Estimates of historical exposures by phase contrast and transmission electron microscopy for pooled exposure--response analyses of North Carolina and South Carolina, USA asbestos textile cohorts

Our plain-English summary of Estimates of historical exposures by phase contrast and transmission electron microscopy for pooled exposure--response analyses of North Carolina and South Carolina, USA asbestos textile cohorts, by J.M. Dement, D. Loomis, D. Richardson, et al (Occupational and Environmental Medicine, 2011).

The study

• Authors: J.M. Dement, D. Loomis, D. Richardson, S.H. Wolf, E.D. Kuempel
• Journal: Occupational and Environmental Medicine
• Published: 2011;68(8):593-8
• Cited by: 14 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: To develop pooled size-specific asbestos fiber exposure estimates for North Carolina and South Carolina asbestos textile plants.

Methods: Airborne sample data and prior exposure estimates by phase-contrast microscopy (PCM) for the two cohorts were reviewed and compared. Estimates by transmission electron microscopy (TEM) for 160 membrane filter samples from all plant were pooled. Poisson regression models were developed to predict bivariate diameter/length airborne fiber size distributions based on independent categorical variables for fiber diameter, fiber length, plant, and exposure zone. The model predicted bivariate diameter/length distributions were expressed as the proportion of fibers in 28 size-specific cells and these data were used to calculate PCM to TEM adjustment factors in order to estimate fiber size-specific exposures for the pooled cohort.

Results: Exposure levels in the North Carolina plants were in excess of 50 f/cc for many operations through about 1955 owing to lack of dust control measures in early years whereas levels in the South Carolina plant were generally less than 10 f/cc by about 1950. The Poisson regression models found covariates for plant department to be a stronger predictor of bivariate size proportions than plant; however, a plant effect was observed. The final Poisson models demonstrated good fit to the observed data.

Conclusions: Consistent with early studies, fiber exposures in the North Carolina plants were much higher than in South Carolina plant. Use of the predicted size-specific TEM exposures by plant and department based on the Poisson model predictions should reduce exposure.

In plain English

This study estimated asbestos fibre exposures in four US asbestos textile plants, three in North Carolina and one in Charleston, South Carolina, to prepare for pooled lung cancer analyses of their workers. It did not examine disease. The authors compared previously published phase contrast (optical) microscopy exposure estimates. They also pooled electron microscopy results from 160 archived air filter samples (83 South Carolina, 77 North Carolina). A Poisson regression model, built on 38 490 fibres or fibre bundles, predicted fibre width and length proportions by plant and department. Exposures in the North Carolina plants exceeded 50 fibres per cc for many operations through about 1955. South Carolina levels were generally below 10 fibres per cc by about 1950. Department predicted fibre size more strongly than plant, though plant also had a statistically significant effect. Predicted fibre size fractions correlated closely with observed ones (overall correlation 0.99), but several predicted adjustment factors for converting optical counts differed from observed values by 25% or more, mostly in North Carolina plants with sparse counts. The authors concluded the model-based estimates should reduce exposure misclassification.

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 assessment and statistical modelling study (Poisson regression of electron microscopy fibre size data) supporting planned pooled epidemiological analyses of lung cancer risk
• Who was studied: Four asbestos textile plants: three in North Carolina and one in Charleston, South Carolina. 160 archived membrane filter air samples (83 from the South Carolina plant, 77 from the three North Carolina plants), collected from the mid-1960s through the early 1970s. Phase contrast exposure estimates covered 1935 to 1975.
• Exposure: Airborne asbestos fibres in textile production departments (preparation, carding, spinning, twisting, weaving, winding, finishing and shipping). Exposure was measured as fibres per cc by phase contrast microscopy and by fibre diameter and length with transmission electron microscopy. The article body does not name the asbestos fibre type.
• Main results:
  • Exposure levels in the North Carolina plants were above 50 f/cc for many operations through about 1955. Levels in the South Carolina plant were generally below 10 f/cc by about 1950.
  • The North Carolina plants' exposures were much higher than the South Carolina plant's, especially in fibre preparation and carding.
  • 38 490 fibres or fibre bundles were included in the combined data set used for the Poisson model.
  • Textile department (exposure zone) had much stronger effects on fibre size than plant. The plant effect was still statistically significant (p less than 0.05) after zone was included.
  • Observed and model-predicted fibre diameter/length size fractions were highly correlated, with an overall Pearson correlation coefficient of 0.99.
  • For fibres longer than 5 (unit printed as 'mm', see text problems), the Pearson correlation coefficient between observed and predicted size fractions was 0.94.
  • Several model-predicted PCM-to-TEM adjustment factors differed from the observed factors calculated from raw data by 25% or more. Most of these were in North Carolina plants where fibre counts were sparser.
  • In the South Carolina twisting department, the predicted adjustment factor for the thinnest fibres (diameter under 0.25) longer than 5 was about 50% higher than observed.
  • In the electron microscopy data from the four plants, most airborne fibres were shorter than 5. A substantial fraction of fibres longer than 5 were too thin to be detected by phase contrast optical microscopy.
  • For size categories with zero observed fibres (about 10% of cells in the North Carolina raw data), the model predicted fractions of 0.0088% to 0.0491%.
• The authors' conclusion: The authors concluded that North Carolina workers had much higher exposures than South Carolina workers. They concluded that using the Poisson model-predicted size-specific electron microscopy exposures should reduce exposure misclassification in later exposure-response analyses.
• Limitations the authors state:
  • Fewer samples were analysed by electron microscopy for the North Carolina plants, giving more statistical noise in their size distributions.
  • Lack of information on process and control changes over time in the North Carolina plants prevented pooled modelling of the phase contrast exposure data.
  • Occupational histories and exposure data were of lower quality for the North Carolina plants than for the South Carolina cohort.
  • The final Poisson model showed slight overdispersion, which the authors adjusted for.

Topics

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

Medical terms in this study, explained in our Lexicon: Transmission Electron Microscopy (TEM), Fiber Length, Dust Control.

Related studies

• 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)
• Lung cancer mortality in North Carolina and South Carolina chrysotile asbestos textile workers — L. Elliott, D. Loomis, et al. (2012)
• Lung cancer mortality and fibre exposures among North Carolina asbestos textile workers — D. Loomis, J.M. Dement, et al. (2009)
• A technical comparison of evaluating asbestos concentration by phase-contrast microscopy (PCM), scanning electron microscopy (SEM), and analytical transmission electron microscopy (ATEM) as illustrated from data generated from a case report — R.F. Dodson, S.P. Hammar, et al. (2008)
• Assessment of occupational exposure to asbestos fibers: Contribution of analytical transmission electron microscopy analysis and comparison with phase-contrast microscopy — C. Eypert-Blaison, A. Romero-Hariot, et al. (2018)
• Comments on Dodson et al., A technical comparison of evaluating asbestos concentration by phase contrast microscopy (PCM), scanning electron microscopy (SEM), and analytical transmission electron microscopy (ATEM) as illustrated from data generated from a case report — V.L. Roggli, T.A. Sporn, et al. (2008)

Browse more research in Occupational and Environmental Medicine, or return to medical research.