THE BIOPERSISTENCE AND PATHOGENICITY OF MAN-MADE VITREOUS FIBERS AFTER SHORT-TERM AND LONG-TERM INHALATION

A summary is given of the biopersistence and pathology after inhalatio n by rats of two different Man-made Vitreous Fibres, MMVF21 (tradition al stone wool) and MMVF34 (HT stone wool), and the results are discuss ed in relation to biopersistence measured after intra-tracheal instill ation. The results are given from a short-term inhalation biopersisten ce study, a completed chronic inhalation study, and interim results fr om an on-going chronic inhalation study. In both the short-term and ch ronic studies, laboratory rats were exposed by nose-only inhalation to well-characterised fibre test atmospheres that had been selected to b e largely rat respirable. The shortterm inhalation study included grou ps exposed to aerosols targeted at 150 fibres longer than 20 mu m per cm(3). The exposure duration was 6 hours/day for 5 days, with subseque nt post-exposure periods lasting up to 12 months. For lung burden anal yses, interim sacrifices were performed at regular intervals. The ongo ing chronic study comprises a group of rats exposed to the MMVF34 fibr e at one exposure level of 30 mg/m(3). The negative control group is f iltered air. The exposure duration is 6 hours/day, 5 days/week for 2 S ears, with a subsequent post-exposure period lasting until approximate ly 20% survival in the test fibre group. Interim sacrifices are perfor med at months 3, 6, 12, 18 and 24 and biopersistence monitored for rat s exposed for 3 and 12 months, with subsequent post-exposure periods l asting 6 months. Effectively the main protocol for the previously cond ucted chronic study tr as the same, except that there were 3 fibre exp osure groups (3, 16 and 30 mg/m(3)) and no specific biopersistence sat ellite groups mere included. For MMVF34, the inhalation tests of diffe rent duration show a similar biopersistence pattern, while the intra-t racheal test gives longer elimination half-times especially for long f ibres. The MMVF34 fibre is considerably less biopersistent than the tr aditional MMVF21 fibre when comparing the calculated elimination half- times after short-term inhalation. When comparing the pathology after 3, 6, 12 and 18 months exposure, MMVF34 showed minor histopathological changes compared to MMVF21. The carcinogenicity and toxicity results of the chronic study with MMVF21 suggest that this fibre does not pose a significant health risk to humans and the current results with MMVF 34 indicate that this fibre consequently should pose an even smaller r isk, if any. (C) 1998 British Occupational Hygiene Society. Published by Elsevier Science Ltd.