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Particle size distribution (Granulometry)

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

particle size distribution (granulometry)

Remarks:

Dustiness

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2017

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

Heubach-Dust-Meter connected to a cascade impactor

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:

Heubach-dust-meter connected to a cascade impactor

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: EBRC (2017)
The Multiple-Path Particle Dosimetry Model (MPPD, v2.1; CIIT, 2009) 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

Remarks:

connected to a seven stage cascade impactor

Type of distribution:

volumetric distribution

Remarks on result:

other: p1 (16.7 %): MMAD1 = 3.70 µm, GSD1 = 1.83; p2 (83.3 %): MMAD2 = 100 µm, GSD2 = 1.93

Remarks on result:

not measured/tested

Remarks on result:

not measured/tested

Dustiness (airborne fraction):      total: 74.90 mg/g.

In the original study report by DMT, the mass median diameter was not calculated. 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. The weighting factors p, the MMADs and GSDs were calculated as follows:      

p1 (16.7 %): MMAD1 = 3.70 µm, GSD1 = 1.83;

p2 (83.3 %): MMAD2 = 100 µm, GSD2 = 1.93

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.

These data 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): 19.00 %

Tracheobronchial (TB): 0.43 %

Pulmonary (PU): 1.26 %

Conclusions:

Dustiness (airborne fraction):      total: 74.90 mg/g.

- p1 (16.7 %): MMAD1 = 3.70 µm, GSD1 = 1.83;
- p2 (83.3 %): MMAD2 = 100 µm, GSD2 = 1.93

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

Head (ET): 19.00 %
Tracheobronchial (TB): 0.43 %
Pulmonary (PU): 1.26 %

Reference 2

Endpoint:

particle size distribution (granulometry)

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2017

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 110 (Particle Size Distribution / Fibre Length and Diameter Distributions - Method A: Particle Size Distribution (effective hydrodynamic radius)

GLP compliance:

no

Type of method:

Laser scattering/diffraction

Type of distribution:

volumetric distribution

Remarks on result:

not measured/tested

Percentile:

D10

Mean:

0.7 µm

Remarks on result:

other: No St. dev. was stated

Key result

Percentile:

D50

Mean:

2.1 µm

Remarks on result:

other: No St. dev. was stated

Percentile:

D90

Mean:

6.1 µm

Remarks on result:

other: No St. dev. was stated

The parameters d₉₀, d₅₀and d₁₀are the cut off particle size below which 90 %, 50 % and 10 % of the total particle volume lies. The parameter d_vand d_sare respectively the volume mean diameter and the surface area mean diameter.

All values are calculated assuming that the particles are spherical.

d₉₀= 6.1 µm

d₅₀= 2.1 µm

d₁₀= 0.7 µm

d_v= 2.8 µm

d_s= 1.5 µm

Conclusions:

The particle size distribution of the test material is:
d90= 6.1 µm
d50= 2.1 µm
d10= 0.7 µm

Description of key information

Particle size distribution:

d90= 6.1 µm

d50= 2.1 µm

d10= 0.7 µm

Dustiness:

- total dustiness: 74.90 mg/g.

Mass median aerodynamic diameter:

- p1 (16.7 %): MMAD1 = 3.70 µm, GSD1 = 1.83;

- p2 (83.3 %): MMAD2 = 100 µm, GSD2 = 1.93

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

- Head (ET): 19.00 %

- Tracheobronchial (TB): 0.43 %

- Pulmonary (PU): 1.26 %

Additional information

The so-called physical particle size distribution (PSD) was obtained by the laser diffraction method in a wet dispersion after ultrasonic treatment for individualisation of the particles and further mechanical stirring. The particle size ofthe individualised particlesis provided.

Any agglomerates of particles normally existing in the pigment powder were destroyed by (i) the contact with water, (ii) the ultrasonic treatment and (iii) the mechanical stirring. Such agitation of the dry pigment does however not occur under intended and foreseeable manufacture and use conditions and is therefore not suitable to deduce the likelihood of inhalation exposure under workplace conditions.

 

A suitable method for determining the PSD of a dry powder to assess the inhalation potential of airborne dust resulting from the handling of that powder is cascade impactor testing (Dustiness). During the cascade impactor testing, the material gets moderately agitated in a rotating drum (to simulate agitation during typical occupational powder handling activities). A constant airstream directs any generated airborne dust to a cascade impactor in which the particles and their agglomerates get separated according to their size.

The aerodynamic PSD is described as being bimodal.With the given parameters it is possible to calculate the cumulated mass percentage of particles at or below 4 µm. This fraction does however not indicate how much is deposited in the deep lung if such aerosol would be inhaled. Instead, the fractional deposition in the human respiratory tract was calculated using the MPPD model.

Thus, only a sub-fraction of1.26 % particles could deposit in the alveoli of the human lung.