Relation between lung asbestos fibre burden and exposure indices based on job history

Our plain-English summary of Relation between lung asbestos fibre burden and exposure indices based on job history, by K. Takahashi, B.W. Case, A. Dufresne, et al (Occupational and Environmental Medicine, 1994).

The study

• Authors: K. Takahashi, B.W. Case, A. Dufresne, R. Fraser, T. Higashi, J. Siemiatycki
• Journal: Occupational and Environmental Medicine
• Published: 1994;51(7):461-9
• Cited by: 26 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Lung asbestos burden was compared with exposure indices derived from job history interviews in 42 male subjects originating from the Montréal Case-Control Study project, 12 of whom had documented asbestos exposed job histories. Job interview data consisting of a chronological timetable of job histories were translated into detailed exposure indices by an expert group of hygienists and chemists. Total and individual asbestos fibre type concentrations were quantified by transmission electron microscopy with fibre identification by energy dispersive chi ray spectrometry after deparaffinisation of tissue blocks and low temperature plasma ashing. Geometric mean or median asbestos content was higher in subjects with an asbestos exposed job history than those without for retained dose of amosite, total commercial amphiboles, and total asbestos fibre. Except for crocidolite fibre diameter, which was significantly less in the lungs of exposed workers, no consistent differences were found in measurements of fibre dimension for any fibre type. Subgroups of subjects exposed to silica, metals, or smokers and non-smokers without significant occupational exposure showed varying patterns of lung asbestos fibre type deficit compared with the asbestos exposed subgroup. There was an overall trend for higher lung asbestos content proportional to higher exposure indices for asbestos representing concentration, frequency, and reliability. These exposure indices as well as duration of exposure (in years) were independent predictors of total asbestos content in regression analyses when combined in a model with age. Stepwise regression indicated that exposure concentration was the most important variable, explaining 32% of the total variation in total asbestos content. Smoking, whether expressed in ever or never smoked dichotomy or in smoked-years, had no relation to lung asbestos content in this model.

In plain English

This study compared lung asbestos content with exposure estimated from job-history interviews in 42 men with cancer from the Montreal Case-Control Study. Twelve had an asbestos-exposed job history; the rest were chosen for silica or metal exposure, or as smokers or non-smokers without such exposure. Experts rated each asbestos job for concentration, frequency and reliability; years exposed were added. Geometric mean total asbestos was 0.28 fibres per microgram of dry lung in exposed men and 0.09 in the 30 unexposed men, not a statistically significant difference. Total commercial amphiboles (crocidolite and amosite) were significantly higher in exposed men (0.16 versus 0.03). All four exposure measures predicted total lung asbestos content. A model with exposure concentration and age explained the most variation, 32%; older age predicted lower content. Smoking did not significantly contribute, but all 12 exposed men smoked and the authors urged caution. Lung chrysotile was not significantly related to chrysotile exposure history. Lung content failed to separate low-level exposure from none. The authors concluded that the results support using carefully determined exposure indices, noting few subjects and selection bias.

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: A comparison of lung tissue fibre analysis by electron microscope with exposure ratings based on job histories. Subjects were selected from a population based case-control study.
• Who was studied: 42 men with cancer at various sites from the Montreal Case-Control Study, selected from about 150 matched necropsy records. Of these, 12 were asbestos exposed, 8 silica exposed and 10 metals exposed; 6 were smokers and 6 non-smokers without significant occupational exposure. Lung tissue came from necropsy (37) or from pneumonectomy or lobectomy (5). Mean age was 61 (range 42-76).
• Exposure: Asbestos exposure judged from job histories (suspected chrysotile and/or commercial amphiboles). Hygienists and chemists rated concentration, frequency and reliability on 0-3 scales, and years worked in asbestos-exposed jobs were added. Smoking was also recorded.
• Main results:
  • Geometric mean total lung asbestos was 0.28 fibres per microgram dry lung in the 12 exposed men and 0.09 in the 30 unexposed men (not significant).
  • Total commercial amphiboles were significantly higher in exposed than in unexposed men: 0.16 versus 0.03 fibres per microgram (p less than 0.05).
  • Median amosite was 0.09 fibres per microgram in exposed men and 0 in unexposed men (p less than 0.05).
  • Lung content above 0.1 fibres per microgram was found in 67% (8/12) of exposed men and 47% (14/30) of unexposed men (not significant).
  • Three of the 12 exposed men exceeded 1 fibre per microgram of dry lung, which the article calls the generally accepted level of unequivocal occupational exposure.
  • One man with lung content above 0.5 fibres per microgram, an acetylene welder, had a negative asbestos job history.
  • In models that each combined one exposure measure with age and smoking, all four exposure measures were significantly related to total lung asbestos content. The variance explained by these models ranged from 23% (the duration model) to 32% (the concentration model).
  • Stepwise regression kept only exposure concentration and age at necropsy or pneumonectomy, with age showing a negative relation. This two-term model explained 32% of the variance.
  • Smoking did not significantly contribute to predicting lung asbestos content.
  • Smokers made up 100% (12/12) of men with an asbestos-exposed job history and 73% (22/30) of those without.
  • Regressions for chrysotile alone showed no significant relation between lung chrysotile content and chrysotile exposure history.
  • Crocidolite fibres were narrower in exposed men than in unexposed men (median 0.18 versus 0.28 micrometres, p less than 0.05).
• The authors' conclusion: The authors concluded that exposure concentration was the most important predictor of lung asbestos content in this study. They wrote that the findings lend support to using carefully determined job-history exposure indices in occupational epidemiological studies.
• Limitations the authors state:
  • Hospital patients with cancer may not represent the general population of workers.
  • Necropsy selection bias.
  • Subjects were selected for specific exposure histories, which the authors called the largest bias.
  • The study had few subjects.
  • The smoking results need caution, because one subgroup was chosen as smokers without occupational exposure.
  • Lung analysis did not identify every man with any asbestos exposure, especially those with low-level exposure.
  • The exposure measures were surrogates based on expert judgment, not historical measurements.
  • Lung fibre methods are not standardised, so the results are hard to compare with other laboratories.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Amosite, Crocidolite.

Medical terms in this study, explained in our Lexicon: Case-Control Study, Transmission Electron Microscopy (TEM), Paraffin Block, Amosite, Amphibole Group, Crocidolite, Occupational Exposure.

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