Zinc selenite

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:

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

Reason / purpose for cross-reference:

reference to same study

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)

Deviations:

yes

Remarks:

see "Principles of method if other than guideline"

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.

GLP compliance:

no

Type of method:

rotating drum method

Type of distribution:

volumetric distribution

Percentile:

D75

Mean:

26.17 µm

Remarks on result:

other: distribution fitted to cascade impactor data

Percentile:

D25

Mean:

13.13 µm

Remarks on result:

other: distribution fitted to cascade impactor data

Dustiness (airborne fraction): total: 151.82 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 bi-modal lognormal distribution to the data by standard non-linear regression procedure. As a result, the MMAD and GSD are calculable and reported (p1: 23.4 %, MMAD1 = 13.13 µm, GSD1 = 3.95, p2: 76.6 %, MMAD2 = 26.17 µm, GSD2 = 1.79). 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): 52.55%

Tracheobronchial (TB): 0.40%

Pulmonary (PU): 0.83%

Conclusions:

-Total Dustiness (airborne fraction): 151.82 mg/g (experimental results, DMT Report).
- Mass median aerodynamic diameter of airborne fraction:
MMAD = 13.13 µm (p1=23.4 %) and MMAD = 26.17 µm (p2=76.6 %) (distribution fitted to cascade impactor data) *
- Geometric standard deviation of MMAD:
GSD = 3.95 (p1=23.4 %) and GSD = 1.79 (p2=76.6 %) *
- Fractional deposition in human respiratory tract (MPPD model, based on calculated MMAD):
Head (ET): 52.55%
Tracheobronchial (TB): 0.40%
Pulmonary (PU): 0.83%
 *The distribution consist basically of two combined lognormal distributions, which are weighted by a factor p.p2 is the weighing factor for the second distribution from a bimodal lognormal distribution, since p2 can be calculated from 1-p1 this parameter has not to be estimated separately but is reported here for the sake of clarity only .

Reference 2

Endpoint:

particle size distribution (granulometry)

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2010-02-01 to 2010-02-22

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP guideline study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: 187: Particle Size Analysis by Laser Diffraction

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: ISO13320-1: Particle Size Analysis - Laser Diffraction Methods

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

signed 2009-10-29

Type of method:

Laser scattering/diffraction

Type of distribution:

volumetric distribution

Percentile:

D10

Mean:

3.9 µm

St. dev.:

0.07

Percentile:

D50

Mean:

17.4 µm

St. dev.:

0.14

Percentile:

D90

Mean:

45.4 µm

St. dev.:

0.1

Conclusions:

The average of the median physical particle size of the test substance zinc selenite is L50 is 17.4 µm.

Description of key information

(i) Total dustiness zinc selenite(airborne fraction): 151.82 mg/g (experimental result, DMT Report). 
MMAD (bimodal distribution) of airborne fraction: MMAD = 13.13 µm (p1=23.4 %) and MMAD = 26.17 µm (p2=76.6 %) (distribution fitted to cascade impactor data, percentage in parentheses indicates weighting factor).
GSD of MMAD: 3.95 (p1=23.4 %) and GSD = 1.79 (p2=76.6 %)
Fractional deposition in human respiratory tract (MPPD model, based on calculated MMAD):
Head (ET): 52.55 %; Tracheobronchial (TB): 0.40 %; Pulmonary (PU): 0.83 %
(ii) Physical particle size: The average of the median physical particle size D50 is 17.4 µm (experimental result, laser diffraction, Krack, 2010)

Additional information

The test data on particle size (GLP, OECD guideline conform) is reliable without restrictions (Krack, 2010). Test procedure for the dustiness testing 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 is reliable without restrictions. This Parr, 2010; Grewe, 2010 - study considers the airborne fraction of zinc selenite, which is exposure-related and relevant for workplace conditions. In the other study (Krack, 2010), the airborne fraction of zinc selenite was not determined, but the total of the substance used for particle size analysis. This is not exposure-related and not relevant for workplace conditions.