Asbestos and drinking water in Canada.

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.