E-glass fibers cause tumors in lab rats, say Scottish researchers

By Robert Horowitz
Tiny glass fibers like those used for years in the U.S. aerospace industry caused as many cancerous tumors as asbestos, but not as many tumors as extra-hard silicon-carbide fibers, in recent laboratory studies. The special-purpose "E-glass" microfibers caused mesothelioma when breathed by and implanted into rats, according to researchers at the Institute of Occupational Medicine in Edinburgh, Scotland.

"The E-glass fibers proved to be carcinogenic to rats by inhalation and of the forty-three long-term survivors, eleven developed a total of twelve pulmonary tumors. These tumors were either benign adenomas, pulmonary carcinomas or mesothelioma. The frequency of these tumors was very similar to the results obtained for amosite asbestos, although silicon carbide had produced many more mesotheliomas," according to researchers.

When implanted into the peritoneum (lung) of another group of rats, the e-glass fibers produced mesothelioma in 21 of 24 specimens. Mesothelioma is the always-fatal and extremely painful cancer of the lung lining which is almost exclusively associated with asbestos exposure.

The "104E" glass microfibers which tested carcinogenic in the study are comprised of up to 16 percent aluminum and up to 25 percent calcium, with silicon dioxide making up the rest. High levels of aluminum typically produce a durable fiber which can persist in human lung fluids for years or even decades. Many household insulation fibers are not so durable; laboratory work indicates they break down in the lungs within a year or two.

A more durable fiber is more dangerous, insist some researchers, who claim fiber "biopersistence" is as an important predictor of carcinogenicity as fiber length and diameter. In Germany, fibers with a high aluminum content are considered carcinogenic and their use is strictly limited. The U.S. has no such restrictions.

Silicon carbide fibers are durable ceramic fibers used primarily in extremely high temperature industrial applications. Several corporations are experimenting with the use of silicon carbide-reinforced metals in high-performance engines and turbines. Silicon carbide fibers are manufactured and used in the United States.

Ken Mentzer, Executive Vice President of the North American Insulation Manufacturers Association, writing to the U.S. Environmental Protection Agency, said E-glass is produced in the United States in the form of "continuous filament" glass fiber with diameters over 3 microns. (Fibers below 3 microns in diameter are generally considered to be respirable for humans. A human hair is approximately 70 microns in diameter.)

"E-glass continuous filaments are used to reinforce plastic, cement, paper and roofing materials, and are woven into fabrics for protective apparel, printed circuit boards and industrial fabrics,' wrote Mentzer. "When previously manufactured in the United States, E glass microfibers were primarily used for specialized filtration and high-temperature aerospace insulation applications."

Previous work in this research "programme" indicated common fiberglass insulation showed "marked evidence of leaching of its constitutional elements..." Researchers have not yet determined whether "e-glass" fibers also broke down in rat lungs.

But the biopersistence debate fails to ask a critical question: "If a fiber breaks down in a human lung, into what does it break down?" Since many common household insulation fibers are coated with known carcinogens such as phenol-formaldehyde resins, is it not logical to assume the end product will be poisonous or even carcinogenic? The prevalence of end-stage kidney disease in fiberglass worker cohorts was noted by epidemiologist John Goldsmith, who theorized this might be related to the dissolution of large amounts of fiberglass in the lungs and stomachs of workers.

The Scottish studies are sponsored by the British government, European fiber manufacturers and the UK-based Colt Foundation, whose primary purpose is "The promotion and encouragement of research into social, medical and environmental problems created by commerce and industry," writes researcher James Jarvis on his World Wide Web site. The Colt Foundation funds Jarvis' research into asthma and dermatitis.

FIN has also reported on a fiberglass inhalation study using hamsters and undertaken by a research laboratory in Switzerland, under contract to NAIMA. A mesothelioma in a fiberglass-exposed rat was reported less than six months into that two-year study. The most recent filings on this research report no new tumors.