Age and sex differences in malignant mesothelioma after residential exposure to blue asbestos (crocidolite)

Our plain-English summary of Age and sex differences in malignant mesothelioma after residential exposure to blue asbestos (crocidolite), by A. Reid, G. Berry, N. de Klerk, et al (Chest, 2007).

The study

• Authors: A. Reid, G. Berry, N. de Klerk, J. Hansen, J. Heyworth, G. Ambrosini, L. Fritschi, N. Olsen, E. Merler, A.W. Musk
• Journal: Chest
• Published: 2007;131(2):376-82
• Cited by: 68 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Blue asbestos was mined and milled at Wittenoom, Western Australia, from 1943 until 1966. Various public records were used to establish a cohort of residents of the nearby township. Mine tailings were distributed throughout the town.

Aims: To report the incident number of malignant mesotheliomas that have occurred in residents of the town who did not work at the mine or mill; and to determine if female subjects are more susceptible to asbestos exposure than male subjects, and if children are more susceptible than adults.

Subjects And Methods: A total of 4,768 residents of the town of Wittenoom have been followed up in cancer and death registries.

Results: There were 67 cases of mesothelioma, and 64 deaths with mesothelioma to the end of 2002. The mortality rate with mesothelioma increased with increasing residence duration, time since first exposure, and estimated cumulative exposure. The mesothelioma mortality rate was consistently lower for female subjects when compared with male subjects, but the dose-response curve was steeper for female subjects. The rate was lower in those first exposed as children compared with those first exposed at > or = 15 years of age. The dose-response slope for asbestos exposure and mortality from mesothelioma was not different between those who were first exposed as children than those who were first exposed at > or = 15 years of age.

Conclusions: Former residents of a crocidolite mining town have a high rate of mesothelioma. The rate is higher in male subjects and those > or = 15 years of age at first exposure, but women have a steeper dose-response curve.

In plain English

This cohort study followed 4,768 former residents (2,608 female, 2,160 male) of Wittenoom, Western Australia, near a crocidolite (blue asbestos) mine and mill. All had lived there for at least a month and had not been exposed to asbestos at work. Residents were assigned estimated cumulative exposures from airborne fiber surveys and residence time; exposure was unknown for some. By the end of 2002 there were 67 cases of mesothelioma (62 pleural, 3 peritoneal, 2 site not stated), and 64 of these people had died. Mesothelioma death rates rose with longer residence, higher estimated exposure and more time since first exposure. After adjustment for exposure and age at first residence, men had a higher rate than women (hazard ratio 2.37, 95% CI 1.39 to 4.05). A separate analysis found the rate rose more steeply with exposure in women. Those first exposed at 15 or older had a higher mesothelioma death rate than those first exposed as children (relative risk 2.4, 95% CI 1.4 to 4.2), though the authors noted children's lifetime risk may not be lower. Exposure estimates, the authors noted, came from environmental measurements rather than individual data.

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: Cohort study of former town residents, followed through Australian cancer, mesothelioma and death registries
• Who was studied: 4,768 former residents of Wittenoom, Western Australia (2,608 female, 2,160 male). They had lived in the town at least 1 month and had no occupational asbestos exposure. They included spouses and children of mine and mill workers, government employees and others.
• Exposure: Residential (non-occupational) exposure to crocidolite, including mine tailings spread through the town. Residents were assigned 1.0 f/mL from 1943 to 1957 and 0.5 f/mL from 1958 to 1966, interpolated down to 0.01 f/mL by 1992. Cumulative figures were multiplied by 4.2 to represent round-the-clock residential exposure. Mean cumulative exposure was 5.5 fibers/mL-years.
• Main results:
  • By the end of 2002 there were 67 known mesothelioma cases among former residents: 36 male, 31 female.
  • Of the 67 cases, 62 were pleural, 3 peritoneal and 2 of unstated site.
  • 64 of the people with mesothelioma had died.
  • Mesothelioma mortality increased with length of residence, cumulative exposure and time since first exposure.
  • Cumulative exposure was unknown for some residents. Table 3 lists 8 mesothelioma deaths (2 female, 6 male) in the unknown-exposure category.
  • Mesothelioma death rates per 100,000 person-years, counted from 20 years after first exposure, were 57 for female residents (25 deaths) and 91 for male residents (29 deaths). The rate for all residents was 71 (54 deaths).
  • In the base model adjusted for cumulative exposure and age at first residence, men had a higher mesothelioma rate than women (hazard ratio 2.37, 95% CI 1.39 to 4.05).
  • In a separate model that included a sex-by-exposure interaction, the rise in mesothelioma risk with exposure was steeper for women than for men. The interaction hazard ratio was 0.63 (95% CI 0.40 to 0.99), p = 0.047. In this model the male effect declines with increasing exposure.
  • Residents first exposed at 15 or older had a relative risk of 2.4 (95% CI 1.4 to 4.2) for mesothelioma mortality compared with those first exposed as children. Mesothelioma death rates were 112 versus 47 per 100,000 person-years.
  • The dose-response slope did not differ between those first exposed as children and those first exposed at 15 or older.
  • 27 of the 31 female cases had lived with an asbestos miner or miller, and this was significantly associated with mesothelioma mortality in women. The association did not hold for men (13 male cases had lived with an ABA worker).
  • The shortest time from first exposure to diagnosis was 24 years in women and 19 years in men.
  • No cases were diagnosed in children; the youngest age at diagnosis was 26 years.
• The authors' conclusion: The authors concluded that Wittenoom was an area of high environmental crocidolite exposure, resulting in a high mesothelioma mortality rate. The rate was higher in men and in those first exposed at 15 or older, although women had a steeper dose-response slope.
• Limitations the authors state:
  • Exposures were estimated from interpolated environmental measurements, not individual data.
  • Exposure may have been measured less accurately in men, who may have had asbestos exposure in other jobs before or after living at Wittenoom.
  • People first exposed as children have more years left to live, so their lifetime risk may not be lower.

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: Malignant Mesothelioma, Crocidolite, Wittenoom, Tailings, Asbestos Exposure, Mesothelioma, Cumulative Exposure, Dose-response relationship.

Related studies

• Aerodigestive and gastrointestinal tract cancers and exposure to crocidolite (blue asbestos): incidence and mortality among former crocidolite workers — A. Reid, G. Ambrosini, et al. (2004)
• Environmental exposure to crocidolite and mesothelioma: exposure-response relationships — J. Hansen, N.H. de Klerk, et al. (1998)
• Mortality of former crocidolite (blue asbestos) miners and millers at Wittenoom — A.W. Musk, N.H. de Klerk, et al. (2008)
• Predicted mortality from malignant mesothelioma among women exposed to blue asbestos at Wittenoom, Western Australia — A. Reid, G. Berry, et al. (2009)
• Retinol supplementation and mesothelioma incidence in workers earlier exposed to blue asbestos (Crocidolite) at Wittenoom, Western Australia — H.S. Alfonso, A. Reid, et al. (2010)
• Cancer incidence among women and girls environmentally and occupationally exposed to blue asbestos at Wittenoom, Western Australia — A. Reid, J. Heyworth, et al. (2008)

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