Short asbestos fibres

In 2003, a publication[1] raised many questions in the scientific community about the potential pathogenicity of short asbestos fibres. These new data led to uncertainty concerning the way in which risks related to asbestos are taken into account in regulations. ANSES therefore received a formal request from its supervisory ministries in February 2005 for a risk assessment on short asbestos fibres (SAF: length L < 5 µm, diameter D < 3 µm and L/D ratio ≥ 3). An additional mission letter requesting that the scope of the assessment be widened to include thin asbestos fibres (TAF: L ≥ 5 µm, D < 0.2 µm and L/D ratio ≥ 3), was sent to the Agency on 16 May 2007.

Following preliminary evaluation of the contents and possible impact of the publication that led to the formal request, the Agency’s objectives were primarily to:

• evaluate the toxicity of short asbestos fibres and thin asbestos fibres;
• characterise the granulometric distribution of fibres based on exposure conditions (general or occupational population) and the type of asbestos (chrysotile or amphiboles);
• assess the risk to human health associated with exposure to short asbestos fibres and thin asbestos fibres.

A further aim of the assessment was to evaluate the relevance of the current regulatory framework, specifically the current thresholds and absence of dust accumulation measurements for short and thin asbestos fibres.

Description of the method

In the framework of the assessment, ANSES commissioned the National Institute of Health and Medical Research (Inserm) to conduct a bibliographic review of current data on the role of particle size in the toxicity of asbestos fibres.

In addition to the literature review carried out by the working group, the Agency called on the Research laboratory on inhaled particles (LEPI – City of Paris) and the Occupational Health and Safety Research Institute Robert-Sauvé (IRSST – Quebec) to collect data on the granulometric distribution of asbestos in various environments, such as indoor and outdoor spaces, the types of materials found and the occupational environment. on,.

Furthermore, in order to compare assessments and activities, and subsequently to discuss working group proposals, ANSES organised two exchange meetings in Paris on 17 and 18 September 2008, at the request of the experts. Participants included representatives from the Agency for Toxic Substances and Disease Registry (US ATSDR), the National Institute for Occupational Safety and Health (US NIOSH), the Environmental Protection Agency (US EPA), the Health & Safety Laboratory (HSL - UK) and the Finnish Institute of Occupational Health (FIOH).

Main results

Based on analysis of the various studies, it was not possible to conclude with certainty that short asbestos fibres do not have carcinogenic properties. If short asbestos fibres were found to be toxic, the hazard level would definitely be lower than that of long fibres. Data acquired during the expert appraisal concerning the granulometric distribution of asbestos fibres, whether in the general environment, occupational setting, or in proximity to natural asbestos outcrops, highlight a greater proportion of short fibres in high concentrations.

In the general environment, samples containing only short asbestos fibres were found following release from asbestos-containing materials or products located nearby, highlighting the degradation of these materials. Overall, given the current status of knowledge, it was not possible to carry out a quantitative evaluation of the health risks associated with asbestos fibres of all sizes nor of those associated only with short asbestos fibres.

Concerning thin fibres, toxicological and epidemiological data confirm the existence of a carcinogenic effect associated with inhalation of fibres in this granulometric class. Analysis of findings on granulometric distribution in all environments shows that thin asbestos fibres account for a small proportion of the total amount.

Conclusion of the expert appraisal

With regard to thin asbestos fibres, the results of the expert appraisal confirm that it would be useful to measure these substances in the framework of regulations on the general environment, and the experts agreed on the need to take this granulometric class into account in regulations concerning the occupational environment.

In view of the results obtained concerning short asbestos fibres, and despite the number of unanswered questions still to be clarified, a potential risk associated with these fibres cannot be ruled out. Moreover, this granulometric class is systematically found in large proportions when concentrations are measured. In addition, identifying and quantifying short asbestos fibres could contribute to detection of pollution in a given environment from a potential source.

For the general environment, short asbestos fibres could be used in regulations as an indicator of deterioration of materials or products containing asbestos.

For the occupational environment, including short asbestos fibres in epidemiological studies could help to improve knowledge of dose-effect relationships and possibly to increase the accuracy of current models for quantitative assessment of health risks.

Recommendations based on the expert appraisal

Given the results of the collective expert appraisal published in 2009, the Agency considers it justified to revise regulations for the general and occupational environments, and proposes that risk management provisions on the health effects of asbestos take the following considerations into account:

• revision of standard measurement methods, with use of transmission electron microscopy (TEM) for all environments;
• revision of regulatory thresholds, both in the general and occupational environments, for fibres with lengths greater than or equal to 5 µm.

The Agency’s OEL Committee has published a detailed and substantiated notice proposing OELs for asbestos and an associated measurement method.

• extension of dust accumulation measurements to the general environment for all asbestos-containing products (especially asbestos flooring and asbestos cement) when regulatory visual inspections detect deterioration of materials, along with a specific measurement for short asbestos fibres to assess breakdown of materials.

The scope of recommendations and inclusion of new references such as short asbestos fibres reinforce the need to ensure information dissemination and adequate communication with stakeholders.

Furthermore, the Agency recommends improving knowledge on the role of fibre size for the assessment of asbestos health risks, particularly in the following fields:

• toxicology, with the acquisition of new experimental data on short asbestos fibres;
• exposure assessment, with the acquisition of new data on the granulometric distribution of asbestos fibres, for:
  • the occupational environment;
  • the general outdoor environment in order to collect samples that are more recent and more representative of the overall situation, specifically after the ban on use of asbestos;
  • release of fibres from asbestos-containing products in the general indoor environment.

[1] “Asbestos fiber length as related to potential pathogenicity: a critical review”, published in the American Journal of Industrial Medicine. Dodson, RF. et al., 2003.