Pulmonary changes after exposure to vermiculite contaminated with fibrous tremolite

Our plain-English summary of Pulmonary changes after exposure to vermiculite contaminated with fibrous tremolite, by J.E. Lockey, S.M. Brooks, A.M. Jarabek, et al (The American Review of Respiratory Disease, 1984).

The study

• Authors: J.E. Lockey, S.M. Brooks, A.M. Jarabek, P.R. Khoury, R.T. McKay, A. Carson, J.A. Morrison, J.F. Wiot, H.B. Spitz
• Journal: The American Review of Respiratory Disease
• Published: 1984;129(6):952-8
• Cited by: 60 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. 000553).

Abstract

Workers exposed to vermiculite contaminated with fibrous tremolite were surveyed for the presence of respiratory symptoms by questionnaire, and for pneumoconiosis by chest radiograph. Pulmonary function was measured by spirometry and single-breath carbon monoxide diffusing capacity ( DLCOsb ). Fiber exposure indexes, expressed as fiber/ml-yr, were derived for each worker from available industrial hygiene data and work histories. The estimated cumulative exposure for the work force ranged from 0.01 to 39 fiber/ml-yr. Discriminant analysis demonstrated significant correlates with shortness of breath and pleuritic chest pain to cumulative fiber exposure. The radiographic changes were limited to pleural changes and involved 4.4% of the population. Parametric and discriminant analysis demonstrated a significant correlation with radiographic changes and cumulative fiber exposure. There were no correlations between spirometry or DLCOsb and fiber exposure. Exposure to vermiculite contaminated with fibrous tremolite can cause pleural changes in occupationally exposed workers. This is supported by the previously identified 12 cases of benign pleural effusions in this working population and the association of pleural radiographic changes and pleuritic chest symptoms with cumulative fiber exposure. The lack of significant parenchymal radiographic, spirometric, and DLCOsb changes most likely reflects the low cumulative fiber exposure.

In plain English

This cross-sectional study surveyed workers at a rural plant that expanded vermiculite contaminated with fibrous tremolite. Of 530 employees asked, 512 (97%) took part. Each worker's cumulative fiber exposure was calculated from department exposure estimates and length of employment in each department. The highest value for any employee was 39 fiber/ml-yr. Employees below 1 fiber/ml-yr served as the comparison group. Of 501 readable chest X-rays, 11 showed costophrenic angle blunting only, 10 showed pleural thickening, plaques or calcification, and 1 showed small irregular opacities in the lung. These changes were found in 2.4% of the comparison group, 5.0% of workers with 1 to 10 fiber/ml-yr and 12.5% of those above 10 fiber/ml-yr. Pleuritic chest pain was associated with cumulative exposure. Shortness of breath was associated with both exposure and smoking. Spirometry and diffusing capacity were not related to exposure. The authors concluded that this exposure can cause pleural changes. They judged that the absence of significant lung-tissue or exposure-related lung-function changes most likely reflected the short time since first exposure and low, probably underestimated, cumulative exposure.

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 epidemiologic study (questionnaire, limited physical examination, spirometry, single-breath carbon monoxide diffusing capacity, chest radiographs)
• Who was studied: 512 of 530 employees (97%) of a rurally located vermiculite-processing company. The group included employees with past vermiculite exposure and a control group without it: 480 males and 32 females, mean age 37.5 yr. Plant location and survey dates are not stated.
• Exposure: Vermiculite contaminated with fibrous tremolite. Each employee's cumulative fiber exposure (fiber/ml-yr) was calculated from department fiber exposure indexes and length of employment in each department. The indexes were 8-h time-weighted averages, with separate indexes for up to 1973 and from 1974. Workers were also grouped as Group I (controls), Group II (low exposure) and Group III (high exposure).
• Main results:
  • The highest cumulative fiber exposure for any employee was 39 fiber/ml-yr.
  • Chest radiographs were reviewed for 501 of 512 employees (97.9%). Of these, 479 (95.6%) had no significant changes.
  • 11 employees (2.2%) had costophrenic angle blunting only.
  • 10 employees (2%) had significant pleural changes (thickening, plaques and/or calcifications).
  • 1 employee (0.2%), in the high exposure group (Group III), had bilateral small irregular opacities in the lung tissue.
  • Combined radiographic changes (costophrenic angle blunting or pleural/parenchymal changes) by cumulative exposure: 6 of 253 (2.4%) in controls (less than 1 fiber/ml-yr) and 10 of 200 (5.0%) at 1 to 10 fiber/ml-yr.
  • Among 48 employees with more than 10 fiber/ml-yr cumulative exposure, 12.5% had costophrenic angle blunting or pleural/parenchymal changes.
  • In an age-matched analysis, the 22 employees with abnormal radiographs differed significantly in cumulative fiber exposure from matched employees with normal radiographs (mean difference 5.8 fiber/ml-yr, paired t test p 0.041). The nonparametric Wilcoxon test showed only a trend (p < 0.098).
  • History of pleuritic chest pain was significantly associated with cumulative fiber exposure (p < 0.05).
  • Shortness of breath Grade I and Grade II was significantly related (p < 0.05) to both smoking in pack-years and cumulative fiber exposure.
  • Spirometry and diffusing capacity (DLcosb) showed no correlation with fiber exposure. Low DLcosb was associated with smoking (p < 0.01).
  • 7 still-employed workers had previously documented benign pleural effusions. Of these, 4 had residual pleural changes on radiograph and were counted among the 22 abnormal radiographs.
• The authors' conclusion: The authors concluded that exposure to vermiculite contaminated with fibrous tremolite can cause pleural changes in occupationally exposed workers.
• Limitations the authors state:
  • The authors stated that the reported exposure levels likely underestimate actual cumulative exposure. There were no industrial hygiene data before 1972, and personal sampling began only in 1976.
  • Extensive overtime was worked, but precise figures for past work days per year were not available for the exposure estimates.
  • The authors attributed the absence of significant parenchymal (lung-tissue) changes most likely to the short interval since initial exposure and the low cumulative fiber exposure. They gave the same explanation for the lack of association between lung-function results and exposure. Only 10.7% had been employed 20 yr or more since initial exposure.

Topics

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

Medical terms in this study, explained in our Lexicon: vermiculite, Tremolite, Pneumoconiosis, Chest X-Ray, Spirometry, Diffusing Capacity (DLCO), Industrial Hygiene, Cumulative Exposure.

Related studies

• Health of vermiculite miners exposed to trace amounts of fibrous tremolite — J.C. McDonald, A.D. McDonald, et al. (1988)
• Cohort study of mortality of vermiculite miners exposed to tremolite — J.C. McDonald, A.D. McDonald, et al. (1986)
• Radiological survey of past and present vermiculite miners exposed to tremolite — J.C. McDonald, P. Sebastien, et al. (1986)
• 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)
• 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)

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