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Particle size distribution (Granulometry)

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Description of key information

29.1 % of the test material was determined to be less than 100 µm in size; less than 0.1 % of the test material was determined to be less than 10.0 µm in size, OECD 110, O'Connor & Woolley (2007).

Additional information

The particle size distribution of the test material was investigated in a study which was conducted under GLP conditions and in accordance with the standardised guideline OECD 110, using a cascade impactor.

Particle size distribution data obtained during the study differed from particle size distribution data which had already been generated using a laser diffraction method.

The discrepancy between the particle size distribution data as generated by laser analysis (a D10 value of 4.3 µm, a D50 value of 6.9 µm and D90 value of 10.7 µm) and that obtained within this study can be attributed to the different techniques employed. Whereas the laser diffraction data may remain an accurate reflection of the actual particle size of individual particles, the cascade impactor technique addresses the equivalent aerodynamic diameter of the particles. The sedimentation technique applied to inhalation risk assessment is dependent on not only the size and shape of the particles, but also their density. The extremely high relative density value of 4.63 for the test material would account for the discrepancy between the two techniques. Thus a particle size of small diameter but high density would result in a much higher equivalent aerodynamic diameter when addressing the potential for penetration of the airways and lungs due to rapid sedimentation under the influence of gravity. In addition, the test material was observed to be a non-free flowing powder, which did not readily form an aerosol, and thus the test material did not freely exist as individual particles.

Under the conditions of the study 29.1 % of the test material was determined to be less than 100 µm in size; less than 0.1 % of the test material was determined to be less than 10.0 µm in size.