Niobium oxide

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:

2016-09-29 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

Type of test:

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

Mean dissolved conc.:

0.27 µg/L

Element analysed:

Niobium

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

pH 8

Remarks on result:

other: CV: 32 %

Type of test:

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

Mean dissolved conc.:

0.4 µg/L

Element analysed:

Niobium

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

pH 8

Remarks on result:

other: CV: 21 %

Type of test:

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

Mean dissolved conc.:

0.83 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: 6 %

Key result

Type of test:

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

Mean dissolved conc.:

1.74 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 : 26 %

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; SD.: 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	-	-
Nb(II)O 80K	0	21.9	6.6	6.03	BDL	-	-
	24	23.5	7.2	5.89	0.2	0.03	13
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	-	-
Nb(II)O 80K	0	21.5	7.4	7.08	BDL	-	-
	24	22.3	7.0	7.03	0.55	0.03	5
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	-	-
Nb(II)O 80K	0	21.2	7.0	7.90	BDL	-	-
	24	22.5	7.4	7.89	3.6	0.1	3

Very low solubility values were measured in the screening test for Nb(II) oxide 80K. In the case of pH 6, blanks and sample measurements were below the practical quantitation level (PQL = 0.5 μg/L). For pH 7 and 8, metal release values are above the PQL (PQL pH 7 = 0.45 μg/L and PQL pH 8 = 2 μg/L).

Conclusions:

The results showed that Niobium(II) 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(II) 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 3.6 ± 0.1 µg Nb/L at pH 8, while the mean release of Nb at pH 6 and 7 was 0.2 ± 0.03 respectively 0.55 ± 0.03 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: 0.27 ± 0.085 µg Nb/L

- 1 mg/L loading after 28 days: 0.4 ± 0.086 µg Nb/L,          

- 10 mg/L loading after 7 days: 0.83 ± 0.052 μg Nb/L, and

- 100 mg/L loading after 7 days: 1.74 ± 0.449 μg Nb/L.

Therefore, Niobium(II) 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(II) oxide to release metal ions to the environment showing that the test substance is highly insoluble (< 0.1 mg/mL).

Key value for chemical safety assessment

Water solubility:

1.74 µg/L

at the temperature of:

22 °C

Additional information

A transformation/dissolution (T/D) test, according to OECD 29, was carried out to study the potential of Niobium(II) 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 3.6 ± 0.1 µg Nb/L at pH 8, while the mean release of Nb at pH 6 and 7 was 0.2 ± 0.03 respectively 0.55 ± 0.03 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: 0.27 ± 0.085 µg Nb/L

- 1 mg/L loading after 28 days: 0.4 ± 0.086 µg Nb/L,          

- 10 mg/L loading after 7 days: 0.83 ± 0.052 μg Nb/L, and

- 100 mg/L loading after 7 days: 1.74 ± 0.449 μg Nb/L.

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