Risk assessment of hazardous substances revisited

It is needless for occupational health doctors and scientists to mention about the importance of risk assessment of hazardous substances used in workplaces. Since the US Supreme Court sentenced the " benzene verdict " requiring better ground for the occupational exposure limit (OEL) for benzene in 1980, the research and scientific knowledge on risk assessment for hazardous substances have been greatly advanced, and the concept of risk for hazardous substances used in workplaces has been introduced into the field of occupational health. Since then, many hazardous substances have been reevaluated for effects on worker health in light of the risk assessment approach. In particular, the occupational health standards for occupational carcinogens are noteworthy. The Japan Society for Occupational Health (JSOH) recommends the reference values of 1 ppm and 0.1 ppm for benzene, corresponding to individual excess lifetime risks of cancer of 1 × 10 −3 and 1 × 10 −4 , respectively, on the basis of the average relative risk model, instead of the conventional OEL value. The JSOH also recommends the reference values for other occupational carcinogens including arsenic and its compounds (as As), asbestos and nickel smelting dusts (as Ni) as well as ionizing radiation. A characteristic feature of these carcinogenic reference values is that they are expressed as occupational standard concentrations with an excess lifetime cancer risk level of 1/1,000 or 1/10,000. It was thus suggested that there is no threshold level for induction of cancer in comparison with noncarcinogenic compounds having a threshold level below which there is no risk of any adverse health effect. Recently in Japan, we had two tragic incidents that raised serious concerns regarding the health of workers handling two hazardous substances, i.e., indium and 1,2-dichloropropane (DCP). The first was 10 cases of lung diseases attributable to occupational exposure to indium and its compounds reported in Japan as of 2010, including 7 cases of interstitial pneumonia. In 2010, the Japan Ministry of Health, Labour and Welfare (MHLW) issued a Technical Guideline for Preventing Health Impairment of Workers Engaged in the Indium-Tin Oxides Handling Processes. In order to protect workers from excessive exposure to indium and its compounds in workplaces , employers are required to implement actions and measures by assessing workplace air concentrations of indium-containing respirable dust, using two occupational standards. The MHLW established the two standards: a target concentration of indium in respirable dust of 0.01 mg In/m 3 and an …