Development of occupational exposure limits in Japan

Area of Science:

• Occupational Health
• Toxicology
• Environmental Science

Background:

• Occupational exposure limits (OELs) are crucial for protecting worker health.
• Benzene is a known human carcinogen, while trichloroethylene is classified as probably carcinogenic to humans.
• Japan's OEL committee evaluates chemical risks to set appropriate exposure standards.

Purpose of the Study:

• To describe the development of OELs for benzene and trichloroethylene in Japan.
• To explain the risk assessment methodologies used for setting these OELs.
• To propose reference values for occupational and environmental exposure.

Main Methods:

• For benzene: epidemiological data (Pliofilm cohort), exposure estimates, and a relative risk model were used to calculate leukemia risk.
• For trichloroethylene: neurological effects of long-term exposure were evaluated, considering its potential epigenetic carcinogenicity.
• Risk-based approaches were employed, linking exposure levels to specific health outcomes and acceptable risk probabilities.

Main Results:

• Benzene OELs are proposed based on lifetime leukemia risk, with reference values of 1 ppm for 10(-3) risk and 0.1 ppm for 10(-4) risk.
• Trichloroethylene OEL is set at 25 ppm (135 mg/m3) based on neurotoxic effects, not carcinogenicity.
• Proposed environmental air standards are 1/1,000 of the occupational reference values for both chemicals.

Conclusions:

• OELs for benzene are determined by carcinogenic risk, focusing on leukemia.
• OELs for trichloroethylene are based on neurotoxicity, acknowledging uncertainty in its carcinogenic mechanism.
• The study advocates for distinct risk-based approaches for different chemical hazards in occupational health settings.