New type of stonewool (HT fibres) with a higli dissolution rate at pH = 4.5

Abstract

A representative, the HT-3 fibre, of a new type of stonewool (HT fibres), characterized by a relatively high content of a lumina and a relatively low content of silica, has recently been tested in-vivo by Bellmann et al. to have a low biopersistence after intratracheal instilladon in rat lungs. Several advantages of this fibre were found: - a half-time T50 which is 2 respectively 4 times lower than that for the reference fibres glasswool and stonewool (after correcting to 1 µm median diameter), - a better ultimate clearance after 18 months, resulting in 3 % remaining for the HT-3 fibre compared to 32 % for normal stonewool, - an effective clearance of fibres with a diameter < 0.5 µm. Fibres with a diameter belonging to this class are generally thought to be those with the highest potency for tumour formadon. The HT fibres have a relatively low in-vitro dissolution rate at p H = 7.5, similar to that of normal stonewool fibres, but a high in-vitro dissolution rate at pH = 4.5. The explanation of the favourable in-vivo properties of t h e HT-3 fibre is based on the recent investigations of the ability of alveolar macrophages to dissolve certain fibres, coupled with the Observation of the high dissolution rate of the HT fibres at the pH value of 4.5 to 5 prevailing inside the macrophages. All HT fibres have been shown t o have comparable, high dissolution rates at pH = 4.5 to 5.