Mortality from lung cancer and respiratory disease among pottery workers exposed to silica and talc

Our plain-English summary of Mortality from lung cancer and respiratory disease among pottery workers exposed to silica and talc, by T.L. Thomas, P.A. Stewart (American Journal of Epidemiology, 1987).

The study

• Authors: T.L. Thomas, P.A. Stewart
• Journal: American Journal of Epidemiology
• Published: 1987;125(1):35-43
• Cited by: 42 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. 001004).

Abstract

A cohort mortality study of white men employed for at least one year between 1939 and 1966 at three plants of a single United States company was conducted to evaluate the risk of lung cancer and nonmalignant respiratory disease among workers exposed to silica dust and nonfibrous (nonasbestiform) talc in the manufacture of ceramic plumbing fixtures. Follow-up of 2,055 men through January 1, 1981, indicated a substantial excess of nonmalignant respiratory disease among those with high levels of exposure to silica dust (standardized mortality ratio = 2.26). The risk of nonmalignant respiratory disease rose with the number of years exposed, was not further enhanced by talc exposure, and appeared to be appreciably lower among those exposed in more recent time periods. For lung cancer, men exposed to high levels of silica dust with no talc exposure had a nonsignificant standardized mortality ratio of 1.37. However, those exposed to nonfibrous talc in addition to high levels of silica had a significant 2.5-fold excess risk of lung cancer. Among this group, the lung cancer standardized mortality ratio rose with increasing years of talc exposure to 3.64 among those exposed for 15 or more years. Although the role of silica as a cofactor cannot be ruled out, these data suggest that nonfibrous talc exposure is associated with excess lung cancer risk.

In plain English

The authors studied deaths among 2,055 white men employed at least one year between 1939 and 1966 at three U.S. plants of one company making ceramic plumbing fixtures, followed to 1981. The main exposure was silica dust; from about 1955 casters dusted molds with nonfibrous Montana steatite talc, which appeared to contain no asbestiform fibers, and some glazes contained tremolitic (fibrous) talc until 1976. Without dust measurements, an industrial hygienist classified jobs by exposure. Men with high silica exposure had 54 nonmalignant respiratory disease deaths against 23.9 expected (standardized mortality ratio, SMR, 2.26, significant). For lung cancer, high-silica workers without talc had a nonsignificant SMR of 1.37, while those also exposed to nonfibrous talc had a significant SMR of 2.54, rising to 3.64 with 15 or more years of talc exposure. One death certificate listed malignant mesothelioma, for a maintenance mechanic who never held a production job. Smoking data were unavailable. The authors concluded the data suggest nonfibrous talc exposure is associated with excess lung cancer risk, though silica's role as a cofactor or promoting agent cannot be ruled out.

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 deaths with deaths expected from U.S. white male death rates (standardized mortality ratios)
• Who was studied: 2,055 white men employed for at least one year between January 1, 1939 and January 1, 1966 at three U.S. plants of one company making ceramic plumbing fixtures (midwestern, east coast and northeastern U.S.), followed through January 1, 1981. Nonwhite men (55) and women (169) were excluded from the analyses because of their small numbers.
• Exposure: Quartz (crystalline free silica) dust from clays, feldspar and flint. Nonfibrous (nonasbestiform) Montana steatite talc was used to dust molds in the cast shop from about 1955. Tremolitic (fibrous) talc was used in some glazes until 1976. There were no dust measurements; an industrial hygienist classified each job as no, low or high silica, and high-silica jobs as no talc, nonfibrous talc or fibrous talc.
• Main results:
  • Men with high silica exposure had a significant excess of nonmalignant respiratory disease deaths: 54 observed, 23.9 expected, SMR 2.26.
  • Nonmalignant respiratory disease risk rose with years of silica exposure, was not further increased by talc exposure, and was lower in more recent periods. By year of hire: before 1940 SMR 2.24 (significant), 1940-1949 SMR 0.78, 1950-1965 SMR 0.58.
  • Lung cancer among high-silica workers with no talc exposure: 18 observed, 13.2 expected, SMR 1.37, not statistically significant. Among high-silica workers also exposed to nonfibrous talc: 21 observed, 8.3 expected, SMR 2.54, significant. Among those exposed to fibrous talc: 5 observed, 2.9 expected, SMR 1.74.
  • All 21 lung cancer deaths in the nonfibrous talc group had worked as casters (expected 7.7, SMR 2.73, p less than 0.05). Casters who presumably had no talc exposure had 10 lung cancer deaths against 7.1 expected (SMR 1.46), not statistically significant.
  • Lung cancer SMR rose with years of nonfibrous talc exposure: less than 5 years 0.95 (2 observed, 2.1 expected), 5-14 years 2.76 (11 observed, 4.0 expected), 15 or more years 3.64 (8 observed, 2.2 expected).
  • Lung cancer mortality did not increase with duration of silica exposure.
  • None of the lung cancer deaths were attributed to malignant mesothelioma. Only one death certificate listed malignant mesothelioma (site not specified) as the underlying cause of death. That man had worked as a maintenance mechanic and had never held a production job.
• The authors' conclusion: The authors concluded that their data suggest nonfibrous talc exposure is associated with (related to) excess lung cancer risk, although the role of silica as a cofactor or promoting agent cannot be ruled out. They also stated that the decline in nonmalignant respiratory disease risk over time was probably due to better dust control.
• Limitations the authors state:
  • There was no information on smoking, so possible confounding of lung cancer by tobacco use could not be examined directly. The authors noted that other smoking-related causes of death were not in excess.
  • No current or historical measurements of airborne silica or talc dust were available; exposure was classified from knowledge of processes and job duties.
  • The excess lung cancer occurred mainly among casters who were exposed to nonfibrous talc and silica at the same time, so the roles of the two agents cannot be entirely separated.
  • For men hired in 1950 or later, the time since exposure was probably too short to show whether a significant lung cancer excess occurred.

Topics

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

Medical terms in this study, explained in our Lexicon: Lung Cancer, Talc, Non-Asbestiform, standardized mortality ratio (SMR).

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• Re: "Dose-response associations of silica with nonmalignant respiratory disease and lung cancer mortality in the diatomaceous earth industry" — M.J. Mirliss (1998)
• Respiratory symptoms and functional status in workers exposed to silica, asbestos, and coal mine dusts — X.R. Wang, D.C. Christiani (2000)
• Respiratory impairments due to dust exposure: a comparative study among workers exposed to silica, asbestos, and coalmine dust — X. Wang, E. Yano, et al. (1997)
• The pulmonary toxicity of talc and granite dust as estimated from an in vivo hamster bioassay — B.D. Beck, H.A. Feldman, et al. (1987)

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