Extrapolation from occupational studies: a substitute for environmental epidemiology

Our plain-English summary of Extrapolation from occupational studies: a substitute for environmental epidemiology, by P.E. Enterline (Environmental Health Perspectives, 1981).

The study

• Author: P.E. Enterline
• Journal: Environmental Health Perspectives
• Published: 1981;42:39-44
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000735).

Abstract

Extrapolation from occupational data to general environmental exposures gives some interesting results, and these results might be useful in our decision-making process. These results could never be observed by environmental epidemiology and this method probably represents the only way of quantifying the health effects of low-exposure levels. Three linear models for extrapolating to low levels are presented--one from Canadian data, one from American data and one from British data. One or more of these is applied to two recently publicized asbestos exposures; exposures resulting from asbestos heat shields in hair dryers and exposures in public school buildings. Predictions are derived as to the effects of asbestos exposures on cancer mortality. A comparison is made between predictions made on the basis of a linear and nonlinear model.

In plain English

This was a risk-estimation paper, not a new study of people. Using data from Quebec miners and millers, American asbestos products workers (both with several dose levels) and one British point joined to zero, the author drew straight-line lung cancer models and extended them to low doses. Assuming 15 minutes of daily use in an 18 m3 room with specified ventilation, the author estimated that hair dryers with asbestos heat shields added 0.000037 fibers per cc longer than 5 micrometres. For lifelong daily use, living all the time in that room, treated as continuous exposure, the Canadian, American and British models gave 0.24, 0.85 and 1.94 extra lung cancer deaths per million over 70 years. Adding other asbestos-related cancers gave 0.36, 1.27 and 2.91 cancers per million users. In schools, the American linear model gave up to 110 deaths per million for lifetime exposure where asbestos was deteriorating. An alternative curvilinear model gave relatively little response at low levels. The author concluded that the school problem was more important and the hair dryer problem probably was not a problem.

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: Risk-estimation (extrapolation) paper. Linear dose-response models were built from published occupational studies and applied to two low-level exposure scenarios (hair dryers and school buildings), with a comparison to a curvilinear model.
• Who was studied: No new population was studied. The models drew on earlier studies of asbestos miners and millers in Quebec Province (Canada) and of American asbestos products workers, which reported several dose levels. A British worker population contributed a single dose point. The models were applied to hypothetical lifetime users of hand-held hair dryers and to United States school children (60 million children in 107,000 schools).
• Exposure: Airborne asbestos (fiber type not specified). For hair dryers, the author modeled 15 minutes of use each day in an 18 m3 room with 12 air turnovers per day and 50% replacement per turnover. That gave an increment of 0.00074 fibers/cc of all sizes, which was divided by 20 to give 0.000037 fibers/cc longer than 5 micrometres. In schools, levels ranged from ambient air where asbestos was in good condition, to about 500 ng/m3 where it was worn or damaged, to possibly 50,000 ng/m3 where it was abused. Occupational doses were measured as cumulative dose in mppcf-years and converted to fibers/cc-years.
• Main results:
  • NIOSH tests of hand-held hair dryers showed up to 0.034 fibers of all sizes per cubic centimeter in the air stream. The average was about 0.0072 asbestos fibers.
  • The mathematically fitted American regression line was SMR = 100.0 + 0.658 (mppcf-years). The Canadian line was forced through zero. Because the British study supplied only one data point, its line was drawn through zero. Coefficients per fibers/cc-year for 8 hr/day, 5 days/week exposure were 31.2 (Canadian), 109.6 (American) and 250.0 (British).
  • The scenario was lifetime use of a hand-held hair dryer for 15 minutes each day while living all the time in the small room where it was used. Assuming continuous exposure, the estimated incremental lung cancer deaths in 70 years per million exposed were 0.24 (Canadian model), 0.85 (American model) and 1.94 (British model). For 8 hr/day, 5 days/week exposure the figures were 0.06, 0.20 and 0.46.
  • Adding other asbestos-related cancers, assumed to occur at one for every two lung cancers, the lifetime effect of hair dryers was estimated at 0.36, 1.27 and 2.91 cancers per million users under the Canadian, American and British models.
  • If asbestos use in new dryers had stopped without a recall (remaining dryer life about 5 years), the estimates were 0.03, 0.12 and 0.29 cancers per million users.
  • Under the American linear model, lifetime exposure at the level found in some schools with deteriorating asbestos was estimated to produce up to 110 deaths per million exposed.
  • An alternative model assumed a longer time to cancer at lower doses and varied susceptibility. It gave a curvilinear dose-response curve with relatively little response at lower levels.
• The authors' conclusion: The author concluded that the school building problem was more important than the hair dryer problem, and that the hair dryer problem probably was not a problem. The author also stated that extrapolation from occupational data probably represented the only way of quantifying health effects of low exposure levels.
• Limitations the authors state:
  • Extrapolation requires assurance that a dose-response relationship exists and knowledge of its form, including whether there is a threshold.
  • The linear fit was best for the Canadian data and less good for the American data sets, which involved fewer workers.
  • The time-to-tumor assumption in the curvilinear model is supported in animal experiments, but there are few human data to support it.
  • The choice between linear and nonlinear models makes a big difference to the estimates, particularly at lower doses.
  • The school estimates assume a lifetime in school, so actual exposure should be reduced proportionately.

Topics

Medical terms in this study, explained in our Lexicon: Epidemiology, Environmental Exposure, Asbestos Exposure.

Related studies

• The potential impact of epidemiology on the prevention of occupational disease — D.H. Wegman (1992)
• Design and conduct of occupational epidemiology studies: IV. The analysis of case-control data — N. Pearce, H. Checkoway, et al. (1989)
• Epidemiology of environmental and occupational cancer — P. Boffetta (2004)
• Epidemiology: a foundation of environmental decision making — K.C.K. Deener, J.D. Sacks, et al. (2018)
• Missing records in occupational disease epidemiology — P.E. Enterline, G.M. Marsh (1982)
• Epidemiology of Environmental Exposure and Malignant Mesothelioma — B. Liu, M. van Gerwen, et al. (2017)

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