Effect of exposure route, regimen, and duration on benzene-induced genotoxic and cytotoxic bone marrow damage in mice.

Mice were exposed to benzene for 13 to 14 weeks by inhalation for either 3 or 5 consecutive days per week or by gavage for 5 consecutive days per week. A weekly evaluation of peripheral blood smears for micronucleated (MN) erythrocyte frequencies and for the percentage of polychromatic erythrocytes (PCE) indicated that the induction of MN-PCE by benzene depended on the sex and strain of mice and on the route of exposure, but not on the inhalation regimen or on the exposure duration. The frequency of MN normochromatic erythrocytes (NCE) not only depended on the sex and strain of mice and on the route of exposure, but directly depended on the inhalation regimen and on the exposure duration. Similarly, the extent of erythropoietic depression in benzene-exposed mice was dependent on sex, mouse strain, exposure duration, and route. However, in contrast to the MN-NCE data, the 3 day/week exposure regimen induced a more persistent depression in erythropoiesis than the 5 day/week exposure regimen. Exposure to benzene also induced in mice a significant depression in packed cell volume (PCV) and bone marrow cellularity, the magnitude of which depended on the sex and strain of mice and on the regimen and route of exposure.