An update on the detoxification processes for silica particles and asbestos fibers: successess and limitations

Our plain-English summary of An update on the detoxification processes for silica particles and asbestos fibers: successess and limitations, by M. Gulumian (Journal of Toxicology and Environmental Health. Part B, Critical Reviews, 2005).

The study

• Author: M. Gulumian
• Journal: Journal of Toxicology and Environmental Health. Part B, Critical Reviews
• Published: 2005;8(6):453-83
• Type of article: Review
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Inhalation of asbestos fibers and crystalline silica produces a number of diseases including fibrosis and cancer. Investigations into the mechanisms involved in mineral particle-induced toxicity indicated the importance of their surfaces in the pathological consequences. Masking of the surface sites has therefore featured prominently in a number of detoxification processes that have been investigated. The majority of the detoxification processes were, however, conducted to elucidate the involvement of a particular surface site in the toxicity of a specific mineral. Others were investigated with the aim of large industrial applications to be applied during mining, handling, processing, transporting, and disposing of minerals. It can be concluded that, to date, there is no single detoxification process that could be applied universally to all different types of mineral particles. Those that have shown some success could not completely abolish all adverse effects. Further elucidation of mechanisms of particle-induced toxicity may open new possibilities for detoxification processes.

In plain English

This article was a review in which the author summarized published processes intended to make asbestos fibers (chrysotile, crocidolite and amosite) and crystalline silica less toxic, mainly by changing or covering the particle surfaces. It covered chemical methods (metal coatings, chelating agents, phosphorus fixation, organosilane coatings, polymers and acids) and physical methods (heating, microwave irradiation and grinding). The studies reviewed gave mixed results. Phosphorylated chrysotile was less carcinogenic after peritoneal injection in rats and mice, but other rat and sheep studies found no reduction. Surface-coated amosite was less carcinogenic after injection into the pleura of rats, but a study in pathogen-free animals found no significant difference in pleural mesotheliomas. Heating crocidolite and amosite at 400 degrees C did not reduce hydroxyl radical generation, while heating at 800 degrees C abolished it. The author considered grinding difficult to endorse for asbestos, and wrote that acid treatments that destroy the fibers may not be detoxification in the true sense. The author concluded that no complete detoxification process had yet been achieved for any of the minerals studied.

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 of published detoxification processes (laboratory, animal, industrial and patent literature); no new experiments
• Who was studied: Published studies and patents on detoxifying the three commercially used asbestos fibers (chrysotile, crocidolite, amosite) and crystalline silica; the reviewed work included cell cultures, animals (rats, mice, sheep, guinea pigs) and some human silicosis trials
• Exposure: Chemical treatments (metal ions, chelating agents, phosphorus fixation, rare earth compounds, organosilanes, polymers such as CMC and PVPNO, acids) and physical treatments (heating, microwave irradiation, grinding) applied to the minerals
• Main results:
  • Phosphorylated chrysotile ('chrysophosphate') was less carcinogenic after peritoneal injection in rats and mice, but showed no reduction in activity when given to the tracheal lobe of rats and sheep or to rats by inoculation. It was concluded that this surface modification was not effective.
  • Amosite coated with C8 or C18 organosilanes was less carcinogenic after intrapleural injection in rats. In pathogen-free animals, however, treated and untreated fibers did not differ significantly in producing pleural mesotheliomas.
  • For crocidolite and amosite, heating at 400 degrees C did not reduce the ability to generate the hydroxyl radical, while heating at 800 degrees C abolished it. The author judged heat treatment insufficient for amphibole asbestos.
  • The 'metal-micelle' (ferric iron) coating reduced cytotoxic properties of asbestos fibers in vitro, but whether this applies in living animals had not been evaluated.
  • In human trials against silicosis, PVPNO was effective for some patients but not others. PVPNO and similar polymers were found ineffective against chrysotile-induced toxicity.
  • Because study results on fiber length and milling conflicted, the author did not support grinding as a way to detoxify asbestos.
  • Acid solutions were used to partially or completely dissolve asbestos, especially chrysotile, in products. The author wrote that treatments which destroy the fibers may not be detoxification in its true sense.
• The authors' conclusion: The author concluded that no single detoxification process met all the required criteria, and that no complete detoxification process had yet been achieved for any of the mineral particles investigated.
• Limitations the authors state:
  • The author noted that many of the processes reviewed were designed to identify which surface properties cause toxicity, not to detoxify material on a large scale.

Topics

Medical terms in this study, explained in our Lexicon: Crystalline, Fibrosis.

Related studies

• Plasma lipid peroxides among workers exposed to silica or asbestos dusts — A.A. Kamal, A. Gomaa, et al. (1989)
• The relationship between various exposure metrics for elongate mineral particles (EMP) in the taconite mining and processing industry — J. Hwang, G. Ramachandran, et al. (2014)
• Chrysotile asbestos detoxification with a combined treatment of oxalic acid and silicates producing amorphous silica and biomaterial — A. Valouma, A. Verganelaki, et al. (2016)
• Asbestos fibers and silica particles stimulate rat alveolar macrophages to release tumor necrosis factor. Autoregulatory role of leukotriene B4 — C.M. Dubois, E. Bissonnette, et al. (1989)
• Tremolite-actinolite fiber coatings of sub-nanometer silica-rich particles in lungs from deceased Quebec miners — M. Germine, J.H. Puffer (2020)
• Chest pain in asbestos and silica-exposed workers — E.K. Park, P.S. Thomas, et al. (2011)

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