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Silica, Some Silicates, Coal Dust and para-Aramid Fibrils

IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, No. 68


This volume evaluates the carcinogenic risks to humans posed by exposure to crystalline and amorphous silica, some silicates (palygorskite, sepiolite, wollastonite, and zeolites other than erionite), coal dust, and para-aramid fibrils. The volume opens with a discussion of the many complexities involved in assessing the cancer risks associated with occupational exposure to inhaled mineral dusts, and the special toxicological considerations required when evaluating the results of experimental studies. Against this background, the first and most extensive monograph evaluates human and animal carcinogenicity data on silica, concentrating on evidence of an increased risk for lung cancer. On the basis of this evaluation, crystalline silica inhaled in the form of quartz or cristobalite from occupational sources was classified as carcinogenic to humans. For amorphous silica, evidence from both epidemiological and experimental studies was judged inadequate, and amorphous silica could not be classified.

For palygorskite, the evaluation found sufficient evidence from studies in rats that long fibres were carcinogenic; studies of exposure to short fibres showed no significant increase in the incidence of tumours. The few studies in humans were judged inadequate. Long palygorskite fibres were classified as possibly carcinogenic to humans. Short fibres could not be classified.

For coal dust, several limitations in human studies, largely concerned with excessive mortality from lung and stomach cancer, hindered interpretation of the epidemiological literature. The few adequate experimental studies showed no increase in tumours. Coal dust therefore could not be classified. para-Aramid fibrils likewise could not be classifed in view of inadequates in both the epidemiological and experimental data.


Corrigenda to the IARC Monographs are published online at:



In 1969, the International Agency for Research on Cancer (IARC) initiated a programme on the evaluation of the carcinogenic risk of chemicals to humans involving the production of critically evaluated monographs on individual chemicals. The programme was subsequently expanded to include evaluations of carcinogenic risks associated with exposures to complex mixtures, life-style factors and biological agents, as well as those in specific occupations.

The objective of the programme is to elaborate and publish in the form of monographs critical reviews of data on carcinogenicity for agents to which humans are known to be exposed and on specific exposure situations; to evaluate these data in terms of human risk with the help of international working groups of experts in chemical carcinogenesis and related fields; and to indicate where additional research efforts are needed.

This project is supported by PHS Grant No. 5-UO1 CA33193-15 awarded by the United States National Cancer Institute, Department of Health and Human Services. Additional support has been provided since 1986 by the European Commission.

  • ©International Agency for Research on Cancer, 1997
  • IARC Library Cataloguing in Publication Data
  • Silica, some silicates, coal dust and para-aramid fibrils /
  • IARC Working Group on the Evaluation of
  • Carcinogenic Risks to Humans (1996 : Lyon,
  • France).
  • (IARC monographs on the evaluation of carcinogenic
  • risks to humans ; 68)
  • 1. Silica – congresses 2. Some silicates – congresses 3. Coal dust – congresses 4. para-Aramid fibrils – congresses I. IARC Working Group on the Evaluation of Carcinogenic Risks to Humans II. Series
  • ISBN 92 832 1268 1
  • ISSN 0250-9555
  • (NLM Classification: W 1)
  • Publications of the World Health Organization enjoy copyright protection in accordance with the provisions of Protocol 2 of the Universal Copyright Convention.
  • All rights reserved. Application for rights of reproduction or translation, in part or in toto, should be made to the International Agency for Research on Cancer.
  • Distributed by IARCPress (Fax: +33 04 72 73 83 02; E-mail: rf.crai@sserp)
  • and by the World Health Organization Distribution and Sales,
  • CH-1211 Geneva 27 (Fax: +41 22 791 4857)
©International Agency for Research on Cancer, 1997.
Bookshelf ID: NBK410047


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