Evidence for hematotoxicity and tumorigenesis in rats exposed to 100 ppm benzene.

A group of 40 Sprague-Dawley rats was exposed to 100 ppm benzene for 6 h/day, 5 days/week for life. Another group of 40 rats received air under the same exposure regimen. During the exposures, treated rats exhibited continuously depressed peripheral erythrocyte and lymphocyte counts. Although the incidences of these peripheral cell depressions were statistically significant, the magnitudes of the depressions were not. Histopathologic evaluation revealed that splenic hemosiderin pigments were much more prevalent in exposed rats than in controls, indicating either red cell hemolysis or ineffective erythropoiesis. The mortality-corrected tumor incidences between exposed and control mice were not statistically different. However, several exposed rats died with tumors that, because of their rare spontaneous incidence, are most likely treatment-related. Four rats died with liver tumors, two died with zymbal gland carcinoma, and one died with chronic myelogenous leukemia.