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Particle size distribution (Granulometry)

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Reference
Endpoint:
particle size distribution (granulometry)
Type of information:
experimental study
Adequacy of study:
key study
Study period:
29 July 2003 to 30 July 2003
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: The study was reported to a high standard with a good level of detail in the methodology and results. The experimental portion of the study was performed in line with good scientific principles.
Qualifier:
no guideline followed
Principles of method if other than guideline:
A vertical elutriator was set up containing approximately 30 g of dried test material. The amount of test substance eluted from the starting material at a range of air velocities (corresponding to an appropriate range of settling velocities and hence aerodynamic equivalent diameters (AED)), was measured on duplicate samples, allowing 30 minutes elutriation at each velocity.
GLP compliance:
yes
Type of method:
sedimentation (gravitational settling)
Type of particle tested:
primary particle
Type of distribution:
other: Aerodynamic equivalent diameters
No.:
#1
Size:
<= 115 µm
Distribution:
ca. 13.2 %
No.:
#2
Size:
<= 15 µm
Distribution:
ca. 0 %

Table 2: Results

AED* (µm)

Weight loss (%)

Mean weight loss (%)

Mean cumulative loss (%)

Sample 1

Sample 2

≤15

0.00

0.00

0.00

0.00

≤35

0.89

1.36

1.12

1.12

≤50

1.84

2.35

2.09

3.22

≤75

2.53

4.13

3.33

6.55

≤115

6.50

6.65

6.58

13.12

 * This represents the aerodynamic cut points of the various elutriator velocities employed.

From these data it was determined that 13.12 % of the test substance was of AED115 µm (AED100 µm classified as inhalable according to current UK and ISO definitions, HSE, 2000; ISO, 1995). Of this inhalable percentage, none (0.00 %) is considered as respirable i.e. <15 µm AED.

Conclusions:
Under the conditions of the test, it was apparent that some of the test material was capable of becoming airborne; 13.2% being less that or equal to 115 µm aerodynamic equivalent diameter (AED). No material eluted with an AED of <15 µm. Based on the the UK and ISO definitions (AED <100 µm inhalable and <15 µm respirable) the test material is considered to be of low inhalability and none of the sample is respirable. The study is considered to be reliable, relevant and adequate for risk assessment purposes.
Executive summary:

The particle size distribution of the test material was determined by air elutriation. A vertical elutriator was set up containing approximately 30 g of dried test material. The amount of test material eluted from the starting material at a range of air velocities (corresponding to an appropriate range of settling velocities and hence aerodynamic equivalent diameters (AED)), was measured on duplicate samples, allowing 30 minutes elutriation at each velocity.

Under the conditions of the test, it was apparent that some of the test substance was capable of becoming airborne; 13.2% being less that or equal to 115 µm aerodynamic equivalent diameter (AED). No test material eluted with an AED of <15 µm. Based on the the UK and ISO definitions (AED <100 µm inhalable and <15 µm respirable) the test material is considered to be of low inhalability and none of the sample is respirable.

Description of key information

Aerodynamic Equivalent Diameters (AED), 13.2% ≤115 µm aerodynamic equivalent diameter (AED). No material eluted with an AED of <15 µm, Air Elutriation, Rattray 2003

Additional information

The particle size distribution of the test substance was assessed by vertical elutriation in Rattray (2003). A vertical elutriator was set up containing approximately 30 g of dried test material. The amount of test material eluted from the starting material at a range of air velocities (corresponding to an appropriate range of settling velocities and hence aerodynamic equivalent diameters (AED), was measured on duplicate samples, allowing 30 minutes elutriation at each velocity. Under the conditions of the test, it was apparent that some of the test substance was capable of becoming airborne; 13.2% being less than or equal to 115 µm aerodynamic equivalent diameter (AED). No material eluted with an AED of <15 µm. Based on the UK and ISO definitions (AED <100 µm inhalable and <15 µm respirable) the test material is considered to be of low inhalability and none of the sample is respirable. This study was assigned as the key study as it accurately measures the aerodynamic equivalent diameter and allows assessment of the potential inhalation hazard that could arise from the test substance.

Supporting information was available in the form of Füldner 2003, a study investigating the particle size of the test material was determined using the method of light diffraction (Fraunhofer diffraction method). Under the conditions of the test, the median size distribution of the particles was determined to be 103.31 µm. The particles were qualitatively reported to be irregularly shaped.

Both studies were performed in compliance with GLP and were reported to a high standard. Although neither study was performed to a standardised guideline, both methods were designed in line with good scientific principles. Both studies were therefore assigned a reliability score of 2, and considered suitable and adequate for assessment.

The available data is considered complete. The observations of the aerodynamic equivalent diameters (AED), 13.2% ≤115 µm AED, no material with an AED of <15 µm, and the conclusion, the test material was considered to be of low inhalability and none of the sample was respirable, were taken forward for risk assessment.