Mesothelioma: cases associated with non-occupational and low dose exposures

Our plain-English summary of Mesothelioma: cases associated with non-occupational and low dose exposures, by G. Hillerdal (Occupational and Environmental Medicine, 1999).

The study

• Author: G. Hillerdal
• Journal: Occupational and Environmental Medicine
• Published: 1999;56(8):505-13
• Type of article: Review
• Cited by: 169 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: To estimate the importance of low dose exposure to asbestos on the risk of mesothelioma.

Methods: A review of the literature.

Results And Conclusions: There is no evidence of a threshold level below which there is no risk of mesothelioma. Low level exposure more often than not contains peak concentrations which can be very high for short periods. There might exist a background level of mesothelioma occurring in the absence of exposure ot asbestos, but there is no proof of this and this "natural level" is probably much lower than the 1-2/million/year which has been often cited.

In plain English

This was a single-author literature review of how low dose and non-occupational asbestos exposure affects mesothelioma risk. It drew on reports of exposure from workers' clothes, homes near mines and factories, consumer goods, city air, drinking water, buildings, and local mineral deposits such as tremolite whitewash. The author found no proof of a threshold below which asbestos cannot cause mesothelioma. So-called low or non-occupational exposure often included brief high peaks. Cited studies reported peaks above 100 fibres/ml from brushing clothes, and up to 15 fibres/ml from deteriorating asbestos in buildings, against below 0.001 fibres/ml when undisturbed. If mesothelioma occurs at all without asbestos or erionite fibres, the author judged this background rate probably much below 1 case per million people per year, lower than the often-cited 1 to 2 per million. From the non-occupational studies, the author concluded that occasional high level exposures were probably most important, more than hardly measurable background concentrations. The author added that patients with normal-range lung fibre levels could not be shown to be background cases, because no truly unexposed group exists for comparison.

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: Literature review (no new data collected)
• Who was studied: Published studies and case reports on mesothelioma, including people with occupational and non-occupational exposure (household contacts, residents near mines and factories, building occupants, villagers near local mineral deposits). No new population was studied.
• Exposure: Low dose and non-occupational asbestos exposure: domestic (from workers' clothes), residence near mines, factories and dockyards, consumer goods, urban air, drinking water, asbestos in place in buildings, and local deposits (tremolite, anthophyllite, amosite, crocidolite). The non-asbestos fibre erionite was also discussed.
• Main results:
  • The author found no proof of a threshold exposure below which asbestos fibres cannot cause mesothelioma.
  • In cited reports on domestic exposure, brushing clothes could give peaks of more than 100 fibres/ml. The author stated that domestic exposure is not low exposure.
  • For asbestos in place in buildings, air concentrations were zero or below 0.001 fibres/ml when the asbestos was undisturbed, but could rise to 15 fibres/ml once it deteriorated. Mean concentrations were estimated at 0.003 fibres/ml in US schools and 0.006 in federal buildings.
  • The author considered it possible, but not proven, that mesothelioma occurs in the complete absence of asbestos or erionite fibres. If so, the author judged this background level must be very low, probably much less than 1 case per million people per year. This is lower than the 1 to 2 per million per year estimated by McDonald and McDonald.
  • From a cited study of Wittenoom, Western Australia (a crocidolite mining town), it was estimated that 1.1% of child residents and 1.9% of female residents have died or will die from mesothelioma, compared with 6% of the workforce.
  • In a cited German study of 324 malignant mesotheliomas (46 lung samples available), a lung fibre concentration of 100 000 to 200 000 fibres/g was associated with a fivefold increased risk of mesothelioma, which was statistically significant.
• The authors' conclusion: Based on the studies of non-occupational exposures, the author concluded that occasional high level exposure situations are probably the most important, and that the cumulative risk from hardly measurable background concentrations is probably minor. The author also concluded that patients with lung fibre levels in the normal range cannot be dismissed as background cases.
• Limitations the authors state:
  • Whether mesotheliomas in people with background-range exposure are background cases cannot be proven, because no truly non-exposed group exists for comparison.
  • Cases reported as having no exposure might actually have had exposure that the patients did not know about or had forgotten.
  • National cancer registries likely contain both overdiagnosis and underdiagnosis of mesothelioma.
  • The true background figure can only be guessed.

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelioma.

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