Mobilization of asbestos fibers by weathering of a corrugated asbestos cement roof

Our plain-English summary of Mobilization of asbestos fibers by weathering of a corrugated asbestos cement roof, by T. Ervik, S. Eriksen Hammer, P. Graff (Journal of Occupational and Environmental Hygiene, 2021).

The study

• Authors: T. Ervik, S. Eriksen Hammer, P. Graff
• Journal: Journal of Occupational and Environmental Hygiene
• Published: 2021;18(3):110-117
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Mobilization of asbestos fibers from a 60-year-old corrugated asbestos cement roof was studied in material samples collected from a domestic house in Southern-Norway. Samples included pieces of the roof itself, rainfall simulated run off-water and moss growing on the roof surface. Weathered roof debris below the rain water system was investigated for asbestos fibers leached from the roof, and air samples were collected for asbestos concentrations in ambient air. Micrographs obtained by scanning electron microscopy show that weathering exposed asbestos fibers on the deteriorated roof surface. A high number of fibers found in the run off-water as well as in the weathered roof debris sample illustrates that exposed fibers are prone to mobilization. Investigation of weathering-induced magnesium depletion by scanning electron microscopy energy dispersive X-ray spectroscopy of asbestos fibers collected from the moss, roof underside and surface revealed that fibers had MgO weight % comparable to reference material. The major element chemistry of the fibers is therefore unaltered. Our findings demonstrate that care must be taken when working on and handling old corrugated asbestos cement roof as asbestos fibers might be released. In order to limit exposure to mobile fibers, moss covering asbestos cement roof should not be removed.

In plain English

This short report was a case study of asbestos fibers loosening from a weathered corrugated asbestos cement roof on one house in southern Norway. The roof was fitted in the 1960s and had been exposed to weathering for more than 50 years. The authors examined roof pieces, moss growing on the roof, gutter debris, water poured over the roof to imitate rain, and one 7-hour air sample. Chrysotile, amosite and crocidolite fibers were identified. Fibers were clearly exposed on the upper surface, while the underside showed almost none. A high number of fibers were found in the run-off water, chrysotile was found in the gutter debris, and fibers were tangled in the moss. The authors said sampling uncertainties were too large to reliably quantify asbestos in these samples. Roofs from six other Norwegian houses showed similar deterioration. No fibers were detected in the air sample, which was taken inside wind-sheltering plastic sheeting. Chrysotile fibers showed no significant magnesium loss. The authors concluded that care is needed when working on old roofs and that moss should not be removed.

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: Case study (short report) of one house: laboratory examination of material, water and air samples, mainly by scanning electron microscopy with X-ray chemical analysis
• Who was studied: One wooden domestic house in southern Norway with a corrugated asbestos cement roof. The authors also examined roof samples from six other houses elsewhere in Norway.
• Exposure: A weathered corrugated asbestos cement roof fitted in the 1960s. Chrysotile, amosite and crocidolite fibers were identified in the samples.
• Main results:
  • On the weathered upper roof surface, asbestos fibers were clearly exposed. The underside of the roof had almost no visible fibers.
  • Fibers of chrysotile, amosite and crocidolite were identified in the roof, gutter debris and run-off water samples.
  • A high number of fibers were found in the run-off water collected after water was poured over the roof. The fibers were not quantified.
  • Chrysotile fibers were found in the weathered debris collected from the roof gutter.
  • Asbestos fibers were tangled into the moss growing on the roof.
  • Roofs from six other houses around Norway showed similar deterioration. Where roof paint was intact, few fibers were visible.
  • No fibers were detected in the air sample, which was collected for 420 minutes inside plastic sheeting on scaffolding. The concentration was below the detection limit of 0.0012 fibers/cm3.
  • Chrysotile fibers from the moss (n = 53), the uncovered roof surface (n = 34) and the roof underside (n = 23) were analyzed for chemical composition. No significant magnesium (MgO) depletion was observed.
• The authors' conclusion: The authors concluded that weathering leaves a layer of loosely bound fibers on the roof surface. In their view, caution is required when washing, working or walking on, or removing old roofs, and moss already on such roofs should not be removed because removing it might increase the number of mobile fibers. They considered the fibers chemically unchanged by weathering.
• Limitations the authors state:
  • Sampling uncertainties were too large to quantify asbestos fibers in the gutter debris, moss and run-off water samples. These uncertainties included sample load and sample loss. The authors described the uncertainty in counting fibers as smaller.
  • The study was limited to one house.
  • The air sample was taken inside plastic sheeting on scaffolding, which protected the area from wind during measurement.
  • Small cement particles attached to the fiber bundles influenced the chemical analysis. The slight differences in MgO were probably biased by these particles.
  • X-ray chemical information was not obtained from the moss material samples. Fiber types in the moss were identified by shape only.
  • The spot analysis method was restricted by the area of the fibers investigated.

Topics

Medical terms in this study, explained in our Lexicon: Asbestos-Cement, Scanning Electron Microscopy (SEM), energy dispersive X-ray spectroscopy (EDS).

Related studies

• Releasability of asbestos fibers from weathered roof cement — A.F. Oberta, L. Poye, et al. (2018)
• Asbestos Exposure Level and the Carcinogenic Risk Due to Corrugated Asbestos-Cement Slate Roofs in Korea — E.S. Lee, Y.K. Kim (2021)
• Changes in concentrations and characteristics of asbestos fibers dispersed from corrugated asbestos cement sheets due to stabilizer treatment — H.S. Jung, J. Jang, et al. (2021)
• Lichens on asbestos-cement roofs: bioweathering and biocovering effects — S.E. Favero-Longo, D. Castelli, et al. (2009)
• Risk assessment of the decay of asbestos cement roofs — A. Campopiano, D. Ramires, et al. (2009)
• The effect of weathering on ecopersistence, reactivity, and potential toxicity of naturally occurring asbestos and asbestiform minerals — S. Enrico Favero-Longo, F. Turci, et al. (2009)

Browse more research in Journal of Occupational and Environmental Hygiene, or return to medical research.