Niobium dioxide

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:

2016-08-17 to 2017-01-17

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

Deviations:

no

GLP compliance:

no

Type of method:

flask method

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Sample: Niobium(IV) oxide (NbO2) < 300 μm
- Source: HC Starck Material: 1048709, batch:SB15003
- Nb content: 74.0 %
- Particle Size Distribution: d50 = 202 µm
d90 = 325 µm
-Surface area (BET): 0.22 m²/g

Type of test:

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

Element analysed:

Niobium

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

pH 8

Remarks on result:

not determinable because of methodological limitations

Type of test:

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

Element analysed:

Niobium

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

pH 8

Remarks on result:

not determinable because of methodological limitations

Type of test:

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

Mean dissolved conc.:

0.35 µg/L

Element analysed:

Niobium

Loading of aqueous phase:

10 mg/L

Incubation duration:

7 d

Test conditions:

pH 8

Remarks on result:

other: CV: 8 %

Key result

Type of test:

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

Mean dissolved conc.:

0.75 µg/L

Element analysed:

Niobium

Loading of aqueous phase:

100 mg/L

Incubation duration:

7 d

Test conditions:

pH 8

Remarks on result:

other: CV 17 %

Results of the Pre-Test

A screening test to determine the pH of maximum dissolution between 6, 7 and 8 was performed for the niobium compound. The results correspond to the metal release after 24 hours of incubation at 22 °C with 200 rpm agitation rate and a mass loading of 100 mg/L. The data of metals released from the transformation / dissolution assays, is shown with the blanks information on the top half of the table and the samples information in the bottom half of the table.

Mean: is the average metal release μg/L; St. Dev.: Standard deviation. CV, %: Coefficient of variation (ratio of Standard deviation respect to the mean concentration, in percentage). BDL: Below detection limit.

Niobium, µg/L
Screening pH 6
	Time [h]	T [°C]	O2[mg/L]	pH	Mean	SD	CV [%]
Blanks	0	21.9	6.6	6.03	BDL	-	-
	24	22.7	7.1	5.89	BDL	-	-
NbO2	0	21.9	6.6	6.03	BDL	-	-
	24	23.2	7.0	5.94	0.3	0.03	9
Screening pH 7
	Time [h]	T [°C]	O2[mg/L]	pH	Mean	SD	CV [%]
Blanks	0	21.5	7.4	7.08	BDL	-	-
	24	21.5	7.0	7.02	BDL	-	-
NbO2	0	21.5	7.4	7.08	BDL	-	-
	24	21.7	7.1	7.03	0.51	0.15	29
Screening pH 8
	Time [h]	T [°C]	O2[mg/L]	pH	Mean	SD	CV [%]
Blanks	0	21.2	7.0	7.90	BDL	-	-
	24	23.1	7.0	7.91	BDL	-	-
NbO2	0	21.2	7.0	7.90	BDL	-	-
	24	22.5	7.3	7.85	1.8	0.18	10

Very low solubility values were measured in the screening test for Nb(IV) oxide < 300 μm. In the case of pH 6, blanks and sample measurements were below the practical quantitation level (PQL = 0.5 μg/L). And for pH 7 and 8 the values are just in the magnitude of the PQL (PQL pH 7 = 0.45 μg/L and PQL pH 8 = 2 μg/L).

Conclusions:

The results showed that Niobium(IV) oxide can be considered as insoluble (< 0.1 mg/L) in aqueous solution in this study conducted according to OECD 29.

Executive summary:

A transformation/dissolution (T/D) test according to OECD 29 was carried out to study the potential of Niobium(IV) oxide to release metal to the environment. A 24 hour screening test to determine the pH of maximum niobium release was performed at pH 6, 7 and 8 with a loading rate of 100 mg/L. The pH screening test showed niobium releases of 1.8 ± 0.18 µg Nb/L at pH 8, while the mean release of Nb at pH 6 and 7 was 0.3 ± 0.03, respectively 0.51 ± 0.15 μg Nb/L.

The full T/D test was conducted at pH 8. The acute endpoint (7 days), was performed at sample loadings of 1, 10 and 100 mg/L; the chronic endpoint was determined from the extension of the 1 mg/L loading test to 28 days. The results of the study documented niobium release measurements as follows:

- 1 mg/L loading after 7 days: below detection limit

- 1 mg/L loading after 28 days: below dection limit          

- 10 mg/L loading after 7 days: 0.35 ± 0.029 μg Nb/L, and

- 100 mg/L loading after 7 days: 0.75 ± 0.131 μg Nb/L.

Therefore, Niobium(IV) oxide is considered to be highly insoluble in water.

Description of key information

A transformation/dissolution (T/D) test was carried out, according to OECD Series on Testing and Assessment No 29 (2001): Transformation dissolution of metals and metal compounds in aqueous media, to study the potential of Niobium(IV) oxide to release metal ions to the environment. The test results are showing that the test substance is highly insoluble (< 0.1 mg/L).

Key value for chemical safety assessment

Water solubility:

0.75 µg/L

at the temperature of:

21.7 °C

Additional information

A transformation/dissolution (T/D) test according to OECD 29 was carried out to study the potential of Niobium(IV) oxide to release metal to the environment.

A 24 hour screening test to determine the pH of maximum niobium release was performed at pH 6, 7 and 8 with a loading rate of 100 mg/l. The pH screening test showed niobium releases of 1.8 ± 0.18 µg Nb/L at pH 8, while the mean release of Nb at pH 6 and 7 was 0.3 ± 0.03 respectively 0.51 ± 0.15 μg Nb/L.

The full T/D test was conducted at pH 8. The acute endpoint (7 days), was performed at sample loadings of 1, 10 and 100 mg/L; the chronic endpoint was determined from the extension of the 1 mg/L loading test to 28 days. The results of the study documented niobium release measurements as follows:

- 1 mg/l loading after 7 days: below detection limit

- 1 mg/l loading after 28 days: below dection limit          

- 10 mg/L loading after 7 days: 0.35 ± 0.029 μg Nb/L, and

- 100 mg/L loading after 7 days: 0.75 ± 0.131 μg Nb/L.

Therefore, Niobium(IV) oxide is considered to be highly insoluble in water.