The Incidence Of Pneumoconiosis, Mesothelioma And Other Respiratory Cancer In Men Engaged In Mining And Milling Crocidolite In Western Australia

Our plain-English summary of The Incidence Of Pneumoconiosis, Mesothelioma And Other Respiratory Cancer In Men Engaged In Mining And Milling Crocidolite In Western Australia, by M.S.T. Hobbs, S.D. Woodward, B. Murphy, et al (1980).

The study

• Authors: M.S.T. Hobbs, S.D. Woodward, B. Murphy, A.W. Musk, J.E. Elder
• Published: Biological Effects Of Mineral Fibres (J.C. Wagner, Editor), Lyon: Iarc Scientific Publications, Volume 30, Pp. 615-625 (1980)
• Type of article: Conference paper
• Our copy: from Johns-Manville's own medical library, J-M no. 000812. The article is still under copyright, so we describe it here rather than post it.

In plain English

This progress report followed 6200 male former employees of Australian Blue Asbestos, which mined and milled crocidolite (blue asbestos) at Wittenoom Gorge, Western Australia. Of these, 220 (3.5%) developed pneumoconiosis and 26 pleural mesothelioma; no peritoneal mesothelioma was identified. Pneumoconiosis rose with employment length, reaching 52.1% in men employed five years or more, and was highest in heavy-exposure jobs. Fifteen or more years after first employment, mesothelioma rates per 10,000 man-years, standardized for employment duration and interval since first employment, were 10.9 in the heavy, 6.8 in the medium/light and 5.8 in the uncertain exposure groups. Before 1978, 60 men died of respiratory cancer other than mesothelioma, against about 38 expected (mortality ratio 1.57). The ratio rose from 1.18 among men employed under three months to 2.03 among those employed over 12 months. The authors concluded that asbestos exposure intensity was strongly related to these diseases. Their results suggested asbestos accounted for nearly 30% of these respiratory cancer deaths, assuming no asbestos effect in comparison groups or within 10 years of first employment. They could not determine the role of smoking.

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: Follow-up (cohort) study of former employees, reported as a progress report; respiratory cancer deaths were compared with deaths expected from Western Australian male death rates
• Who was studied: 6200 male employees identified from the employment records of Australian Blue Asbestos (ABA), Wittenoom Gorge, Western Australia. A further 800 employees found in another source were not included. Mesothelioma and pneumoconiosis cases diagnosed before 1 July 1979 were counted; mortality analysis covered deaths before 1 January 1978.
• Exposure: Mining and milling of crocidolite (blue asbestos) at Wittenoom Gorge, which was mined between 1938 and 1966. Workers were grouped by duration of employment and by occupation: Heavy, Medium/Light, or Uncertain (occupation not recorded).
• Main results:
  • Of the 6200 male employees, 220 (3.5%) developed pneumoconiosis.
  • Pneumoconiosis Board records indicated 59 cases of asbestosis, 122 of silico-asbestosis and 17 of silicosis.
  • Among men employed 5 years and over, pneumoconiosis incidence was 65.4% (36 cases) in the Heavy group, 40.0% (16) in Medium/Light, 40.9% (9) in Uncertain, and 52.1% (61) in all occupations.
  • After standardization for duration of employment, pneumoconiosis incidence was highest in the Heavy group, followed by the Uncertain group, and lowest in the Medium/Light group (1.8%).
  • 26 men developed pleural mesothelioma; no cases of peritoneal mesothelioma were identified.
  • Mesothelioma rates per 10,000 man-years of follow-up 15 or more years after first employment, standardized for duration of employment and interval from first employment (direct method): Heavy 10.9 (14 cases), Medium/Light 6.8 (8 cases), Uncertain 5.8 (3 cases), all groups 8.6 (25 cases).
  • Before 1978, 60 men died of respiratory cancer other than mesothelioma, compared with 38.24 expected from Western Australian male rates, a mortality ratio of 1.57.
  • Mortality ratios for the whole cohort were 0.90 for all causes and 0.83 for non-respiratory causes of death.
  • For all intervals from first employment, the respiratory cancer mortality ratio was 1.18 for men employed less than three months, 1.47 for three to 12 months, and 2.03 for more than 12 months.
  • At intervals of 15 years and over from first employment, the respiratory cancer mortality ratio was 0.87 for men employed less than three months, 1.67 for three to 12 months, and 2.46 for over 12 months.
  • The excess respiratory cancer mortality was accounted for mainly by deaths in workers with previously diagnosed pneumoconiosis, in whom 1.9 respiratory cancer deaths would have been expected.
• The authors' conclusion: The authors concluded that the incidence of pneumoconiosis and mesothelioma, and mortality from other respiratory cancer, indicated a strong relationship with intensity of asbestos exposure. They stated that their results suggested asbestos exposure accounts for nearly 30% of respiratory cancer deaths other than mesothelioma. This estimate assumed no asbestos contribution in the comparison groups or within 10 years of first employment, and would be an underestimate if that assumption were wrong.
• Limitations the authors state:
  • The extent to which the excess respiratory cancer could be due to factors such as smoking could not be determined from the data.
  • The follow-up period for most employees was too short to predict the likely future extent of mesothelioma.
  • Some inconsistencies in respiratory cancer ratios may reflect instability of ratios based on small expected numbers.
  • The 30% estimate assumed no asbestos contribution in some groups; if that assumption is wrong, the asbestos contribution was underestimated.
  • Reduced mortality ratios for other causes may reflect a 'well worker' effect and loss from follow-up.
  • About 800 further employees identified from the Mine Workers' Relief Fund were not included.

Topics

Medical terms in this study, explained in our Lexicon: Pneumoconiosis, Mesothelioma, Crocidolite, Wittenoom, Pleural Mesothelioma, Peritoneal Mesothelioma, Asbestos Exposure.

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