A review of carcinogenicity studies of asbestos and non-asbestos tremolite and other amphiboles

Our plain-English summary of A review of carcinogenicity studies of asbestos and non-asbestos tremolite and other amphiboles, by J. Addison, E.E. McConnell (Regulatory Toxicology and Pharmacology, 2008).

The study

• Authors: J. Addison, E.E. McConnell
• Journal: Regulatory Toxicology and Pharmacology
• Published: 2008;52(1 Suppl):S187-99
• Type of article: Review
• Cited by: 49 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Experimental animal studies comparing asbestos and non-asbestos varieties of tremolite indicate tremolite asbestos is markedly more carcinogenic. By direct analogy, the differences in carcinogenicity between tremolite asbestos and non-asbestos prismatic tremolite should be the same for the other types of amphibole that also crystallize in the asbestos and non-asbestos habits. The earliest of the experiment animal studies, done more than 25 years ago, have design limitations by modern standards including the use of injection or surgical implantation as the route of administration rather than the more relevant route of inhalation. However, the differences in the carcinogenicity of amphibole asbestos and non-asbestos amphiboles are sufficiently large to be clearly discernable even with the study limitations. Together with later studies on these and related minerals, there is strong evidence of a much lower hazard associated with the shorter, thicker fibers of the non-asbestos amphiboles, than is found for the asbestos analogues of the same mineral. It is possible that the non-asbestos amphiboles are no more hazardous than other silicate minerals widely considered nuisance dusts.

In plain English

This article reviewed animal studies comparing the cancer-causing potential of tremolite asbestos and non-asbestos (prismatic) tremolite. It also covered actinolite, ferro-actinolite and grunerite (amosite) asbestos. Most reviewed studies injected or implanted dust; only one exposed rats to tremolite asbestos by inhalation. In that study, Korean tremolite asbestos produced 16 carcinomas and two mesotheliomas among 39 rats. Tremolite asbestos that was injected or implanted produced mesotheliomas in 14 of 47 rats in one study, and in 21 and 22 of 28 animals in another. Most non-asbestos tremolites produced few or no tumors. The exception was a needle-like non-asbestos tremolite from Ala di Stura, Italy, which produced mesothelioma in 24 of 36 rats. The authors suggested this response could reflect a trace asbestos component in that sample. In one amosite injection study, long fibers produced mesothelioma in 88% of rats at 10 mg and 95% at 25 mg. Short fibers produced 0% and 4% (one animal) at those doses. The authors concluded there was very little evidence that prismatic amphibole fragments or short fibers cause cancer in animals. They noted that injection methods have limits for predicting human risk.

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 experimental animal studies (inhalation, intrapleural and intraperitoneal injection, pleural implantation), with brief mention of cell studies
• Who was studied: Laboratory animals (rats and hamsters) in previously published studies by other researchers, including Smith et al. (1979), Stanton et al. (1981), Wagner et al. (1982), Davis et al. (1985) and Davis et al. (1991)
• Exposure: Tremolite asbestos, non-asbestos (prismatic) tremolite and tremolitic talc from various locations. Also actinolite, ferro-actinolite, and long- and short-fiber grunerite (amosite) asbestos.
• Main results:
  • Davis et al. (1985) was the only inhalation experiment using tremolite asbestos. In it, rats exposed to Korean tremolite asbestos developed 16 carcinomas and two mesotheliomas among 39 treated animals.
  • In hamsters injected intrapleurally (Smith et al., 1979), asbestiform tremolite FD72 produced tumors in 3/13 at the 10 mg dose and 5/23 at the 25 mg dose. Non-asbestos tremolite sample 275 produced tumors in 0/34 and 0/31.
  • In rats injected intrapleurally (Wagner et al., 1982), tremolite asbestos from Korea produced mesotheliomas in 14 of 47 rats (30%). The two non-asbestos tremolites produced no tumors in 31 and 48 rats.
  • In rats with pleural implants (Stanton et al., 1981), two tremolite asbestos samples produced mesotheliomas in 21 and 22 of 28 animals. A New York State tremolitic talc (talc 6) produced no tumors.
  • In rats injected intraperitoneally (Davis et al., 1991), the three tremolite asbestos samples produced mesothelioma in 36 of 36 (California), 35 of 36 (Swansea) and 32 of 33 (Korea) rats. The non-asbestos tremolites produced mesothelioma in 24 of 36 (Italy, Ala di Stura), 4 of 33 (Dornie) and 2 of 36 (Shinness).
  • The authors stated that the Ala di Stura sample contains a sub-set of asbestiform tremolite fibers. They suggested its tumor response could be what might be expected from a trace asbestos component.
  • In intraperitoneal injection experiments with grunerite (amosite) asbestos (Davis et al., 1986), long fibers produced mesothelioma in 88% (10 mg) and 95% (25 mg) of rats. Short fibers produced 0% (10 mg) and 4%, one animal (25 mg).
• The authors' conclusion: The authors concluded that there is very little evidence of carcinogenicity in animals from mineral fragments or short fibers formed from normal prismatic amphibole minerals.
• Limitations the authors state:
  • Injection and implantation methods bypass normal defences and introduce large doses to sensitive tissues. Positive results from them are of limited use for predicting human risk from inhalation.
  • The early studies of Wagner et al. (1982) and Smith et al. (1979) were limited by poor survival and uninformative fiber size measurements.
  • In the Davis et al. (1991) study, an overdose of fibers in the asbestos samples may have masked differences. A multi-dose experiment might clarify relative potencies.

Topics

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

Medical terms in this study, explained in our Lexicon: Tremolite, Amphibole Group, Carcinogenic, Habit, Amphibole Asbestos, Silicate.

Related studies

• Rapporteur's Report Session 5: assessment of health risk associated with exposure to non-asbestiform amphiboles including ingestion studies — B. Price (2008)
• Sumas Mountain chrysotile induces greater lung fibrosis in Fischer344 rats than Libby amphibole, El Dorado tremolite, and Ontario ferroactinolite — J.M. Cyphert, A. Nyska, et al. (2012)
• Variations in the carcinogenicity of tremolite dust samples of differing morphology — J.M. Davis, J. Addison, et al. (1991)
• Environmental mesothelioma associated with tremolite asbestos: lessons from the experiences of Turkey, Greece, Corsica, New Caledonia and Cyprus — S.H. Constantopoulos (2008)
• Rapporteur's Report Session 4: grunerite asbestos (amosite) and tremolite-ferroactinolite asbestos: risk of environmental mesothelioma — J.F. Gamble (2008)
• Tremolite, other amphiboles, and mesothelioma — J.C. McDonald (1988)

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