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Water solubility

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Endpoint:
water solubility
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 105 (Water Solubility)
Deviations:
yes
Remarks:
Standard water pH 8 ISO 6341 OECD TGD 29
GLP compliance:
yes (incl. QA statement)
Type of method:
flask method
Water solubility:
< 1 µg/L
Temp.:
20 °C
pH:
8

A similar study has been performed which is however not valid due to scattering results.

Conclusions:
Interpretation of results (migrated information): insoluble (< 0.1 mg/L)
A very low water solubility was determined according to OECD Guideline 105. With a loading of 10 g zinc ferrite to water at pH 8 the dissolved iron was determined to be < 1 µg/L, and the content of zinc was 4.3 µg/L.
Executive summary:

The Study was performed according to OECD Guideline 105.

For the determination six test mixtures with two different loading concentrations (1 g/L and 10 g/L) were agitated with a magnetic stirrer for 24 hours at 20 °C. The received suspensions were filtrated through a

0.1 μm (100 nm) membrane filter. Also three blank solutions (standard water pH 8 to ISO 6341, OECD-Guidance-Document 29) were investigated. After filtration of all mixtures and blank solutions iron- and zinc-determination was performed in each filtrate with Graphite Furnace Atomic Absorption Spectrometry (GFAAS).

With a loading of 10 g zinc ferrite to water at pH 8 the dissolved iron was determined to be < 1 µg/L, and the content of zinc was 4.3 µg/L.

Endpoint:
transformation / dissolution of metals and inorganic metal compounds
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2020-02-23 to 2021-07-22
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP 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
Deviations:
no
Principles of method if other than guideline:
The dissolution of Zinc Ferrite (Bayferrox 3950) in environmentally relevant test medium was assessed via ICP-OES over 28 d with a loading of 1 mg/L at target pH values of 6 and 8 and samplings after 1, 7 and 28 days.
GLP compliance:
yes (incl. QA statement)
Type of method:
flask method
Key result
Type of test:
full transformation/dissolution test - metals and sparingly soluble metal compounds
Mean dissolved conc.:
12.5 µg/L
Element analysed:
Zn
Loading of aqueous phase:
1 mg/L
Incubation duration:
28 d
Test conditions:
pH 6; centrifugal filtration (~2.1 nm)
Remarks on result:
other: corrected for background
Key result
Type of test:
full transformation/dissolution test - metals and sparingly soluble metal compounds
Mean dissolved conc.:
9.16 µg/L
Element analysed:
Zn
Loading of aqueous phase:
1 mg/L
Incubation duration:
7 d
Test conditions:
pH 6; centrifugal filtration (~2.1 nm)
Remarks on result:
other: corrected for background
Type of test:
screening transformation/dissolution test - sparingly soluble metal compounds
Mean dissolved conc.:
2.38 µg/L
Element analysed:
Zn
Loading of aqueous phase:
1 mg/L
Incubation duration:
24 h
Test conditions:
pH 6; centrifugal filtration (~2.1 nm)
Remarks on result:
other: corrected for background
Key result
Type of test:
full transformation/dissolution test - metals and sparingly soluble metal compounds
Mean dissolved conc.:
8.01 µg/L
Element analysed:
Zn
Loading of aqueous phase:
1 mg/L
Incubation duration:
28 d
Test conditions:
pH 8; centrifugal filtration (~2.1 nm)
Remarks on result:
other: corrected for background
Key result
Type of test:
full transformation/dissolution test - metals and sparingly soluble metal compounds
Mean dissolved conc.:
3.04 µg/L
Element analysed:
Zn
Loading of aqueous phase:
1 mg/L
Incubation duration:
7 d
Test conditions:
pH 8; centrifugal filtration (~2.1 nm)
Remarks on result:
other: corrected for background
Type of test:
screening transformation/dissolution test - sparingly soluble metal compounds
Mean dissolved conc.:
1.25 µg/L
Element analysed:
Zn
Loading of aqueous phase:
1 mg/L
Incubation duration:
24 h
Test conditions:
pH 8; centrifugal filtration (~2.1 nm)
Remarks on result:
other: corrected for background
Key result
Type of test:
full transformation/dissolution test - metals and sparingly soluble metal compounds
Mean dissolved conc.:
< 0.164 µg/L
Element analysed:
Fe
Loading of aqueous phase:
1 mg/L
Incubation duration:
28 d
Test conditions:
pH 6; centrifugal filtration (~2.1 nm)
Remarks on result:
other: < LOD (0.055 µg Fe/L)
Key result
Type of test:
full transformation/dissolution test - metals and sparingly soluble metal compounds
Mean dissolved conc.:
< 2.59 µg/L
Element analysed:
Fe
Loading of aqueous phase:
1 mg/L
Incubation duration:
7 d
Test conditions:
pH 6; centrifugal filtration (~2.1 nm)
Remarks on result:
other: < LOD (0.862 µg Fe/L)
Type of test:
screening transformation/dissolution test - sparingly soluble metal compounds
Mean dissolved conc.:
0.312 µg/L
Element analysed:
Fe
Loading of aqueous phase:
1 mg/L
Incubation duration:
24 h
Test conditions:
pH 6; centrifugal filtration (~2.1 nm)
Remarks on result:
other: corrected for background
Key result
Type of test:
full transformation/dissolution test - metals and sparingly soluble metal compounds
Mean dissolved conc.:
< 0.055 µg/L
Element analysed:
Fe
Loading of aqueous phase:
1 mg/L
Incubation duration:
28 d
Test conditions:
pH 8; centrifugal filtration (~2.1 nm)
Remarks on result:
other: < LOD (0.055 µg Fe/L)
Key result
Type of test:
full transformation/dissolution test - metals and sparingly soluble metal compounds
Mean dissolved conc.:
< 0.862 µg/L
Element analysed:
Fe
Loading of aqueous phase:
1 mg/L
Incubation duration:
7 d
Test conditions:
pH 8; centrifugal filtration (~2.1 nm)
Remarks on result:
other: < LOD (0.862 µg Fe/L)
Type of test:
screening transformation/dissolution test - sparingly soluble metal compounds
Mean dissolved conc.:
< 1.34 µg/L
Element analysed:
Fe
Loading of aqueous phase:
1 mg/L
Incubation duration:
24 h
Test conditions:
pH 8; centrifugal filtration (~2.1 nm)
Remarks on result:
other: < LOQ (1.34 µg Fe/L)
Details on results:
Background concentrations:
Mean zinc background concentrations in the tests were measured to be in the range of 0.845 µg/L to 4.41 µg/L Zn. Mean iron background concentrations in the tests were in the range of 0.039 µg/L to 1.66 µg/L Fe. All results are background corrected if possible, i.e. when measured Zn or Fe background concentrations were > LOQ.

