High-temperature calcination products of diiron trioxide and amorphous silica resulting in a glassy silica matrix

Water solubility

Link to relevant study record(s)

Reference

Endpoint:

transformation / dissolution of metals and inorganic metal compounds

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2009-08-03 to 2010-03-10

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

(a) the 28-day test with a loading of 1 mg/L was conducted at pH 6 instead of 5.5 (b) the within-vessel variation was not always < 10 % (c) `mass balance (%) after completion of the transformation test´ is missing.

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:

yes

Remarks:

please refer to the field "Rationale for reliability incl. deficiencies" above

GLP compliance:

yes

Type of method:

flask method

Remarks:

transformation/dissolution

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

0.002 µg/L

Element analysed:

Fe

Loading of aqueous phase:

100 mg/L

Incubation duration:

24 h

Test conditions:

pH 8

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

0.131 µg/L

Element analysed:

Fe

Loading of aqueous phase:

100 mg/L

Incubation duration:

24 h

Test conditions:

pH 6

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

204.019 µg/L

Element analysed:

Si

Loading of aqueous phase:

100 mg/L

Incubation duration:

24 h

Test conditions:

pH 8

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

215.745 µg/L

Element analysed:

Si

Loading of aqueous phase:

100 mg/L

Incubation duration:

24 h

Test conditions:

pH 6

Type of test:

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

Mean dissolved conc.:

0.734 µg/L

Element analysed:

Fe

Loading of aqueous phase:

100 mg/L

Incubation duration:

7 d

Test conditions:

T = 19.7 - 21.4 °C, pH = 6 ± 0.2

Remarks on result:

other: SD: ± 0.0828 µg/L

Type of test:

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

Mean dissolved conc.:

< 0.069 µg/L

Element analysed:

Si

Loading of aqueous phase:

100 mg/L

Incubation duration:

7 d

Test conditions:

T = 19.7 - 21.4 °C, pH = 6.00 ± 0.2

Remarks on result:

other: < LOD

Type of test:

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

Mean dissolved conc.:

< 0.224 µg/L

Element analysed:

Fe

Loading of aqueous phase:

1 mg/L

Incubation duration:

24 h

Test conditions:

T = 19.7 - 19.9 °C, pH: 6.15

Remarks on result:

other: < LOD

Type of test:

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

Mean dissolved conc.:

< 0.069 µg/L

Element analysed:

Si

Loading of aqueous phase:

1 mg/L

Incubation duration:

24 h

Test conditions:

T= 19.7 - 19.9 °C, pH= 6.15

Remarks on result:

other: < LOD

Key result

Type of test:

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

Mean dissolved conc.:

< 0.224 µg/L

Element analysed:

Fe

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

T = 19.7 - 21.2 °C, pH = 6.00 ± 0.2

Remarks on result:

other: < LOD

Key result

Type of test:

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

Mean dissolved conc.:

< 0.069 µg/L

Element analysed:

Si

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

T = 19.7 - 21.2 °C, pH = 6.00 ± 0.2

Remarks on result:

other: < LOD

Key result

Type of test:

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

Mean dissolved conc.:

0.291 µg/L

Element analysed:

Fe

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

T = 19.7 - 22.4 °C, pH = 6.00 ± 0.2

Remarks on result:

other: SD: ± 0.0464 µg/L

Key result

Type of test:

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

Mean dissolved conc.:

< 0.069 µg/L

Element analysed:

Si

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

T = 19.7 - 22.4 °C, pH = 6.00 ± 0.2

Remarks on result:

other: < LOD

Details on results:

Silicium concentrations were below the detection limit in aqueous solutions with 1 mg/L and 100 mg/L loadings. Iron ions dissolved/transformed in aqueous solutions. At each time point dissolved Fe concentrations were < 1 μg/L.

Test conditions were predominantly in accordance with guideline:

- Vessel Variation:

The within-vessel variations from the 100mg/L loadings for selected vessels were >10 % (not guideline comform) due to concentrations being close to the LOQ. The between-vessel variation was always ≤ 20 %.

The within-vessel variations from the 1mg/L loading for selected vessels was >10 % (not guideline comform) due to concentrations being close to the LOQ. However, the between-vessel variation was always ≤ 20 % (guideline comform).

Oxygen:

- The oxgen concentrations were in the range of 4.7 and 9.7 mg/L with three values below the acceptable limit (>70 % of air O₂ concentration = 5.46 mg/L). However, a results-changing impact on dissolved Fe concentrations can be excluded.

Temperature:

- The temperature was in the range from 19.7 °C to 22.4 °C.

Solution pH:

- The pH was in the range of 6.05 to 6.19 (i.e. in the range of pH 6 + 0.2 units)

Conclusions:

The transformation/dissolution of the reaction mass of fumes, silica and diiron trioxide resulted in the following dissolved concentrations:

loading, Time Fe [µg/L] Si [µg/L]
1mg/L, 7 days < 0.22 (1mg/L, 28 days 0.29+/- 0.05 < 0.07 (100mg/L,7 days 0.73 +/- 0.08 < 0.07 (
As dissolved Fe and Si concentrations were below 1 µg/L even at the highest loading of 100 mg/L, the pigment can be considered environmentally inert.

Description of key information

The solubility of High-temperature calcination products of diiron trioxide and amorphous silica resulting in a glassy silica matrix is < 0.001%. In a GLP-conform transformation/dissolution screening test with a loading of 100 mg/L a higher release was observed at pH 6 (Grane, 2010). In a short-term transformation/dissolution test with a loading of 100 mg/L at pH 6, a dissolved Fe concentration of 0.73 microg/L was determined whereas the dissolved Si concentration was below LOD (0.07 microg/L) after 7 days (Grane, 2010). Transformation/dissolution at a loading of 1 mg/L resulted in dissolved Si concentrations below the LOD (< 0.07 microg/L) at pH 6 after 7 and 28 days (Grane, 2010). The dissolved Fe concentrations at pH 6 was below the LOD (< 0.22 microg/L) after 7 and at 0.29 microg/L after 28 days (Grane, 2010). The particle size of the tested sample (BET surface area 4.21 m2/g) is representative for the particle size marketed. Thus, the extent to which "High-temperature calcination products of diiron trioxide and amorphous silica resulting in a glassy silica matrix" can produce soluble available ionic and other metal-bearing species in aqueous media is limited.