Research and development item ② “Development of low-cost, simple hazard assessment methods to acquire basic hazard information”

As for nanomaterials, the exposure route of greatest concern for humans is the inhalation route, and many of the toxicity tests using test animals reported up to the present have assumed such inhalation route of exposure. There are examples of application of regulations, such as requiring 90-day inhalation toxicity testing for a nanomaterial of each company under the Toxic Substances Control Act (TSCA) in the United States.

Inhalation toxicity testing is the gold standard for hazard assessment for the inhalation route. However, when performing inhalation toxicity tests on nanomaterials, a) technical difficulties arise, as it is necessary to generate an aerosol and install an inhalation exposure chamber, and b) the tests require remarkable time and expense. Thus, it may not be realistic to employ the inhalation toxicity testing as a standard assessment method to acquire basic hazard information on a wide range of nanomaterials. Intratracheal administration testing is a method in which the tested nanomaterial is introduced into the lungs by dripping a dispersion of the material onto the trachea, rather than by inhalation of the aerosol. To date, this method has been used only for qualitative hazard assessment, and has not been established as a standard assessment method that can be used for administrative purposes, as seen in the fact that it has not been accepted as OECD Test Guidelines.

Accordingly, we are developing hazard assessment methods to acquire basic hazard information on nanomaterials for administrative purposes, by illuminating the relationship between intratracheal administration testing and inhalation toxicity testing and by studying standardization of the intratracheal administration testing. For wider uses of the intratracheal administration testing, we are also developing a method of sample preparation by capturing aerosols in liquids — aerosols of nanomaterials at the workplace or generated by methods of simulating the workplace.