WC132 SeptOct 2023 - Magazine - Page 20
FEATURE
While installation of asbestos cement pipes has been
largely discontinued since the 1970s, they are still in use
in some drinking water systems in Canada.
contained potentially significant concentrations of fibres, which
they attributed to leaching from cement-asbestos pipes. In 1974,
through the Safe Drinking Water Act, the EPA set seven million
fibres per litre of asbestos in drinking water as the threshold value
for determining an increased risk of developing intestinal polyps.
North of the border, however, Health Canada has no comparable standard, citing the lack of what it considers consistent,
convincing evidence that asbestos ingested through water is
harmful to human health. “Your risk of exposure to airborne
asbestos from tap water is very low,” reads a 2021 circular, the
department’s most current edict on the matter. “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.” The advisory further
states that research has shown “very low percentages” of asbestos
fibres transferring into the air from humidifiers or showers, and
that exposure can also occur from mine tailings, improperly disposed contaminated household wastes, and groundwater contact
with asbestos-bearing bedrock.
The science indeed appears rather muted on the topic of
waterborne asbestos. In one prominent study in 1981, a group
of Canadian researchers analyzed samples of raw, treated,
and distributed tap water from 71 Canadian municipalities
for asbestos content. Using a detection method known as
transmission electron microscopy, they identified roughly
5 per cent of public water supplies containing asbestos at
concentrations greater than 10 million fibres per litre. “In
certain cases, there is evidence to suggest that erosion of asbestos
from pipe material is taking place,” the team wrote in its paper,
Asbestos and drinking water in Canada. However, the authors
noted improvement in the removal of chrysotile fibres from
drinking water during coagulation/filtration treatment. The
group also reviewed mortality rates for gastrointestinal cancers,
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but attributed any elevated numbers of deaths to occupational
exposure and concluded that “further statistical analyses are
required…before the significance of these observations can be
fully assessed.”
A follow-up involving some of the same researchers in 1983
acknowledged concern over the potential ingestion of asbestos in
food and drinking water due to what they called “the widespread
occurrence of chrysotile asbestos in drinking water supplies.”
However, they concluded that the risk to health associated
with the ingestion of asbestos at the levels found in municipal
drinking water supplies “is so small that it cannot be detected by
currently available epidemiologic techniques.”
Drowning in doubt
While little research has been published since then, asbestos
generally began to fall out of favour in the 1970's and the installation of cement-asbestos pipes slowly came to an end in Canada.
Still, with no concerted move to swap old pipes for newer ones,
asbestos-cement pipes remain in use in Canada and globally,
generally seeing the end of the line when they age and fail.
Dr. Giovanni Brandi, an associate professor with the School of
Medical Oncology at the University of Bologna in Italy, acknowledges that risks from exposure to waterborne asbestos appear to
be lower than from its airborne counterpart. However, he says
studies conducted back in the 1980s correlated waterborne asbestos with gastrointestinal and liver tumours, found that waterborne fibres can vaporize when water is heated, and established
that, while most fibres are eliminated through bodily waste, a
small percentage are absorbed through gastrointestinal mucosal
membranes into the bloodstream. Brandi says one might reasonably expect the research to have continued, but it largely hasn’t.
“All these observations strongly suggest that the issue of asbestos
in the water has been closed too quickly,” he adds, noting that
WAT E R C A N A D A . N E T
