Development of Hazard Assessment System for Durable Suspended Particulute Matters

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Approximately 50,000 kinds of chemical substances are used by Japanese industry while more than several hundreds are developed anew every year to meet the demands of diversification. Chemical substances contribute to industrial development and the realization of an affluent lifestyle and thus they have become indispensable to modern society. However, many such substances are harmful and may be adverse to health, depending on the way they are handled, and therefore they need to be adequately managed.To control these risks, it is necessary to perform risk assessment by comprehending the degree of hazard and the amount of exposure. Mutagenicity tests or carcinogenicity tests are legally required for evaluating the potential hazards of chemical substances on human health, but they are no valid testing methods for durable particulate matters.Among durable particulate matters, some, as typified by asbestos and crystalline silica, induce pneumoconiosis, lung cancer or mesothelioma twenty to t … More hirty years after the exposure. As this raises the possibility that some of the newly developed substances are similarly harmful, establishment of a hazard prediction/evaluation system for durable particulate matters is required. To achieve this goal, five-step tests have been systematically conducted, namely : physical and chemical, in vitro, intratracheal instillation, short-term and long-term inhalation tests. With crystalline silica as positive control, the test samples used were potassium titanate with different shapes, fibrous and particulate, composed of the same chemical components and silicon carbide whisker whose demand is expected to increase. The hazard assessment method has been established by integrating the obtained data while a system applicable to all the durable particulate matters has been developed by generalizing the data. The result was particularly suggestive of the direction for the development of new chemical substances by illuminating the difference in activity and biopersistence of the particles in the lung, depending on their shape. Less