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Comparison of Oral and Inhalation Exposures to Toluene

Male Fisher-344 rats were exposed to [14C]toluene by either liquid gavage or vapor inhalation and blood toluene levels were measured by radiospectroscopy. Oral doses of 110, 336, 741, and 911 mg toluene/kg body weight were administered to 82 rats by gavage and blood toluene levels were followed for 6 h. For the inhalation group (120 rats), 3-h exposures to 99, 549, and 1,145 ppm were given and blood toluene levels were measured during this 3-h uptake phase and during a 4-h elimination period. The data for these two exposure methods were fitted to parametric kinetic models, and the resulting curves were then integrated. The blood toluene versus time profiles for oral and inhalation exposures were then compared and the equation: In(oral dosage, mg/kg) = -1.44 + 0.95 In(3-h inhalation exposure concentration, ppm) was derived (where In represents the natural logarithm). This equation describes the relation between toluene inhalation and oral exposure methods used in this study. This investigation demonstrates that oral toluene administration produces high blood toluene concentrations that can simulate the blood levels achieved after inhalation exposure to this solvent.