28-day inhalation study of a cross-linked polyacrylate superabsorbent in the hamster.
Male and female Syrian Golden hamsters (20 of each sex) breathed respirable cross-linked polyacrylate dust (0.3, 1.0 or 10 mg m-3) for 6 h a day, 5 days a week for 28 exposures. More than 99% of the particles were 3-4 microns or smaller. No differences in overall health or body weight were observed among the groups, nor were there deaths during exposure or during the post-exposure period. In animals killed within 24 h after the final exposure, foreign material was detected in the lungs in a dose-related manner. In animals examined 4 weeks post-exposure, much of this material had been cleared from the lungs. There was a significant alveolar macrophage and a non-significant inflammatory cell response following exposure; both responses appeared to decrease during the post-exposure period. There was no evidence of fibrosis in the low- or medium-exposure groups after the exposure or post-exposure periods. In the high-exposure group there was equivocal evidence of fibrosis in one set of lungs at the end of the exposure and in another set after the post-exposure period. These results indicate that subacute exposure of Syrian Golden hamsters to low concentrations of cross-linked polyacrylate dust in particle sizes capable of reaching deep lung structures does not cause pulmonary fibrosis in the hamsters and that resolution of the cellular response induced by these particles occurs. These results also indicate that the test material was cleared from the lung following termination of exposure.