Area under the blood concentration-time curve (AUC) of ethylbenzene concentration in rats: relationship to inhalation and oral administration route-dose

For human risk assessment of toxic chemicals, especially volatile organic compounds (VOCs), the Ministry of the Environment, Government of Japan, has called for the interconversion of inhalation-dose and oral-dose data, two common exposure routes. To address this issue, the present study investigated the time-course changes of ethylbenzene (EB) concentrations in the blood of rats during and after 6-hr inhalation exposure to EB (25, 50, 100, and 200 ppm) and after oral administration of EB by a single oral gavage (25, 50, 100, and 200 mg/kg) of EB. The Area Under the blood concentration-time Curve (AUC) at each blood collection time point (0, 30, 60, 120, 180, 360, 420, 540, and 1440 min, after starting exposure) was determined. The inhalation dose of 25 ppm corresponded closely to the oral administration of 25 mg/kgbw (r value of 0.859), and the inhalation dose of 200 ppm correlated with the oral administration of 100 mg/kgbw (r value of 0.948). These results suggest that this comparison using the AUC data at each blood collection time point is valuable for understanding the route- and dose-effects of EB. This study will improve risk assessment of human exposure to EB and other VOCs.