Haemopoietic stem cells in mice chronically exposed to styrene vapour.

Female C57BL/6X DBA/2 hybrid mice were exposed to two concentrations of styrene in inhalation chambers for 6 h/day, 5 days per week. The concentrations were 220 ppm for a period of up to 8 weeks and 440 ppm for 2 days, followed by 330 ppm for up to 8 weeks due to early deaths after 440 ppm. Parallel groups were also treated with 5% ethanol in the drinking water during the days of styrene exposure. In the peripheral blood only a lymphocytopenia was found. The numbers of pluripotent haemopoietic stem cells, CFU-S, were unaffected, as were granuloid committed stem cells, CFU-C. Early and late erythroid stem cell numbers, BFU-E and CFU-E, showed high variability. At 220 ppm about half of the animals had CFU-E numbers below 80% of controls, at 440/330 ppm about two-thirds of the animals had BFU-E and CFU-E numbers below this level. An additional effect of ethanol was not found.