Niobium doped titanium dioxide

Water solubility

Link to relevant study record(s)

Reference

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2018-09-14 to 2018-09-28

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Deviations:

yes

Remarks:

The preliminary test showed a water solubility < 10 mg/L. In such a case the column elution method is recommended. However, when the test item is inorganic the suitable method according to ECHA guidance R.7a is the flask method with two loading rates.

Qualifier:

according to guideline

Guideline:

EU Method A.6 (Water Solubility)

Version / remarks:

European Commission Regulation (EC) No. 440/2008 and No.260/2014

Deviations:

yes

Remarks:

The preliminary test showed a water solubility < 10 mg/L. In such a case the column elution method is recommended. However, when the test item is inorganic the suitable method according to ECHA guidance R.7a is the flask method with two loading rates.

GLP compliance:

no

Type of method:

flask method

Water solubility:

>= 0.006 - <= 0.021 mg/L

Conc. based on:

test mat. (dissolved fraction)

Loading of aqueous phase:

0.1 g/L

Incubation duration:

>= 24 - <= 72 h

Temp.:

20 °C

pH:

>= 6.7 - <= 7.3

Remarks on result:

other: Niobium

Water solubility:

>= 0.016 - <= 0.22 mg/L

Conc. based on:

test mat. (dissolved fraction)

Loading of aqueous phase:

0.1 g/L

Incubation duration:

>= 24 - <= 72 h

Temp.:

20 °C

pH:

>= 6.7 - <= 7.3

Remarks on result:

other: Titanium

Key result

Water solubility:

>= 0.027 - <= 0.057 mg/L

Conc. based on:

test mat. (dissolved fraction)

Loading of aqueous phase:

1 g/L

Incubation duration:

>= 24 - <= 72 h

Temp.:

20 °C

pH:

>= 9.1 - <= 9.8

Remarks on result:

other: Niobium

Key result

Water solubility:

>= 1.1 - <= 2.1 mg/L

Conc. based on:

test mat. (dissolved fraction)

Loading of aqueous phase:

1 g/L

Incubation duration:

>= 24 - <= 72 h

Temp.:

20 °C

pH:

9.1 - 9.8

Remarks on result:

other: Titanium

As the test item is an inorganic compound the concentration (c_s) of Niobium and Titanium in the water extracts was determined in this study as representative parameters for the solubility of the complete test item.

The main test was performed with two loading rates (0.1 g/L and 1 g/L). Therefore, three flasks (experiment A - C) were prepared with about 10 mg of the test item and 100 mL demineralized water and three flasks (experiment E - G) with about 100 mg of the test item and 100 mL demineralized water, respectively. The batches were stirred for different times at 30 °C (experiments A and E for 24 h, experiments B and F for 48 h, experiments C and G for 72 h) in tightly closed flasks.

After equilibration (further stirring for 24 h at 20 °C) precipitate was observed in the flasks of the experiments excluding the blank experiment. The samples were analysed by ICP-MS.

One other experiment was performed according to this procedure but without test item ("blank" = D).

The data for the evaluation are given in Table 3 and Table 4. The concentrations were calculated from the measured and unrounded concentration values and not from the rounded values given in the tables.

Table 3: Niobium and Titanium concentration in the water extracts - experiments A to D (loading rate 0.1 s/L)

Experiment	A	B	C	D (blank)
Amount of test item / mg	11.1	14.8	9.7	---
Amount of demin. water / mL	100	100	100	100
Stirring time at 30 °C / h	24	48	72	72
pH at 25 °C	6.7	7.0	7.3	6.6
Measured Niobium concentration / mg/L	0.021	0.007	0.006	< 0.005^1)
Measured Titanium concentration / mg/L	0.016	0.041	0.22	< 0.005^1)

¹⁾ < indicates below the quantification limit

Table 4: Niobium and Titanium concentration in the water extracts - experiments E to G (loading rate 1.0 g/L)

Experiment	E	F	G	D (blank)
Amount of test item / mg	100.4	105.2	100.9	---
Amount of demin. water / mL	100	100	100	100
Stirring time at 30 °C / h	24	48	72	72
pH at 25 °C	9.8	9.6	9.1	6.6
Measured Niobium concentration / mg/L	0.046	0.057	0.027	< 0.005^1)
Measured Titanium concentration / mg/L	1.2	2.1	1.1	< 0.005^1)

¹⁾ < indicates below the quantification limit

The concentrations found in the experiments with different loading rates were different orders of magnitude for both elements. Therefore a dependency of the loading rate was observed.

According to the guideline OECD 105 the individual results from the experiments of with different stirring times should not differ by more than 15 %. In the present study the relative standard deviation is considerably higher. However, the flask method is generally used for solubilities higher than 10 mg/L. Therefore the deviations of more than 15 % may result from the low concentration ranges found in the experiments. Another reason may be an inhomogeneity of the present test item.

