The morbidity and mortality of vermiculite miners and millers exposed to tremolite-actinolite: Part III. Radiographic findings

Our plain-English summary of The morbidity and mortality of vermiculite miners and millers exposed to tremolite-actinolite: Part III. Radiographic findings, by H.E. Amandus, R. Althouse, W.K. Morgan, et al (American Journal of Industrial Medicine, 1987).

The study

• Authors: H.E. Amandus, R. Althouse, W.K. Morgan, E.N. Sargent, R. Jones
• Journal: American Journal of Industrial Medicine
• Published: 1987;11(1):27-37
• Cited by: 34 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000297).

Abstract

A study was conducted to estimate the exposure-response relationship for tremolite-actinolite fiber exposure and radiographic findings among 184 men employed at a Montana vermiculite mine and mill. Workers were included if they had been employed during 1975-1982 and had achieved at least 5 years tenure at the Montana site. Past fiber exposure was associated with an increased prevalence of parenchymal and pleural radiographic abnormalities. Smoking was not significantly related to the prevalence of small opacities. However, the number of workers who had never smoked was small, and this prevented measurement of the smoking effect. Under control for smoking and age, the prevalence of small opacities was significantly greater for vermiculite workers with greater than 100 fiber/cc-years exposure than for comparison groups (cement workers, blue collar workers, and coal miners) who had no known occupational fiber exposure. A logistic model predicted an increase of 1.3% in the odds ratio for small opacities at an additional exposure of 5 fiber-years.

In plain English

Researchers studied chest X-rays of 184 men employed during 1975-1982, with at least 5 years' tenure, at a vermiculite mine and mill near Libby, Montana. Their average estimated cumulative exposure to tremolite-actinolite fibers was 119.4 fiber-years. Three readers classified each man's most recent X-ray. Small opacities (small lung shadows) appeared in 10% of the men, any pleural change in 15%, pleural calcification in 4% and pleural thickening on the chest wall in 13%. Exposure was significantly related to small opacities, any pleural change and wall thickening, but not to calcification. Once age was allowed for, only small opacities stayed significantly related to exposure. Allowing for both smoking and age, the links between exposure and small opacities, and between exposure and any pleural change, were not significant. Among current and former smokers aged 45-60, 4 of 13 vermiculite workers with over 100 fiber-years (30.8%) had small irregular opacities. That was significantly more than in comparison groups of cement workers, blue-collar workers and coal miners. The authors noted that few men had never smoked and that poor-quality films were more common at higher exposure. They concluded that, under stated assumptions, 5 fiber-years was associated with a 1.3% increase in the relative risk of small opacities.

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 study with exposure-response analysis (including logistic models adjusted for age) and comparison with external groups of workers without known fiber exposure
• Who was studied: 191 men employed at the Libby, Montana vermiculite mine and mill during 1975-1982 with at least 5 years tenure. Chest radiographs were available for 184 and smoking/symptom questionnaires for 121.
• Exposure: Tremolite-actinolite fibers at a vermiculite mine and mill, measured as individual cumulative fiber-years. For men with radiographs the average was 119.4 fiber-years, with an average age of 44.4 years and average tenure of 14.4 years.
• Main results:
  • Among the 184 men, small opacities (ILO category 1/0 or more) were found in 10%, any pleural change in 15%, pleural calcification in 4% and pleural thickening on the wall in 13%.
  • Fiber-years were significantly related to small opacities, any pleural change and pleural thickening on the wall, but not to pleural calcification.
  • Under joint control for cigarette smoking and age, the association of fiber-years with small opacities and with any pleural change was not significant.
  • In logistic models with age included, only small opacities were significantly related to fiber-years.
  • For the total group at the mean age of 44, the model gave odds ratios for small opacities of 1.01, 1.13 and 1.30 at 5, 50 and 100 fiber-years. The estimated prevalences were 2.1%, 2.4% and 2.5%.
  • Among current and former smokers aged 45-60, small irregular opacities were more common in vermiculite workers than in the comparison groups. The difference was significant only for vermiculite workers with more than 100 fiber-years: 4 of 13, or 30.8%. In the comparison groups the figures were 1.1% of blue-collar workers, 3.6% of cement workers and 0.3% of coal miners.
  • Irregular opacities were the main type of opacity in 17 of the 18 cases of small opacities.
  • Readers A and C each found small opacities in 10% of films, and reader B found them in 16%.
• The authors' conclusion: The authors concluded that 5 fiber-years was associated with a 1.3% increase in the relative risk of small opacities, provided three assumptions hold: smoking is not a confounder, the logistic model fits, and the fiber-year index applies whether exposure was high or low. On the same assumptions, they stated that 0.1 f/cc over a working lifetime is not a conservative standard for preventing radiographic small opacities.
• Limitations the authors state:
  • The confounding effect of smoking could not be adequately measured because there were few nonsmokers: 25 overall and 8 aged 45 or older.
  • The number of vermiculite workers aged 45-60 in the external comparison was small.
  • Radiographs of the comparison groups were generally of better quality.
  • Different readers classified the films of the comparison and study groups.
  • Film quality was highly correlated with cumulative exposure. The authors said poor film quality would likely lead to underestimation of disease prevalence.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Libby vermiculite mine, Montana

All asbestos mines

Topics

The National Library of Medicine indexes this study under subjects our site covers: Actinolite, Talc and vermiculite, Tremolite.

Medical terms in this study, explained in our Lexicon: vermiculite, Tremolite, Actinolite, Odds Ratio, Fiber Year.

Related studies

• The morbidity and mortality of vermiculite miners and millers exposed to tremolite-actinolite: Part II. Mortality — H.E. Amandus, R. Wheeler (1987)
• The morbidity and mortality of vermiculite miners and millers exposed to tremolite-actinolite: Part I. Exposure estimates — H.E. Amandus, R. Wheeler, et al. (1987)
• Cohort study of mortality of vermiculite miners exposed to tremolite — J.C. McDonald, A.D. McDonald, et al. (1986)
• Health of vermiculite miners exposed to trace amounts of fibrous tremolite — J.C. McDonald, A.D. McDonald, et al. (1988)
• Asbestos-related radiographic findings among household contacts of workers exposed to Libby vermiculite: impact of workers' personal hygiene practices — T.J. Hilbert, A. Franzblau, et al. (2013)
• Radiological survey of past and present vermiculite miners exposed to tremolite — J.C. McDonald, P. Sebastien, et al. (1986)

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