More on the dynamics of dust generation: the effects of mixing and sanding chrysotile, calcium carbonate, and other components on the characteristics of joint-compound dusts

Our plain-English summary of More on the dynamics of dust generation: the effects of mixing and sanding chrysotile, calcium carbonate, and other components on the characteristics of joint-compound dusts, by D.W. Berman, G.P. Brorby, P.J. Sheehan, et al (The Annals of Occupational Hygiene, 2012).

The study

• Authors: D.W. Berman, G.P. Brorby, P.J. Sheehan, K.T. Bogen, S.E. Holm
• Journal: The Annals of Occupational Hygiene
• Published: 2012;56(7):852-67
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

An ongoing research effort designed to reconstruct the character of historical exposures associated with use of chrysotile-containing joint compounds naturally raised questions concerning how the character (e.g. particle size distributions) of dusts generated from use of recreated materials compares to dusts from similar materials manufactured historically. This also provided an opportunity to further explore the relative degree that the characteristics of dusts generated from a bulk material are mediated by the properties of the bulk material versus the mechanical processes applied to the bulk material by which the dust is generated. In the current study, the characteristics of dusts generated from a recreated ready mix and recreated dry mix were compared to each other, to dusts from a historical dry mix, and to dusts from the commercial chrysotile fiber (JM 7RF3) used in the recreated materials. The effect of sanding on the character of dusts generated from these materials was also explored. Dusts from the dry materials studied were generated and captured for analysis in a dust generator-elutriator. The recreated and historical joint compounds were also prepared, applied to drywall, and sanded inside sealed bags so that the particles produced from sanding could be introduced into the elutriator and captured for analysis. Comparisons of fiber size distributions in dusts from these materials suggest that dust from commercial fiber is different from dusts generated from the joint compounds, which are mixtures, and the differences persist whether the materials are sanded or not. Differences were also observed between sanded recreated ready mix and either the recreated dry mix or a historical dry mix, again whether sanded or not. In all cases, however, such differences disappeared when variances obtained from surrogate data were used to better represent the 'irreducible variation' of these materials. Even using the smaller study-specific variances, no differences were observed between the recreated dry mix and the historical dry mix, indicating that chrysotile-containing joint compounds can be recreated using historical formulations such that the characteristics of the modern material reasonably mimic those of a corresponding historical material. Similarly, no significant differences were observed between dusts from sanded and unsanded versions of similar materials, suggesting (as in previous studies) that the characteristics of asbestos-containing dusts are mediated primarily by the properties of the bulk material from which they are derived.

In plain English

This laboratory study compared dusts from six materials. They were a dry mix and a ready mix joint compound re-created from historical formulations, a dry mix the article describes as represented to be historical joint compound ('Bestwall'), and the commercial chrysotile fiber (7RF3) used in the re-created products. The joint compounds were applied to drywall and sanded by hand inside sealed bags. Dusts from sanded and unsanded materials were generated in the laboratory and examined by transmission electron microscopy. Most fibers in all the dusts were short, under 5 micrometres. Using the study's own sample variation, fiber size distributions differed significantly across the six materials, but not among sanded and unsanded Bestwall and dry mix. Using larger variation taken from textile-factory surrogate data, no significant differences were found. In the joint-compound dusts more than half of fibers were attached to non-asbestos particles (matrices), compared with 23% for the commercial fiber. The authors concluded that the re-created compound reasonably mimicked the historical material and that sanding had small effects on fiber size. They noted that their own samples may understate true variation.

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 experiment: dusts were generated from bulk materials in a dust generator-elutriator (Modified Elutriator Method) and analyzed by transmission electron microscopy (TEM)
• Who was studied: Six materials: sanded and unsanded re-created dry mix, sanded re-created ready mix, sanded and unsanded 'Bestwall' (a dry mix represented to be historical joint compound), and unsanded commercial chrysotile fiber 7RF3 (from the Johns-Manville mine in Asbestos, Quebec). There were three samples of each material, except two of sanded Bestwall.
• Exposure: Chrysotile in joint compounds that were mostly calcium carbonate with small amounts of binders and anti-fungal agents, plus commercial chrysotile fiber alone. Joint compounds were tested unsanded and after application to drywall and hand sanding inside sealed bags.
• Main results:
  • In the dusts from all materials, 80 to 95% of primary or total fibers were short (under 5 micrometres), and fiber abundance decreased regularly with increasing length.
  • Using variances from this study's samples, fiber length and width distributions differed significantly across the six materials.
  • When the commercial fiber (7RF3) and sanded ready mix were left out, differences among sanded and unsanded Bestwall and sanded and unsanded dry mix disappeared.
  • Using variances from surrogate data (84 airborne dust samples from a South Carolina textile factory), no significant differences were found between materials in fiber length or width categories.
  • No differences were detected between sanded and unsanded Bestwall, or between sanded and unsanded dry mix, even using the study's own smaller variances.
  • In the five joint-compound materials, mean fractions of primary structures that were matrices ranged from 0.56 to 0.80, and mean fractions of fibers in matrices from 0.57 to 0.83 (Table 1). In the commercial fiber 7RF3 these fractions were 18% and 23%, respectively.
  • Matrix fractions differed significantly across all materials (P less than 0.00001). When both 7RF3 and sanded ready mix were excluded, there were no significant differences between Bestwall and dry mix, sanded or not.
• The authors' conclusion: The authors concluded that chrysotile-containing joint compounds can be re-created from historical formulations so that the modern material reasonably mimics the historical one. They also concluded that joint-compound dusts differ from commercial fiber dust because most of their fibers are associated with matrices. Finally, they concluded that sanding has small effects on fiber size and mainly breaks up the hardened matrix rather than the fibers.
• Limitations the authors state:
  • The samples of each material were homogenized splits of one another, so they leave out variation over time in the commercial fiber and may understate true variation.
  • The surrogate data came from textile Grade 3 fiber. The authors assumed its variation was roughly equivalent to that of the Grade 7 fiber used in joint compound.
  • The authors lacked samples manufactured over broadly varying time frames, so they used surrogate data instead.
  • No surrogate data were available for the matrix comparisons.
  • Only two sanded Bestwall samples could be produced because little unsanded Bestwall was available.
  • More samples might change the finding of no sanding effect.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Jeffrey mine, Asbestos, Quebec

All asbestos mines

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Chrysotile, Joint Compound.

Related studies

• Potential artifacts associated with historical preparation of joint compound samples and reported airborne asbestos concentrations — G.P. Brorby, P.J. Sheehan, et al. (2011)
• Re-creation of historical chrysotile-containing joint compounds — G.P. Brorby, P.J. Sheehan, et al. (2008)
• Chamber for testing asbestos-containing products: validation and testing of a re-created chrysotile-containing joint compound — P.J. Sheehan, G.P. Brorby, et al. (2011)
• Exposures from chrysotile-containing joint compound: evaluation of new model relating respirable dust to fiber concentrations — G.P. Brorby, P.J. Sheehan, et al. (2013)
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• Re: Evaluation of the size and type of free particulates collected from unused asbestos-containing brake components as related to potential for respirability — D.J. Paustenbach, B.L. Finley, et al. (2006)

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