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EC number: 215-213-6 | CAS number: 1313-96-8
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- Water solubility
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Water solubility
Administrative data
Link to relevant study record(s)
- 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
- 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. - 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.
- 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.
Referenceopen allclose all
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 |
Time of shaking |
Remarks |
Niobium concentration |
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 |
0a
|
< 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=0a
|
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.
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.
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.
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