Solution pH, oxygen concentrations, temperature:
The mean temperature during the tests was always in the range of 21.5 ± 1.5 °C.
Oxygen levels of all test solutions were in the range recommended by the OECD Test Guidance 29 during the test (> 70 % of oxygen saturation at 8.5 mg/L (70 % of 8.5 mg/L = 6 mg/L). All measured values are above 6.0 ppm oxygen.
At a loading of 1 mg test item/L, the pH value of method blanks and of media containing the test item at target pH value of 6 was measured to be in the range of pH 6.0 – 6.3. The pH value of method blanks and media containing the test item at target pH value of 8 was measured to be in the range of pH 7.8 – 8.0.

Analytical measurements: Within and between vessel variations in zinc concentrations
The within / between vessel variations in vessels containing the test item are not always in accordance with the criteria defined by the guidance document (loading of 1 mg/L). At a loading of 1 mg/L, most measured Zn and Fe concentrations are close to their respective LODs/LOQs (see above). Zn and Fe are ubiquitous metals with significant background concentrations in laboratory products.

Analytical measurements - Full test:
Zinc:
- Dispersed/dissolved zinc concentrations of 0.2 µm filtered samples in the 28-d test at pH 6 (shaking at 100 rpm under dark conditions at 21.5°C) and a loading of 1 mg/L were determined with 2.91, 11.0 and 14.1 µg Zn/L after 1, 7 and 28 days, respectively.
- Dispersed/dissolved zinc concentrations of 0.2 µm filtered samples in the 28-d test at pH 8 (shaking at 100 rpm under dark conditions at 21.5°C) and a loading of 1 mg/L were determined with 1.91, 3.20 and 5.59 µg Zn/L after 1, 7 and 28 days, respectively.
Iron:
- Dispersed/dissolved iron concentrations of 0.2 µm filtered samples in the 28-d test at pH 6 (shaking at 100 rpm under dark conditions at 21.5°C) and a loading of 1 mg/L were determined with < LOQ (1.34 µg Fe /L), < LOQ (2.59 µg Fe /L) and < LOD (0.055 µg Fe /L) after 1, 7 and 28 days, respectively.
- Dispersed/dissolved iron concentrations of 0.2 µm filtered samples in the 28-d test at pH 8 (shaking at 100 rpm under dark conditions at 21.5°C) and a loading of 1 mg/L were determined with < LOQ (1.34 µg Fe /L), < LOD (0.862 µg Fe /L) and 0.321 µg Fe/L after 1, 7 and 28 days, respectively.

