An environmental survey in chrysotile asbestos milling processes in India

Our plain-English summary of An environmental survey in chrysotile asbestos milling processes in India, by A.K. Mukherjee, H.R. Rajmohan, S.K. Dave, et al (American Journal of Industrial Medicine, 1992).

The study

• Authors: A.K. Mukherjee, H.R. Rajmohan, S.K. Dave, B.K. Rajan, Y. Kakde, S.R. Rao
• Journal: American Journal of Industrial Medicine
• Published: 1992;22(4):543-51
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Environmental monitoring to determine airborne asbestos fiber levels has been carried out in four different mills processing chrysotile asbestos in the Cuddapah District (Andhra Pradesh) of India. The "membrane filter method" comprising standard asbestos sampling techniques, acetone-triacetin method for sample preparation, fiber counting, and sizing using the phase contrast optical microscope were adopted in the study. Fiber concentrations both with respect to personal exposures and processing areas were found in most of the cases to be much higher than the prescribed Threshold Limit Value (TLVs) of the developed and developing countries for chrysotile asbestos. By optical microscopy, fiber length distribution showed 70% of fibers in the milling processes were in size range > 5-10 microns, whereas in > 10-20 and > 20 microns, 20% and 8%, respectively. Fiber identification for major elemental content, also done by using scanning electron microscope equipped with an energy dispersive X-ray analyzer, indicated the presence of tremolite along with chrysotile. The study stresses the urgent need to adopt suitable engineering controls at the dust generating sources to reduce the fiber level in the mill environment below the threshold limit.

In plain English

This 1989 survey measured airborne fibers in four mills processing chrysotile asbestos in Cuddapah District, Andhra Pradesh, India. The authors analysed 106 short-term, personal and static air samples by phase contrast optical microscopy. They wrote that all short-term values were well above India's 2 fibers/cm3 standard, though their table shows one range starting at 1.9. The authors placed the highest level, 26 times the limit, in the fiber room during collection; this appears to be an average, as one decorticator range reached 57.7 fibers/ml. Personal samples exceeded the limit in almost all cases; static averages did everywhere except the jaw crusher. Of sized fibers longer than 5 µm, 66.5% to 76.5% were up to 10 µm long and 4.1% to 12.4% exceeded 20 µm. Electron microscopy found magnesium, silicon and calcium; the authors said calcium could reflect tremolite or rock particles, but their conclusions treated tremolite as present. A medical examination of 637 workers found asbestosis in 21.1% of mill workers and 3.3% of mine workers. The authors concluded high fiber levels may be the major contributing factor to mill workers' asbestosis.

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: environmental (airborne fiber) survey, with a medical examination of workers carried out in the same period
• Who was studied: Four asbestos mills (A, B, C, D) in Cuddapah District, Andhra Pradesh, India, studied in 1989; 106 environmental air samples analysed; medical examination of 637 mine and mill workers
• Exposure: Airborne chrysotile asbestos fibers in milling processes (jaw crusher, pulverizer, lime-mix/edge runner, huller, eccentric screens, decorticator, fiber room, manual screening), with tremolite reported as a possible contaminant
• Main results:
  • Short-term samples near processes: the authors wrote that all values were well above the Indian standard for chrysotile asbestos of 2 fibers/cm3. Their short-term table, however, includes one sample range starting at 1.9 fibers/ml.
  • Short-term table: one range runs from 1.9 to 8.2 fibers/ml, which is below the 2 fibers/cm3 standard at its lower end
  • The authors described the highest fiber level as 26 times the prescribed TLV, found in the fiber room during fiber collection. This appears to correspond to a process average (about 51.7 fibers/ml) rather than the highest single reading.
  • In the short-term table, a decorticator sample range reached 57.7 fibers/ml
  • When the same processes were compared, the highest concentrations were always in Mill A, the largest of the four mills
  • Personal samples for mill workers were above the TLV in almost all cases
  • Static area samples: average fiber levels were above the TLV around all processes except the jaw crusher
  • Optical sizing counted only fibers longer than 5 µm. Among those fibers, 66.5% to 76.5% were over 5 and up to 10 µm long, 15.9% to 21.0% were over 10 and up to 20 µm, and 4.1% to 12.4% were over 20 µm.
  • Fiber length ranges across processes (sized fibers longer than 5 µm only)
  • No significant difference in fiber length distribution was observed between milling processes
  • More than 70% of fibers were less than 1.6 µm in diameter
  • SEM with X-ray analysis of a few samples showed magnesium, silicon and calcium. The authors stated the calcium may be due to tremolite along with chrysotile or to fine particles from the chrysotile-bearing rock.
  • Medical examination of 637 workers: overall asbestosis prevalence was 11.5%; it was 21.1% among milling workers compared with 3.3% among mining workers
• The authors' conclusion: The authors concluded that the very high chrysotile fiber concentrations in the four mills may be the major contributing factor to the higher prevalence of asbestosis among mill workers. They also concluded that immediate measures to reduce fiber levels are essential, and that the presence of tremolite as a contaminant in Indian chrysotile calls for thorough medical examination of chrysotile mining and milling workers.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Membrane Filter Method, Triacetin, Fiber Counting, Threshold Limit Value (TLV), Fiber Length, Fiber Identification, Tremolite.

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