Comparing milled fiber, Quebec ore, and textile factory dust: has another piece of the asbestos puzzle fallen into place?

Our plain-English summary of Comparing milled fiber, Quebec ore, and textile factory dust: has another piece of the asbestos puzzle fallen into place?, by D.W. Berman (Critical Reviews in Toxicology, 2010).

The study

• Author: D.W. Berman
• Journal: Critical Reviews in Toxicology
• Published: 2010;40(2):151-88
• Type of article: Review
• Cited by: 25 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Results of a meta-analysis indicate that the variation in potency factors observed across published epidemiology studies can be substantially reconciled (especially for mesothelioma) by considering the effects of fiber size and mineral type, but that better characterization of historical exposures is needed before improved exposure metrics potentially capable of fully reconciling the disparate potency factors can be evaluated. Therefore, an approach for better characterizing historical exposures, the Modified Elutriator Method (MEM), was evaluated to determine the degree that dusts elutriated using this method adequately mimic dusts generated by processing in a factory. To evaluate this approach, elutriated dusts from Grade 3 milled fiber (the predominant feedstock used at a South Carolina [SC] textile factory) were compared to factory dust collected at the same facility. Elutriated dusts from chrysotile ore were also compared to dusts collected in Quebec mines and mills. Results indicate that despite the substantial variation within each sample set, elutriated dusts from Grade 3 fiber compare favorably to textile dusts and elutriated ore dusts compare to dusts from mines and mills. Given this performance, the MEM was also applied to address the disparity in lung cancer mortality per unit of exposure observed, respectively, among chrysotile miners/millers in Quebec and SC textile workers. Thus, dusts generated by elutriation of stockpiled chrysotile ore (representing mine exposures) and Grade 3 milled fiber (representing textile exposures) were compared. Results indicate that dusts from each sample differ from one another. Despite such variation, however, the dusts are distinct and fibers in Grade 3 dusts are significantly longer than fibers in ore dusts. Moreover, phase-contrast microscopy (PCM) structures in Grade 3 dusts are 100% asbestos and counts of PCM-sized structures are identical, whether viewed by PCM or transmission electron microscope (TEM). In contrast, a third of PCM structures in ore dusts are not asbestos and only a third that are counted by PCM are also counted by TEM. These distinctions also mirror the characteristics of the bulk materials themselves. Perhaps most important, when the differences in size distributions and PCM/TEM distinctions in these dusts are combined, the combined difference is sufficient to completely explain the difference in exposure/response observed between the textile worker and miner/miller cohorts. Importantly, however, evidence that such an explanation is valid can only be derived from a meta-analysis (risk assessment) covering a diverse range of epidemiology study environments, which is beyond the scope of the current study. The above findings suggest that elutriator-generated dusts mimic factory dusts with sufficient reliability to support comparisons between historical exposures experienced by the various cohorts studied by epidemiologists. A simulation was also conducted to evaluate the relative degree that the characteristics of dust are driven by the properties of the bulk material processed versus the nature of the mechanical forces applied. That results indicate it is the properties of bulk materials reinforces the theoretical basis justifying use of the elutriator to reconstruct historical exposures. Thus, the elutriator may be a valuable tool for reconstructing historical exposures suitable for supporting continued refinements of the risk models being developed to predict asbestos-related cancer risk.

In plain English

In this article, labeled a review, the author generated dust in a laboratory device (the Modified Elutriator Method) from three samples each of Quebec chrysotile ore and Grade 3 milled fiber used for textiles. Grade 3 dust had significantly longer structures. In two Grade 3 samples, counts of PCM-sized structures by phase-contrast microscopy (PCM) and transmission electron microscopy (TEM) were virtually identical. For ore dust, TEM counted about one third as many as PCM, and the text reported 20% to 30% of these as not asbestos, though its table lists one ore sample at 64% asbestos. For primary fibers and bundles, the author found no evidence of a real size-distribution difference between Grade 3 dust and archived 1964 to 1968 South Carolina textile plant air samples, and called this preliminary. Combined, the size and counting differences gave factors of up to 30. An earlier estimate had put lung cancer potency 47 times higher for South Carolina textile workers than for Quebec miners and millers. The author called these results only suggestive and concluded the elutriator may be a valuable tool for reconstructing historical exposures.

