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Inhaled or ingested, asbestos causes cancer

Since its 1989 review, Health Canada has maintained that asbestos causes cancer when inhaled; however, “[t]here is no consistent, convincing evidence that ingested asbestos is hazardous.”

There is no doubt that asbestos is a potent carcinogen. The Global Burden of Disease Study 2019 reports that occupational exposure to asbestos is among the world’s top ten causes of cancer.1

In 2012, the International Agency for Research on Cancer updated its asbestos monograph, following assessments in 1972, 1976 and 1987. The working group concluded:

There is sufficient evidence in humans for the carcinogenicity of all forms of asbestos (chrysotile, crocidolite, amosite, tremolite, actinolite, and anthophyllite). Asbestos causes mesothelioma and cancer of the lung, larynx, and ovary. Also positive associations have been observed between exposure to all forms of asbestos and cancer of the pharynx, stomach, and colorectum.

There is sufficient evidence in experimental animals for the carcinogenicity of all forms of asbestos. All forms of asbestos (chrysotile, crocidolite, amosite, tremolite, actinolite and anthophyllite) are carcinogenic to humans (Group 1).  For cancer of the colorectum, the Working Group was evenly divided as to whether the evidence was strong enough to warrant classification as sufficient for inclusion in Group 1.

Is asbestos a carcinogen that is safe to swallow?

Health Canada relies on the Guideline Technical Document – Asbestos (1989) for Canadian Drinking Water Quality as the scientific basis for the position that asbestos is not carcinogenic when ingested. The research included in this document was published between 1967 and 1987,2 and study conclusions are often linked to the incorrect assumption that inhaled asbestos principally affects the respiratory system, and not the gastrointestinal system.

There has long been a school of thought that asbestos is a multi-site carcinogen. For example the landmark 1964 study Asbestos Exposure and Neoplasia by Selikoff et al., published in the Journal of the American Medical Association3 described a cohort of asbestos-exposed tradesmen followed from 1943 to 1962. There were 255 deaths including four cases of mesothelioma (usually a very rare disease), as well as three times the expected number of deaths from stomach, and colorectal cancer (28 deaths observed; 9.4 expected).

Research in the intervening decades has failed to find that airborne carcinogens are benign when swallowed.

The route of exposure does not eliminate the risk of potential health outcomes. Inhaled asbestos is coughed up then swallowed, water-borne asbestos is inhaled in showers and from humidifiers, and ingested asbestos could be regurgitated and inhaled. Asbestos particles move throughout the body, with fibres appearing in the urine,4,5 and numerous organs (kidney, heart, liver, spleen, adrenals, pancreas, brain, prostate and thyroid).6

The Health Canada position on asbestos in drinking water says in part:
  • There’s no consistent, convincing evidence that asbestos ingested through drinking water is harmful to your health.

Prevent Cancer Now response:
There is certainly no evidence of safety, and this research has largely not been carried out. Studies in Health Canada’s 1989 analysis implicitly assumed that occupational asbestos exposure only causes respiratory cancers, but asbestos is a multi-site carcinogen even when only inhaled.
Due to corruption of the scientific record for all commercially important carcinogens, it would be extraordinary to see consistent evidence that ingested asbestos causes cancer. Contested science is the norm for all commercially important carcinogens, such as tobacco and pesticides.

  • If you drink water containing asbestos fibres, you eliminate the fibres, mostly through feces. For this reason, Health Canada has not established drinking water guidelines for asbestos.

Prevent Cancer Now response:
Excretion of a carcinogen is no reason to expect no harm.

Most tobacco smoke is exhaled, but tobacco causes cancers throughout the body: mouth, throat, oesophagus, larynx, bronchus, trachea, lung, acute myeloid leukemia, kidney, renal pelvis, urinary bladder, cervix, liver, stomach, pancreas, colon and rectum.7

Most pesticides are washed off, or excreted after ingestion, but cancers happen. Even intergenerational cancers can occur (e.g., the insecticide DDT increases risks of breast cancer in granddaughters).8

Ingested asbestos can cause cancer

Asbestos-related cancers typically take a long time to appear, so unless there is a high index of suspicion (such as with known occupational exposure), and investigation, asbestos-related cancers will be under-detected. Uterine and ovarian cancers associated with asbestos in talc 9 is one well known example of migration of carcinogenic fibres to sensitive tissue.

