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5 Toxicological Studies
Pages 34-40

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From page 34...
... However, some relevant toxicological material published since the Navy's 1997 report might inform the Navy's selection of an occupational · ~ exposure ~ emit. The Navy correctly notes that inhalation studies have yielded the most relevant data, as they were conducted using the route of administration that most closely mimics expected human exposures.
From page 35...
... Because various rodent species respond differently to selected inhaled materials, it is essential to consider numerous factors such as anatomy and deposition patterns, physiology and macrophage clearance efficiency, biochemistry and inflammation and fibrogenic potential when extrapolating the results of animal inhalation studies to humans. Therefore, knowledge of morphological and functional pulmonary characteristics is essential for full understanding of structure-function relationships among species but it is also necessary if one is to develop accurate risk estimates with regard to the toxicity-of inhaled particles in exposed humans.
From page 37...
... After exposure, no significant histopathological effects were observed in the lungs of rats exposed to the short fibers, but one-third of the rats exposed to the long fibers developed lung tumors. Nearly all the rats exposed to the long fibers also developed diffuse pulmonary fibrosis.
From page 39...
... The subcommittee agrees with a WHO scientific panel's conclusion that the intraperitoneal mode} should not be used for quantitative risk assessment or for comparing relative hazards posed by different fibers (WHO 19921. CONCLUSIONS It appears reasonable to conclude that extrapolations from animal toxicity data to humans for MVF can best be made when experimental animals are exposed to fibers via inhalation.
From page 40...
... Short-term inhalation testing should be used for estimating toxicity, evaluating mechanisms, and setting doses for subchronic or chronic inhalation studies. With regard to the latter goal, it is likely that the data generated from short-term inhalation tests could be used to set dose levels for 90-day inhalation studies, thus obviating costly 2-week or 28-day dose-setting inhalation studies.

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