Molybdenum trioxide

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

Study period:

2007-10-04

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 110 (Particle Size Distribution / Fibre Length and Diameter Distributions)

Deviations:

no

Principles of method if other than guideline:

The purpose of this study was the determination of the particle size distribution of the test item by laser diffraction according to the consolidated version of Guideline 67/548/EEC (council Directive 92/69/EEC) and under consideration of the following guidelines:
OECD 110 (1981): Particle Size Distribution,
CIPAC MT 187: Particle Size Analysis by Laser Diffraction,
ISO 13320-1: Particle Size Analysis – Laser Diffraction Methods.

GLP compliance:

yes (incl. QA statement)

Type of method:

Laser scattering/diffraction

Type of distribution:

volumetric distribution

Percentile:

other: L50

Mean:

194.9 µm

St. dev.:

9.23

Percentile:

other: L10

Mean:

21.3 µm

St. dev.:

4.49

Percentile:

other: L90

Mean:

365.3 µm

St. dev.:

21.23

Reference 2

Endpoint:

particle size distribution (granulometry)

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2008-02-04 to 2008-02-21

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

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

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

Qualifier:

according to guideline

Guideline:

DIN 55992-1 (Determination of a parameter for the dust formation of pigments and extenders - Part 1: Rotation method)

Deviations:

yes

Remarks:

original method modified to include a seven stage cascade impactor for the determination of the particle size distribution of the airborne dust

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 20L/min via the coarse dust seperator needed to supply the cascade impactor with 40L/min air current as specified in the manufacturer´s specifications.

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 (for further information see "attached background material").

GLP compliance:

no

Type of method:

rotating drum method

Remarks:

***new after migration from I5.6 to I6

Type of distribution:

volumetric distribution

Mass median aerodynamic diameter:

ca. 30 µm

Geometric standard deviation:

ca. 1.73

Key result

Percentile:

other: MMAD

Mean:

ca. 30 µm

St. dev.:

1.73

Dustiness (airborne fraction): total: 2.22 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 a standard non-linear regression procedure. As a result, the MMAD and GSD are calculable and reported (p1: 8.8%, MMAD1 = 3.83 µm, GSD1 = 2.22 / p2: 91.2%, MMAD2 = 29.88 µm, GSD 2 = 1.73). 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): 48.48%

Tracheobronchial (TB): 0.30%

Pulmonary (PU): 0.63%

Conclusions:

Total Dustiness (airborne fraction): 2.22 mg/g (experimental result, DMT Report).

Mass median aerodynamic diamaters (bi-modal distribution) of airborne fraction: MMAD1 = 3.83 µm (8.8%) , MMAD2 = 29.88 µm (91.2%) (distribution fitted to cascade impactor data, percentage in parentheses indicates weighting factor).

Geometric standard deviation of MMAD: GSD1 = 2.22 , GSD 2 = 1.73

Fractional deposition in human respiratory tract (MPPD model, based on calculated MMAD):
Head (ET): 48.48%
Tracheobronchial (TB): 0.30%
Pulmonary (PU): 0.63%

Description of key information

The following parameters have been determined with a representative sample:
Median particle size (laser diffraction method): D50 = ca. 195 µm
Mass median aerodynamic diameters of airborne fraction (rotating drum method, bi-modal distribution fitted to cascade impactor data): MMAD1 =  3.83 µm (8.8%) , MMAD2 = 29.88 µm (91.2%) (percentage in parentheses indicates weighting factor of bimodal distribution).