The science relied up by Health Canada is outdated, and relies upon some weak studies. Studies of groups of individuals with specific data, known as “cohorts,” have the strengths that exposures (or differences in exposures) are generally better-defined than in ecological studies (e.g., studies comparing two cities), as well as means for follow-up. (Only recently, with linkages to provincial health data, is it becoming possible to follow general populations in research studies, but we have not seen this regarding asbestos.) For example, early asbestos cancer research did not always include major factors such as smoking. As well, recent visualization of asbestos fibres at tumour sites is compelling evidence.

Some recent examples of research indicating that asbestos causes gastrointestinal cancers include:

  • A Cohort Study on Cancer Incidence among Women Exposed to Environmental Asbestos in Childhood with a Focus on Female Cancers, including Breast Cancer (2022)10
    Environmental asbestos exposure in childhood is associated with an increased risk of cancer of the corpus uteri and malignant mesothelioma in women.
  • Increased Risk of Gastric Cancer in Asbestos-Exposed Workers: A Retrospective Cohort Study Based on Taiwan Cancer Registry 1980–2015 (2021)11
    A total of 123 worksites were identified to have cases of malignant mesothelioma, where increased risk for gastric cancer was found with a relative risk of 1.76 (95% CI: 1.63–1.90)
  • Asbestos fiber identification in liver from cholangiocarcinoma patients living in an asbestos polluted area: a preliminary study (2019)12
    Cholangiocarcinoma (CC) tumours from patients with bile duct cancer, from Casale Monferrato, Italy, a highly asbestos-polluted town, were examined microscopically. Fibers/bundles of fibers of chrysotile were detected in 5 out of 7 patients (71%). The boundary between healthy and neoplastic tissue or the fibrocollagen tissue produced by the neoplasia were identified as areas of fiber incorporation. This study is the first report the detection of chrysotile asbestos fibers in the liver of patients with CC.
  • Occupational Asbestos Exposure and Incidence of Colon and Rectal Cancers in French Men: The Asbestos-Related Diseases Cohort (ARDCo-Nut) (2017)13
    In the overall cohort, after adjusting for smoking, colon cancer was significantly associated with cumulative exposure; particularly for those 20–40 years since first exposure, who were almost five times more likely to develop the malignancy.
  • Cancer Attributable to Asbestos Exposure in Shipbreaking Workers: A Matched-Cohort Study (2015)14
    Follow-up generated 109,932 person-years, with 940 deaths and 436 cancer cases, from 1985 to 2008. The high asbestos exposure group had statistically significant higher risk of overall cancer (adjusted Hazard Ratio (aHR)= 1.71), esophagus cancer (aHR= 2.31), liver and intrahepatic bile duct cancer (aHR= 1.60), and trachea, bronchus, and lung cancer (aHR= 3.08). Mesothelioma cases were found in the high asbestos exposure group.
  • Stomach cancer and occupational exposure to asbestos: a meta-analysis of occupational cohort studies (2015).
    This is a publication of the most recent International Agency for Research on Cancer (IARC) analysis. There is limited evidence for a causal association between exposure to asbestos and stomach cancer.15

