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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
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
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 no data for: - Analytical purity - Purity test date - Expiration date of the batch
Qualifier:
according to guideline
Guideline:
DIN 55992-1 (Determination of a parameter for the dust formation of pigments and extenders - Part 1: Rotation method)
Version / remarks:
2006
Deviations:
yes
Remarks:
Modified Heubach-Method, in which the generated dust is not collected as a “bulk mass sample", but instead collected in a 7-stage cascade impactor, which allows a discrimination of the generated dust particles according to their aerodynamic diameters
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 specificcations.
The calculation report: EBRC (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
Mass median aerodynamic diameter:
25.4 µm
Geometric standard deviation:
2.8
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: 90.77 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 = 25.4 µm, GSD = 2.8). As the cascade impactor already takes aerodynamic characteristics of the particles into account, the reported mass median diameter can be interpreted as the mass medianaerodynamicdiameter.

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): 50.1 %

Tracheobronchial (TB): 0.4 %

Pulmonary (PU): 0.7 %

Conclusions:
Silver Powder - Batch PMC 2

Total Dustiness (airborne fraction): 90.77 mg/g (experimental results, DMT Report).

Mass median aerodynamic diamater of airborne fraction: MMAD = 25.4 µm (distribution fitted to cascade impactor data).
Geometric standard deviation of MMAD: GSD = 2.8

Fractional deposition in human respiratory tract (MPPD model, based on calculated MMAD):
Head (ET): 50.1 %
Tracheobronchial (TB): 0.4 %
Pulmonary (PU): 0.7 %
Endpoint:
particle size distribution (granulometry)
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
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. no data for: - Analytical purity - Purity test date - Expiration date of the batch
Qualifier:
according to guideline
Guideline:
DIN 55992-1 (Determination of a parameter for the dust formation of pigments and extenders - Part 1: Rotation method)
Version / remarks:
2006
Deviations:
yes
Remarks:
Modified Heubach-Method, in which the generated dust is not collected as a “bulk mass sample", but instead collected in a 7-stage cascade impactor, which allows a discrimination of the generated dust particles according to their aerodynamic diameters
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 specificcations.
The calculation report: EBRC (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
Mass median aerodynamic diameter:
30.1 µm
Geometric standard deviation:
1.7
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: 155.45 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 = 30.1 µm, GSD = 1.7). 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): 45.3 %

Tracheobronchial (TB): 0.1 %

Pulmonary (PU): 0.0 %

Conclusions:
Silver Powder - Batch PMC 1

Total Dustiness (airborne fraction): 155.45 mg/g (experimental results, DMT Report).

Mass median aerodynamic diamater of airborne fraction: MMAD = 30.1 µm (distribution fitted to cascade impactor data).
Geometric standard deviation of MMAD: GSD = 1.7

Fractional deposition in human respiratory tract (MPPD model, based on calculated MMAD):
Head (ET): 45.3 %
Tracheobronchial (TB): 0.1 %
Pulmonary (PU): 0.0%
Endpoint:
particle size distribution (granulometry)
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Information provided by a producer of silver metal powder.
Principles of method if other than guideline:
Various established methods/equipment for particle size distribution measurements were used, e.g. a Mastersizer 2000 or CILAS 1180.
GLP compliance:
no
Type of method:
other: Various established methods/equipment for particle size distribution measurements were used, e.g. a Mastersizer 2000 or CILAS 1180.
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:
D10
Mean:
ca. 12 µm
St. dev.:
0
Remarks on result:
other: Representative sample Batch PMC1
Percentile:
D50
Mean:
ca. 30 µm
St. dev.:
0
Remarks on result:
other: Representative sample Batch PMC1
Percentile:
D90
Mean:
ca. 50 µm
St. dev.:
0
Remarks on result:
other: Representative sample Batch PMC1
Endpoint:
particle size distribution (granulometry)
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Information provided by a producer of silver metal powder.
Principles of method if other than guideline:
Various established methods/equipment for particle size distribution measurements were used, e.g. a Mastersizer 2000 or CILAS 1180.
GLP compliance:
no
Type of method:
other: Various established methods/equipment for particle size distribution measurements were used, e.g. a Mastersizer 2000 or CILAS 1180.
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:
D10
Mean:
ca. 0.8 µm
St. dev.:
0
Remarks on result:
other: Representative sample Batch PMC2
Percentile:
D50
Mean:
ca. 2 µm
St. dev.:
0
Remarks on result:
other: Representative sample Batch PMC2
Percentile:
D90
Mean:
ca. 11 µm
St. dev.:
0
Remarks on result:
other: Representative sample Batch PMC2

Description of key information

Silver is produced in various forms: powders (non-nano and nano-size) and massives (ingots, wires...).

Powders are produced with variable specifications, including various particle size distributions. Member companies of the Precious Metals Consortium have provided two representative samples of commercial non-nano silver metal powders (Batches PMC 1 and PMC 2) and provided particle size data. In addition to these specifications provided by the producers, experimental investigations on the dustiness (rotating drum method) and on the particle size distribution of material that becomes airborne during such tests have been performed.

Further, particle size data have been generated for the nanosilver forms covered by the REACH registration dossier (Nano sample 1 and 2).

Additional information

The particle size parameters for the two representative samples of silver metal powders (non-nano PMC 1 +2) are presented in the following format:

Batch: D10, D50, D90; Mass Median Aerodynamic Diameter of airborne dust (geometric standard deviation):

Batch PMC 1: 12 µm, 30 µm, 50 µm; 30.1 µm (1.7)

Batch PMC 2: 0.8µm, 2 µm, 11 µm; 25.4µm (2.8)

Further, two members of the Precious Metals REACH Consortium registering nanosilver have provided nanosilver products for physico-chemical characterisation. Nanosilver is usually marketed in suspension/wet powder form. The table below gives an overview of registered nanosilver products. For confidentiality reasons, the information on coatings and solvents has been omitted from the summary table below. The morphology was determined by visual inspection of TEM images. Quantitative analysis was done by TEM combined with ParticleSizer software. The volume specific surface area was calculated from the particle size (mean diameter).

Code Type Size of primary particles by TEM (Min. Feret diameter) Morphology

Volume Specific Surface Area

1

suspension/wetted powder

Min = 5 nm, D25 = 7 nm, D50 = 8 nm, D75 = 9 nm, Max = 61 nm

spherical

714 m2/cm3

2

suspension/wetted powder

Min = 11 nm, D25 = 25 nm, D50 = 34 nm, D75 = 48 nm, Max = 161 nm

spherical

150 m2/cm3