Apparently similar glass microfibres show contrasting toxicity

Previous results from the Colt Fibre Research Programme supported the idea that the number of long thin fibres and their ability to persist in the lung are predictors for the risk of cancer. The results were based on nine fibres, including one glass microfibre (100/475) which had low biological activity. New results with a second glass microfibre (104E) show greater cell proliferation than with 100/475 following short-term inhalation and much greater carcinogenic potential in both chronic inhalation and i.p. experiments, equalling or exceeding that of amosite asbestos. New measurements are used to characterize the durability of the fibres. The extended data still support a dependence of pathogenicity on dose and durability, but with some other factor, perhaps differential leaching affecting surface properties, modifying the relative potency of the two microfibres.