  1. Tran KB, Lang JJ, Compton K, Xu R, Acheson AR, Henrikson HJ, et al. The global burden of cancer attributable to risk factors, 2010–19: a systematic analysis for the Global Burden of Disease Study 2019. The Lancet. 2022 Aug 20;400(10352):563–91. https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(22)01438-6/fulltext
  2. Canada H. Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Asbestos. 1986. https://www.canada.ca/en/health-canada/services/publications/healthy-living/guidelines-canadian-drinking-water-quality-guideline-technical-document-asbestos.html
  3. Selikoff IJ, Churg J, Hammond EC. Asbestos Exposure and Neoplasia. JAMA. 1964 Apr 6;188(1):22–6. https://doi.org/10.1001/jama.1964.03060270028006
  4. Boatman ES, Merrill T, O’Neill A, Polissar L, Millette JR. Use of quantitative analysis of urine to assess exposure to asbestos fibers in drinking water in the Puget Sound region. Environ Health Perspect. 1983 Nov;53:131–41. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1569110/
  5. Finn M, Hallenbeck W. Detection of Chrysotile Asbestos in Workers’ Urine. American Industrial Hygiene Association Journal. 1984 Nov 1;45(11):752–9. https://doi.org/10.1080/15298668491400566
  6. Auerbach O, Conston AS, Garfinkel L, Parks VR, Kaslow HD, Hammond EC. Presence of Asbestos Bodies in Organs Other than the Lung. Chest. 1980 Feb 1;77(2):133–7. https://www.sciencedirect.com/science/article/pii/S0012369216411232
  7. U.S. Centers for Disease Control and Prevention (CDC). “Tobacco and Cancer,” Nov 18, 2021. https://www.cdc.gov/cancer/tobacco/index.htm.
  8. Cirillo PM, Merrill MAL, Krigbaum NY, Cohn BA. Grandmaternal Perinatal Serum DDT in Relation to Granddaughter Early Menarche and Adult Obesity: Three Generations in the Child Health and Development Studies Cohort. 2021 Apr 14. Cancer Epidemiol Biomarkers Prev.  http://cebp.aacrjournals.org/content/early/2021/04/13/1055-9965.EPI-20-1456
  9. Stoiber T, Fitzgerald S, Leiba NS. Asbestos Contamination in Talc-Based Cosmetics: An Invisible Cancer Risk. EnvironHealthInsights. 2020 Jan;14:1178630220976558. https://doi.org/10.1177/1178630220976558
  10. Dalsgaard SB, Würtz ET, Hansen J, Røe OD, Omland Ø. A Cohort Study on Cancer Incidence among Women Exposed to Environmental Asbestos in Childhood with a Focus on Female Cancers, including Breast Cancer. Int J Environ Res Public Health. 2022 Feb;19(4):2086. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8872294/
  11. Fang YJ, Chuang HY, Pan CH, Chang YY, Cheng Y, Lee LJH, et al. Increased Risk of Gastric Cancer in Asbestos-Exposed Workers: A Retrospective Cohort Study Based on Taiwan Cancer Registry 1980–2015. International Journal of Environmental Research and Public Health. 2021 Jan;18(14):7521. https://www.mdpi.com/1660-4601/18/14/7521
  12. Grosso F, Croce A, Libener R, Mariani N, Pastormerlo M, Maconi A, et al. Asbestos fiber identification in liver from cholangiocarcinoma patients living in an asbestos polluted area: a preliminary study. Tumori. 2019 Oct 1;105(5):404–10. https://doi.org/10.1177/0300891619839305
  13. Paris C, Thaon I, Hérin F, Clin B, Lacourt A, Luc A, et al. Occupational Asbestos Exposure and Incidence of Colon and Rectal Cancers in French Men: The Asbestos-Related Diseases Cohort (ARDCo-Nut). EHT. 2017;125:409–15. https://ehp.niehs.nih.gov/ehp153/
  14. Wu WT, Lin YJ, Li CY, Tsai PJ, Yang CY, Liou SH, et al. Cancer Attributable to Asbestos Exposure in Shipbreaking Workers: A Matched-Cohort Study. PLOS ONE. 2015 Jul 20;10(7):e0133128. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0133128
  15. Fortunato, L., and L. Rushton. Stomach Cancer and Occupational Exposure to Asbestos: A Meta-Analysis of Occupational Cohort Studies. British Journal of Cancer. 2015. 112, no. 11 (May 2015): 1805–15. https://doi.org/10.1038/bjc.2014.599.