In accordance with Chemical Substances Control Law (CSCL), Priority Assessment Chemicals (PACs) are substances regulated and jointly released by the Ministry of Economy, Trade and Industry (METI), the Ministry of Health, Labour and Welfare (MHLW), and the Ministry of the Environment (MOE). PACs refer to substances whose long-term toxicity to humans or to flora and fauna in the human living environment is unclear, that have been found, or are expected to be found, in considerable amounts over a substantially extensive area of the environment. They were therefore published under the Chemical Substances Control Law. Based on their characteristics, these substances are classified into three categories: substances that pose risks to human health, substances that pose risks to ecosystems, and substances that pose risks to both human health and ecosystems.