아래는 BBC 1월 24일자 기사입니다.
음용수가 흘러가는 석면시멘트 파이프가 수명을 다해가며 석면 노출이 우려된다. 과학자들은 음용수 내 석면의 유해성에 대해 갑론을박이 일고 있다.
영국은 1988년까지 37,000km의 석면파이프가 설치되었고, 미국은 1백만km, 호주는 40,000km에 달한다. 보통 석면파이프의 수명은 50~70년이다.
공기 중에 노출된 석면은 심각한 폐질환을 일으키지만, 삼켜진 석면의 대부분은 장을 통과하고 대변으로 배출되는 것으로 알려져 있다.
WHO에서도 삼켜진 석면은 인간의 건강에 심각한 영향을 끼친다고 생각하지 않고 있다. 하지만, 몇몇 역학조사에는 음용수의 석면이 위암 발생과 연관이 있다고 보고 있다.
WHO에서 매년 4년마다 발간하는 음용수의 기준에는 석면 노출 제한 등을 두지 않았다. 하지만, 2022년의 최근 가이드라인에는 조사할 필요가 있다고 있으며 음용수 내 석면의 갯수를 최소화하는 것이 적절하다고 되어 있다.
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"The water pipe burst on the top of the hill and flooded into the gas network," remembers Alan Walker, owner of the Village Stores in Stannington, a suburb of Sheffield on the edge of the Peak District in England. "By the morning, people were turning on their gas hobs and water was coming out. It was one of the worst winters we had. We were one of the last houses to be reconnected, 13 days later."
He is recalling an incident from December 2022. The burst water main affected more than 3,000 homes, and around 10,000 people in Stannington. More than a year on, it should be just a bad memory of a cold and unpleasant winter. But the water burst highlighted another nagging concern.
"At the time we were cold and tired, and very frustrated," says Penny Baker, a local councillor for the area. "Everybody's mind was focused on heat, food, and vulnerable people. It was only later that we started to think, is there a concern?"
The pipe that burst was constructed from a mix of asbestos and cement, known as AC piping. To create the material, asbestos is mixed into cement to improve its tensile strength when under stress, for instance when being stretched or pulled, as well as preventing corrosion. These type of pipes have been installed across the world since the early 1900s. Although many water authorities have stopped installing them, existing asbestos cement piping is regarded to have a lifespan of 50-70 years and water is still supplied through these pipes in many areas.
By 1988, 23,000 miles (37,000km) of asbestos cement piping had been installed in the UK, delivering water to 12 million people. Depending on where you look in the country, they still account for up to 27% of water pipes in the UK (the BBC obtained figures from all water companies in the UK). There are also more than 630,000 miles (1.01 million km) of asbestos cement pipe buried across the US, according to the Environmental Protection Agency. Many communities in Canada still have their water supplied through asbestos cement pipes and Australia has 25,000 miles (40,000km) of water mains pipes made from the material.
There are growing concerns that as these ageing pipes near the end of their expected lifespan they will deteriorate, leading to more breakages. But even before that stage, after decades of water running through them, the walls of the pipes can soften due to calcium from the cement leaching out, leading to corrosion. According to one study of 50-year-old pipes in Slovenia, this allows asbestos fibres to be released into the water.
This risk of water contamination is a concern for scientists and public health campaign groups. Although asbestos can enter water supplies from natural sources in areas where it is found, these degrading pipes are emerging as another source of exposure, leading to questions about the impact this may have on human health.
The evidence is mixed as best.
"My concern is that it is in drinking water," says Arthur Frank, professor of public health and professor of medicine at Drexel University in Philadelphia. He is one of the leading international experts on asbestos and has been sounding the alarm about ingestion as a possible mechanism for asbestos-related conditions. "The risk may not be great. But it is generally accepted that there is no safe level of exposure to asbestos."
Asbestos is a known carcinogen to humans, meaning it is capable of causing cancer. When asbestos fibres become airborne and are inhaled, they are known to lodge in the lungs and other parts of the airways, where they can cause scarring, inflammation, asbestosis – an inflammatory condition leading to permanent lung damage – and cell damage that lead to cancers, including mesothelioma, an incurable cancer of the lining that covers organs such as the lungs. For decades, however, the risk from swallowing asbestos has been thought of as small as most fibres were assumed to pass through the gut and be expelled in faeces.
