Degradation of asbestos - Reinforced water supply cement pipes after a long-term operation

Our plain-English summary of Degradation of asbestos - Reinforced water supply cement pipes after a long-term operation, by J. Zavašnik, A. Šestan, S. Škapin (Chemosphere, 2022).

The study

• Authors: J. Zavašnik, A. Šestan, S. Škapin
• Journal: Chemosphere
• Published: 2022;287(Pt 1):131977
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Potable water supply system in major countries still uses a large proportion of asbestos-cement (AC) pipes for fresh drinking water delivery. Generally, after installation and initial purging, the AC tubes are believed to self-passivate by calcite scale and bio-film, especially when conveying hard water. However, the overall performance of AC tubes after decades of operation is significantly reduced and is still mainly unknown. In the current research, we investigated the AC water supply tube after 56 years of operation with high-hardness conveyed water. Our results show that asbestos fibres are emitted from degraded AC pipes as a result of wall softening due to calcium leaching from hydrated cementitious materials, resulting in the loss of mechanical stability. Although the water pumped into the system is not considered aggressive, the seasonal variations of water temperature and chemistry results in an interplay of calcite scaling and Ca leaching, the latter being the dominating process. By comparing the experimental observations with the long-term chemistry reports of the water supplied through the pipes, a positive relationship was established between the temperature and quality of the conveyed water with the corrosion and the calcite scale formation, which are dictating the emission of the fibres into the drinking water. In addition to the health risks posed by asbestos, these processes have many adverse effects on drinking water supply, such as pipe malfunction and destruction resulting in water loss, reduction of hydraulic capacity, microbial proliferation, and water quality deterioration, a topic of interest for global water industries process.

Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.

In plain English

This laboratory study examined sections of an asbestos-cement drinking water main in Ljubljana, Slovenia. The pipe was installed in 1963 and collected in April 2019 during reconstruction of the water system, after 56 years carrying high-hardness water. The authors examined the inner pipe surface by electron microscopy and compared what they found with 10 years of public water-quality records. By their calculations, the water was corrosive to the pipe most of the time and tended to form calcite scale only at the highest water temperatures, above 21 degrees C. The cement at the inner surface had lost calcium, leaving a porous layer up to 15 micrometres deep with exposed asbestos fibres. Only isolated thin islands of calcite scale were found. To imitate years of vibration, the authors treated a sample with ultrasound for 30 seconds in ethanol, and this removed the whole porous layer. Fibres released in that test, not fibres collected from tap water, were identified as chrysotile (clinochrysotile). The authors concluded that calcium leaching from the cement is the main reason asbestos fibres are released into drinking water. They stated that estimating the rate of fibre release into drinking water is extremely difficult.

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: Laboratory materials analysis of field-collected asbestos-cement pipe sections (scanning and transmission electron microscopy, elemental analysis, an ultrasonic vibration test), compared with water-quality records
• Who was studied: Sections of one asbestos-cement water main (110 mm diameter) installed in 1963 under a road in Ljubljana, Slovenia, collected in April 2019 during reconstruction of the system. The water system supplies about 36,000 users.
• Exposure: High-hardness drinking water carried through the asbestos-cement pipe for 56 years. Water temperature ranged from about 5 to 20 degrees C (winter to summer) and pH from about 7 to 8. Water chemistry was taken from 10 years of quarterly public quality-control records.
• Main results:
  • The calculated Langelier index for the conveyed water was negative (water corrosive to the pipe) most of the time. It approached neutral in summer.
  • Positive index values, at which scale forms, occurred only at the highest water temperatures, above 21 degrees C.
  • On the inner pipe surface, the cement bonding material appeared dissolved, exposing numerous asbestos fibres toward the drinking water side.
  • A porous, calcium-depleted layer extended up to 15 micrometres deep into the inner pipe wall.
  • The calcium loss throughout this porous layer was attributed to selective leaching.
  • Ultrasonic treatment for 30 seconds in ethanol, used as a stand-in for years of vibration, removed the whole 15-micrometre porous layer.
  • Particles released in the ultrasonic test included numerous fibres up to several microns long.
  • The released fibres were identified as monoclinic clinochrysotile.
  • The released fibres were hollow. Their diameters fell into two groups: 55 plus or minus 2.07 nm and 33 plus or minus 1.13 nm.
  • Only a few isolated thin islands of calcite scale were found on the inner surface.
  • Because the surface was mainly deteriorated and scale was sparse, the authors judged calcium dissolution to be the dominant process.
• The authors' conclusion: The authors concluded that cement degradation by calcium leaching is the main reason asbestos fibres are released into drinking water from these pipes.
• Limitations the authors state:
  • The authors stated that estimating the rate at which asbestos fibres are released into drinking water is extremely difficult and requires physical examination of pipe samples.
  • The authors stated that no simple model could link the measured degradation to the water chemistry data, because of several interfering factors.
  • The authors stated that the maximum internal degradation over 50-plus years could not be established.

Topics

Medical terms in this study, explained in our Lexicon: Asbestos-Cement, Hardness (Mohs Scale).

Related studies

• The use of asbestos-cement pipe for public water supply and the incidence of cancer in selected communities in Utah — T.D. Sadler, W.N. Rom, et al. (1984)
• Improving pipe failure predictions: Factors affecting pipe failure in drinking water networks — N.A. Barton, T.S. Farewell, et al. (2019)
• An investigation of the use of asbestos cement pipe for public water supply and the incidence of gastrointestinal cancer in Connecticut, 1935-1973 — J.M. Harrington, G.F. Craun, et al. (1978)
• Epidemiology study of the use of asbestos-cement pipe for the distribution of drinking water in Escambia County, Florida — J.R. Millette, G.F. Craun, et al. (1983)
• Is there a risk to health in using asbestos--cement pipes for the carriage of drinking water? — S.F. McCullagh (1980)
• Evidence of arsenic release promoted by disinfection by-products within drinking-water distribution systems — S.S. Andra, K.C. Makris, et al. (2014)

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