Derivation of human health hazard assessment values of 1,2-dichloroethane under the Japan Chemical Substances Control Law

Abstract

1,2-Dichloroethane, a priority assessment chemical substance under the Japan Chemical Substances Control Law (CSCL), required a detailed human health hazard assessment under Assessment II. We evaluated its general, reproductive, and developmental toxicities, genotoxicity, and carcinogenicity, based on the hazard information provided by domestic and international risk assessment organizations, and the hazard assessment values (HAVs) for oral and inhalation exposure were proposed. For oral exposure, a 78-week gavage carcinogenicity study (US NCI, 1978) with incidence data of hemangiosarcoma in male rats was selected as a significant toxicological endpoint and the lower confidence limit of benchmark dose (BMD) at 10% benchmark response (BMDL₁₀) of 9.3 mg/kg/day was obtained as a point of departure (POD). A slope factor of 1.07 × 10⁻² (mg/kg/day)⁻¹ from which a carcinogenic 10⁻⁵ risk of 0.93 µg/kg/day was derived as an oral HAV. For inhalation exposure, a 104-week inhalation exposure carcinogenicity study (Nagano et al., 2006) with a BMDL₁₀ of 11.5 ppm based on the incidence data of mammary gland tumors (adenocarcinoma + adenoma + fibroadenoma, combined) in female rats was obtained, and the human equivalent BMDL₁₀ of 15.7 mg/m³ was calculated. Therefore, a unit risk of 6.40 × 10⁻⁶ (µg/m³)⁻¹ from which a carcinogenic 10⁻⁵ risk of 1.6 µg/m³ (0.00039 ppm) was derived as an inhalation HAV.