Gadolinium zirconium oxide (Gd2Zr2O7)

Water solubility

Link to relevant study record(s)

Reference

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Study period:

November 09 - December 18, 2015

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

GLP compliance:

no

Type of method:

flask method

Key result

Water solubility:

4 mg/L

Conc. based on:

test mat.

Temp.:

20 °C

pH:

6.5

Details on results:

Individual results
Preliminary visual estimation of the water solubility
Three preliminary tests were carried out with specified amounts of the test item and 100 ml and 500 ml distilled water, respectively. After each addition of an amount of water, the mixture was stirred for at least 24 hours, and visually checked for any undissolved particles (see Table 1).
The solubility of the test item in water was found to be below 9.8 mg/l (without correction for the purity). In this range the water solubility of test items should be determined with the column elution method. However as the present test item Gadolinium Zirkonat is an inorganic substance the suitable method according to ECHA guidance R.7a is the flask method with two loading rates.

Flask method
The flask method was performed as described above. The data for the evaluation are given in Table 2. After the equilibration time a small amount of precipitate was observed in the flasks of the experiments A – C (see Table 2) and considerable precipitate in the flasks of the experiments E - G (see Table 3). The water solubility was calculated under assumption of the molecular formula and the molecular weight given above.
The calculated water solubility for gadolinium was deviating from the calculated water solubility for zirconium. This was most likely caused by a different chemical behaviour of the elements gadolinium and zirconium. It was assumed that zirconium formed insoluble compounds during the stirring time.
The water solubility experiments showed no significant dependence on the loading rate but a dependence on the stirring time. Therefore the experiment with a loading rate of 0.1 g/l was repeated with extended stirring times. The results are summarised in Table 4.
The water solubility of the test item Gadolinium Zirkonat showed an unusual behaviour that was most likely caused by the chemical nature of the test item. As a conservative approach the highest measured water solubility was taken as final result.
The water solubility of the test item at 20 °C was determined to be 4.0 mg/l.

Table 1: Results of the preliminary visual estimation of the water solubility

Amount of the test item / mg	Total volume / ml	Appearance of mixture
9.9	100	undissolved
12.2	500	undissolved
4.9	500	undissolved

Table 2: Water solubility experiments A - D, loading rate 0.1 g/l

Experiment	A	B	C	Blank experiment (D)
Amount of test item / mg	5.9	5.9	6.1	--
Amount of distilled water / ml	50	50	50	50
Stirring time at 30 °C / h	24	48	72	72
pH at 23 °C	6.5	6.4	6.5	6.2
Measured concentration gadolinium / mg/l	0.01	0.02	2.1	< 0.01
Water solubility based on gadolinium concentration / mg/l	0.02	0.04	4.0	< 0.02
Measured concentration zirconium / mg/l	< 0.02	< 0.02	< 0.02	< 0.02
Water solubility based on zirconium concentration / mg/l	< 0.07	< 0.07	< 0.07	<0.07

Table 3: Water solubility experiments E - H, loading rate 1.0 g/l

Experiment	E	F	G	Blank experiment (H)
Amount of test item / mg	53.5	52.6	53.4	--
Amount of distilled water / ml	50	50	50	50
Stirring time at 30 °C / h	24	48	72	72
pH at 23 °C	6.8	6.7	6.7	6.3
Measured concentration gadolinium / mg/l	< 0.01	0.20	0.56	< 0.01
Water solubility based on gadolinium concentration / mg/l	< 0.02	0.38	1.1	< 0.02
Measured concentration zirconium / mg/l	< 0.02	< 0.02	< 0.02	< 0.02
Water solubility based on zirconium concentration / mg/l	< 0.07	< 0.07	< 0.07	<0.07

Table 4: Water solubility experiments I - L, loading rate 0.1 g/l

Experiment	I	J	K	Blank experiment (L)
Amount of test item / mg	5.7	5.3	5.5	--
Amount of distilled water / ml	50	50	50	50
Stirring time at 30 °C / h	72	96	120	120
pH at 23 °C	6.2	6.3	6.3	5.9
Measured concentration gadolinium / mg/l	< 0.01	< 0.01	< 0.01	< 0.01
Water solubility based on gadolinium concentration / mg/l	< 0.02	< 0.02	< 0.02	< 0.02
Measured concentration zirconium / mg/l	< 0.02	< 0.02	< 0.02	< 0.02
Water solubility based on zirconium concentration / mg/l	< 0.07	< 0.07	< 0.07	<0.07

Conclusions:

Interpretation of results (migrated information): slightly soluble (0.1-100 mg/L)
The water solubility of the test item at 20 °C was determined to be 4.0 mg/l.

Executive summary:

In a study according to OECD Guideline 105 the water solubility of gadolinium zirconium oxide was determined (flask method).

The water solubility at a temperature of 20 °C of the test item gadolinium zirconium oxide showed an unusual behaviour: the calculated water solubility for gadolinium was deviating from the calculated water solubility for zirconium. This was most likely caused by a different chemical behaviour of the elements gadolinium and zirconium. It was assumed that zirconium formed insoluble compounds during the stirring time. As a conservative approach the highest measured water solubility was taken as final result. It was found to be: c_S= 4.0 mg/l

Description of key information

The water solubility of gadolinium zirconium oxide is 4.0 mg/L.

Key value for chemical safety assessment

Water solubility:

4 mg/L

at the temperature of:

20 °C

Additional information

In a study according to OECD Guideline 105 the water solubility of gadolinium zirconium oxide was determined (flask method).

The water solubility at a temperature of 20 °C of the test item gadolinium zirconium oxide showed an unusual behaviour: the calculated water solubility for gadolinium was deviating from the calculated water solubility for zirconium. This was most likely caused by a different chemical behaviour of the elements gadolinium and zirconium. It was assumed that zirconium formed insoluble compounds during the stirring time. As a conservative approach the highest measured water solubility was taken as final result. It was found to be: c_S= 4.0 mg/l