Mice exposed in utero to 20 ppm benzene exhibit altered numbers of recognizable hematopoietic cells up to seven weeks after exposure.

Pregnant Swiss Webster mice were exposed from Day 6 through Day 15 of gestation to either air, 5 ppm, 10 ppm, or 20 ppm benzene. On Day 16 of gestation, 2 days after birth, and 6 weeks after birth, progeny of the exposed dams were assayed for the amount and type of hemoglobin produced and for recognizable hematopoietic cells in the peripheral blood and hematopoietic organs. None of the benzene exposures induced significant changes in the indices assayed from the 16-day fetuses. In contrast, 2-day neonates exposed in utero to all concentrations of benzene exhibited reduced numbers of circulating erythroid percursor cells. In addition, those 2-day neonates exposed in utero to 20 ppm benzene exhibited increased numbers of hepatic hematopoietic blast cells and granulopoietic precursor cells accompanied by decreased numbers of erythropoietic precursor cells. Six-week adult mice exposed in utero to 20 ppm benzene exhibited a similar pattern of enhanced granulopoiesis. These animals exhibited elevated numbers of splenic hematopoietic blast cells and granulopoietic precursor cells accompanied by decreased numbers of marrow erythropoietic precursor cells. These results suggest that in utero exposures to low concentrations of benzene can induce persistent enhanced production of recognizable granulopoietic elements in the hematopoietic systems of mice.