Assessment of airborne asbestos exposure at an asbestos cement sheet and pipe factory in Iran

Our plain-English summary of Assessment of airborne asbestos exposure at an asbestos cement sheet and pipe factory in Iran, by H. Marioryad, H. Kakooei, S.J. Shahtaheri, et al (Regulatory Toxicology and Pharmacology, 2011).

The study

• Authors: H. Marioryad, H. Kakooei, S.J. Shahtaheri, M. Yunesian, K. Azam
• Journal: Regulatory Toxicology and Pharmacology
• Published: 2011;60(2):200-5
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Iran imports nearly 55,000 metric tons of asbestos per year, and asbestos cement (AC) plants contribute nearly 94% of the total national usage. In the present study, asbestos fiber concentrations during AC sheet and pipe manufacturing were measured by phase-contrast microscopy (PCM) and polarized light microscopy (PLM) in 98 personal air samples. The fiber type and its chemical composition were also evaluated by scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). Personal monitoring of fiber levels indicated a range from 0.02 to 0.55PCM f/ml (0.02-0.69PLM f/ml). The AC workers' geometric mean asbestos exposure was 0.09 PCM f/ml (0.11 PLM f/ml), with arithmetic mean of 0.13 PCM f/ml (0.16 PLM f/ml). The observed fiber concentrations in many processes were higher than the threshold limit value (TLV) proposed by the American Conference of Governmental Industrial Hygienists (ACGIH), which is 0.1 f/ml. Based on these findings, the PLM values were approximately 25% higher than PCM values. The SEM data demonstrate that fibrous particles contained chrysotile. The thinnest fiber recognized by SEM had a diameter of 0.2μm. Mean exposure exceeded the TLV for asbestos in pipe molding and finishing (100%) as well as sheet molding and finishing (45.5-83.3%). In conclusion exposure control may be needed to be in compliance with the ACGIH TLV and other guidance levels. Also, with regard to PCM limitations for airborne fiber analysis, the use of microscopic methods other than PCM can be used to improve the techniques used presently.

Copyright © 2011 Elsevier Inc. All rights reserved.

In plain English

This study measured airborne asbestos at one asbestos cement sheet and pipe factory in Tehran, Iran, in 2010. The factory employed 350 workers, and chrysotile made up 14 to 20% of its raw materials. The authors collected 98 personal air samples from different work areas. They counted fibers with two light-microscope methods, phase-contrast (PCM) and polarized light (PLM), and checked fiber type by scanning electron microscopy. Results were in fibers per milliliter of air (f/ml). Samples ranged from 0.02 to 0.55 f/ml by PCM (0.02 to 0.69 by PLM). The overall geometric mean was 0.098 f/ml by PCM. Half the samples (49 of 98) were above the 0.1 f/ml limit set by the ACGIH. Every sample from pipe molding, pipe finishing and recycling (residual mill) was above it. Recycling had the highest geometric mean, 0.450 f/ml by PCM. PLM counts were higher than PCM counts (p less than 0.05). Only chrysotile was found, with no amphiboles. The authors concluded that methods other than PCM could improve fiber measurement. They said it is unknown whether these exposures have health consequences for the workers.

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: Cross-sectional workplace air-sampling (exposure assessment) study using personal air samples counted by PCM and PLM, with SEM and energy-dispersive X-ray analysis to identify fiber type
• Who was studied: 98 personal air samples from different work areas of one asbestos cement sheet and pipe plant in Tehran, Iran, in 2010. The factory employed 350 workers with a mean age of 40 years and mean employment length of 15 years.
• Exposure: Airborne asbestos fibers during asbestos cement sheet and pipe manufacturing (a wet process). Raw materials were chrysotile (14–20%), polypropylene fibers (under 1%) and cement (75–80%). Work areas included storage, raw-material feeding, sheet and pipe molding, sheet and pipe finishing (cutting, drilling, grinding), recycling, laboratory, administration and others.
• Main results:
  • All 98 samples: concentrations ranged from 0.02 to 0.55 f/ml by PCM and 0.02 to 0.69 f/ml by PLM. The geometric mean was 0.098 f/ml by PCM (geometric standard deviation 2.23) and 0.118 f/ml by PLM (2.26).
  • 50% of the personal samples (49 of 98) exceeded the ACGIH threshold limit value of 0.1 f/ml.
  • All samples exceeded the 0.1 f/ml limit in pipe molding (12 of 12), pipe finishing (13 of 13) and the recycling process, or residual mill (7 of 7).
  • Sheet finishing: 10 of 12 samples (83.3%) exceeded the limit, with a PCM arithmetic mean of 0.168 f/ml.
  • Sheet molding: 5 of 11 samples (45.5%) exceeded the limit, with a PCM arithmetic mean of 0.085 f/ml.
  • The highest geometric mean was in the recycling process (residual mill): 0.450 PCM f/ml, geometric standard deviation 1.14. The lowest was in the laboratory: 0.039 PCM f/ml, geometric standard deviation 1.45.
  • Arithmetic and geometric means from PLM counts were higher than those from PCM counts (p less than 0.05).
  • Electron microscopy found only chrysotile asbestos in the samples examined. The authors state the chrysotile used in this factory contained no amphiboles, and no polypropylene fibers were seen in the samples.
• The authors' conclusion: The authors concluded that, because PCM has limitations for airborne fiber analysis, other microscopic methods could improve current techniques. They noted that 50% of samples exceeded the 0.1 f/ml level. They recommended periodic monitoring, engineering controls and respiratory protection to comply with OSHA and NIOSH recommendations.
• Limitations the authors state:
  • Fiber counting by PCM, especially of chrysotile, may underestimate airborne asbestos levels.
  • The study measured exposure only. The authors state it is unknown whether these exposures have health consequences for the workers.

Topics

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

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Asbestos-Cement, Polarized Light Microscopy (PLM), Scanning Electron Microscopy (SEM), Threshold Limit Value (TLV), Chrysotile.

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