[New regulation of tap water quality and exposure assessment]

Recently, social concerns regarding tap water quality have increased, mainly because of the possible reduction in safety due to contamination of tap water by various chemicals and more frequent occurrence of the strange odors and tastes in as a result of resource water eutrophication. Consequently, the Ministry of Health and Welfare conducted a detailed two-year investigation of the Water Quality Standards of the Water Works Law by summoning an expert committee, and as a result, totally revised the Standards in December 1992. This was the first overall revision since 1958 when the Water Quality Standards were established, and an additional 21 items, including mainly hazardous chemicals including pesticides and chlorinated by-products, were newly added. Values and testing methods are now listed for 46 items, and the Law obliges every water supply to conduct periodical water testing for the necessary items almost every month with ad-hoc testing, as required of hydrants. Simultaneously, 26 monitoring items are listed in hazardous contaminants guidelines which should be checked, when necessary. The new Water Quality Standards and the guidelines were brought into force in December 1993, and the quality of all parts of the water supply is now tested in accordance. Risk assessment is a scientific process that includes some form of measurement as one of its central elements. In many cases, the measured parameter is the level of exposure to a hazard. Also, measurements are essential in establishing the quantitative relationship between exposure and response, and in determining natural baseline conditions in the environment. Exposure assessment is the process of measuring or estimating the intensity, frequency, and duration of human or other population exposures to risk agents. Exposures may occur in a variety of ways, such as through ingestion, dermal contact, or inhalation. For many risk assessments, exposure assessment is the most difficult task. The reason for this is that exposure assessment often depends on factors that are hard to estimate and for which there are few data. Critical information on the conditions of exposure is often lacking. To be comprehensive, an exposure assessment must describe the levels of exposure and all conditions that might be needed to assess the effects of such exposures, including their magnitude, duration, schedule, and route. This report presents the various problems covered in exposure assessment relevant to monitoring, testing, and methodology.