Benzene disposition in the rat after exposure by inhalation.

Abstract Little information is available on benzene disposition after exposure by inhalation despite the importance of this route in man. Benzene metabolites as a group have been measured in bone marrow, but quantitation of individual metabolites in this target tissue has not been reported. Male Fischer-344 rats were exposed to 500 ppm benzene in air and the uptake and elimination was followed in several tissues. Concentrations of free phenol, catechol, and hydroquinone in blood and bone marrow were also measured. Steady-state concentrations of benzene (11.5, 37.0, and 164.0 μg/g in blood, bone marrow, and fat, respectively) were achieved within 6 hr in all tissues studied. Benzene half-lives during the first 9 hr were similar in all tissues (0.8 hr). A plot of amount of benzene remaining to be excreted in the expired air was biphasic with t 1 2 values for the α and β phases of 0.7 and 13.1 hr, respectively. Phenol was the main metabolite in bone marrow at early times (peak concentration, 19.4 μg/g). Catechol and hydroquinone predominated later (peak concentrations, 13.0 and 70.4 μg/g, respectively). Concentrations of these two metabolites declined very slowly during the first 9 hr. These data indicate that free catechol and hydroquinone persist in bone marrow longer than benzene or free phenol.