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Particle size distribution (Granulometry)

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Endpoint:
particle size distribution (granulometry)
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2010-05 to 2010-08
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Test procedure in accordance with national standards DIN 55992-1:2006 ("Determination of a parameter for the dust formation of pigments and extenders - Part 1: Rotation method"), modified Heubach method
Qualifier:
according to guideline
Guideline:
other: DIN 55992-1:2006 (Determination of a parameter for the dust formation of pigments and extenders – Part 1: Rotation method)
Deviations:
yes
Remarks:
see "Principles of method if other than guideline"
Principles of method if other than guideline:
The Heubach dust meter is modified in a way that a seven stage cascade impactor is connected to the system. This involves an additional air fed of 20 L/min via the coarse dust separator needed to supply the cascade impactor with 40 L/min air current as specified in the manufacturer’s specifications.
The calculation report: Grewe, T. (2010)
The Multiple-Path Particle Dosimetry Model (MPPD, v2.0; CIIT, 2006) was used to predict this fractional deposition behaviour for workers.
The model algorithms calculate the deposition (and clearance) of mono-disperse and polydisperse aerosols in the respiratory tract for particles ranging from ultra-fine (0.01 microns) to coarse (20 microns) sizes. Within each airway, deposition is calculated using theoretically derived efficiencies for deposition by diffusion, sedimentation and impaction within the airway or airway bifurcation. Filtration of aerosols by the head is determined using empirical efficiency functions.
GLP compliance:
no
Type of method:
rotating drum method
Type of distribution:
volumetric distribution
Percentile:
D50
Remarks on result:
other: Migrated from fields under 'Mass median diameter' as D50 percentile. No source field for Standard deviation.

Dustiness (airborne fraction): total: 30.88 mg/g.

In the original study report by DMT, a calculation of the mass median diameter was not conducted. Since the deposited fractions were provided for each of the cascade impactor stages, it was possible to fit a mono modal lognormal distribution to the data by standard non-linear regression procedure. As a result, the MMAD and GSD are calculable and reported (MMAD = 29.23 µm, GSD = 1.61). As the cascade impactor already takes aerodynamic characteristics of the particles into account, the reported mass median diameter can be interpreted as the mass median aerodynamic diameter.

This figure and the corresponding GSD were used as distribution parameters for the MPPD model enabling an estimation of deposited dust fractions in the human respiratory tract: These fractions were estimated as follows:

Head (ET): 46.6 %

Tracheobronchial (TB): 0.1 %

Pulmonary (PU): 0.0 %

Conclusions:
Cobalt stearate

Total Dustiness (airborne fraction): 30.88 mg/g (experimental results, DMT Report).

Mass median aerodynamic diameter of airborne fraction: MMAD = 29.23 µm (distribution fitted to cascade impactor data).
Geometric standard deviation of MMAD: GSD = 1.61

Fractional deposition in human respiratory tract (MPPD model, based on calculated MMAD):
Head (ET): 46.6 %
Tracheobronchial (TB): 0.1 %
Pulmonary (PU): 0.0 %
Endpoint:
particle size distribution (granulometry)
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
A preliminary abrasion test was perfomed to generate dust with a rotating drum. The following test procedure is in accordance with national standards DIN 55992-1:2006 ("Determination of a parameter for the dust formation of pigments and extenders - Part 1: Rotation method"), modified Heubach method.
Qualifier:
according to guideline
Guideline:
other: DIN 55992-1:2006 (Determination of a parameter for the dust formation of pigments and extenders – Part 1: Rotation method)
Deviations:
yes
Remarks:
see "Principles of method if other than guideline"
Principles of method if other than guideline:
The Heubach dust meter is modified in a way that a seven stage cascade impactor is connected to the system. This involves an additional air fed of 20 L/min via the coarse dust separator needed to supply the cascade impactor with 40 L/min air current as specified in the manufacturer’s specifications.

Determination of the friability of the sample to assess if any fine material/dust would be abraded and subsequently the dust fractions of this substance. In this preliminary test, the provided lumps were subjected to mechanically agitation in a rotating steel drum, to simulated mechanical stress under typical industrial handling conditions.
GLP compliance:
no
Type of method:
rotating drum method
Type of distribution:
volumetric distribution
Percentile:
D50
Remarks on result:
other: Migrated from fields under 'Mass median diameter' as D50 percentile. No source field for Standard deviation.
No.:
#1
Size:
65 µm
Distribution:
19.15 %
Remarks on result:
other: cumulated particle size distribution
No.:
#2
Size:
30.89 µm
Distribution:
43.99 %
Remarks on result:
other: cumulated particle size distribution
No.:
#3
Size:
15.06 µm
Distribution:
71.46 %
Remarks on result:
other: cumulated particle size distribution
No.:
#4
Size:
7.75 µm
Distribution:
75.05 %
Remarks on result:
other: cumulated particle size distribution
No.:
#5
Size:
3.87 µm
Distribution:
87.91 %
Remarks on result:
other: cumulated particle size distribution
No.:
#6
Size:
1.95 µm
Distribution:
97.37 %
Remarks on result:
other: cumulated particle size distribution
No.:
#7
Size:
0.94 µm
Distribution:
98.88 %
Remarks on result:
other: cumulated particle size distribution
No.:
#8
Size:
0.45 µm
Distribution:
99.74 %
Remarks on result:
other: cumulated particle size distribution

