Zinc ferrite brown spinel

Water solubility

Link to relevant study record(s)

Reference

Reference 1

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.

Reference 2

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.

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.