What are the health effects on workers of cleavage fragments of quarried minerals?
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News of 17/12/2015
Cleavage fragments are mineral particles naturally present in rocks used, among other purposes, in public engineering works (road surfacing). Through their chemical composition and their dimensions, some of these can be considered comparable to asbestos fibres. While the effects of asbestos fibres on health are well documented, there is uncertainty regarding the toxicity of cleavage fragments. In addition, current analytical methods cannot easily distinguish between cleavage fragments and asbestos fibres. ANSES was requested by the Ministries of Health, Labour and the Environment to document the exposure of workers to cleavage fragments, the resulting health effects, and the methods or criteria for refining the analyses of materials and air. In the Opinion and the Report published today, the Agency concludes that in the current state of knowledge, cleavage fragments of minerals comparable to regulated forms of asbestos with the same dimensions as asbestos fibres, and also cleavage fragments of certain mineral species not currently regulated, can lead to health effects similar to those caused by asbestos. Against this background, the Agency recommends that these potential effects be taken into account in the applicable regulatory framework.
In the European regulations, the term asbestos refers to six minerals naturally present in several types of rock: one serpentine, chrysotile (white asbestos), and five amphiboles, actinolite-asbestos, anthophyllite-asbestos, tremolite-asbestos, amosite and crocidolite.
Asbestos fibres and cleavage fragments
In the natural environment, actinolite and the other amphiboles are found in different morphologies, described as either asbestiform or non-asbestiform. Non-asbestiform minerals and their asbestiform counterparts (i.e., actinolite and actinolite-asbestos) have the same chemical composition but are differentiated by the way they form in rocks. Currently, only chrysotile and the asbestiform versions of the five aforementioned amphiboles are regulated substances.
When mechanical stress is applied to non-asbestiform minerals, as when rock extracted from quarries is ground up to produce aggregate, for example, they can split and release particles of different lengths called "cleavage fragments." These particles can sometimes be counted as asbestos fibres, especially because of their dimensions.
Following the identification of fibres of actinolite-asbestos and cleavage fragments of actinolite in rock granulate for road surfaces, ANSES was requested by the Ministries of Health, Labour and the Environment to carry out an expert appraisal on the exposure of workers to cleavage fragments, the potential health effects, and the methods or criteria for analysing materials and air. The cleavage fragments of interest are those likely to be counted as asbestos fibres during air analyses, that is to say the cleavage fragments of minerals comparable to the regulated types of asbestos, namely actinolite, anthophyllite, tremolite, grunerite and riebeckite whose dimensions are those of a “fibre” as defined by the World Health Organization (length greater than 5 μm, diameter less than 3 µm, aspect ratio greater than 3), and therefore likely to be inhaled. In addition, the Agency also studied those amphiboles for which there are data raising health concerns and which have a chemical composition very close to that of any of the five aforementioned amphiboles.
As a general remark, ANSES stresses the difficulty of identifying health data specific to cleavage fragments, because of the co-exposures to asbestiform fibres or other respiratory risk factors, but also because of the absence of data regarding the dimensions or morphology of the mineral particles studied. In addition, the available studies only discuss dimensional criteria and none of the parameters influencing the toxicity of these particles, such as biopersistence, contaminants, surface reactivity, etc.
In the light of the data analysed, ANSES concludes that it is not possible to exclude a risk to health linked to exposure to cleavage fragments of actinolite, anthophyllite, tremolite, grunerite and riebeckite. Moreover, some data indicate risks to health similar to those induced by asbestos for chemical species that are not currently regulated: winchite, richterite, fluoro-edenite and erionite.
Finally, it has not been possible to find any exposure data specific to cleavage fragments, in particular because of co-exposure with asbestos fibres, and analytical difficulties in distinguishing them formally from asbestos fibres.
The Agency's recommendations
In the light of the data analysed, ANSES concludes that it is not possible to exclude a risk to health related to exposure to cleavage fragments of actinolite, anthophyllite, tremolite, grunerite and riebeckite, if their fibres are of a length specified by the WHO.
In addition, considering that the health effects observed for winchite, richterite, fluoro-edenite and erionite are similar to those of asbestos, ANSES also recommends that the regulations in force be extended to include these four mineral species.
Furthermore, ANSES makes recommendations with respect to the conduct of work likely to lead to exposure to these mineral particles in quarrying and road works. Other areas, such as the construction and public works sectors in the natural environment or using substances manufactured from natural materials, can also be concerned by this problem. Before starting this type of work, it appears necessary to map sites to identify the presence of particles.
Finally, in the field of metrology, ANSES makes recommendations to improve the collection and analysis of mineral particles in natural materials, and to homogenise laboratory results.