IRSST - Institut de recherche Robert-Sauvé en santé et en sécurité du travail

Synthesis of knowledge on tremolite contained in talc

Summary

Talc is widely used in different workplaces, mainly in the ceramics, paint (antirust paint), gypsum joint compound, cosmetics, plastics and rubber industries. Since some talcs can contain amphiboles including tremolite, possibly with asbestiform (or fibrous) and non-asbestiform morphology (cleavage fragments), it is important to know their origin and composition to be able to implement exposure monitoring strategies and means of prevention appropriate for workers and other users.

Several definitions and applications of the term asbestos are used to classify amphiboles, whether it is in studies on health effects, in exposure monitoring, or for regulatory purposes. Considering the different opinions and contradictory studies regarding definitions, analytical methods, regulations, and the health effects of non-asbestiform tremolite, the CSST (Québec workers' compensation board) asked the IRSST to carry out a literature review on tremolite, present in talc and vermiculite, in order to clarify the impacts on worker health and safety and to facilitate the implementation of means of prevention in the Québec context. This report covers the synthesis of the results obtained for tremolite present in talc. Vermiculite and its components will be the subject of another study.

The primary objective of this study is to produce a summary and a synthesis of the knowledge about tremolitic talc according to the different morphologies, asbestiform (asbestos) and non-asbestiform (cleavage fragments), and according to the following parameters:

  • Metrology (definitions, characterization of the materials, sampling and exposure);
  • Regulations (standards and regulatory criteria applied in the different countries);
  • Epidemiological data on the health effects.

Since the early 1990s, several studies have focused on the elongated mineral particles (EMPs) generated from the crushing and fracturing of non-asbestiform amphibole minerals, defined as cleavage fragments. More particularly, the studies addressed tremolite, contained naturally in certain talc and vermiculite deposits, ores that are used in different consumer products. However, the information is still limited on the exposures and health effects of these EMPs. Experts, analysts, researchers and government scientists have not reached a consensus on the definition or the differentiation of asbestiform and non-asbestiform amphiboles (cleavage fragments). While the distinction between cleavage fragments and fibres is theoretically clear, it is rather obscure from the analytical standpoint.

The use of complementary analytical methods such as phase contrast optical microscopy, scanning electron microscopy, transmission electron microscopy with selected area electron diffraction (SAED), or analytical electron transmission microscopy (SAED coupled with energy dispersion X-ray spectrometry) would make it possible to confirm the presence of asbestos fibres in an ore or a material and, more specifically, to determine the concentration in the air of fibres, asbestiform tremolite fibres, cleavage fragments of tremolite and talc fibres, if there were a consensus on the differentiation criteria to be used. Most of the studies describing the health effects related to talc exposure contain very little information on the characterization of the talc involved. Even if the analytical methods characterized the presence of amphiboles beyond any doubt and quantified the asbestiform part and the non-asbestiform part, it is very unlikely that toxicology studies can be performed on completely pure products because talcs are generally a mixture of different minerals in variable concentration. However, this information would be invaluable in epidemiology in attempting to better establish dose/response relationships.

Exposure to talc dust is associated with respiratory diseases such as NMRD (non-malignant respiratory disease), particularly pneumoconioses, and lung cancer, in the presence of other carcinogenic agents. In fact, talc ore dust can cause silicosis, talcosis, and mixed pneumoconiosis, but the causal share between talc, quartz and the other silicosis causative agents cannot be determined.

Mill workers do not present a significant increase in lung cancer risk, but miners could show tendencies or significant increases in risk in the presence of other carcinogens such as radon, quartz or asbestos. The use of the weighted concentration (dust or respirable dust) as exposure metric is a poor predictor of the fibre or elongated mineral particle concentration. The result is a possibility of improper classification of cases, which complicates the establishment of a dose/response relationship.

The possibility of mesothelioma related to talc dust exposure remains a controversial subject. Mesothelioma presents diagnostic and causal recognition difficulties. With the current state of knowledge, there is no proof linking mesothelioma and exposure to talc that does not contain asbestos or asbestiform fibre.

From the results provided to us by the epidemiological studies, it is difficult to answer definitively, with supporting proof, the question on the health risk of non-asbestiform tremolite (cleavage fragments), due to deficiencies in exposure characterization. In fact, no study had at its disposal results of concentrations of well characterized and well sampled cleavage fragments in the workers' breathing zones.

Considering all these uncertainties about exposures and health effects, research is still necessary in both toxicology and epidemiology as well as on exposure measurements, sampling, and analytical methods. In addition, mineralogical studies of lung tissues (biometrology) could identify abnormal overloads and characterize fibres and EMPs. These studies could help in defining the analytical and sampling methods that will more suitably measure the relevant toxicity characteristics. The results should also contribute to the development of recommendations for worker protection.

Additional Information

Category: Research Report
Author(s):
  • Chantal Dion
  • Guy Perrault
  • Mounia Rhazi
Research Project: 0099-5560
Online since: January 24, 2012
Format: Text