Pii: S0003-4878(99)00017-4

The study objectives were to assess the ability of intratracheal injection methods to discriminate between nine ®bre types in respect of pulmonary biopersistence, and to provide approximate estimates of relative biopersistence and durability for a study of general relationships with biological and toxicological responses. The test ®bres included six samples of size-selected ®bre types specially prepared for research purposes, two commercially available ®bres, and amosite. A 1 mg dose of each ®bre type was administered to rats by intratracheal injection. The relative biopersistence of ®bres in di€erent size categories was assessed from the changes in mean lung burden, as determined by electron microscopy, at 3 days and 1, 6 and 12 months after injection. The ability of the test materials to resist dissolution was measured in a parallel series of simple in vitro acellular experiments at two pHs and in a continuous ̄ow dissolution test. The observed di€erences in the persistence of ®bres of di€ering length recovered from rat lungs were consistent with the current hypothesis that short ®bres are cleared by cellular processes and long ®bres by dissolution and disintegration. Di€erences in persistence of long (>20 mm) ®bres were correlated with measured rates of dissolution in vitro. Di€erences in persistence among those ®bre types also studied by others workers were consistent with their ®ndings after inhalation and intratracheal injection. Overall, the di€erences in the biopersistences of the test ®bres following intratracheal injection were sucient to enable an examination of the relationship of biopersistence with other biological and toxicological responses. Biopersistence was in ̄uenced by both ®bre dimensions and solubility. # 1999 Published by Elsevier Science Ltd on behalf of BOHS. All rights reserved.