Comparing epidemiologic studies of ingested asbestos for use in risk assessment

Our plain-English summary of Comparing epidemiologic studies of ingested asbestos for use in risk assessment, by L.S. Erdreich (Environmental Health Perspectives, 1983).

The study

• Author: L.S. Erdreich
• Journal: Environmental Health Perspectives
• Published: 1983;53:99-104
• 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. 000606).

Abstract

Epidemiologic data can be used in risk assessment in various ways: to calculate the dose-response relationship between exposure levels and adverse effects; to establish ranges of exposure known to be safe or unsafe; to verify an endpoint in humans derived from a route or species extrapolation; to support assumptions necessary for performing extrapolation procedures. These points are illustrated in the risk assessment for exposure to asbestos in drinking water. A previous risk assessment for asbestos, the EPA's Ambient Water Quality Criteria (AWQC) for Asbestos, was derived from cohort studies of inhalation exposure. Epidemiologic studies of ingested asbestos, all of geographical correlation design, were compared on the basis of their ability to add information in support of both the route extrapolation and low-dose extrapolation used in this risk assessment. Results of these ingestion studies were inconsistent due to variable ability to detect a risk from chronic low-level exposure. After preliminary comparisons of factors that determine scientific validity and statistical power, two ingestion studies were selected to determine if they had the potential to detect the risk predicted by the AWQC. This evaluation has shown that these studies do not offer quantitative data for estimating levels associated with a defined risk. Due to short exposure duration and limited power, clearly safe and clearly unsafe ranges could not be definitely identified. The most appropriate ingestion studies suggest, but do not prove, the endpoint derived from the route extrapolation in the AWQC.

In plain English

This paper was a review. It compared nine published geographic correlation (ecological) studies of cancer and asbestos in drinking water, including water carried in asbestos-cement pipe. The author asked whether these studies could support the EPA's Ambient Water Quality Criteria for asbestos, which had been derived from studies of workers who inhaled asbestos. The results of the nine studies were inconsistent. Using the criterion's prediction, the author estimated the relative risk of gastrointestinal cancer at 1.01 for the exposed California group and 1.1 for the Puget Sound group. A cohort the size of the California study would have had an 80% chance of detecting a relative risk of 1.1, and one the size of the Puget Sound study a relative risk of 1.5. The author judged these studies probably too small to detect the expected risk. The author concluded that clearly safe and clearly unsafe exposure ranges could not be identified. The California study suggested, but did not prove, the link to digestive cancers assumed by the criterion. The author also noted that diet, smoking and occupational exposures were not well evaluated in these studies.

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 comparison of published geographic correlation (ecological) studies of ingested asbestos, judged on their statistical power to detect the risk predicted by the EPA's Ambient Water Quality Criteria for asbestos
• Who was studied: Nine published ingestion studies covering populations in Duluth, Minnesota; Connecticut; the San Francisco Bay Area, California; Puget Sound, Washington; Escambia County, Florida; and Quebec
• Exposure: Asbestos in drinking water, including water distributed through asbestos-cement pipe. Probable exposure levels listed ranged from below 0.1 MFL (Connecticut) to 200 MFL (Puget Sound) and 80-220 MFL (Quebec). MFL means million fibers per litre.
• Main results:
  • The results of the ingestion studies were inconsistent with one another.
  • In the Minnesota, Florida and Connecticut studies, exposure duration was barely as long as the suspected cancer latency period. The Quebec study's results were biased by occupational exposures in the exposed group.
  • From the criterion's predicted risk and stated background incidence rates, the author estimated the relative risk of gastrointestinal cancer for exposed groups at 1.01 in California and 1.1 in Puget Sound.
  • A cohort sample the size of the California study would have an 80% probability of detecting a relative risk of 1.1 at alpha 0.05.
  • A cohort sample the size of the Puget Sound study would have an 80% probability of detecting a relative risk of 1.5 at alpha 0.05.
  • If the risk is similar to that predicted by the criterion, the author judged that these correlation studies would probably be too small to detect it.
  • The author read the 6-year California study (Conforti et al.) as suggesting a positive association between ingested asbestos and cancer of the digestive system. The Puget Sound study had been interpreted as negative.
• The authors' conclusion: The authors concluded that the ingestion studies did not give quantitative data for estimating levels linked to a defined risk, and that clearly safe and clearly unsafe ranges could not be identified. They also concluded that the Bay Area study by Conforti et al. suggested, but did not prove, the endpoint derived from the route extrapolation.
• Limitations the authors state:
  • Confounding risk factors such as diet, smoking habits and occupational exposures were not well evaluated in the geographic correlation studies.
  • Power cannot properly be estimated for ecological designs from sample size alone, because misclassification introduces biases that cannot be measured.
  • The comparison with cohort studies can only show whether a study is too small, not whether its size is adequate.
  • Using incidence rather than mortality may overstate the estimated risk. Using an average exposure duration of 31 years rather than 70 years may understate it.

Topics

Medical terms in this study, explained in our Lexicon: Dose-response relationship.

Related studies

• Asbestos in drinking water: a status report — J.A. Cotruvo (1983)
• An assessment of the Environmental Protection Agency's asbestos hazard evaluation algorithm — M.E. Findley, V.E. Rose, et al. (1983)
• Critical review of epidemiologic studies related to ingested asbestos — G.M. Marsh (1983)
• Additional thoughts on the review of epidemiologic studies related to ingested asbestos — G.M. Marsh (1983)
• Assessment of studies on cancer risks from asbestos in Connecticut drinking water — J.W. Meigs (1983)
• EPA as a public health agency — B.D. Goldstein (1988)

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