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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:
Experimental starting and completion dates were 06 April 2010 (laser diffraction) and 07 June 2010 (sieve analysis), respectively.
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Guideline study
Qualifier:
according to
Guideline:
OECD Guideline 110 (Particle Size Distribution / Fibre Length and Diameter Distributions)
Deviations:
no
GLP compliance:
no
Type of method:
Laser scattering/diffraction
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.
Percentile:
D50
Mean:
993.68 µm
Remarks on result:
other: determined by laser diffraction
Percentile:
D50
Mean:
1 440 µm
Remarks on result:
other: determined by sieving

Laser diffraction

The particle size D10 of the test item deduced from the particle size distribution is 534.13 µm.

The particle size D90 of the test item deduced from the particle size distribution is 1574.14 µm.

Sieving

The particle size D10 of the test item deduced from the particle size distribution is approximately 1060 µm.

The particle size D90 of the test item deduced from the particle size distribution is approximately 2080 µm.

Conclusions:
Laser diffraction:
The particle size D10 of the test item deduced from the particle size distribution is 534.13 µm.
The median particle size D50 of the test item deduced from the particle size distribution is 993.68 µm.
The particle size D90 of the test item deduced from the particle size distribution is 1574.14 µm.
Sieving:
The particle size D10 of the test item deduced from the particle size distribution is approximately 1060 µm.
The median particle size D50 of the test item deduced from the particle size distribution is approximately 1440 µm.
The particle size D90 of the test item deduced from the particle size distribution is approximately 2080 µm.
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:
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 (2009)
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: 0.43 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 bimodal lognormal distribution to the data by standard non-linear regression procedure. As a result, the MMAD and GSD are calculable and reported (MMAD1 = 9.87 µm and MMAD2 = 53.94 µm, GSD1 = 6.56 and GSD2 = 1.77). 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): 22.0%

Tracheobronchial (TB): 0.2%

Pulmonary (PU): 0.5%

Conclusions:
Cobalt nitrate hexahydrate

Total Dustiness (airborne fraction): 0.43 mg/g (experimental results, DMT Report).

Mass median aerodynamic diameter of airborne fraction: MMAD1 = 9.87 µm and MMAD2 = 53.94 µm (distribution fitted to cascade impactor data).
Geometric standard deviation of MMAD: GSD1 = 6.56 and GSD2 = 1.77

Fractional deposition in human respiratory tract (MPPD model, based on calculated MMAD):
Head (ET): 22.0%
Tracheobronchial (TB): 0.2%
Pulmonary (PU): 0.5%

Description of key information

The particle size of cobalt dinitrate hexahydrate was determined to be:

- Laser diffraction:

D10 = 534.13 µm,

D50 = 993.68 µm,

D90 = 1574.14 µm.

- Sieving:

D10 approximately 1060 µm,

D50 approximately 1440 µm,

D90 approximately 2080 µm.

Total Dustiness (airborne fraction):  0.43 mg/g (experimental results, DMT Report).

Mass median aerodynamic diameter of airborne fraction: MMAD1 = 9.87 µm and MMAD2 = 53.94 µm.

Geometric standard deviation of MMAD: GSD1 = 6.56 and GSD2 = 1.77

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

Head (ET): 22.0%

Tracheobronchial (TB): 0.2%

Pulmonary (PU): 0.5%

Additional information

The particle size distribution of the test item was determined be laser diffraction (light scattering) and in a second measurement by sieving in accordance with OECD guideline 110.

The test item was analysed with the Master-Sizer 2000 (Version 5.12G) of Malvern Instruments with a measuring range of 0.02 to 2000 µm. In addition, the test item was sieved for 15 minutes through 6 different sieves with mesh sizes of 2500, 2000, 1600, 1400, 1250 and 1000 µm. The amount of test item on each sieve and on the receiver pan was measured by weighting.

It has to be considered that a second measurement with the laser diffraction was not possible with the first delivery of the test item due to the limited amount available. The second delivery, however, was too moist for a measurement with laser diffraction. A drying of the test item would have resulted in a change of the properties of the test item. Therefore and due to a large size of the particles from the second sample it was not possible to perform a second laser diffraction. A possible explanation for the differences in the deliveries could be an inhomogeneous nature of the test item (providing smaller particles in the first delivery than in the second).

As method the laser diffraction yields more exact results due to multiple measurements (3 measurements) performed for one result and due to the continuous measurement over all particle sizes. The sieving on the other hand is restricted to selected sieves which have certain separation efficiency and are limited in their number (due to the apparatus used and the amount of test item available). However, for particles larger than 1000 µm (median particle size) the laser diffraction con not be used anymore.