Hematologic and myelogenous effects of inhaled benzene in the pig and the rat.

Four groups of 4 domestic pigs were exposed to 0, 20, 100, and 500 ppm benzene vapor 6 h/d, 5 d/wk, for 3 wk. Two groups of 10 rats were exposed to 0 and 500 ppm: the exposed rats for 6 h/d, 5 d/wk, for 3 wk, the nonexposed rats for 6 h/d, 5 d. Rats were killed within 72 h after exposure; values for pigs were obtained shortly after exposure and on final examination at 4-16 wk after exposure. Pigs were evaluated for changes in white and red blood cell counts, hemoglobin level, lymphocyte count, proportion of E-rosette-forming lymphocytes, myeloid-erythroid ratio, and presence of multinucleate erythroblasts. With the exception of the E-rosette test, the same parameters were measured in the rat. Statistically significant (p less than 0.05) depression of white cell counts, total lymphocytes, and proportion of E-rosette-forming lymphocytes was observed in pigs exposed to 500 ppm; recovery to values not significantly different from control values was observed on final examination. Fewer postexposure effects were seen at 100 ppm, and there were no significant differences from control values at 20 ppm. Both pigs and rats exposed to 500 ppm showed a significant decrease in the mean myeloid-erythroid ratio within 72 h. These values returned to normal in the pig 4-16 wk after exposure; recovery in the rat was not evaluated. An increased number of bone marrow erythroblasts with more than 2 nuclei was found on final examination of pigs exposed to 500 and 100 ppm, but the difference was significant only at the 100-ppm level because of the variability at the higher level. A significant increase (p less than 0.004) in multinucleate cells was seen in the rats exposed to 500 ppm.