Detailed hazard assessment of ethylbenzene to establish an indoor air quality guideline in Japan.

Background: Indoor air quality (IAQ) is an important determinant of human health. In Japan, IAQ guidelines have been established for 13 chemicals since 1997. Regarding ethylbenzene (EB), a previous guideline value of 3800 µg/m³ was established in 2000. However, the Ministry of Health, Labour, and Welfare decided to revise the value because of the publication of new hazard information after the establishment of the previous guideline value and the establishment of their respective IAQ guidelines by foreign organizations based on the new hazard information. This study conducted a detailed hazard assessment on EB and derived hazard assessment values to provide a toxicologically valid basis for revising the IAQ guideline value.

Methods: As it was defined that the IAQ guidelines would not exert adverse health effects on humans even if they inhaled the chemicals from indoor air over a lifetime, we investigated the general toxicity, developmental and reproductive toxicity, genotoxicity, and carcinogenicity of EB based on reliable hazard information cited in published assessment documents by domestic, foreign, or international risk assessment organizations. All the collected hazard information was examined, and we originally judged the no-observed adverse effect level and the lowest observed adverse effect level of each toxicity study. We then selected the most appropriate key study, an endpoint, and a point of departure and derived the hazard assessment values for each toxicity category. Finally, we selected a representative hazard assessment value for EB from the minimum hazard assessment value among general toxicity, developmental and reproductive toxicity, and carcinogenicity.

Results: Among the three toxicity categories, the minimum hazard assessment value was obtained from general toxicity, which was 0.0858 ppm (370 µg/m³) based on the loss of the outer hair cells in the organ of Corti in the cochlea observed in a 13-week repeated-dose inhalation toxicity study using rats.

Conclusions: It would be appropriate to adopt 0.0858 ppm (370 µg/m³) as a representative hazard assessment value to provide a basis for revising the IAQ guideline value for EB.