Environmental Factor, July 2009, National Institute of Environmental Health Sciences
Expert Panel Reviews Glass Wool Fibers
By Robin Mackar
An expert panel convened in Chapel Hill, N.C. on June 9-10 by the National Toxicology Program (NTP) to review the scientific literature and consider a recommendation by the North American Insulation Manufacturers Association to change the listing status for glass wool fibers in the upcoming 12th Report on Carcinogens (RoC). The expert panel decided to make separate recommendations for different categories of glass wool fibers.
The panel recommended by a unanimous vote that most glass wool fibers should not be classified either as "known to be a human carcinogen" or as "reasonably anticipated to be a human carcinogen," and should be removed from the RoC listing. Glass wool of respirable size is currently listed in the 11th RoC as "reasonably anticipated to be a human carcinogen."
However, the panel made a distinction for special glass wool fibers of concern, which they defined as longer, thinner, and less soluble fibers. The expert panel recommended that glass fibers with these characteristics -15 micrometer or greater in length with a dissolution rate equal to or less than 100 nanograms per square centimeter per hour - are listed as "reasonably anticipated to be a human carcinogen" in the 12th RoC. The vote was seven to zero with one abstention, with panel members citing sufficient evidence of carcinogenicity in well-conducted animal inhalation studies as the basis for the recommendation.
After receiving oral public comments from a number of groups, the glass wool fibers expert panel carried out an in-depth review of the draft background document and voted unanimously to accept the background document with the panel's suggested changes. They then discussed the scientific information for glass wool fibers, applied the RoC listing criteria to the body of evidence, and made a recommendation for listing status in the RoC.
Glass wool refers to fine glass fibers forming a mass resembling wool and is most commonly used for insulation and filtration. There are two categories of glass wool based upon commercial application - insulation glass wool, which is now among the most extensively used insulating material worldwide, and special-purpose fibers, which are used in special applications and make a much up smaller fraction of the market. There are differences in the chemical compositions and physical characteristics of glass fibers, which may influence the toxicology and potential carcinogenicity of different fibers.
Fibers have also been examined based upon other characteristics including persistence, retention and clearance rates, and durability. The European Union and Germany have established criteria for labeling and classifying synthetic vitreous fibers based on their potential human health hazard.
Next, the NTP will solicit public comment on the expert panel's listing recommendation and scientific justification through the Federal Register and finalize the background document, taking into consideration the panel's recommended edits and public comments. Afterwards, the agency will convene two independent review groups who will also apply the RoC listing criteria and make a recommendation for listing status in the RoC.
Information about this meeting and the review of wool glass fibers or any other RoC nominated chemical is available online.
(Robin Mackar is the news director in the NIEHS Office of Communications and Public Liaison and a regular contributor to the Environmental Factor.)