Man-made respirable-sized organic fibers: what do we know about their toxicological profiles?

Our plain-English summary of Man-made respirable-sized organic fibers: what do we know about their toxicological profiles?, by D.B. Warheit, K.L. Reed, T.R. Webb (Industrial Health, 2001).

The study

• Authors: D.B. Warheit, K.L. Reed, T.R. Webb
• Journal: Industrial Health
• Published: 2001;39(2):119-25
• Type of article: Review
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Man-made organic fibers (MMOFs) have been manufactured for over 50 years. Until recently, there have been few concerns raised regarding the safety of organic fiber dusts. This is due, in large part, to the perception that the dimensions of most, if not all, of these products were too large to be inhaled into the distal lungs of workers, i.e., were considered to be nonrespirable. A brief review of some of the issues related to organic fiber toxicology is presented herein. Some of the organic fiber-types used in commerce are identified and some fundamental tenets of fiber toxicology are discussed. In addition, the European Union, in their recent consideration for banning chrysotile asbestos fibers, evaluated some organic fiber substitutes and compared them to the hazards of asbestos. A brief review of their conclusions is described below. Finally, the results of some recent studies assessing the mechanisms of biodegradability of para-aramid respirable-sized, fiber-shaped particulates (RFP) are presented. Para-aramid (p-aramid) RFP are the most extensively-studied respirable organic fiber-type and RFP is the new term which describes respirable-sized organic fibers (ECETOC, 1996) (1). The results of these studies provide clues regarding the mechanism(s) of p-aramid RFP shortening in the lungs of exposed animals, and may be relevant for humans.

In plain English

This review examined the toxicology of man-made organic fibers small enough to reach deep into the lungs, called respirable-sized fiber-shaped particulates (RFP). It described a European Union evaluation of three chrysotile asbestos substitutes, para-aramid, polyvinyl alcohol (PVA) and cellulose fibers. The EU committee concluded that chrysotile is fundamentally more hazardous than all three. The review cited another group's study of 447 PVA-exposed and 2416 non-exposed male workers, which reported a lung cancer SMR of 0.86 for those employed 20 or more years. It also cited rat studies finding para-aramid RFP less biopersistent than chrysotile asbestos. The authors then summarized their own experiments, citing a paper then in press. Rats received para-aramid or cellulose RFP into the lungs. A day later the lungs were dissolved by either an enzyme-based method or a conventional KOH method. The enzyme method, but not KOH, artificially shortened the recovered para-aramid RFP, and neither method changed cellulose RFP lengths. In cell cultures, para-aramid fibrils were shortened where macrophages were present but not in epithelial cells alone. The authors concluded that their results strongly suggest lung fluid components coat and activate para-aramid RFP before enzymes cleave them.

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: Review article, including a summary of the authors' own animal (rat) and laboratory cell-culture experiments on para-aramid fiber breakdown
• Who was studied: The review covered published studies of man-made organic fibers. The authors' own experiments used rats whose lungs were instilled with para-aramid or cellulose RFP. They also used cultures of rat lung epithelial cells, alveolar macrophages and co-cultures of both. The number of animals was not given.
• Exposure: Organic fiber substitutes for chrysotile asbestos (para-aramid, polyvinyl alcohol (PVA) and cellulose fibers), compared with chrysotile asbestos and, in one cited study, crocidolite
• Main results:
  • The European Commission scientific committee (as reviewed) concluded that chrysotile asbestos is fundamentally more hazardous than para-aramid, PVA or cellulose fibers.
  • A cited cohort study by Morinaga and colleagues evaluated 447 PVA-exposed and 2416 non-exposed male workers. It reported a lung cancer SMR of 0.86 for workers with 20 or more years of employment.
  • Cited inhalation studies in rats found that para-aramid RFP were less biopersistent than chrysotile asbestos.
  • A cited exposure study (Cherrie et al.) of para-aramid process workers in the United Kingdom reported geometric mean time-weighted average exposures ranging from 0.005 to 0.4 f/ml.
  • In 1997, IARC used the findings of fibril shortening in two rodent species, and the lack of lung or serosal tumors in rats, to support a Category 3 classification (inadequate evidence for carcinogenicity) for para-aramid.
  • In the authors' experiments, rat lungs were digested 1 day after instillation. The enzyme digestion method, but not the KOH method, artificially reduced the lengths of para-aramid RFP recovered from the lungs. Neither method affected the lengths of cellulose RFP.
  • In the authors' cell-culture experiments, no fibril cleavage was seen in epithelial cell cultures. Cleavage of para-aramid RFP was seen at 1 day and at 1 week in macrophage cultures and in co-cultures.
• The authors' conclusion: The authors concluded that their studies strongly suggest that components of lung fluids coat and activate para-aramid RFP as a prerequisite for enzymatic cleavage. They said this could play a significant role in the shortening of inhaled para-aramid RFP in rats and hamsters.
• Limitations the authors state:
  • The authors noted that little information exists on the lung effects of inhaled man-made organic fibers.
  • The authors noted that there are few data on the lung toxicity of inhaled cellulose RFP.

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.

Related studies

• Comparative hazards of chrysotile asbestos and its substitutes: A European perspective — P.T. Harrison, L.S. Levy, et al. (1999)
• Potential pulmonary effects of man-made organic fiber (MMOF) dusts — D.B. Warheit, G.A. Hart, et al. (2001)
• Lung proliferative and clearance responses to inhaled para-aramid RFP in exposed hamsters and rats: comparisons with chrysotile asbestos fibers — D.B. Warheit, S.I. Snajdr, et al. (1997)
• Pulmonary effects in rats inhaling size-separated chrysotile asbestos fibres or p-aramid fibrils: differences in cellular proliferative responses — D.B. Warheit, M.A. Hartsky, et al. (1996)
• A comparative study of the clearance of respirable para-aramid, chrysotile and glass fibres from rat lungs — A. Searl (1997)
• Assessments of lung digestion methods for recovery of fibers — D.B. Warheit, H.C. Hwang, et al. (1991)

Browse more research in Industrial Health, or return to medical research.