Diniobium pentaoxide

Water solubility

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

transformation / dissolution of metals and inorganic metal compounds

Type of information:

experimental study

Adequacy of study:

key study

Study period:

21 July 2010 to 21 October 2010

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:

yes

Type of method:

other: Guidance document o transformation/dissolution of metals and metal compounds in aqueous media

Type of test:

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

Mean dissolved conc.:

< 0.5 µg/L

Element analysed:

Nb

Incubation duration:

7 d

Test conditions:

ph 8

Type of test:

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

Mean dissolved conc.:

< 0.5 µg/L

Element analysed:

Nb

Incubation duration:

28 d

Test conditions:

pH 8

Results

Preliminary Test

 pH that maximizes the concentration

The test was performed according the description in chapter4.4obtaining the following results:

Table1:     Results preliminary test– concentration of Nb after 24h shaking

pH planned	pH observed	Test Item added (mg/L)	Time of shaking (h)	Remarks	Niobium concentration (µg/L)
5.5	6.2	100	24	no solution observed	< 0.01
6	6.4	100	24	no solution observed	< 0.01
7	6.9	100	24	no solution observed	< 0.01
8	7.9	100	24	no solution observed	0.09

 

Within the tested range from pH 6 to 8, the vessel at pH=8 showed a clear higher concentration than the others. Therefore the main test was performed at pH=8.

Figure1:      Niobium concentrations in different pH media within 24 hours of shaking

Table2:     Results preliminary test – concentration trend within 24h

Time	"pH5.5"	pH6	pH7	pH8
0	0.01	0.01	0.01	0.01
2	0.01	0.01	0.01	0.03
6	0.01	0.01	0.01	0.04
24	0.01	0.01	0.01	0.09

 

 

 pH stability over a one week period

The stability test for the buffered systems showed, that for the salt mixtures given in OECD Guidance Document 29 (pH 6, 7 and 8) and after an equilibration time of 24 hours, the pH values are within the expected range.

The guidance document recommends to test the solubility of the test item additional at pH 5.5, if a long term test is planned. In fact for pH 5.5 no salt mixture is given in the guidance document, so that the medium for pH 6 was used with an increase of the carbon dioxide concentration to 1.5%. Although this buffered pH 5.5 media is very instable, it was the best found in non GLP pre tests. Nevertheless, this unavailability of a pH 5.5 medium doesn’t affect the outgoing of the study, as the concentrations of Diniobium Pentaoxide showed clear the highest values in solubility tests at pH 8.

It was found that the gas phases need to be replaced, with every sampling time.

Results for the pH stability are shown in the table below:

Table3:       Results pH-stability

Time	pH 5.5	pH 6	pH 7	pH 8
2 h	6.1	6.4	6.9	7.8
6 h	6.1	6.3	6.8	7.8
24 h	5.7	6.0	7.1	7.8
48 h	5.7	6.1	7.0	7.9
168 h	5.7	6.0	7.0	7.8

 

Test conditions are listed in Appendix A1.

Short Term Test

The short term test at pH=8 was performed as described in chapter4.5, obtaining the following results:

Table4:        Test results of the short term test period of one week (ph=8)

Sample	Sampling	Mean Conc.	Mean Conc.^b
	time	Nb (µg/L)	Nb2O5(µg/L)
Control 1	0^a	< 0.01
Control 2		n.d.
Vessel 1mg-1		n.d.
Vessel 1mg-2		n.d.
Vessel 1mg-3		n.d.
Vessel 10mg-1		n.d.
Vessel 10mg-2		n.d.
Vessel 10mg-3		n.d.
Vessel 100mg-1		n.d.
Vessel 100mg-2		n.d.
Vessel 100mg-3		< 0.01
Control 1	2 hours	n.d.	n.d.
Control 2		n.d.
Vessel 1mg-1		n.d.	< 0.01
Vessel 1mg-2		< 0.01
Vessel 1mg-3		< 0.01
Vessel 10mg-1		< 0.01	< 0.01
Vessel 10mg-2		< 0.01
Vessel 10mg-3		< 0.01
Vessel 100mg-1		0.022	0.03
Vessel 100mg-2		0.024
Vessel 100mg-3		0.023
Control 1	6 hours	n.d.	n.d.
Control 2		n.d.
Vessel 1mg-1		< 0.01	< 0.01
Vessel 1mg-2		< 0.01
Vessel 1mg-3		< 0.01
Vessel 10mg-1		0.010	0.01
Vessel 10mg-2		0.010
Vessel 10mg-3		0.012
Vessel 100mg-1		0.043	0.06
Vessel 100mg-2		0.044
Vessel 100mg-3		0.042

n.d.= not detectable (< 0.003 µg/L)

