Certain drinking water pipes are made of asbestos cement. Under some circumstances, therefore, asbestos fibres can be found in drinking water. ANSES has conducted an initial review of the scientific literature to characterise the hazards associated with asbestos ingestion.
Before it was banned in France in 1997, when respiratory exposure was found to be hazardous to humans, asbestos was used in a variety of sectors, particularly in construction. In fact, 4% of the French public drinking water supply network still consists of asbestos cement. "The risk of asbestos fibres being released into the water supply remains low when the pipes have been installed in stable non-aggressive soil, and when the water carried by these pipes contains calcium, because the build-up of scale protects the pipe. However, risks from the presence of asbestos in drinking water cannot be ruled out in the case of badly deteriorated pipes," say scientists from ANSES's Water Risk Assessment Unit. As people are mainly exposed to asbestos by air, studies on the health risks of asbestos have, until now, mainly focused on this source of exposure. The last baseline analysis conducted by the International Agency for Research on Cancer (IARC) in 2012 on the links between asbestos and the occurrence of cancer did not explicitly address the hazards associated with ingestion.
The expert appraisal was prompted by two alarmist studies, which nevertheless had limitations
Two studies by an Italian research team, published in 2016 and 2017, had concluded that the health risks associated with asbestos ingestion, mainly through the daily consumption of drinking water, may be underestimated. In its scientific and technical analysis note published in 2017, ANSES observed that these two studies were not sufficiently robust: they had not assessed the quality of the publications on which they had based their conclusions and had not taken into account all the scientific publications available on the subject. The Agency was therefore asked to characterise the hazards of asbestos by ingestion, by conducting a systematic review of the scientific literature.
Not enough evidence to rule on a causal relationship
In order to study the health hazards of asbestos ingestion, in particular concerning the development of digestive cancers (oesophagus, stomach, small intestine, liver, etc.), the Agency conducted a comprehensive review of current knowledge on this subject. Of the 4409 human and 1107 animal studies on the effects of asbestos, the experts identified 17 studies examining asbestos ingestion in the general population, 19 examining asbestos ingestion in animals and 41 examining occupational exposure to asbestos. The working group conducted a standardised assessment of these studies to determine the levels of evidence that could be used to characterise the plausibility of a link between asbestos exposure and the occurrence of digestive cancers. This assessment led the experts to conclude that the levels of evidence were "inadequate", i.e. the data published to date cannot be used to rule on the possibility or absence of an association between asbestos ingestion and digestive cancers. "Most of the existing studies are old or have methodological limitations that mean they are unable to demonstrate a causal link between asbestos ingestion and the occurrence of these cancers," explain the experts of the working group.
Signals for some cancers but no certainty
However, the existence of signals suggesting the possibility of an association between asbestos ingestion and three specific digestive cancers was highlighted. These are cancers of the oesophagus, stomach and colon. This possibility is supported by epidemiological studies conducted in occupational settings that report more cases of these cancers in workers exposed to asbestos than in the general population. This is because a fraction of the asbestos inhaled by workers can be swallowed and pass directly into the digestive tract. However, the data do not enable a reliable estimate of the extent of this fraction compared with that reaching these organs via the respiratory route, through the lungs and the bloodstream, and mean that these results cannot be extrapolated to exposure by ingestion.
Surveillance campaigns recommended
Given the past use of asbestos in certain pipes, the Agency recommends conducting targeted campaigns to detect the presence of possible asbestos fibres in drinking water liable to contain them. These data could then be used for future studies or epidemiological surveillance work. The Agency also recommends monitoring the condition of asbestos cement pipes to ensure that they are renovated or replaced in the event of damage.