Biopersistence and durability of nine mineral fibre types in rat lungs over 12 months

The study objectives were to assess the ability of intratracheal injection methods to discriminate between nine fibre types in respect of pulmonary bi opersistence, and to provide approximate estimates of relative biopersisten ce and durability for a study of general relationships with biological and toxicological responses, The test fibres included six samples of size-selec ted fibre types specially prepared for research purposes, two commercially available fibres, and amosite, A 1 mg dose of each fibre type was administe red to rats by intratracheal injection. The relative biopersistence of fibr es in different size categories was assessed from the changes in mean lung burden, as determined by electron microscopy, at 3 days and 1, 6 and 12 mon ths after injection, The ability of the test materials to resist dissolutio n was measured in a parallel series of simple in vitro acellular experiment s at two pHs and in a continuous flow dissolution test, The observed differ ences in the persistence of fibres of differing length recovered from rat l ungs were consistent with the current hypothesis that short fibres are clea red by cellular processes and long fibres by dissolution and disintegration . Differences in persistence of long (> 20 mu m) fibres were correlated wit h measured rates of dissolution in vitro. Differences in persistence among those fibre types also studied by others workers were consistent with their findings after inhalation and intratracheal injection. Overall, the differ ences in the biopersistences of the test fibres following intratracheal inj ection were sufficient to enable an examination of the relationship of biop ersistence with other biological and toxicological responses, Biopersistenc e was influenced by both fibre dimensions and solubility. (C) 1999 Publishe d by Elsevier Science Ltd on behalf of BOHS, All rights reserved.