Asbestos Fibers Research Roadmap

Research Into Physiological Effects of Asbestos Fibers

A document released by the National Institute for Occupational Safety and Health (NOISH) titled, "Asbestos Fibers and Other Elongated Mineral Particles: State of the Science and Roadmap for Scientific Research", was produced to outline and define the research strategies and other technical issues related to health risks from exposure to asbestos fibers and other elongated mineral particles (EMPs). The proposed plan offers scientific knowledge that may be used for establishing future asbestos-related policies. The research is primarily focused on workers that are exposed to asbestos-related health hazards from airborne fibers in the workplace and how to best protect them.

United States Federal agencies worked together in the 1970s to create regulatory standards and definitions associated with occupational exposure to asbestos fibers after it was shown that some exposed workers developed respiratory disease.

The outlined standards apply to the following six asbestos minerals:

chrysotile
amphibole minerals cummingtonite-grunerite asbestos (amosite)
riebeckite asbestos (crocidolite)
actinolite asbestos
anthophyllite asbestos
tremolite asbestos

Although asbestos mining ended in the United States in 2002, and the use of asbestos products has decreased, there are still several asbestos-containing products that were formally produced and are still in use, as well as, new products that are produced or imported into the United States.

More attention became focused on exposure to other "mineral fibers" as more information showed that there was a correlation between the size of asbestos fibers and their ability to cause respiratory disease and malignant mesothelioma.

"Mineral fiber" is a term that is used by non-mineralogists that refers to thoracic-size elongated mineral particles (EMPs). These fibers may grow in an asbestiform habit or a non-asbestiform habit. It is clear that EMPs that originate from an asbestiform habit are associated with health risks. It is not clear whether or not thoracic-size EMPs that are similar to abestiform minerals cause health risks.

The NIOSH modified its recommendations regarding exposure to airborne asbestos fibers in the workplace in 1990. The organization concentrated on the potential health problems related to exposure to EMPs that had similar characteristics of asbestos minerals. Another concern was the analytical method, phase contrast microscopy (PCM), used to distinguish EMPs from asbestos mineral fibers and its inability to differentiate between different fiber types. The NOISH defined "airborne fibers" to include the six asbestos minerals and EMPS from non-asbestiform origin. In addition, they maintained the use of the PCM method to measure airborne fiber concentrations and count particular EMPs.

The recommendations that NIOSH established in 1990 continue to raise the following concerns:

NIOSH's modified definition for "airborne asbestos fibers" and its addition of EMPs from non-asbestiform amphiboles (primarily because it was established from inconclusive science and is different from OSHA and MSHA regulations).
The revised definition for "airborne asbestos fibers" does not clearly include EMPs from other asbestiform amphiboles or other fibrous minerals that have been shown to cause health problems like those caused by asbestos exposure.
It is suspected that the revised length and aspect ratio of EMPs may not be optimal to protect workers exposed to these fibers because the revisions were not based only on health risk factors.
The revised definition of "airborne asbestos fibers" does not include physicochemical factors such as durability and surface activity. These may be important toxicological factors.
NIOSH's definition of "airborne asbestos fibers" includes airborne EMPs covered by the recommended exposure limit (REL) and is different from the way mineralogists use the definition. This may lead to confusion about EMPs and their related toxicity.

The National Institute for Occupational Safety and Health understands that its revised REL descriptions established in 1990 has caused some confusion and that some may believe that non-asbestiform minerals are asbestos. The organization acknowledges that non-asbestiform minerals are not asbestos minerals. They also acknowledge that EMPs are not asbestos fibers and clarified this in Section 1.8 of the "Roadmap" by not referring to EMPs from non-asbestiform origin as asbestos fibers, but only those specified in the REL.

Epidemiological studies show a relationship between asbestos minerals exposure and a variety of health problems that include mesothelioma and asbestosis; however, the studies do not give clear answers regarding potential toxicity of EMPs from a non-asbestiform origin. NIOSH views the epidemiological study outcomes as inconclusive in regards to health problems and their relationship to exposure from EMPs a non-asbestiform origin.

More studies in epidemiology, toxicology, and assessment of exposure and analytical methods may help resolve some of the current debates and uncertainties. Further research and the answers it provides may help with defining new policies regarding exposure to airborne asbestos fibers and EMPs and how it relates to workers and potential health risks.

Proposed research in the "Roadmap" includes the following goals:

clarify important factors such as toxicity from EMPs
produce information about occupational exposure to EMPs and their related health problems
produce improved analytical methods and sampling techniques for asbestos fibers and EMPs

More research and information regarding exposure to various EMPs in the workplace and their related health risks involve the following:

collecting and analyzing occupational exposure information that may be available to determine the characteristics and levels of exposure to various EMP types
collecting and analyzing health outcomes information related to EMP exposure that may be available
epidemiological studies of workers that have experienced exposure to various EMPs to clearly define the potential health effects for particular EMP types
creating validation methods for screening, diagnosis and secondary prevention for health problems related to exposure from asbestos fibers and various EMPs

Further research may result in clearer scientific evidence that could help in the development of appropriate recommendations and standards for better worker health protection policies as they relate to exposure from asbestos fibers or other EMPs in the workplace.

Source: National Institute of Occupational Safety and Health

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