Asbestos exposure--quantitative assessment of risk

Our plain-English summary of Asbestos exposure--quantitative assessment of risk, by J.M. Hughes, H. Weill (The American Review of Respiratory Disease, 1986).

The study

• Authors: J.M. Hughes, H. Weill
• Journal: The American Review of Respiratory Disease
• Published: 1986;133(1):5-13
• Type of article: Review
• Cited by: 91 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. 000403).

Abstract

Methods for deriving quantitative estimates of asbestos-associated health risks are reviewed and their numerous assumptions and uncertainties described. These methods involve extrapolation of risks observed at past relatively high asbestos concentration levels down to usually much lower concentration levels of interest today--in some cases, orders of magnitude lower. These models are used to calculate estimates of the potential risk to workers manufacturing asbestos products and to students enrolled in schools containing asbestos products. The potential risk to workers exposed for 40 yr to 0.5 fibers per milliliter (f/ml) of mixed asbestos fiber type (a permissible workplace exposure limit under consideration by the Occupational Safety and Health Administration (OSHA) ) are estimated as 82 lifetime excess cancers per 10,000 exposed. The risk to students exposed to an average asbestos concentration of 0.001 f/ml of mixed asbestos fiber types for an average enrollment period of 6 school years is estimated as 5 lifetime excess cancers per one million exposed. If the school exposure is to chrysotile asbestos only, then the estimated risk is 1.5 lifetime excess cancers per million. Risks from other causes are presented for comparison; e.g., annual rates (per million) of 10 deaths from high school football, 14 from bicycling (10-14 yr of age), 5 to 20 for whooping cough vaccination. Decisions concerning asbestos products require participation of all parties involved and should only be made after a scientifically defensible estimate of the associated risk has been obtained. In many cases to date, such decisions have been made without adequate consideration of the level of risk or the cost-effectiveness of attempts to lower the potential risk.

In plain English

This review described methods for estimating cancer risk from asbestos, with their assumptions and uncertainties. It then applied them to two situations: asbestos cement manufacturing workers and students in schools containing asbestos products. The figures were model extrapolations from past, more heavily exposed worker groups, not direct observations. For 10,000 male workers exposed from age 25 to 0.5 fibers per milliliter (f/ml) of mixed fiber types, the models estimated 53 lifetime excess lung cancers and mesotheliomas from 20 years of exposure and 82 from 40 years. For chrysotile only, the estimates were 31 and 57. For one million students exposed for 6 school years to 0.001 f/ml, the estimate was 5 lifetime excess cancers for mixed fibers and 1.5 for chrysotile only, and these figures tripled at 0.003 f/ml. Pooling published studies, mesotheliomas equalled 12% of excess lung cancers in chrysotile-exposed groups, 66% in mixed-fiber groups and 165% in crocidolite-exposed groups. The authors noted that most mesothelioma studies used lacked adequate exposure information. They concluded that decisions about asbestos products should involve all parties and follow a scientifically defensible risk estimate.

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: Review and quantitative risk assessment: lung cancer and mesothelioma risk models built from previously published cohort studies were used to estimate risks for hypothetical exposed groups, and estimates from governmental advisory groups were compared
• Who was studied: Hypothetical modeled groups: a cohort of 10,000 male asbestos cement manufacturing workers starting at age 25, and one million schoolchildren enrolled on average for 6 school years from a mean age of 9 in U.S. schools containing asbestos products
• Exposure: Workers: 0.5 f/ml (a limit OSHA was considering) for 20 or 40 years, mixed fiber types or chrysotile only. Students: an assumed average of 0.001 f/ml (upper estimate 0.003 f/ml) of mixed fibers or chrysotile only, for 6 school years
• Main results:
  • In published studies pooled by fiber type, mesothelioma deaths were 12% of excess lung cancers in chrysotile-exposed populations, 165% in crocidolite-exposed populations, and 66% in mixed-fiber populations. The authors read this as suggesting chrysotile poses about one fifth the mesothelioma risk of mixed fiber exposure.
  • Lifetime estimates for workers exposed for 20 years to 0.5 f/ml (per 10,000): 25.5 (or 26) attributable lung cancers, in addition to 510 background cases, plus 27 mesotheliomas. This gave 53 total cancers with mixed fibers. With chrysotile only, the total was 31.
  • Lifetime estimates for workers exposed for 40 years to 0.5 f/ml of mixed fibers: 82 excess cancers per 10,000 (range 42 to 164), made up of 51 lung cancers and 31 mesotheliomas. With chrysotile only, the total was 57 (29 to 114).
  • Students exposed to 0.001 f/ml of mixed fibers for 6 school years: 5.0 lifetime excess cancers per million (range 2.5 to 10.0), made up of 0.6 lung cancers and 4.4 mesotheliomas.
  • Students exposed to chrysotile only at 0.001 f/ml: 1.5 lifetime excess cancers per million (range 0.7 to 3.0).
  • At an assumed 0.003 f/ml in schools, the estimates tripled: 15.1 per million for mixed fibers and 4.5 per million for chrysotile only.
  • For comparison, about 32,000 of one million students would be expected to die of lung cancer from causes not related to school asbestos. A birth cohort of one million was estimated to have 140 lifetime background mesothelioma cases.
  • The upper school estimate (mixed fibers at 0.003 f/ml) equalled about 0.25 deaths per million per year. The authors compared this with other annual U.S. death rates per million, such as 10 from high school football and 15 from bicycling at ages 10 to 14.
  • When estimates from several advisory groups (CPSC, EPA, HSE, NRC, OSHA) were adjusted to common exposure assumptions, the authors found reasonably good agreement. Important variability remained, mainly from differing model parameter values.
• The authors' conclusion: The authors concluded that decisions about asbestos products should involve all parties and be made only after a scientifically defensible risk estimate. They stated that in many cases such decisions had been made without adequate consideration of the level of risk or of cost-effectiveness.
• Limitations the authors state:
  • Most of the 7 studies used to estimate the mesothelioma model parameter did not meet minimal criteria for availability and validation of exposure information.
  • The lung cancer model's assumptions may lead to an overestimate of risk.
  • For schools, the lung cancer slope may be an overestimate, because fibers released from finished products may be shorter and coarser than those in manufacturing.
  • Limited evidence suggests mesothelioma risk rises less steeply many years after first exposure than the model assumes. If so, the model could substantially overestimate lifetime mesothelioma risk.

Topics

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

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, OSHA, Chrysotile.

Related studies

• Quantitative risk assessment of environmental hazards — S.L. Brown (1985)
• Time-related factors in quantitative risk assessment — K.S. Crump, B.C. Allen, et al. (1987)
• Pleural mesothelioma and occupational and non-occupational asbestos exposure: a case-control study with quantitative risk assessment — D. Ferrante, D. Mirabelli, et al. (2016)
• A trial on the quantitative risk assessment of man-made mineral fibers by the rat intraperitoneal administration assay using the JFM standard fibrous samples — S. Adachi, K. Kawamura, et al. (2001)
• Response to: 'Pleural mesothelioma and occupational and non-occupational asbestos exposure: a case-control study with quantitative risk assessment' by Ferrante et al — G.M. Marsh, S.M. Benson (2017)
• Response to: Pleural mesothelioma, and occupational and non-occupational asbestos exposure: a case-control study with quantitative risk assessment — P. Boffetta (2016)

Browse more research in The American Review of Respiratory Disease, or return to medical research.