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Particle size distribution (Granulometry)

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Description of key information

The proportion of test material having an inhalable particle size less than 100 µm was below 3.3 % w/w, OECD 110 sieve method, Butler & O'Connor (2009)

Additional information

The particle size of the test material was determined following the screening study as outlined in the standardised guideline OECD 110.

On visual assessment the test material was observed to be composed of rocks of various sizes from approximately 10 cm to <1 cm plus some dust. To represent a worst case scenario for potential inhalation risk the larger particles were removed and only smaller particles and dust were sub-sampled. From this sub-sample the percentage of test material with a particle size of <100 µm was calculated by sieve analysis. A representative portion of this sub-sample (14.41 g) was sieved for approximately 30 minutes on an Inclyno sieve shaker using a 100 µm sieve. The mass of the test material passing through the sieve was measured.

From a sub-sample of the test material the percentage of material with a particle size less than 100 µm was determined to be 3.3%. This indicated that the test material was of a particle size that was essentially non-inhalable. It must be noted that this value is a significant overestimate of the true fine particle fraction of the test material due to the sampling procedure.