Human cancer risk from ingested asbestos: a problem of uncertainty

Our plain-English summary of Human cancer risk from ingested asbestos: a problem of uncertainty, by W.J. Nicholson (Environmental Health Perspectives, 1983).

The study

• Author: W.J. Nicholson
• Journal: Environmental Health Perspectives
• Published: 1983;53:111-3
• Cited by: 4 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. 000636).

Summary of the article

This commentary considered whether population studies could show a cancer risk from asbestos in drinking water. The author modeled a hypothetical 10-year study of deaths in a city of 1 million people whose water contained 100 million fibers per liter, which he called a gross overestimate of any real situation. He used the lifetime risk from the U.S. EPA asbestos criteria document (3.3 x 10^-3 per person over 70 years), an average residence time of 14 years, and a 7-year latency. Of about 100,000 deaths, about 40 excess cancers were expected (17 gastrointestinal tumors and 23 peritoneal mesotheliomas). A cruder calculation gave 94. No more than about six mesotheliomas would be expected to appear on death certificates. Against about 4,100 expected gastrointestinal cancers (standard deviation 64), the study would reach statistical significance only if the risk were 7.5 times greater or the population 50 times larger. The author noted that shipyard employment could confound such studies, since areas with high waterborne asbestos were also shipbuilding areas. He argued that animal studies may miss an effect if asbestos acts as a promoter. He concluded that ingestion risk cannot be verified by population studies. He recommended flocculation and sedimentation, which can reduce fiber concentrations by about 90%, in areas with very high concentrations, and treatment or coating to limit erosion of asbestos-cement pipes. He estimated 4.7 deaths per year in a population of 100,000 exposed to 100 million fibers per liter.

PubMed has no abstract for this study, and the article doesn't print one. We wrote this summary from the full article with the help of AI. It is not the authors' wording.

In plain English

This short commentary did not study real people. It used a hypothetical example to ask whether studies of populations drinking asbestos-contaminated water could detect a cancer risk. The author imagined a city of 1 million people whose water held 100 million fibers per liter, a level the author called a gross overestimate of any real situation. The author drew on a U.S. EPA criteria document, which put the added lifetime risk of death at 3.3 per 1,000 people after 70 years of drinking such water. From this, the author estimated about 40 extra cancers among roughly 100,000 deaths over 10 years. If these followed the pattern in the worker groups behind the estimates, 17 would be gastrointestinal cancers and 23 peritoneal mesotheliomas, but no more than about six mesotheliomas would appear on death certificates. Against about 4,100 expected gastrointestinal cancers, this excess would not reach statistical significance. Deaths from a single shipyard of 20,000 workers could produce a similar excess. The author concluded that the risk cannot be verified by population studies and argued that water treatment was justified where fiber levels are very high.

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: Commentary using a hypothetical calculation (not an original study of people or animals)
• Who was studied: A hypothetical city of 1 million people, with about 100,000 deaths analysed over a 10-year period. No real population was studied.
• Exposure: Asbestos fibers in drinking water at a hypothetical 100 million fibers per liter, described by the author as a gross overestimate of any real situation. No fiber type is specified. Asbestos-cement water pipes are also discussed.
• Main results:
  • Using the U.S. EPA criteria document estimates, drinking such water for 70 years would give an added risk of death of 3.3 x 10 to the minus 3 (3.3 per 1,000) per person.
  • In the hypothetical city, about 40 additional cancers in total were expected (39.5 in the author's table). A cruder direct calculation gave 94.
  • If the excess followed the pattern seen in the worker groups behind the risk estimates, 17 would be excess gastrointestinal tumors and 23 would be peritoneal mesotheliomas.
  • No more than about six peritoneal mesotheliomas would be expected on death certificates, because the risk estimates were based on review of all pathological material.
  • The low number of excess cancers would not reach statistical significance. About 4,100 gastrointestinal cancers would be expected anyway in this population (standard deviation 64). A study would show a significant result only if the risk were 7.5 times greater or the population 50 times greater.
  • Confounding: the projected excess could be accounted for by excess deaths from a single shipyard employing 20,000 people in the study area.
  • For a water system with 100 million fibers per liter serving 100,000 people, the author calculated 4.7 deaths per year might occur. Standard flocculation and sedimentation can reduce asbestos concentration by about 90%.
• The authors' conclusion: The author concluded that the cancer risk from ingested asbestos cannot be verified by population studies and that animal experiments involve uncertain comparisons between species. In the author's view, human data from a different exposure route suggest significant risk near 100 million fibers per liter, and the author argued that water treatment costs could be justified in such systems.
• Limitations the authors state:
  • The assumed residence-time distribution overestimates how long people actually live in one area.
  • The assumed 7-year latency overestimates the risk of peritoneal mesothelioma, since most such tumors appear 30 or more years after first exposure.
  • The human risk data come from a different exposure route than drinking water.

Topics

Medical terms in this study, explained in our Lexicon: Latency, Peritoneal Mesothelioma, Mesothelioma, Death Certificate, Statistical Significance, Asbestos-Cement Pipe.

Related studies

• Should uncertainty concerning the risk of malignancy be included in diagnostic (nongynecologic) cytopathology reports? — D.N. Poller, F. Schmitt (2021)
• Comparing epidemiologic studies of ingested asbestos for use in risk assessment — L.S. Erdreich (1983)
• Sources of uncertainty in dose-response modeling of epidemiological data for cancer risk assessment — L. Stayner, A.J. Bailer, et al. (1999)
• 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)
• Ingested mineral fibers. Do they penetrate tissue or cause cancer? — P. Gross, R.A. Harley, et al. (1974)

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