Magnesium zirconium oxide

Water solubility

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

April 2015

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study without detailed documentation

Qualifier:

according to guideline

Guideline:

other: DIN 38414-4, German standard methods for the examination of water, waste water and sludge; sludge and sediments (group S); determination of leachability by water (S4)

Deviations:

no

GLP compliance:

not specified

Type of method:

other: DIN 38414-4, leachability by water

Water solubility:

2.7 mg/L

Temp.:

20 °C

Remarks on result:

other: dissolved Mg for the 3.25% w/w MgO sample

Water solubility:

9.2 mg/L

Temp.:

20 °C

Remarks on result:

other: dissolved Mg for the 4.53% w/w MgO sample

Table 1: Results of the ICP-AES measurement of magnesium directly on the eluate

	Concentration of Mg analysed (mg/L)
3.25% MgSZ	2.7
4.53% MgSZ	9.2

Conclusions:

The leachability of Mg after suspending two different samples of magnesium zirconium oxide (3.25% MgO w/w and 4.53% MgO w/w, both with particle size -325 mesh) was determined to be 2.7 mg/L and 9.2 mg/L, respectively, at 20°C (i.e. 0.0027 and 0.0092% w/w, respectively, when related to the total amount of test sample.

Reference 2

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

July 2014

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study without detailed documentation

Qualifier:

according to guideline

Guideline:

other: DIN 38414-4, German standard methods for the examination of water, waste water and sludge; sludge and sediments (group S); determination of leachability by water (S4)

GLP compliance:

not specified

Type of method:

other: DIN 38414-4, leachability by water

Water solubility:

3 mg/L

Temp.:

20 °C

Remarks on result:

other: dissolved Mg (sample with 3.25% w/w MgO, -325 mesh)

Water solubility:

5 mg/L

Temp.:

20 °C

Remarks on result:

other: dissolved Mg (sample with 3.25% w/w MgO, D50=5-6 µm)

Table 1: Results of the ICP-AES measurement of magnesium directly on the eluate

	Particle size / sieve fraction	Concentration of Mg analysed (mg/L)
3.25% MgSZ	-325 mesh	3
3.25% MgSZ	D50 = 5-6 µm	5

Concentration of dissolved Zr was not analysed.

Conclusions:

The leachability of Mg after dissolving two different samples of magnesium zirconium oxide (3.25% w/w MgO, one sample -325 mesh, and another with D50 = 5-6 µm) was determined to be 3 mg Mg/L and 5 mg Mg/L, respectively (i.e. 0.003% and 0.005% w/w, respectively, when related to the total amount of test sample), at 20°C.

Reference 3

Endpoint:

water solubility

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Justification for type of information:

Read across based on the available handbook data for ZrO2. The read across justification document is attached in IUCLID Section 13.

Reason / purpose for cross-reference:

read-across source

Remarks on result:

other: Based on data for the water solubility of ZrO2, it can be concluded that Mg will dissolve to a relatively higher extent than Zr from the substance. Magnesium zirconium oxide should be considered as slightly soluble (0.1-100 mg/L) in pure water

Reference 4

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

2008-02-25 to 2009-11-20

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method A.6 (Water Solubility)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

certificate provided by Rheinlandpfalz

Type of method:

column elution method

Water solubility:

< 55 µg/L

Temp.:

20 °C

pH:

6.5

Details on results:

Limit of detection was calculated from the calibrated range to be 40.8 µg/L Zr, corresponding to 55 µg/L ZrO2. As none of the samples showed a signal at the voltage of the Zr-Alizarin-peak, concentration in the samples and therefore water solubility was considered to lie below LOD.
No observations arousing doubts concerning the accuracy of the results and the validity of the study were made.

Conclusions:

The water solubility of the test item was found to be < 55 µg/L at a temperature of 20 +/- 0.5 degrees C and a pH of 6.5.

Description of key information

Two studies on the leachability of Mg from magnesium zirconium oxide (Eidam, 2015, 2016) are included in a weight of evidence approach, together with a guideline study for pure zirconium dioxide (Paulus, 2010). Based on the results of these studies, it can be concluded that, when in contact with aqueous media, Mg will dissolve to a relatively higher extent than Zr from the substance. Based on the results for the 4.53% w/w MgO sample (i.e., 9.2 mg Mg/L), the water solubility of the test substance was back-calculated to be 42.65 mg/L. Although a worst case value (because it is based on dissolved Mg in the eluate, without taking account of the much lower expected leachability of Zr in the eluate), magnesium zirconium oxide should be considered as slightly soluble (0.1-100 mg/L) in pure water.

Additional information

As is known from a water solubility study performed according to OECD Guideline 105 and conform GLP, zirconium dioxide is extremely insoluble in water (< 55 µg/L at 20°C and a pH of 6.5; Paulus, 2010). Because magnesium oxide is more water soluble than zirconium dioxide, it was assumed that magnesium would be able to dissolve relatively more than zirconium when magnesium zirconium oxide is in contact with aqueous media. The two leachability tests from Eidam (2015, 2016), performed according to the DIN 38414-4 guideline and an internal company testing procedure, therefore analysed dissolved magnesium only.

In the first study (Eidam, 2015), concentrations of 2.7 and 9.2 mg Mg/L were measured in the eluate for the 3.25 and 4.53% w/w MgO sample, respectively. Both samples had the same particle size (-325 mesh). This represents 0.0027 and 0.0092% of the total amount of test substance added, which is very limited.

In the second study (Eidam, 2016), two samples with 3.25% w/w MgO and a different particle size (one -325 mesh sample and the other with a D50 of 5-6 µm) were tested. The dissolved Mg concentrations in the eluate were measured to be 3 and 5 mg/L, respectively, representing 0.003 and 0.005% of the total amount of test substance, respectively.

Assuming that Mg leaches relatively more from the test substance compared to Zr, and taking the value of 9.2 mg Mg/L (i.e. Mg released from a 4.53% w/w MgO sample) as a worst case value, the water solubility of magnesium zirconium oxide can be calculated as follows. The molecular weight of a 4.53% w/w MgO sample (mole fraction of MgO is 0.1267) is theoretically 112.71 g/mol ((0.1267 x 40.3 g/mol) + (0.8733 x 123.22 g/mol)). Mg represents 21.57% (40.3 g/mol / 112.71 g/mol) of the test item. Therefore, the value of 9.2 mg Mg/L can be recalculated to a water solubility value of 42.65 mg/L. This is clearly a worst case value, based on the extent to which Mg is dissolved, without taking account of the Zr, which most likely leaches much less from the substance. Based on this worst case value, the substance should be considered as slightly soluble (0.1-100 mg/L).