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Particle size distribution (Granulometry)

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Description of key information

Sieve analysis:
The median particle size D50 of the test item was determined to be 155 µm. (717)
The median particle size D50 of the test item was determined to be 151 µm. (727)
Laser diffraction analysis (test item: sieve fraction <75µm):
The median particle size D50 of the test item was determined to be 51.2569 µm. (727)
The median particle size D50 of the test item was determined to be 52.6483 µm. (717)
Total dustiness (worst case figures):
inhalable dust for “Tiwest SR-product”: 253 mg/kg = 0.025%
respirable dust for “Capel synthtic rutile, premium grade”: 16.7 mg/kg = 0.002%

Additional information

The standard commercial product received from the Beacher process is “sand” size, i.e. has a particle size of 0.1 to 0.5 mm.

Sieve analysis

In addition, data from a sieve analysis are available. However, this information is included as supportive information only. D50 for the same batches as tested by laser diffraction is approximately 153 µm. The fraction in the receiver pan (<75µm) was taken forward to the laser diffraction analysis.

 

Laser diffraction

For the evaluation of this endpoint data from experimental studies (conducted similar to OECD guideline 110) in which the particle size distribution was determined by laser diffraction were used as key information, supported by results from experimental sieving.

The particle size distribution of two batches of Synthetic Rutile were determined by laser diffraction. Synthetic Rutile has a D50 value of 52 µm.

 

Total dustiness

Based on the total dustiness data, the following conclusions can be drawn for risk characterisation purposes:

(i) total dustiness measurements with tree different synthetic rutile samples show very low dustiness, maximum values were determined as follows:

inhalable dust for “Tiwest SR-product”: 253 mg/kg = 0.025%

respirable dust for “Capel synthtic rutile, premium grade”: 16.7 mg/kg = 0.002%

(ii) Synthetic rutile has a limited ability to be inhaled by humans: 0.025 % of airborne material is estimated to be inhalable.

(iii) only about 0.002 % or less of inhaled material is predicted to be deposited in the pulmonary region (PU), i.e. respirable fraction. The material deposited in the tracheobronchial (TB) and the extrathoracic region (Head) may be assumed to be cleared to the GI tract (i.e., by mucociliary escalation and subsequent swallowing)