Influence of dose and fiber type on respiratory malignancy risk in asbestos cement manufacturing

Our plain-English summary of Influence of dose and fiber type on respiratory malignancy risk in asbestos cement manufacturing, by H. Weill, J. Hughes, C. Waggenspack (The American Review of Respiratory Disease, 1979).

The study

• Authors: H. Weill, J. Hughes, C. Waggenspack
• Journal: The American Review of Respiratory Disease
• Published: 1979;120(2):345-54
• Cited by: 64 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. 001064).

Abstract

This investigation provides information concerning the risk or respiratory malignancy in relation to duration, degree, and fiber type of exposure to asbestos in a manufacturing cohort of 5,645 with long-term follow-up. Excess mortality for this cause was found in groups with moderate and high cumulative exposure (standard mortality ratios of 290 and 226). Analysis of the influence of components of total exposure dose (duration, average concentration) revealed no detectable excess risk in persons employed for less than 2 years or with low-degree average exposure. Exposure to corcidolite (blue) fiber in addition to the predominantly used chrysotile in pipe making appeared to be associated with higher risk than was exposure to chrysotile alone.

In plain English

This retrospective cohort mortality study followed 5,645 men who had worked at least one month before 1970 at two asbestos cement building-materials plants in New Orleans and had at least 20 years of follow-up. Deaths were identified through Social Security records up to the end of 1974. The asbestos used was mainly chrysotile; crocidolite was also used in one plant's pipe department. Exposure was estimated as cumulative total dust, measured in millions of particles per cubic foot-years. Deaths from respiratory cancer were not raised in the three lowest exposure groups. They were raised in the two highest groups, with standard mortality ratios of 290 and 226 (100 means the expected number). Men employed for at least 10 years had a ratio of 2.15 of observed to expected respiratory cancer deaths. No other cause of death was in excess. Workers exposed to crocidolite as well as chrysotile appeared to be at higher risk than chrysotile-only workers, especially those exposed intermittently in maintenance jobs. The authors concluded that any excess risk at low exposure is small. They had no information on smoking and noted that deaths may have been undercounted.

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: Retrospective cohort mortality study comparing observed with expected deaths (man-years method), with an additional matched case-control analysis of lung cancer cases within the cohort
• Who was studied: 5,645 men with at least 20 years of follow-up from first employment, out of all persons employed for at least one continuous month before January 1, 1970 at two asbestos cement building materials plants in New Orleans, Louisiana. The 312 women were excluded. Deaths were traced through the Social Security Administration to December 31, 1974; 601 men (11 per cent) were identified as dead.
• Exposure: Asbestos cement manufacturing (shingles, corrugated sheet, roofing, pipe, asphalt flooring). The predominant fiber was chrysotile. Crocidolite was used in the pipe department of the second plant, where it made up 3 per cent of the product. Amosite (1 per cent of products) was used in the first plant. Silica was used in both plants. Exposure was estimated from midget impinger total dust sampling as cumulative dust in millions of particles per cubic foot-years (mppcf-yr), counting only exposure accumulated within 20 years of first employment.
• Main results:
  • Standard mortality ratios for respiratory system cancer across the five cumulative dust categories (under 10, 11 to 50, 51 to 100, 101 to 200, and over 200 mppcf-yr) were 77, 70, 26, 290 and 226. Only the two highest categories were statistically significant (P less than 0.01; 9 observed versus 3.1 expected, and 14 observed versus 6.2 expected).
  • Standard mortality ratios for all causes combined were generally low across the five exposure categories: 60, 64, 75, 80 and 94.
  • No excess mortality was found in any exposure group for any cause other than respiratory cancer.
  • When exposure was split into duration of employment and average dust concentration, respiratory cancer risk generally rose with duration and with average concentration, each depending on the other. Men employed for at least 10 years had an observed-to-expected ratio of 2.15 for respiratory cancer (20 observed versus 9.3 expected). Men employed under 2 years had a standard mortality ratio of 74 (24 observed versus 32.4 expected).
  • In the fiber type comparison (amosite-exposed workers excluded), the respiratory cancer standard mortality ratios were as follows. Chrysotile-only workers (n = 4,201): 77 (30 observed versus 38.8 expected). Workers with intermittent crocidolite exposure through occasional maintenance work in the pipe plant (n = 235): 304 (7 versus 2.3; p less than 0.05). Workers with steady employment in the pipe plant (n = 1,004): 155 (9 versus 5.8). The authors said the addition of crocidolite to chrysotile appeared to enhance risk, particularly for the intermittently exposed maintenance workers.
  • In the matched case-control analysis (47 lung cancer cases, 188 controls), mean cumulative dust exposure was 164.1 mppcf-yr for cases and 77.8 for controls. Odds ratios relative to the lowest category were 2.85 and 2.75 in the two highest exposure categories (p less than 0.05).
  • In the highest exposure group (over 100 mppcf-yr), respiratory cancer standard mortality ratios rose with time since first exposure for up to 30 years or more. The ratios were 233, 333 and 308 for 25 to 30, 30 to 35, and over 35 years. The two lower exposure groups showed no clear pattern.
  • Two pleural mesotheliomas were diagnosed in the total study population. One man worked 10 months with known exposure only to chrysotile. The other worked 14 years, mostly in the pipe plant, with exposure to chrysotile and crocidolite. Both died 18 and 19 years after first employment, so neither was included in the main analysis.
• The authors' conclusion: The authors concluded that excess respiratory cancer risk was found with moderate and heavy exposure but not in the lowest exposure categories. They said this is not necessarily incompatible with a linear dose-response at low doses, because epidemiologic methods are relatively insensitive to slight increases in risk, but that it does indicate any excess risk at low exposure is small. They also concluded that workers exposed to crocidolite in addition to chrysotile appear to be at greater risk of respiratory cancer.
• Limitations the authors state:
  • Men not recorded as dead by Social Security were assumed to be alive, which may underestimate mortality. Twenty-five per cent of the population had no Social Security transaction in 1974 and could not be traced further.
  • There was no information on smoking habits, so the excess risk in nonsmokers could not be determined.
  • Exposure was reconstructed as total particulates, which correlate poorly with fiber counts. The results therefore cannot be used directly to set an occupational standard expressed in fibers.
  • Total fiber exposure might be systematically underestimated when crocidolite is present, so the higher risk could reflect a higher true dose.
  • The authors considered it possible that mesothelioma was underdiagnosed in this population.
  • Personnel records for the first plant were poorly maintained before 1942.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer.

Medical terms in this study, explained in our Lexicon: Asbestos-Cement, Cumulative Exposure, Chrysotile.

Related studies

• Biological effects: asbestos-cement manufacturing — H. Weill (1994)
• Type of asbestos and respiratory cancer in the asbestos industry — P.E. Enterline, V. Henderson (1973)
• Absence of radiographic asbestosis and the risk of lung cancer among asbestos-cement workers: Extended follow-up of a cohort — M.M. Finkelstein (2010)
• Exposure to cement dust, related occupational groups and laryngeal cancer risk: results of a population based case-control study — A. Dietz, H. Ramroth, et al. (2004)
• Dose-response associations of silica with nonmalignant respiratory disease and lung cancer mortality in the diatomaceous earth industry — H. Checkoway, N.J. Heyer, et al. (1997)
• Workplace risk factors for cancer in the German rubber industry: Part 1. Mortality from respiratory cancers — S.K. Weiland, K. Straif, et al. (1998)

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