Exposures from chrysotile-containing joint compound: evaluation of new model relating respirable dust to fiber concentrations

Our plain-English summary of Exposures from chrysotile-containing joint compound: evaluation of new model relating respirable dust to fiber concentrations, by G.P. Brorby, P.J. Sheehan, D.W. Berman, et al (Risk Analysis, 2013).

The study

• Authors: G.P. Brorby, P.J. Sheehan, D.W. Berman, K.T. Bogen, S.E. Holm
• Journal: Risk Analysis
• Published: 2013;33(1):161-76
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The potential for fiber exposure during historical use of chrysotile-containing joint compounds (JCC) has been documented, but the published data are of limited use for reconstructing exposures and assessing worker risk. Consequently, fiber concentration distributions for workers sanding JCC were independently derived by applying a recently developed model based on published dust measurements from sanding modern-day (asbestos-free) joint compound and compared to fiber concentration distributions based on limited historical measurements. This new procedure relies on factors that account for (i) differences in emission rates between modern-day and JCC and (ii) the number of fibers (quantified by phase contrast microscopy [PCM]) per mass of dust generated by sanding JCC, as determined in a bench-scale chamber study using a recreated JCC, that convert respirable dust concentrations to fiber concentrations. Airborne respirable PCM-fiber concentration medians (and 95% confidence intervals) derived for output variables using the new procedure were 0.26 (0.039, 1.7) f/cm(3) and 0.078 (0.013, 0.47) f/cm(3) , and corresponding total fiber concentrations were 1.2 (0.17, 9.2) f/cm(3) and 0.37 (0.056, 2.5) f/cm(3) , in enclosed and nonenclosed environments, respectively. Corresponding estimates of respirable and total PCM fiber concentrations measured historically during sanding of asbestos-containing joint compound-adjusted for differences between peak and time-weighted average (TWA) concentrations and documented analytical preparation and sampling artifacts-were 0.15 (0.019, 0.95) f/cm(3) and 0.86 (0.11, 5.4) f/cm(3) , respectively. The PCM-fiber concentration distributions estimated using the new procedure bound the distribution estimated from adjusted TWA historical fiber measurements, suggesting reasonable consistency of these estimates taking into account uncertainties addressed in this study.

© 2012 Society for Risk Analysis.

In plain English

This study tested a model, published earlier by Sheehan et al., for estimating asbestos fiber concentrations from sanding chrysotile-containing joint compound. The model uses dust measurements from sanding modern asbestos-free joint compound. Its conversion factors came from a bench-scale chamber in which a recreated chrysotile joint compound was sanded. In a subset of samples, virtually all fibers were chrysotile. The authors applied the model to respirable dust data from five published studies. They compared the results with fiber measurements from three historical studies, adjusted for sample duration, laboratory preparation method and sampling device. Estimated respirable fiber medians were 0.26 fibers per cubic centimeter (95% interval 0.039 to 1.7) in enclosed settings. The median was 0.078 (0.013 to 0.47) in a nonenclosed category, which combined three well-ventilated samples with 21 lacking ventilation information. The adjusted historical respirable median was 0.15 fibers per cubic centimeter (0.019 to 0.95). In the chamber, open-face cassettes measured significantly higher fiber concentrations than respirable-dust samplers. The authors concluded that the model's predictions were reasonably consistent with historical measurements. They noted that the model factors came from one chrysotile-containing and one modern compound.

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: Exposure-modeling study: a model with conversion factors from bench-scale chamber tests was applied, using probabilistic (Monte Carlo) methods, to published dust measurements, and the results were compared with published historical fiber measurements
• Who was studied: Published measurements, not people studied directly. These were personal respirable dust measurements from five published studies of workers sanding modern-day joint compound (in two Rhodes and Ingalls data sets, asbestos-containing compound). They also included historical fiber measurements, reported as summary statistics in three studies (Rhodes and Ingalls 1976, Fischbein et al. 1979, Verma and Middleton 1980), of workers sanding asbestos-containing joint compound. Bench-scale and room-scale chamber tests were added to these.
• Exposure: Sanding of chrysotile-containing joint compound: a recreated version in the chamber, and historical products in the field studies. Fibers were counted by phase contrast microscopy (PCM) as respirable and total fibers. In a subset analyzed by NIOSH Method 7402, virtually all fibers were chrysotile.
• Main results:
  • Fiber concentrations estimated with the new model, given as medians with 95% intervals. Respirable PCM fibers: 0.26 (0.039, 1.7) f/cm3 in enclosed environments and 0.078 (0.013, 0.47) f/cm3 in nonenclosed environments. Total PCM fibers: 1.2 (0.17, 9.2) f/cm3 in enclosed environments and 0.37 (0.056, 2.5) f/cm3 in nonenclosed environments.
  • The nonenclosed category combined three samples stated to come from open, well-ventilated areas with 21 samples for which no ventilation information was provided.
  • Historical measurements were adjusted for differences between peak and time-weighted average concentrations and for preparation and sampling artifacts. After adjustment, they gave respirable PCM fiber concentrations of 0.15 (0.019, 0.95) f/cm3 and total PCM fiber concentrations of 0.86 (0.11, 5.4) f/cm3.
  • Median estimated fiber concentrations for enclosed environments were about three times those for nonenclosed environments.
  • Median respirable dust concentrations in the published data differed significantly between the nonenclosed category (n = 24) and the enclosed category (n = 10), with p = 0.0041.
  • In the bench-scale chamber, fiber concentrations measured with open-face cassettes (total dust) during sanding were significantly greater than those measured with cyclones (respirable dust). The cassette-to-cyclone ratio extrapolated to the dust source had a median of 5.7.
  • Particle size distributions of respirable dust were consistent between the bench-scale and room-scale chambers. Only the two smallest size ranges differed significantly.
• The authors' conclusion: The authors concluded that the adjusted historical fiber distribution fell between the model's enclosed and nonenclosed estimates. They took this to suggest that the new procedure's predictions are reasonably consistent with historically measured values.
• Limitations the authors state:
  • The model factors were determined from a single chrysotile-containing joint compound and a single modern joint compound, but were applied to all of the published dust data.
  • In the published data, the effects of measurement conditions and the effects of joint compound characteristics could not be separated.
  • The peak-to-time-weighted-average adjustment ratio was estimated from limited data and carried considerable estimation error.
  • The authors suggested that predictions made by applying the model factors generically may be good only to within a factor of three to ten.

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, phase contrast microscopy (PCM), confidence interval, Time-Weighted Average (TWA).

Related studies

• 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)
• 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 — D.W. Berman, G.P. Brorby, et al. (2012)
• Re-creation of historical chrysotile-containing joint compounds — G.P. Brorby, P.J. Sheehan, et al. (2008)
• Potential artifacts associated with historical preparation of joint compound samples and reported airborne asbestos concentrations — G.P. Brorby, P.J. Sheehan, et al. (2011)
• Comparative Risks of Cancer from Drywall Finishing Based on Stochastic Modeling of Cumulative Exposures to Respirable Dusts and Chrysotile Asbestos Fibers — F.W. Boelter, Y. Xia, et al. (2015)
• Lung injury and expression of p53 and p16 in Wistar rats induced by respirable chrysotile fiber dust from four primary areas of China — Y. Zeng, Y. Cui, et al. (2018)

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