Environmental exposure to crocidolite and mesothelioma: exposure-response relationships

Our plain-English summary of Environmental exposure to crocidolite and mesothelioma: exposure-response relationships, by J. Hansen, N.H. de Klerk, A.W. Musk, et al (American Journal of Respiratory and Critical Care Medicine, 1998).

The study

• Authors: J. Hansen, N.H. de Klerk, A.W. Musk, M.S. Hobbs
• Journal: American Journal of Respiratory and Critical Care Medicine
• Published: 1998;157(1):69-75
• Cited by: 120 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

This study aimed to estimate exposure-response relationships for mesothelioma and environmental exposure to crocidolite. All 4,659 former residents of Wittenoom, Western Australia (WA) who lived there between 1943 and 1993 for at least 1 mo and were not directly employed in the crocidolite industry, were followed-up through the WA death, cancer and mesothelioma registries, electoral rolls, and telephone books. In 1992, all subjects who should be traced were sent a questionnaire. Exposure levels were estimated from results of periodic environmental surveys and duration of residence. Incidence rates were standardized to the World Population and Cox Regression was used to estimate the effects of exposure on incidence. To the end of 1993, 27 cases of mesothelioma were diagnosed. Mesothelioma cases stayed longer at Wittenoom, had a higher average intensity of exposure, and a higher cumulative exposure to crocidolite than control subjects. The standardized incidence of mesothelioma was 260 per million person-years, and was similar for males and females. The rate increased significantly with time from first exposure, duration of exposure and cumulative exposure. At these levels of crocidolite exposure, there is a significantly increased risk of mesothelioma, which is dose-dependent.

In plain English

This cohort study followed 4,659 former residents of Wittenoom, Western Australia, who lived there at least one month between 1943 and 1993 and were not directly employed mining or milling crocidolite. A further 151 who reported other occupational crocidolite exposure there were excluded. Exposure was estimated from environmental surveys and length of residence. By the end of 1993, 27 cases of malignant pleural mesothelioma had been diagnosed, 18 in women and 9 in men. Of these, 24 lived in the same house as a Wittenoom crocidolite worker. Compared with the rest of the cohort, cases had stayed longer (mean 64.8 versus 32.8 months) and had higher estimated cumulative exposure (mean 16.3 versus 5.4 fibers per milliliter years). The standardized incidence among residents aged 15 and over was 260 per million person-years, similar for males and females. Rates rose with time since first exposure, length of stay and cumulative exposure. Estimated intensity of exposure was not significantly associated. Cases arose after as little as 2 months' residence. The authors concluded that at these exposure levels mesothelioma risk was significantly increased and dose-dependent.

