Germanium dioxide

Water solubility

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

transformation / dissolution of metals and inorganic metal compounds

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

no guideline available

Principles of method if other than guideline:

For the chronic aquatic effects classification of substances, it is needed to assess their "rapid degradability". This concept, which is characteristic for organic substances, is not applicable to metals. For this reason, the concept of removal from the water column has been developed. This measures the amount of metal that remains in the water column upon addition, and thus, the potential for exerting a chronic effect. in analogy with the degradability protocol for organic substances, the refernce point is 70% or more removal after 28 days. If this is observed the substance can be considered as "equivalent to rapidly degradable" in the sense of chronic aquatic toxicity. The approach is still under development and discussion. Rather than rely on modelling, it was decided to setup an experiment, according to the present state of the discussions, and in the medium used for transformation dissolution testing according to OECD 29.

GLP compliance:

not specified

Type of method:

flask method

Key result

Type of test:

other: removal from the water column test

Mean dissolved conc.:

ca. 20 other: %

Element analysed:

Ge

Loading of aqueous phase:

10 g/L

Incubation duration:

28 d

Test conditions:

test medium according to OECD 29

Remarks on result:

other: 80 % Ge-removal from the water column after 28 days

GeO2 was fully dissolved at the start of the experiment. Ge concentration in the water column rapidly decreased to reach a level of 20% after 28 days. after resuspension, the Ge concnetration remained at the low level; so, Ge did not enter back into the water column in dissolved form.

time (hrs)	Ge concnetration replica 1	Ge concentration replica 2	% removal from water column (mean)
0	974.9	974.9	2.5
6	812.9	795.0	17.5
24	761.9	750.6	22.4
96	517.8	505.7	47.5
168	432.4	409.7	56.8
672	228.5	173.3	79.4
after resuspension 673.5	223.6	170.9	79.8
675	220.0	168.0	80.1
679	218.6	171.7	80.0
697	212.5	166.3	80.6
769	184.0	153.2	82.7

Conclusions:

Results are considered relevant for describing the residence time and removal from Ge , introduced in a water column. Test conditions are chosen as realistic worst case. Notably, the test was performed at lower pH, which solubilises most metal.

Executive summary:

Removal from Ge after addition to a water column in the presence of a thin layer of natural sediment was measured over time. Test conditrions have not been standardised, but the medium was the OECD 29 T/D medium at the lower pH end (pH 6.0), at which highest solubilisation of Ge is expected.

The results demonstrate that Ge is removed from the water column to reach a level of 20% of original concentration after 28 days. Referring to the criterion of 70% removal after that period for organic substances, Ge and Ge-substances are considered to be "equivalent to rapidly degradable" in water.

Reference 2

Endpoint:

transformation / dissolution of metals and inorganic metal compounds

Type of information:

experimental study

Adequacy of study:

key study

Study period:

17 Jul 2019 - 20 Mar 2021

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Series on Testing and Assessment No. 29 (23-Jul-2001): Guidance document on transformation/dissolution of metals and metal compounds in aqueous media

GLP compliance:

yes (incl. QA statement)

Other quality assurance:

ISO/IEC 17025 (General requirements for the competence of testing and calibration laboratories)

Type of method:

flask method

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Source (i.e. manufacturer or supplier) and lot/batch number of test material: PPM Pure Metals GmbH Am Bahnhof 1 D-38685 Langelsheim Germany ; batch number: C 100328
- Purity, including information on contaminants, isomers, etc.: purity 99.999 % (5N); Moisture: <0.75 % ; i.e. 69.4 % Ge

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: Room temperature (20 - 23 °C), in the dark.
- Stability and homogeneity of the test material in the vehicle/solvent under test conditions (e.g. in the exposure medium) and during storage: not specified
- Stability in the medium, i.e. sensitivity of the test material to hydrolysis and/or photolysis: not specified
- Solubility and stability of the test material in the solvent/vehicle and the exposure medium: not specified
- Reactivity of the test material with the incubation material used (e.g. plastic ware): not specified

TREATMENT OF TEST MATERIAL PRIOR TO TESTING
- Treatment of test material prior to testing (e.g. warming, grinding): No
- Preliminary purification step (if any): No
- Final concentration of a dissolved solid, stock liquid or gel: No
- Final preparation of a solid (e.g. stock crystals ground to fine powder using a mortar and pestle): No

OTHER SPECIFICS
- Other relevant information needed for characterising the tested material, e.g. if radiolabelled, adjustment of pH, osmolality and precipitate in the culture medium to which the test chemical is added: homogenous, density: 4.228 g/cm3 ; particle size distribution: d50: <50 μm ; colour: white

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

631 µg/L

Element analysed:

Ge

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

Temperature: 21.2 °C - 23.0 °C
pH: 8.00 - 8.05
Dissolved oxygen concentration: 8.24 - 8.46 mg/L O2
TOC of the medium: <1.0 mg/L C
The test medium at the start of the test and the blank control vessels during the test showed small average concentrations of germanium above the limit of detection (0.02 μg/L Ge).

