産総研:安全科学研究部門サイト > Development of Innovative Methodology for Safety Assessment of Industrial Nanomaterials > Research Activities and Results (June 2015) > Research and development item: ①(a) Development of equivalence criteria based on comparison of nanomaterials by intratracheal administration testing results

Research and development item: ①(a) Development of equivalence criteria based on comparison of nanomaterials by intratracheal administration testing results

Implemented by the Chemicals Evaluation and Research Institute

Final objective: Nanomaterials composed of the same elements in the same ratios can still exhibit different physicochemical properties such as size (i.e., particle size) and shape, and the hazard posed by such materials may differ because of such differences in their physicochemical properties. Therefore, hazard assessment is necessary for individual nanomaterials; however, it involves considerable expense and labor. In this study, to clarify the different pulmonary toxicities of multiple nanomaterials with different physicochemical properties of nanomaterials, we performed intratracheal administration testing using rats and obtained hazard data (bronchoalveolar lavage fluid (BALF) testing and histopathological testing of the lung). By elucidating the differences in pulmonary toxicity due to difference in physicochemical properties of nanomaterials, we compile and release equivalence criteria that outline the conditions under which different physicochemical properties of nanomaterials do not affect pulmonary toxicity and under which nanomaterials can be considered to be equivalent.

Main results:
We used F344 rats (male, 12 weeks old) to perform intratracheal administration testing of nanomaterials with different physicochemical properties such as particle size, shape, and surface coating. As nanomaterials, we used seven TiO2, seven SiO2, and four NiO samples. We obtained hazard data using lung inflammation as an endpoint 3 and 28 days and 13 weeks after single intratracheal administration of each nanomaterial.

With respect to TiO2, differences in shape and crystal structure (rutile or anatase) had little impact. In the case of differences in particle size, 3 days after administration, materials with a small particle size in the administered liquid exhibited strong pulmonary toxicity, suggesting that a difference in particle size contributed to a difference in pulmonary toxicity. Materials with an Al(OH)3 surface coating continued to exhibit pulmonary toxicity 28 days after administration, suggesting that surface coating may contribute to a difference in long-term pulmonary toxicity (Table ①(a)-1). Materials without a surface coating disappeared pulmonary toxicity 28 days after administration.

Table①(a)-1 Provisional equivalence criteria of TiO2

Physicochemical property Effects on pulmonary toxicity
Particle size May contribute to the difference in the pulmonary toxicity of acute phase
(Especially secondary particle size)
Shape May not have effect
Surface coatings May contribute to the differences in the acute or subacute pulmonary toxicity
Crystallinity May not have effect

With respect to differences in the particle size of SiO2, materials with a small particle size in the administered liquid exhibited strong pulmonary toxicity 3 days after administration, suggesting that a difference in particle size contributed to a difference in pulmonary toxicity. Regarding the effect of different surface coatings, materials with COOH modification exhibited weaker pulmonary toxicity than materials without modification 3 days after administration. This result suggested that a difference in surface coating contributed to differences in pulmonary toxicity in the initial stage after administration. With respect to differences in crystallinity, amorphous materials exhibited pulmonary toxicity 3 days after administration but showed some recovery 28 days after administration. In contrast, crystalline materials exhibited strong pulmonary toxicity 3 days after administration and continued to show pulmonary toxicity 28 days after administration, which suggested that differences in crystallinity may contribute to differences in pulmonary toxicity in the initial stage after administration and in long-term pulmonary toxicity (Table ①(a)-2).

Table①(a)-2 Provisional equivalence criteria of SiO2

Physicochemical property Effects on pulmonary toxicity
Particle size May contribute to the difference in the pulmonary toxicity of acute phase
(Especially secondary particle size)
Surface coatings May contribute to the differences in the acute pulmonary toxicity
Crystallinity May contribute to the differences in the acute or subacute pulmonary toxicity

With respect to differences in the particle size of NiO, materials with a small particle size in the administered fluid exhibited strong pulmonary toxicity 3 days after administration and continued to exhibit pulmonary toxicity 28 days after administration, which suggested that differences in particle size may contribute to differences in pulmonary toxicity in the initial stage after administration and in longer-term pulmonary toxicity. With respect to differences in shape, fibrous materials exhibited strong pulmonary toxicity 3 days after administration but showed recovery 28 days after administration. In contrast, spherical materials exhibited strong pulmonary toxicity 3 days after administration and continued to show pulmonary toxicity 28 days after administration, which suggested that differences in shape may contribute to differences in pulmonary toxicity in the initial stage after administration and in longer-term pulmonary toxicity (Table ①(a)-3).

Table①(a)-3 Provisional equivalence criteria of NiO

Physicochemical property Effects on pulmonary toxicity
Particle size May contribute to the differences in the acute or subacute pulmonary toxicity
(Especially secondary particle size)
Shape May contribute to the differences in the acute or subacute pulmonary toxicity