Lung dust analysis in the assessment of past exposure of man-made mineral fibre workers

Our plain-English summary of Lung dust analysis in the assessment of past exposure of man-made mineral fibre workers, by J.C. McDonald, B.W. Case, P.E. Enterline, et al (The Annals of Occupational Hygiene, 1990).

The study

• Authors: J.C. McDonald, B.W. Case, P.E. Enterline, V. Henderson, A.D. McDonald, M. Plourde, P. Sébastien
• Journal: The Annals of Occupational Hygiene
• Published: 1990;34(5):427-41
• Cited by: 43 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

In the cohort of American MMMF workers reported by ENTERLINE et al. [Ann. occup. Hyg. 31, 625-656 (1987)] autopsies were recorded in 652 (13.5%) of 4840 deaths. Lung tissue samples were sought from all pathologists and obtained in 145 (22.2%), together with similar samples from 124 matched referents. Lung fibre counts by phase contrast microscopy were 60% higher (P less than 0.05) in workers than referents. Electron microscopy (ATEM) also showed more fibres of all kinds--MMMF, asbestos and other--but no convincing excess of any one type. Lung samples of only 26% of workers contained any MMMF, almost all siliceous in nature and in low concentration. There were too few cases of lung cancer (19) for any useful conclusion; however, in the plant with the highest lung cancer SMR (200), and a probable mesothelioma, amosite at greater than 1.0 fibres per micrograms (f micrograms-1) was found in four of six workers but in none of their matched referents. Although our findings contribute little to the interpretation of the results obtained by ENTERLINE et al. they indicate the potential value of tissue analyses in monitoring epidemiological studies of MMMF exposure.

In plain English

This study analysed autopsy lung tissue from a U.S. cohort of man-made mineral fibre (MMMF) production and maintenance workers previously reported by Enterline and colleagues. Of 652 deaths with a recorded autopsy, lung samples were obtained for 145 workers; 124 of them also had samples from matched male referents who died of non-cancer causes. After technical problems, 112 pairs were usable for the main analysis. Under a light microscope, workers' lungs held more fibres than referents' (average 0.22 vs 0.13 fibres per microgram of dry lung). Under an electron microscope, MMMF were found in only 29 of 112 workers and 28 referents, almost all of a 'siliceous' type and at low levels. Ten workers and two referents had total asbestos above 1.0 fibre per microgram, a statistically significant difference. In one mineral wool plant, four of six workers had high amosite levels; none of their referents did. The 19 lung cancers were too few for firm conclusions. The authors concluded that the method clearly showed past exposure to other mineral fibres, particularly amphibole asbestos. Smoking histories were unknown.

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: Autopsy lung tissue (lung dust) analysis comparing deceased workers from an existing cohort with matched deceased referents. Selection was of case-control type. Fibres were counted by phase contrast optical microscopy and by analytical transmission electron microscopy.
• Who was studied: Deceased U.S. MMMF production and maintenance workers who died 1950-1979 after at least 1 year of employment between 1940 and 1963 in one of 17 plants. Of 4840 deaths, 652 had a recorded autopsy. Lung tissue was obtained for 145 workers, from 57 hospital pathology departments; 124 of them had matched referents. Referents were male autopsies of similar birth and death years who died of non-malignant causes. After technical exclusions, 112 pairs and 131 workers were analysed. Only 11 workers came from the six mineral wool plants.
• Exposure: Employment in fibrous glass and mineral wool (MMMF) production plants. Lung content was measured for MMMF, mostly 'siliceous' fibres; for asbestos (chrysotile, tremolite, amosite and crocidolite); for talc or anthophyllite, which could not be told apart; and for other fibres.
• Main results:
  • By phase contrast optical microscopy, workers had more lung fibres than referents. The arithmetic mean was 0.22 vs 0.13 total fibres per microgram of dry lung, in 104 workers vs 107 referents (P = 0.01 for the arithmetic mean). The excess was seen in both matched and unmatched analyses.
  • By electron microscopy, MMMF were present in 29 of the 112 workers and 28 of the referents in the paired analysis, almost all siliceous.
  • Siliceous fibres at 0.2 fibres per microgram of dry lung or more were found in 14 workers vs six referents. The authors called this a difference of low significance (P less than 0.1); no difference was seen at other cutoffs.
  • Total asbestos above 1.0 fibre per microgram of dry lung was found in 10 workers vs two referents (P less than 0.05). The excesses of tremolite, amosite, total amphibole and total asbestos were not statistically significant at other cutoffs.
  • Most of the amosite excess was in one mineral wool plant (Plant 17). There, four of six workers examined had high lung amosite content (above 1.0 fibre per microgram) but no MMMF, compared with none of their matched referents. Asbestos cement products were apparently made at this plant, but amosite use was not recorded.
  • Among the 19 workers who died of lung cancer, all from fibrous glass plants, MMMF concentrations exceeded the matched referent's value more often than the reverse (7/19 vs 2/18; P = 0.01). No lung cancer case had more than 0.2 MMMF fibres per microgram. For total asbestos there was no difference.
  • In exploratory logistic regression, workers with lung cancer had an odds ratio of 2.8 (95% CI 0.96-8.23; P = 0.07) for having any MMMF vs none. No term was statistically significant.
  • Electron microscopy MMMF concentrations in the 131 workers' lungs did not correlate significantly with any exposure estimate.
• The authors' conclusion: The authors concluded that the method had some success in assessing past MMMF exposure but was limited by removal of these fibres from the lung. They found it more useful for showing past exposure to other mineral fibres, particularly amphibole asbestos. They said their largely negative lung cancer findings should not be interpreted either way. They recommended that future studies of MMMF carcinogenicity be accompanied by tissue analyses to exclude confounding by asbestos and other mineral fibres.
• Limitations the authors state:
  • The exact nature of the so-called 'siliceous MMMF' was uncertain.
  • Smoking status could not be determined.
  • There were few lung cancer cases (19).
  • The mineral wool subgroup was very small (11 workers).
  • It is unknown to what extent MMMF are cleared from the lung by biological mechanisms.
  • Significance tests were subject to multiple testing bias, and the shape of the data distribution was unknown.
  • Referents may have had MMMF exposure in other industries.
  • The effects of low-temperature ashing on MMMF are not fully known.

Topics

Medical terms in this study, explained in our Lexicon: phase contrast microscopy (PCM), Analytical Transmission Electron Microscopy (ATEM), Lung Cancer, Mesothelioma, Amosite.

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