^at=0 samples were taken before the test item was added, to proof the purity of the test medium;

^bConversion factor concentration Nb / Nb₂O5=1.43 (based on the ratio of the molecular masses 266/186);

Table5:           Test results of the short term test period of one week (continued)

 

Sample	Sampling time	Mean Conc. Nb (µg/L)	Mean Conc.^b Nb2O5 (µg/L)
Control 1	1 day	n.d.	n.d.
Control 2		n.d.
Vessel 1mg-1		< 0.01	< 0.01
Vessel 1mg-2		< 0.01
Vessel 1mg-3		< 0.01
Vessel 10mg-1		0.029	0.04
Vessel 10mg-2		0.027
Vessel 10mg-3		0.028
Vessel 100mg-1		0.097	0.14
Vessel 100mg-2		0.087
Vessel 100mg-3		0.104
Control 1	2 days	n.d.	n.d.
Control 2		n.d.
Vessel 1mg-1		< 0.01	< 0.01
Vessel 1mg-2		< 0.01
Vessel 1mg-3		< 0.01
Vessel 10mg-1		0.045	0.06
Vessel 10mg-2		0.035
Vessel 10mg-3		0.045
Vessel 100mg-1		0.128	0.19
Vessel 100mg-2		0.116
Vessel 100mg-3		0.157
Control 1	7 days	n.d.	n.d.
Control 2		n.d.
Vessel 1mg-1		< 0.01	< 0.01
Vessel 1mg-2		< 0.01
Vessel 1mg-3		< 0.01
Vessel 10mg-1		0.086	0.11
Vessel 10mg-2		0.074
Vessel 10mg-3		0.076
Vessel 100mg-1		0.267	0.36
Vessel 100mg-2		0.221
Vessel 100mg-3		0.269

n.d.= not detectable (< 0.003 µg/L)

^at=0 samples were taken before the test item was added, to proof the purity of the test medium;

^bConversion factor concentration Nb / Nb₂O5=1.43 (based on the ratio of the molecular masses 266/186);

Test conditions (temperature, pH and oxygen conc.) are listed in Appendix A3

The graphs below show the mean concentrations of Niobium, expressed as Niobium Pentaoxide, plotted versus time:

Figure2:      Mean concentrations of Niobium, calculated as Niobium Pentaoxide, versus time

The plot in the figure above indicates an increasing solubility with the amount of added test item. But as all the three test item amounts (1, 10 and 100 mg/L Nb₂O₅) are added in an enormous overspill, compared to the highest concentration found (below 0.5 µg/L), this result doesn’t reflect the real solubility.

In fact the test item is a very fine powder and it seems that after separation there are still smallest particles left, which can’t be separated - not by filtration and not even by hard centrifugation.

A similar effect was reported in a solubility study of Diniobium Pentaoxide by A. Königer (2009). Here it was assumed, that Diniobium Pentaoxide forms a dispersed or colloidal system in water.

According to that, these results express the soluble part plus a dispersed or colloidal, non soluble amount. This non soluble amount depends on the total quantity of test item added in overspill.

Thus, it is considered to be justified that the solubility of Diniobium Pentaoxide in water is below 0.5 µg/L.

 

 Long Term Test

The long term test was performed as described in chapter4.6, obtaining the following results:

Table6:        Test conditions during long term test period of four weeks

Sample	Sampling	Mean Conc.	Mean Conc.^b
	time	Nb (µg/L)	Nb2O5(µg/L)
Control 1	t=0^a	n.d.	n.d.
Control 2		n.d.
Vessel 1		n.d.
Vessel 2		n.d.
Vessel 3		n.d.
Control 1	2 hours	n.d.	n.d.
Control 2		n.d.
Vessel 1		n.d.	n.d.
Vessel 2		n.d.
Vessel 3		n.d.
Control 1	6 hours	n.d.
Control 2		n.d.
Vessel 1		n.d.	< 0.01
Vessel 2		< 0.01
Vessel 3		< 0.01
Control 1	1 day	n.d.	n.d.
Control 2		< 0.01
Vessel 1		0.016	0.03
Vessel 2		0.024
Vessel 3		0.019
Control 1	2 days	n.d.
Control 2		n.d.
Vessel 1		< 0.01	< 0.01
Vessel 2		< 0.01
Vessel 3		< 0.01
Control 1	7 days	n.d.
Control 2		n.d.
Vessel 1		< 0.01	0.01
Vessel 2		0.010
Vessel 3		0.010
Control 1	14 days	n.d.
Control 2		n.d.
Vessel 1		< 0.01	0.02
Vessel 2		0.011
Vessel 3		0.012

