Asbestos and drinking water in Canada

Our plain-English summary of Asbestos and drinking water in Canada, by P. Toft, D. Wigle, J.C. Meranger, et al (The Science of the Total Environment, 1981).

The study

• Authors: P. Toft, D. Wigle, J.C. Meranger, Y. Mao
• Journal: The Science of the Total Environment
• Published: 1981;18:77-89
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Samples of raw, treated and distributed tap water were collected from 71 municipalities across Canada and analyzed for asbestos content by transmission electron microscopy. Chrysotile asbestos was identified as the major asbestos type present in drinking water with some 5% of public water supplies containing asbestos at concentrations greater than 10 million fibres per litre. Improvement factors of up to 300 were observed for the removal of chrysotile fibres from drinking water during treatment, indicating that coagulation/filtration treatment is efficient for this purpose. In certain cases there is evidence to suggest that erosion of asbestos from pipe material is taking place. Age-standardized mortality rates for gastro-intestinal cancers were calculated for each city for the period of 1966 to 1976. Rates for the 2 localities with the highest (congruent to 10(8)/L) concentrations of asbestos fibres in treated drinking water were compared with the weighted average of the rates for the 52 localities with asbestos concentrations not significantly greater than zero. Eleven localities had intermediate concentrations of asbestos and six were too small for meaningful statistical analysis. Relatively high mortality rates were apparent amongst males in city 1 for cancer of the large intestine except rectum, and in both sexes in city 1 and males in city 2 for stomach cancer. It is felt that these findings are probably related to occupational exposure to asbestos. Further statistical analyses are required, however, before the significance of these observations can be fully assessed.

In plain English

This study surveyed Canadian drinking water for asbestos and examined death rates. In August and September 1977, raw, treated and tap water from 71 locations across Canada was examined by electron microscopy. Chrysotile was the main asbestos type, and amphibole fibres were detected in only 7% of 336 samples. About 5% of the population received water with more than 10 million fibres per litre. The highest tap-water sample, 1800 million fibres per litre, came from Baie Verte, Newfoundland. Coagulation and filtration treatment reduced chrysotile fibres by factors of 18 to 300 at 7 locations, and Winnipeg data indicated erosion of asbestos-cement pipes. For 1966 to 1976, death rates in Sherbrooke and Thetford Mines (water over 100 million fibres per litre) were compared with those of 52 cities below 5 million. Men in Thetford Mines had significantly high rates of stomach cancer, lung cancer and non-cancer respiratory disease. The authors concluded that no consistent cancer increase was shown. They judged the men's lung and respiratory findings probably due to work exposure, though work and water exposure could not be fully separated.

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: National survey of asbestos fibres in drinking water, combined with a comparison of age-standardized death rates between cities with high and low fibre levels in their water
• Who was studied: Raw, treated and distribution water samples collected in August and September 1977 from 71 locations across Canada (336 samples). For the mortality part: residents of 2 cities with high fibre levels (Sherbrooke and Thetford Mines) and 52 low-level cities, 1966 to 1976. Cities with intermediate levels or fewer than 10,000 people were excluded.
• Exposure: Asbestos fibres in drinking water, counted by transmission electron microscopy and identified as chrysotile or amphibole. For the mortality comparison, cities with more than 100 million fibres per litre were compared with cities with less than 5 million fibres per litre.
• Main results:
  • Amphibole fibres were detected in only 7% of the 336 samples.
  • Chrysotile was the main asbestos type. About 5% of the population received water with more than 10 million fibres per litre.
  • The highest distribution (tap) water sample was 1800 million fibres per litre, at Baie Verte, Newfoundland.
  • At 7 locations, coagulation and filtration treatment reduced chrysotile fibres by improvement factors of 18 to 300.
  • In Winnipeg, fibre levels increased from raw water to the distribution system. The authors took this as a statistically valid indication of erosion of asbestos-cement pipes.
  • All-cause and all-cancer death rates for males in Thetford Mines were significantly higher than for Sherbrooke or the 52 comparison localities. Rates for females were similar in all 3 regions.
  • Stomach cancer was the only significantly high gastrointestinal cancer rate, among males in Thetford Mines: 38.7 deaths per 100,000 person-years, more than double the comparison group.
  • For cancer of the large intestine except rectum, the rate was 29.0 for males in Thetford Mines versus 17.5 in the comparison group. The difference was not quite significant at the 5% level.
  • All gastrointestinal cancer sites combined were significantly high for males in Thetford Mines: 104 versus 66.5 in the comparison group.
  • Lung cancer was significantly high among males in Thetford Mines: 139 versus 67.0 in the comparison group.
• The authors' conclusion: The authors concluded that no consistent increase in death rates for any cancer was demonstrated in the 2 high-fibre localities. They judged that the high lung cancer and non-cancer respiratory disease rates among males (but not females) in Thetford Mines were probably due to occupational asbestos exposure. They also concluded that amphibole asbestos was not a significant contaminant of Canadian drinking water and that filtration can efficiently remove asbestos fibres.
• Limitations the authors state:
  • The authors stated that there are serious limitations to this type of study.
  • The effects of occupational exposure and drinking-water exposure could not be conclusively separated.
  • Single grab samples may not fully characterize a fibre-contaminated water source, and pooled samples over time may be needed.
  • Filtration efficiency may depend on the time since the filter bed was back-washed, so sampling over the whole cycle would be needed to fully characterize a plant.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Transmission Electron Microscopy (TEM), Chrysotile, Stomach Cancer, Occupational Exposure.

Related studies

• Asbestos-contaminated drinking water: its impact on household air — J.S. Webber, S. Syrotynski, et al. (1988)
• Cancer incidence in relation to asbestos in drinking water in the Puget Sound region — L. Polissar, R.K. Severson, et al. (1982)
• A case-control study of asbestos in drinking water and cancer risk — L. Polissar, R.K. Severson, et al. (1984)
• Cancer morbidity investigations: lessons from the Duluth study of possible effects of asbestos in drinking water — E.E. Sigurdson, B.S. Levy, et al. (1981)
• "Asbestos in drinking water and cancer incidence in the San Francisco Bay area" — K. Browne (1982)
• Asbestos in drinking water and cancer — K.D. MacRae (1988)

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