Method validation summary (ICP-MS/OES)

Zinc

Limits of detection (LODs), limits of quantification (LOQs) and correlation coefficients (r)

Limits of detection (LOD) within all measurement series: 0.135 -1.97 µg Zn/ L.

Limits of quantification (LOQ) within all measurement series: 0.406 -5.90 µg Zn/ L.

Correlation coefficients (r) within all measurement series: > 0.99921

Iron

Limits of detection (LODs), limits of quantification (LOQs) and correlation coefficients (r)

Limits of detection (LOD) within all measurement series: 0.055 -0.862 µg Fe/ L.

Limits of quantification (LOQ) within all measurement series: 0.164 -2.59 µg Fe / L.

Correlation coefficients (r) within all measurement series: > 0.9997

Zn and Fe validation data are provided in Table 2 and Table 3 as an attachment to this entry. Fe and Zn recoveries for the certified reference materials TMDA-64.3 and TMDA-52.4 were in the range of 94.7 to 113 % (see Table 2 and 3)

Conclusions:
The transformation/dissolution test (OECD Series on Testing and Assessment Number 29, 2001) of zinc ferrite (Bayferrox 3950) at a loading of 1 mg/L at pH 6 resulted after 1, 7 and 28 days in dissolved zinc concentrations (operationally defined as the dissolved Zn fraction after centrifugal filtration (~2.1 nm)) of 2.38, 9.16 and 12.5 µg/L, respectively. At pH 8, dissolved zinc concentrations at a loading of 1 mg/L after 1, 7 and 28 days were determined with 1.25, 3.04 and 8.01 µg/L, respectively. Therefore, maximum dissolution of Bayferrox 3950 was observed with dissolved zinc concentrations of 12.5 µg/L at a pH of 6 after 28 days. Dissolved iron concentrations (operationally defined as the dissolved Fe fraction after centrifugal filtration (~2.1 nm)) at a loading of 1 mg/L after 7 and 28 days were below the limit of quantification (< 0.862 µg Fe/L, maximal LOQ) for both pH 6 and pH 8. Thus, the extent to which zinc ferrite (Bayferrox 3950) can produce soluble available ionic and other metal-bearing species in aqueous media at a loading of 1 mg/L, is limited.

Description of key information

The water solubility of zinc ferrite at 20°C was determined with < 1µg/L concerning Fe according to OECD 105 (loading of 10 g/L, pH 8). In addition, the dissolution of zinc ferrite was assessed in environmental media according to the transformation/dissolution protocol (OECD Series on Testing and Assessment Number 29, 2001). At a loading of 1 mg/L, dissolved zinc concentrations (operationally defined as the dissolved Zn fraction after centrifugal filtration (~2.1 nm)) were determined with 2.38, 9.16 and 12.5 µg/L at pH 6 and with 1.25, 3.04 and 8.01 µg/L at pH 8 after 1, 7 and 28 days, respectively. Dissolved iron concentrations (operationally defined as the dissolved Fe fraction after centrifugal filtration (~2.1 nm)) at a loading of 1 mg/L after 7 and 28 days were below the limit of quantification (< 0.862 µg Fe/L, maximal LOQ) for both pH 6 and pH 8. Thus, the extent to which zinc ferrite (Bayferrox 3950) can produce soluble available ionic and other metal-bearing species in aqueous media at a loading of 1 mg/L, is limited.

Key value for chemical safety assessment

Additional information

The Study was performed according to OECD Guideline 105 at pH 8.

For the determination six test mixtures of zinc ferrite with two different loading concentrations (1 g/L and 10 g/L) were agitated with a magnetic stirrer for 24 hours at 20 °C. The received suspensions were filtrated through a

0.1 μm (100 nm) membrane filter. Also three blank solutions (standard water pH 8 to ISO 6341, OECD-Guidance-Document 29) were investigated. After filtration of all mixtures and blank solutions iron- and zinc-determination was performed in each filtrate with Graphite Furnace Atomic Absorption Spectrometry (GFAAS).

With a loading of 10 g zinc ferrite to water at pH 8 the dissolved iron was determined to be < 1 µg/L, and the content of zinc was 4.3 µg/L.