Effects of low concentrations of benzene on mouse hematopoietic cells in vivo: a preliminary report.

Evaluation of benzene-induced hematotoxicity following exposure to low concentrations is important for understanding mechanisms of toxicity and determining the dose response at benzene levels close to the current occupational exposure limit (1 ppm). Male B6C3F1 mice were exposed to O, 1, 10, 100, or 200 ppm benzene by inhalation for 6 hr/day, 5 days/week for 1, 2, 4, or 8 weeks. At each sampling time, we evaluated primitive and committed progenitor cells, differentiating and maturing lineage-specific cells, and stromal cells in the bone marrow; T and B lymphocytes of the spleen and thymus; micronucleated reticulocytes and erythrocytes; and standard blood parameters. At 100 and 200 ppm benzene, there were rapid and significant reductions in number of reticulocytes in the blood, B lymphocytes in the bone marrow and spleen, and an increased frequency of micronucleated reticulocytes in the bone marrow. At 10 ppm, the only parameter affected was a transient reduction in the number of splenic B lymphocytes. There were no significant effects induced by 1 ppm benzene in this study. The present study suggests numbers of B lymphocytes and maturing erythrocytes, and frequency of micronucleated reticulocytes are sensitive indicators of benzene-induced hematotoxicity and will be useful in further investigation of the hematotoxicity induced by 10 to 100 ppm benzene.