Table7:        Test conditions during long term test period of four weeks (continued)

Sample	Sampling time	Mean Conc. Nb (µg/L)	Mean Conc.^b Nb2O5(µg/L)
Control 1	21 days	n.d.
Control 2		n.d.
Vessel 1		0.011	0.02
Vessel 2		0.012
Vessel 3		0.014
Control 1	28 days	n.d.
Control 2		n.d.
Vessel 1		0.011	0.02
Vessel 2		0.010
Vessel 3		0.012

n.d.= not detectable (< 0.003 µg/L)

^at=0 samples were taken before the test item was added, to proof the purity of the test medium;

^bConversion factor concentration Nb / Nb₂O5=1.43 (based on the ratio of the molecular masses 266/186);

Test conditions (temperature, pH and oxygen conc.) are listed in Appendix A4

 

During the 28 day solubility test with Diniobium Pentaoxide, the determined concentrations didn’t exceed 0.05 µg/L for all taken samples. Thus, it is considered to be justified that the solubility of Diniobium Pentaoxide in water is < 0.5 µg/L.

Conclusions:

Interpretation of results (migrated information): insoluble (< 0.1 mg/L)
The solubility of Diniobium Pentaoxide was found to be clearly below 0.5 µg/L for the 7-day short term test as well as for the 28-day long term test in the given test medium at pH 8.

Reference 2

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Deviations:

no

GLP compliance:

yes

Type of method:

flask method

Water solubility:

< 30 µg/L

Temp.:

20 °C

pH:

6

Remarks on result:

other: The results show a low reproducibility. It can not be excluded that a small amount of colloidal distributed test item is still present in the solution.

Details on results:

The water solubility is estimated to be lower than 30 μg/l.

 Results

 

Blank values	Determination 1	Determination 2	Mean value
Niobium content	< 0.5 µg/l	< 0.5 µg/l	< 0.5 µg/l
Diniobium pentaoxide content	< 0.5 µg/l	< 0.5 µg/l	< 0.5 µg/l
pH-value	6.62	--	6.6

 

Table 1: Water solubility at 20 °C (first determination)

 

Water solubility at 20 °C (Standard laboratory procedure)	Flask 1	Flask 2	Flask 3	Mean value
Niobium content (Determination 1 Determination 2)	296.0 µg/l 297.3 µg/l	214.8 µg/l 195.0 µg/l	414.7 µg/l 409.8 µg/l
Niobium content (mean value)	296.7 µg/l	204.9 µg/l	412.2 µgl	300 µg/l
Diniobium pentaoxide content	424,4 µg/l	293.1 µg/l	589.8 µg/l	440 µg/l
pH-value	5.89	5.94	6.01	6.0

 

 

 

Table 2: Water solubility at 20 °C (after centrifugation)

 

Water solubility at 20 °C (after filtration and centrufigation)	Flask 1	Flask 2	Flask 3	Mean value
Niobium content (Determination 1 Determination 2)	23.1 µg/l 23.1 µg/l	7.9 µg/l 7.9 µg/l	30.6 µg/l 30.3 µg/l
Niobium content (mean value)	23.1 µg/l	7.9 µg/l	30.4 µgl	20 µg/l
Diniobium pentaoxide content	33.0 µg/l	11.3 µg/l	43.6 µg/l	30 µg/l

 

The results show a low reproducibility. Although the solution was visibly clear after the second separation, it can not be excluded that a small amount of colloidal distributed test item is still present in the solution. Due to the fact that the water solubility calculated in the second determination is very low no third phase separation was performed.

Conclusions:

Interpretation of results (migrated information): insoluble (< 0.1 mg/L)
Based on the study results the test item is considered to be insoluble in water at 20°C.

Description of key information

< 0.5 μg/L at 20 °C, pH 8, medium

(OECD guideline 29, TD test)

< 30 µg/L at 20 °C, pH 6, water

(OECD 105)

Key value for chemical safety assessment

Water solubility:

0.5 µg/L

at the temperature of:

20 °C

Additional information

The solubility in a transformation dissolution test (TD test) of Diniobium Pentaoxide was found to be clearly below 0.5 µg/L for the 7-day short term test as well as for the 28-day long term test in the given test medium at pH 8.

The water solubility of Diniobium Pentaoxide was determined to be below 30 µg/L at 20 °C at pH 6.