Currently, the World Health Organisation (WHO) does not consider ingestion of asbestos in drinking water to be a serious risk to human health. The evidence is contradictory, with some epidemiological studies showing a correlation between asbestos exposure through drinking water and incidences of stomach and gut cancers. But others have failed to find such a link, and animal studies have also not provided definitive evidence that it can lead to cancers in the gastrointestinal tract.
This has not stopped some countries from adopting a precautionary approach to asbestos in drinking water. The US Environmental Protection Agency (EPA) has had a maximum safety limit of seven million fibres per litre in place since 1974, but this only applies for asbestos fibres longer than 10 micrometres. Longer fibres have been shown to cause the majority of asbestos-related respiratory disease, while the risk from shorter fibres is thought to be low, although the Centres for Disease Control and Prevention still warns there is evidence that fibres as small as five micrometres can cause injury.
The average length of fibres in asbestos cement pipes in the US is just four micrometres, according to one study of water samples from the 1980s. A more recent study from New Zealand also found that mains water supplies in Christchurch had far higher concentrations of shorter fibres than those above 10 micrometres. And the fate of short asbestos fibres when ingested is still unclear.
There are some scientists, such as Frank, who argue it is time for more detailed research on the impact on human health. "The evidence is getting clearer and clearer,” Frank says. One scientific review published last year by Italian researchers highlighted that large numbers of asbestos fibres appear to accumulate in the colon. Other studies have shown links between high levels of industrial asbestos exposure and incidents of colorectal cancer, although often there could be other causes at work, such as exposure to different toxic chemicals or smoking and alcohol use.
There are also tentative concerns that asbestos can migrate from water into the air if high enough levels are reached in turbulent running water.
One place where there is an ongoing and emerging debate about the possible carcinogenic risk from asbestos exposure through ingestion is in Italy. A 2019 Italian research paper looking at potential hazards suggested that a precautionary approach should be adopted, given the "ongoing debate on the possible carcinogenic risk associated with asbestos exposure through ingestion".
Giovanni Brandi, an associate professor of medical oncology at the University of Bologna, has been studying the possibility that ingested asbestos fibres may be responsible for disease in the liver and bile ducts. He recently wrote about his concerns around drinking water as a "hidden source of asbestos exposure" in the public policy journal Open Access Government.
Another Italian scientist, Agostino Di Ciaula, a medical doctor and biomedical researcher at the Policlinico University Hospital of Bari, in southeast Italy, and president of the scientific committee for the campaign group, the International Society of Doctors for the Environment, believes the risk from the long-term consumption of drinking water containing asbestos has been underestimated to date. But he says "definitive and convincing studies aimed at the identification of a risk threshold are lacking".
"Thus, at the moment it is impossible to identify a 'safe' threshold of asbestos fibres in drinking water," says Di Ciaula. "Please consider that asbestos fibres contained in water can be also inhaled."
The WHO produces detailed drinking water quality guidelines every four years, with the next update due in 2026. It currently does not set an exposure limit, and most countries adhere to these guidelines.
The latest version of the WHO guidelines, published in 2022, however, calls for "investigative monitoring" to help determine the number, size and shape of fibres getting into water supplies from older asbestos cement water pipes. The guidelines note it was "appropriate to minimise the concentrations of asbestos fibres in drinking-water as far as practical".
An evaluation in 2012 by the International Agency for Research in Cancer (IARC), which is part of the WHO, stated that the concentration of asbestos fibres can be as high as 10-300 million per litre in some locations.
"The average person drinks about two litres of water per day," the report says. "Risk of exposure to asbestos in drinking-water may be especially high for small children who drink seven times more water per day per kg of body weight than the average adult."
But the WHO notes that the IARC working group was "evenly divided" about whether there was sufficient evidence that asbestos could cause colorectal cancer. A spokesman for the IARC told the BBC that it had no current plans to re-evaluate the issue of asbestos in drinking water.
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Asbestos in drinking water: What does it mean for human health? 