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 study of former town residents (environmental exposure), with incidence rates standardized to the World Population and Cox regression analysis
• Who was studied: 4,659 former residents of Wittenoom, Western Australia, who lived there for at least 1 month between 1943 and 1993 and were not directly employed in mining and milling of crocidolite. They included wives and children of Australian Blue Asbestos workers, government employees and others. 151 who indicated occupational crocidolite exposure at Wittenoom were excluded. Follow-up was to December 31, 1993.
• Exposure: Environmental (neighborhood) exposure to crocidolite from the Wittenoom mine and mill. Residents were assigned 1.0 f/ml from 1943 to 1957 and 0.5 f/ml from 1958 to 1966. After that, exposure was interpolated from hygiene surveys, from 0.5 f/ml in 1966 to 0.010 f/ml in 1992. Intensity was combined with duration of residence to give cumulative exposure in fibers per milliliter years (f/mly), adjusted by a factor of 4.2 for round-the-clock exposure.
• Main results:
  • To the end of 1993, 27 histologically confirmed cases of malignant pleural mesothelioma were diagnosed in the cohort (excluding those with occupational exposure).
  • Of the cases, 18 were female and 9 were male. Twelve were wives, 11 were children and one was a brother of men who worked with crocidolite at Wittenoom.
  • Time from first residence to diagnosis in cases ranged from 20 to 45 years (median 35.9 years).
  • Compared with the rest of the cohort, mesothelioma cases stayed longer at Wittenoom (mean 64.8 versus 32.8 months), had higher estimated intensity of exposure (mean 0.8 versus 0.5 f/ml) and had higher cumulative exposure (mean 16.3 versus 5.4 f/mly). All differences had p less than 0.001.
  • With data censored at date of loss to follow-up, the standardized incidence of mesothelioma in people aged 15 and over was 260 per million person-years. It was 236 for males and 255 for females.
  • Incidence rose with time since first exposure: 207 per million person-years at 20 to 29 years, 1,073 at 30 to 39 years, and 1,649 at 40 or more years.
  • Over all times since first exposure, incidence by length of residence was 80 per million person-years for less than 1 year, 181 for 1 to 5 years, and 904 for longer than 5 years.
  • By estimated cumulative exposure, incidence was 106 per million person-years below 7 f/mly, 367 for 7 to 20 f/mly, and 1,953 above 20 f/mly.
  • In Cox regression, both length of stay and estimated cumulative exposure were significantly associated with increased incidence. Estimated intensity of exposure was not. For a stay of 60 or more months versus 1 to 11 months, RR was 6.7 (95% CI 2.0 to 22.2) when censored at date of loss to follow-up, and 6.2 (2.6 to 14.6) when censored at December 31, 1993.
  • For estimated cumulative exposure as a continuous variable, RR was 1.59 per log unit (95% CI 1.09 to 2.33) when censored at date of loss to follow-up, and 1.79 (1.22 to 2.60) when censored at December 31, 1993.
  • Living with an asbestos worker or washing work clothes (domestic exposure) had no significant effect on mesothelioma incidence beyond cumulative neighborhood exposure.
  • Age at first exposure had no significant effect (RR 1.02, 95% CI 0.99 to 1.04). Those first exposed as children under 10 had a lower rate than those first exposed later (RR 0.7, 95% CI 0.3 to 1.5).
  • All-cause mortality was significantly raised when data were censored at the date of loss to follow-up (SMR 1.48, 95% CI 1.34 to 1.64). It was not raised when data were censored at December 31, 1993 (SMR 0.96, 95% CI 0.87 to 1.06).
  • Mesothelioma cases arose with crocidolite exposure durations as short as 2 months.
• The authors' conclusion: The authors concluded that at these levels of environmental crocidolite exposure there was a significantly increased, dose-dependent risk of mesothelioma. They stated that exposure-response relationships were confirmed at far lower levels than in any previous study.
• Limitations the authors state:
  • Estimated intensity of exposure carried large error, which the authors thought weakened the cumulative exposure estimate. They also reported that intensity was measured with much more error than duration of residence.
  • The true incidence was uncertain. The two censoring schemes were treated as upper and lower estimates.
  • Death and disease data had not yet been sought systematically from Australian states other than Western Australia. This could bias the analysis censored at December 31, 1993.
  • The exposure-response relationships covered neighborhood exposure only. The authors noted that domestic exposure levels would be difficult to measure.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Wittenoom, Western Australia

All asbestos mines

Topics

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

Medical terms in this study, explained in our Lexicon: Environmental Exposure, Crocidolite, Mesothelioma, Wittenoom, Incidence, Cumulative Exposure.

Related studies

• Age and sex differences in malignant mesothelioma after residential exposure to blue asbestos (crocidolite) — A. Reid, G. Berry, et al. (2007)
• Mortality of former crocidolite (blue asbestos) miners and millers at Wittenoom — A.W. Musk, N.H. de Klerk, et al. (2008)
• Asbestos related diseases from environmental exposure to crocidolite in Da-yao, China. I. Review of exposure and epidemiological data — S. Luo, X. Liu, et al. (2003)
• Effects of asbestos and smoking on gas diffusion in people exposed to crocidolite — H.S. Alfonso, L. Fritschi, et al. (2005)
• Effects of asbestos and smoking on the levels and rates of change of lung function in a crocidolite exposed cohort in Western Australia — H.S. Alfonso, L. Fritschi, et al. (2004)
• Plasma retinol, carotene and vitamin E concentrations and lung function in a crocidolite-exposed cohort from Wittenoom, Western Australia: a cohort study — H.S. Alfonso, L. Fritschi, et al. (2005)

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