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 comparison of dusts generated with the Modified Elutriator Method against archived and published air-sample data, with a randomization simulation. The journal labels it a review article, but it reports original analyses.
• Who was studied: Bulk samples rather than people. Three ore samples stockpiled in 2000 at the Jeffrey Mine, Asbestos, Quebec, and three samples of 3T-12 (Grade 3) milled fiber produced at the same mine between 1964 and 1986. These were compared with 83 of 84 archived air filters from a South Carolina textile plant (NIOSH surveys, 1964 to 1968, data from Dement et al. 2007) and with published distributions from Dement and Harris (1979) and Gibbs and Hwang (1980).
• Exposure: Chrysotile: raw ore (representing exposures of Quebec miners and millers) versus Grade 3 milled fiber (representing exposures of South Carolina textile workers). Dusts were analyzed by PCM and TEM, sorted by structure length and width.
• Main results:
  • Elutriated dust from Grade 3 milled fiber contained significantly longer structures than dust from ore (Mann-Whitney tests on three samples each). The category of structures longer than 10 µm was not significant (p = .1).
  • In the two Grade 3 samples with paired PCM and TEM analyses, PCM-sized structures counted by TEM were 100% asbestos, and counts of PCM-sized structures were virtually identical by PCM and TEM.
  • In ore dust, TEM counts of all PCM-sized structures (PCMEall) were only about one third of PCM counts.
  • Of the PCM-sized structures identified by TEM in ore dust, the text says 20% to 30% were nonasbestos material. The table lists one ore sample at 64% asbestos.
  • The target figure came from earlier work, not this study: Berman and Crump (2008a) estimated the lung cancer potency factor for the South Carolina textile cohort at about 47 times that for Quebec chrysotile miners and millers.
  • Combining the size adjustment (up to about 5) with the PCME/PCM adjustment (3.9 to 5.3) gave factors of up to about 30. The author calculated this would reduce the 47-fold difference between the textile and mining cohorts to less than a factor of 2.
  • The author compared size distributions of primary fibers and bundles in the 83 archived South Carolina factory samples with the three elutriated Grade 3 samples across 20 size categories. Only two categories differed under both ways of handling zero counts, and the author judged these to be an artifact and a chance finding. The author called the result preliminary and recommended further evaluation.
  • Comparisons between the factory dusts and the elutriated dusts were restricted to primary structures.
  • Comparing the South Carolina factory samples with elutriated ore dust, three size categories differed consistently, two of them at p less than .001. The author interpreted this as ore dust structures being shorter than those at the textile factory.
  • Against published textile factory distributions (Dement and Harris 1979; Dement et al. 2007), the greatest difference in any size category for Grade 3 dust was less than a factor of 3.
  • Against the published Quebec mine and mill distribution (Gibbs and Hwang 1980), agreement for ore dust was described as reasonable, with one category differing by about a factor of 4.
  • In a simulation that randomly regrouped the South Carolina samples 1000 times, the variation between the factory's 10 zones was within the 25th to 75th percentiles of random groupings for all length categories except 20 to 40 µm. The author took this to mean zone differences were driven mainly by variation in feedstock over time rather than by the mechanical processes in each zone.
• The authors' conclusion: The author concluded that elutriator-generated dusts mimic factory dusts closely enough to support comparisons of historical exposures, and that the elutriator may be a valuable tool for reconstructing them. The author also concluded that size and PCM/TEM differences could potentially explain the textile versus mining difference in lung cancer potency, but that confirming this requires a broader meta-analysis.
• Limitations the authors state:
  • The reconciliation of the two cohorts' lung cancer potencies is only suggestive. The study is not a formal risk assessment and would need a meta-analysis across many environments.
  • Smoking and other factors affecting asbestos-related cancer risk were not considered.
  • The factory and elutriated samples were analyzed by different laboratories using different novel methods, years apart, which adds variation.
  • The Grade 3 samples and the factory dust samples cover largely different time periods.
  • Comparisons with published (summarized) distributions could only be made visually, not statistically.
  • The paired PCM/TEM comparison covered only five of the six samples, because one was lost.
  • Too few samples were analyzed to draw inferences about tremolite content.

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

Medical terms in this study, explained in our Lexicon: Meta-Analysis, Epidemiology, Mesothelioma, Chrysotile, Lung Cancer.

Related studies

• Letter to the editor: "Comparing milled fiber, Quebec ore, and textile factory dust: has another piece of the asbestos puzzle fallen into place?" by D. Wayne Berman — J.M. Dement, L.T. Stayner (2010)
• SV40, growth factors, and mesothelioma: another piece of the puzzle — B.T. Mossman, D.C. Gruenert (2002)
• Estimates of historical exposures by phase contrast and transmission electron microscopy in North Carolina USA asbestos textile plants — J.M. Dement, D. Myers, et al. (2009)
• Environmental measurements of total dust and fiber concentration in manufacturer and user of man-made mineral fibers — J.H. Kim, H.S. Chang, et al. (1999)
• Potential pulmonary effects of man-made organic fiber (MMOF) dusts — D.B. Warheit, G.A. Hart, et al. (2001)
• Exposure to brake dust and malignant mesothelioma: a study of 10 cases with mineral fiber analyses — K.J. Butnor, T.A. Sporn, et al. (2003)

Browse more research in Critical Reviews in Toxicology, or return to medical research.