Chromium (III) oxide

Particle size distribution (Granulometry)

Link to relevant study record(s)

Reference

Reference 1

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:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Qualifier:

equivalent or similar to guideline

Guideline:

ISO 13320 (Particle size analysis - Laser diffraction methods)

Version / remarks:

2009

GLP compliance:

no

Type of method:

Laser scattering/diffraction

Type of particle tested:

primary particle

Remarks:

dispersed in 0.1% Na-P-solution in dest. water

Type of distribution:

volumetric distribution

Key result

Percentile:

D90

Mean:

1.363 µm

St. dev.:

0.033

Key result

Percentile:

D50

Mean:

0.594 µm

St. dev.:

0.006

Key result

Percentile:

D10

Mean:

0.201 µm

St. dev.:

0.012

Conclusions:

The D 50 is given to be 0.594 um

Reference 2

Endpoint:

particle size distribution (granulometry)

Remarks:

Dustiness

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

2019

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:

a seven stage cascade impactor is connected to a heubach dust meter

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

Mass median aerodynamic diameter:

61 µm

Geometric standard deviation:

1.96

Remarks on result:

not measured/tested

Remarks on result:

not measured/tested

Dustiness (airborne fraction):      total: 269.93 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:      

MMAD = 61.0 µm, GSD = 1.96

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 (v3.04) enabling an estimation of deposited dust fractions in the human respiratory tract: These fractions were estimated as follows:

Head (ET): 18.17 %

Tracheobronchial (TB): 0.02 %

Pulmonary (PU): <0.01 %

Conclusions:

Dustiness (airborne fraction):      total: 269.93 mg/g.

MMAD = 61.0 µm, GSD = 1.96;

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

Head (ET): 18.17 %
Tracheobronchial (TB): 0.02 %
Pulmonary (PU): <0.01 %

Description of key information

Particle size distribution (PSD):

D (v, 0.1) = 0.201 μm

D (v, 0.5) = 0.594 μm

D (v, 0.9) = 1.364 μm

Dustiness:

- total dustiness (airborne fraction): 269.93 mg/g

Mass median aerodynamic diameter:

MMAD = 61.0 µm, GSD = 1.96

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

Head (ET): 18.17 %

Tracheobronchial (TB): 0.02 %

Pulmonary (PU): <0.01 %

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 of the individualised particles is provided.

It is noted that any agglomerates of particles normally existing in the powder were destroyed by (i) the contact with water, (ii) the ultrasonic treatment and (iii) the mechanical stirring. Such agitation of the dry powder 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 of the inhalable material (airborne fraction of < 0.01%) could deposit in the alveoli of the human lung.