and six with parenchymal changes had no elicited history of asbestos exposure.
  • The six workers with parenchymal changes and no asbestos exposure had spent an average of 24 years in the mica industry (minimum 15). The rest of the workforce averaged 13 years. The authors described this as a crude association.
  • Careful life histories of eight workers found no exposure to any dust other than mica or silica or both. Six of these had radiographic evidence of lung fibrosis and two had pleural changes.
• The authors' conclusion: The authors concluded that radiologic abnormalities were common in these mica mill workers. Asbestos and silica exposures accounted for some of the abnormalities, but mica could have contributed to the disease burden. An association between mica and radiologic changes could not be convincingly shown.
• Limitations the authors state:
  • Small number of workers (73), despite a 97% participation rate
  • Mixed exposures and insufficient exposure data for each worker did not allow final conclusions, and it was difficult to attribute changes to mica alone
  • Lifetime residence and work movements were hard to record exactly
  • Earlier environmental asbestos exposure from a nearby asbestos mining area could not be ruled out

Topics

Medical terms in this study, explained in our Lexicon: Mica, Chest X-Ray, Environmental Exposure, Occupational Exposure, Pneumoconiosis.

Related studies

• Mica-associated pulmonary interstitial fibrosis — S.K. Landas, D.A. Schwartz (1991)
• Lung cancer, tobacco, and environmental factors in the African population of the Northern Province, South Africa — O. Mzileni, F. Sitas, et al. (1999)
• Asbestosis in South African asbestos miners — G.K. Sluis-Cremer (1970)
• Relationships between simultaneous airborne dust samples taken with five types of instruments at South African asbestos mines and mills — R.S. Du Toit, L.W. Isserow, et al. (1983)
• The morbidity and mortality of vermiculite miners and millers exposed to tremolite-actinolite: Part III. Radiographic findings — H.E. Amandus, R. Althouse, et al. (1987)
• Asbestos and asbestos-related disease: the South African case — J.E. Myers, J. Aron, et al. (1987)

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