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Research paper−31−Synthesiology - English edition Vol.1 No.1 (2008) each element in a consistent manner, and reintegrating each step into one consistent risk assessment process. Toluene is a clear, colorless, and highly volatile liquid at room temperature. Most of the toluene emitted into the environment disperses into the atmosphere. Its volume released into the atmosphere is largest among the 354 chemical substances reported in the PRTR (Pollutant Release and Transfer Registers) system in Japan. Toluene is also known as one of the major indoor air pollutants, and a non-binding guidance value was set by the Ministry of Health and Welfare in 2001. In the second section, we review the relationship between social demands and risk assessment methods. In the third section, we present improvements in the steps of risk assessment and their application to toluene. In the final section, the implications are discussed.2 Social demand and risk assessment methodologyThe current procedures for chemical risk assessment are conducted according to the gray arrows in Figure 1 (from bottom to top). They are divided into two types depending on their objectives (social demands). First is to derive reference values, such as environmental standards or acceptable daily intakes (ADIs), which are compared with measured or estimated exposure levels. Examples are environmental standards and guidance values set by the Ministry of the Environment, and also the indoor guidance values, the tolerance values for pesticide residue, and the standard control concentrations for occupational settings set by the Ministry of Health, Labour and Welfare. The social demands they meet include protecting vulnerable people (such as 1 IntroductionConcept of risk and methodology for risk assessment are essential in rationally addressing environmental, safety, and health issues. Human health risks from chemical substances are determined by two factors, toxicity (hazard) and exposure (intake). Low exposure to a highly hazardous substance may result in low risk, although high exposure to a substance of very low hazard may become high risk. In an established chemical risk assessment methodology, comparisons are conducted between NOAEL (no observed adverse effect level) derived from animal tests or epidemiological studies and actual or potential exposure levels. Then, judgment is made whether the exposure level of target substance is acceptable or not. This thinking is actually applied to establish various environmental and safety standards, as well as in screening assessments for removing chemical substances of low importance. However, this is not the only expected role of risk assessment. To achieve the ultimate goal of minimizing the total risk in our society, it is necessary to quantify and compare the health risks of each chemical substance, estimate the cost-effectiveness of each countermeasure to reduce risk, and rank them accordingly. Methodology of risk assessment suited to these purposes has not yet been developed.In this paper, we propose an alternative framework of risk assessment to address emerging social demands, by returning to the scheme of how conventional risk assessment was established. We then present an application of this framework to chemical substance, toluene [1]. It was a process of trial and error involving returning to social demands, reconsidering - A risk assessment of toluene exposure using quality-adjusted life years -Atsuo KishimotoResearch Center for Chemical Risk Management, AIST Tsukuba West,Tsukuba,Ibaraki 305-8569, Japan E-mail : kishimoto-atsuo@aist.go.jpThe issue of social demands must be taken into consideration when developing a methodology for risk assessment of chemical substances. We classified the objectives of risk assessment into the following three categories: (A) to derive reference values, (B) to establish screening assessment to remove chemical substances of low importance, and (C) to set priorities based on comparisons of health risks and cost-effectiveness of risk reduction measures for different chemical substances. In this categorization, we demonstrated that while the existing risk assessment methods fulfill objectives A and B, they do not satisfy objective C. Therefore, the steps of risk assessment methodology were revised to fulfill objective C, and the effectiveness of the new methodology was demonstrated using toluene as an example. By adopting the loss of quality-adjusted life years (QALYs) as an indicator of human health risks, we could compare the health risks for different chemical substances as well as compare chemical substances and other risks such as accidents and infectious diseases. A strategic approach for comparing different types of health risksKeywords : Chemical substances, risk assessment, social demands, quantification, comparisons, cost-effectiveness[Translation from Synthesiology, Vol.1, No.1, p.31-37 (2008)]

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