Due to the high deviations in the experiments with different stirring times, a concentration range was given instead of a mean value.

 

The test item is an inorganic compound. As a representative parameter for the solubility of the complete test item, the concentration (c_s) of Niobium and Titanium in the water extracts of the test item at 20 °C was determined based on the guideline 4.6. water solubility; flask-method of the European Commission Regulation (EC) No. 440/2008 and No. 260/2014. For results see Table 5.

Table 5: Element concentrations in the experiment A to G (loading rate 0.1 g/L) and in the experiment E to G (loading rate 1.0 g/L)

	Concentration range experiment A to C (loading rate 0.1 g/L)	Concentration range experiment E to G (loading rate 1.0 g/L)
Niobium	0.006 mg/L to 0.021 mg/L	0.027 mg/L to 0.057 mg/L
Titanium	0.016 mg/L to 0.22 mg/L	1.1 mg/L to 2.1 mg/L

 

Conclusions:

Since the test item is an inorganic compound, the concentration of Niobium and Titanium were determined as representative parameters for the solubility of the test item. The concentrations were found to be dependent on the loading rate. Therefore, the highest measured concentration is assumed as worst case value. Following concentration ranges were found for a loading rate of 1.0 g/L: Niobium 0.027 mg/L to 0.057 mg/L and Titanium 1.1 mg/L to 2.1 mg/L at 20 °C and a pH of ca. 9.5 (reference 4.8-1).

Executive summary:

The water solubility was determined according to Regulation (EC) No 440/2008, method A.6 and OECD Guideline No. 105, adopted on 27th July 1995 using the shake flask method with ICP-MS analysis. A preliminary test was undertaken to determine the approximate water solubility. Two different loading rates of 0.1 g/L and 1.0 g/L were investigated. The respective amount of the test item was weighed into three flasks for each loading rate and filled up with demineralized water. Furthermore, a blank sample without test item was prepared. The samples were stirred at 30 °C for 24 h, 48 h and 72 h, respectively. After equilibration for 24 h at 20 °C, aliquots of the mixtures were taken and analysed by ICP-MS. Since the test item is an inorganic compound, the concentration of Niobium and Titanium were determined as representative parameters for the solubility of the test item. The concentrations were found to be dependent on the loading rate. Following concentration ranges were found for a loading rate of 0.1 g/L and 1.0 g/L, respectively.

0.1 g/L: Niobium 0.006 mg/L to 0.021 mg/L, Titanium 0.016 mg/L to 0.22 mg/L at 20 °C and a pH of ca. 7.

1.0 g/L: Niobium 0.027 mg/L to 0.057 mg/L, Titanium 1.1 mg/L to 2.1 mg/L at 20 °C and a pH of ca. 9.5.

The higher concentration range is assumed as worst case scenario and was used as key parameter.

Description of key information

Since the test item is an inorganic compound, the concentration of Niobium and Titanium were determined as representative parameters for the solubility of the test item. The concentrations were found to be dependent on the loading rate. Therefore, the highest measured concentration is assumed as worst case value. Following concentration ranges were found for a loading rate of 1.0 g/L: Niobium 0.027 mg/L to 0.057 mg/L and Titanium 1.1 mg/L to 2.1 mg/L at 20 °C and a pH of ca. 9.5 (reference 4.8-1).

Key value for chemical safety assessment

Water solubility:

2.1 mg/L

at the temperature of:

20 °C

Additional information

The water solubility was determined according to Regulation (EC) No 440/2008, method A.6 and OECD Guideline No. 105, adopted on 27th July 1995 using the shake flask method with ICP-MS analysis. A preliminary test was undertaken to determine the approximate water solubility. Two different loading rates of 0.1 g/L and 1.0 g/L were investigated. The respective amount of the test item was weighed into three flasks for each loading rate and filled up with demineralized water. Furthermore, a blank sample without test item was prepared. The samples were stirred at 30 °C for 24 h, 48 h and 72 h, respectively. After equilibration for 24 h at 20 °C, aliquots of the mixtures were taken and analysed by ICP-MS. Since the test item is an inorganic compound, the concentration of Niobium and Titanium were determined as representative parameters for the solubility of the test item. The concentrations were found to be dependent on the loading rate. Following concentration ranges were found for a loading rate of 0.1 g/L and 1.0 g/L, respectively.

0.1 g/L: Niobium 0.006 mg/L to 0.021 mg/L, Titanium 0.016 mg/L to 0.22 mg/L at 20 °C and a pH of ca. 7.

1.0 g/L: Niobium 0.027 mg/L to 0.057 mg/L, Titanium 1.1 mg/L to 2.1 mg/L at 20 °C and a pH of ca. 9.5.

The higher concentration range is assumed as worst case scenario and was used as key parameter.