Preliminary abrasion test

Mass of generated fines < 1 mm: 7.659 g

Fraction of generated fines per kg original material: 15.318 g/kg

Dustiness test

Dust masses and flow values of the impactor stages

Impactor stage

Average

aerodyn.

diameter

[µm]

Calculated physical particles size

[µm]

Separated dust mass

[mg]

Pass

[%]

Residue

[%]

A

32.40

30.89

68.19

56.01

43.99

B

15.80

15.06

42.58

28.54

71.46

C

8.13

7.75

5.57

24.95

75.05

D

4.06

3.87

19.93

12.09

87.91

E

2.04

1.95

14.67

2.63

97.37

F

0.99

0.94

2.34

1.12

98.88

G

0.47

0.45

1.34

0.26

99.74

< G *)

<0.47

<0.45

0.40

 

 

 

Extrapolated total dust quantity **) [mg]

155.37

Total dust mass, including correction ***) [mg]

155.00

Dust concentration after density correction [mg/m³]

776.84

*) The dust mass is taken into account with the impactor stage "< G" (which was validated independently of the substance in earlier investigations) which is removed from the impactor with the exhaust air (mass extrapolation).

**) The "extrapolated total dust mass" takes into account the dust masses separated at the individual impactor stages and the mass extrapolation resulting from impactor stage "< G".

***) The "total dust mass including correction" is the total from mass extrapolation in accordance with impactor stage "< G" and the dust masses separated at the individual impactor stages which are evaluated with experimentally determined correction factors, taking into account the various separating strengths of the impactor stages (manufacturer’s specifications).

Characteristics of frequency distribution

Particle size

Residue

Average value

Diff. quotient

[µm]

[%]

d

D'

0.45

99.74

0.70

1.76

0.94

98.88

1.44

1.51

1.95

97.37

2.91

4.91

3.87

87.91

5.81

3.31

7.75

75.05

11.41

0.49

15.06

71.46

22.98

1.74

30.89

43.99

47.95

0.73

65.00

19.15

82.50

 

100.00

0.00

 

 

The results are presented in two formats where applicable: (i) based on the mass of material < 1 mm that was weighed into the Heubach-drum and (ii) re-calculated to the original mass of lumps size material.

Experimental results

 

(i) based on material < 1 mm

(ii) re-calculated to original mass of lump-size material

Quantity of the substance used [g]

1

-

Total dust mass in impactor [mg]

155.00

-

Dust concentration in impactor [mg/m³]

776.84

-

Total dustiness [mg/g]

155.00

2.37

Inhalable fraction [mg/g]

99.45

1.52

Thoracic fraction [mg/g]

42.15

0.65

Respirable fraction [mg/g]

20.04

0.31

Conclusions:
Dustiness values of the test item:
(i) based on material < 1 mm (ii) re-calculated to origi-nal mass of lump-size material
Total dustiness [mg/g] 155.00 2.37
Inhalable fraction [mg/g] 99.45 1.52
Thoracic fraction [mg/g] 42.15 0.65
Respirable fraction [mg/g] 20.04 0.31

Description of key information

The commercial product cobalt stearate is placed on the market as solid lumps (particle size >> 1mm). In a friability test the potential to generate fine particles via abrasion and was assessed (Parr, 2012).

The total amount of abraded material was 1.5 % of the starting material. The total dustiness (airborne fraction) of the abraded fraction was 0.237% based on the total amount of starting material, with a mass median aerodynamic diameter of airborne fraction of MMAD = 28.63 µm, GSD = 4.72. The fractional deposition in human respiratory tract (MPPD model, based on calculated MMAD) is: Head (ET): 45.1 %, Tracheobronchial (TB): 0.1 %, Pulmonary (PU): 0.1 %.

Based on the above information it is concluded that cobalt stearate is not likely to generate elevated amounts of abraded particles of a size range in which inhalation is likely to occur under conditions of shear stress.

Using a lab-synthesized cobalt stearate (not relevant for commercial use) the granulometry was assessed:

Total Dustiness (airborne fraction): 30.88 mg/g (experimental results; Parr, 2010).

Mass median aerodynamic diameter of airborne fraction: MMAD = 29.23 µm (distribution fitted to cascade impactor data).

Geometric standard deviation of MMAD: GSD = 1.61

Fractional deposition in human respiratory tract (MPPD model, based on calculated MMAD):

Head (ET): 46.6 %

Tracheobronchial (TB): 0.1 %

Pulmonary (PU): 0.0 %

Additional information