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

602 µg/L

Element analysed:

Ge

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

Temperature: 21.2 °C - 23.0 °C
pH: 8.00 - 8.05
Dissolved oxygen concentration: 8.24 - 8.46 mg/L O2
TOC of the medium: <1.0 mg/L C
The test medium at the start of the test and the blank control vessels during the test showed small average concentrations of germanium above the limit of detection (0.02 μg/L Ge).

Conclusions:

During this transformation/dissolution study on Germanium dioxide at a loading of 1 mg/L, it was shown that:
• For germanium, an average concentration of 631 μg/L Ge (CVoverall = 1 %; N = 9) was found after 7 days, and of 602 μg/L Ge (CVoverall = 1 %; N = 9) was found after 28 days of exposure to the standard medium at pH 8. The 7 days dissolution results corresponded with a germanium release of 99 % (or 116 mg/m²). The 28 days dissolution results corresponded with a germanium release of 98 % (or 117 mg/m²).
The results can be assumed reliable since the test conditions stayed constant during the experiment.

Executive summary:

This study's objective was to obtain information about the dissolution characteristics of Germanium dioxide to classify metal-containing substances and mixtures according to the UN Globally Harmonized System, the EU Classification, Labelling and Packaging Regulation (Reg. 1272/2008 + amendment No 2018/669). Therefore, the OECD Test Guidance No. 29 (2001) was applied to determine the rate and pH-dependent extent of dissolution of Germanium dioxide, tested with a target 1 mg/L loading in standard aqueous solutions at pH 8 for 28 days at an agitation speed of 100 revolutions per minute (rpm).

The short-term (acute) transformation/dissolution endpoint was based on the dissolved germanium concentrations obtained after 7 days. The long-term (chronic) transformation/dissolution endpoint was based on the dissolved germanium concentrations obtained after 28 days.
The study was performed at ECTX. Analyses of the concentrations of dissolved germanium and the determination of the total organic carbon content (TOC) of the test medium have been performed at WLN Business B.V. (The Netherlands), the ISO 17025 accredited laboratory, as delegated by ECTX.
The used test setup was designed by the Sponsor. It was based on the results of study X01-213 (7 days Transformation/Dissolution Study of Germanium dioxide at a 100 mg/L loading in a standard aqueous medium at pH 6 and pH 8.).

As Germanium is light sensitive, extra measures were taken to exclude the influence of light as much as possible: the experiments were performed in the dark. The test vessels were wrapped with black plastic foil, and the preparation and sampling were carried out in diffuse red light.
All test parameter conditions were entirely following the OECD Test Guidance no.29 requirements:
• The medium's measured TOC was <1.0 mg/L C and below the required level of 2.0 mg/L C.
• The temperature of the test solutions fluctuated between 21.2 °C and 23.0 °C and corresponded to the required test conditions of 20 °C – 23 °C.
• The pH measured in the medium at the start of the test, and in the blank and test item vessels during the test varied from 8.00 to 8.05. All measured data were within the specifications of pH 8 ± 0.2.
• The dissolved oxygen concentration measured in the blank and test item vessels at pH 8 varied from 8.24 to 8.46 mg/L O2. These values were higher than the required value of ± 6 mg/L O2 at 22 °C, corresponding to a minimum saturation level in the air of 70 %.

The test medium at the start of the test and the blank control vessels during the test showed small average concentrations of germanium above the limit of detection (0.02 μg/L Ge). The detection limit was determined as three times the standard deviations of the germanium measurements of all blank control samples in this study rounded up to one significant figure (N = 30).
During this study on Germanium dioxide at a loading of 1 mg/L to standard medium at pH 8, it was shown that:
The following average dissolved germanium concentrations were measured: 631 ± 8 μg/L Ge (CVoverall = 1 %; N = 9) and 602 ± 5 μg/L Ge (CVoverall = 1 %; N = 9) after 7 days and 28 days of exposure, respectively. 

Based on the specific surface area of Germanium dioxide (i.e. 5.94 m²/g test item), a germanium release per surface of 116 mg/m² and 117 mg/m² were calculated at the 7 days and 28 days endpoints, respectively taking into account the volume of fresh test medium that was replenished after sampling.

Based on the average germanium content in the test item (69.4 % Ge) and the average dissolved germanium concentrations in the test solutions, a germanium release of 99 % and 98 % could be calculated at the 7 days and 28 days extraction endpoints taking into account the volume of fresh test medium that was replenished after sampling.

Description of key information

Transformation/dissolution (TD) testing was done at 2 pH (6 -8) on GeO2  according to OECD 29.

-it was demonstrated that the TD was highest at pH 8, as compared to pH6.

-at pH 8 the TD after 7d was 0.631 mg/L with 1mg/L loading of the substance

-at pH 8 the TD after 28d was 0.602 mg/L with 1mg/L loading of the substance

Key value for chemical safety assessment

Water solubility:

0.602 mg/L

at the temperature of:

22 °C

Additional information

The solubility of germanium dioxide was defined with the transformation dissolution test. Results relate to 1mg/L loading of the substance over 28days.