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Particle size distribution (Granulometry)

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Reference
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: 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)
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:
other: rotating drum fitted with cascade impactor
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: 2.10 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 = 18.26 µm, GSD = 2.97). 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): 55.7 %

Tracheobronchial (TB): 0.8 %

Pulmonary (PU): 1.1 %

Conclusions:
Total Dustiness (airborne fraction): 2.10 mg/g (experimental results, DMT Report).
Mass median aerodynamic diamater of airborne fraction: MMAD = 18.26 µm (distribution fitted to cascade impactor data).
Geometric standard deviation of MMAD: GSD = 2.97 µm
Fractional deposition in human respiratory tract (MPPD model, based on calculated MMAD):
Head (ET): 55.7 %
Tracheobronchial (TB): 0.8 %
Pulmonary (PU): 1.1 %

Description of key information

Calcium oxide 0-2 mm:

Total Dustiness (airborne fraction): 100.01 mg/g (experimental results, DMT Report).

MMAD of airborne fraction: MMAD = 17.14 µm (distribution fitted to cascade impactor data).

GSD of MMAD: GSD = 2.75 µm

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

Head (ET): 59.2 %; Tracheobronchial (TB): 0.8 %; Pulmonary (PU): 1.1 %

Calcium oxide > 10 mm:

Total Dustiness (airborne fraction): 2.10 mg/g (experimental results, DMT Report).

MMAD of airborne fraction: MMAD = 18.26 µm (distribution fitted to cascade impactor data).

GSD of MMAD: GSD = 2.97 µm

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

Head (ET): 55.7 %; Tracheobronchial (TB): 0.8 %; Pulmonary (PU): 1.1 %

Additional information

For the evaluation of this endpoint, two grades of calcium oxide (calcium oxide ≤ 2 mm and calcium oxide > 10 mm) that were investigated according to national standard (DIN 55992 -1:2006, modified Heubach method). The respective results are used as key information, supported by data from a guideline compliant study (OECD 110).

The key studies were selected based on the fact that these studies consider the airborne fraction of calcium oxide, which is exposure-related and relevant to workplace conditions. The other study, which is only used as supportive information, tested not the airborne fraction of calcium oxide, but the total of the substance fed in a cascade impactor. This is not exposure-related and not relevant for workplace conditions.

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