Abstract
We assessed carcinogenic risk from inhalation exposure of 1, 2-dichloroethane, which is one of 22 hazardous air pollutants proposed as 'substances requiring priority action' by the Central Environmental Council of Japan in 1996. We calculated the carcinogenic unit risk by the benchmark dose approach utilizing data from mammary gland tumors of female rats exposed to 1, 2-dichloroethane for two years. Four groups comprising 50 rats each were exposed to 1, 2-Bdichloroethane of the following concentrations: 0 ppm, 10 ppm, 40 ppm, and 160 ppm. The numbers of rats bearing tumors in their mammary glands for the respective groups were 8, 8, 11, and 25. We estimated the concentration corresponding to an excess risk of 0.10 (EC10) and its lower confidence limit (LEC10). For the methods of interspecies extrapolation from rat to human we utilized two approaches, one was a dosimetric method based on the regional gas dose ratio, and the other was an allometric scaling method based on body size. The dosimetric method for gases as 1, 2-dichloroethane, which exhibits its toxic effects outside of the respiratory tract, assumes that the effects observed are related to the arterial blood concentration. By the dosimetric method, the human equivalent benchmark concentration of 1, 2-dichloroethane was calculated using the ratio of the blood: gas partition coefficient of the chemical for the rat to the human value. Its carcinogenic unit risk from inhalation exposure was estimated to be 6.3 ×10-6 per (μg/m3), and the exposure concentration at the risk level of 10-5 was calculated to be 1.6 μg/m3. Its unit risk was also estimated to be 7.1 ×10-6 per (μg/m3) using the allometric scaling method, and it was almost the same value as when estimated using the dosimetric method.
