Calcium molybdate

Water solubility

Link to relevant study record(s)

Reference

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)

Qualifier:

according to guideline

Guideline:

EU Method A.6 (Water Solubility)

Principles of method if other than guideline:

Two vessels were set up in a parallel design at 20 ± 1.0 °C, each solution was sampled repeatedly over time instead of setting up multiple vessels and sampling solutions from a different vessel at each sampling date. This modification helps to minimize weighing errors as larger amounts are being handled.

GLP compliance:

yes (incl. QA statement)

Remarks:

2011-02-07

Type of method:

flask method

Water solubility:

39.57 mg/L

Conc. based on:

test mat.

Loading of aqueous phase:

1 000 mg/L

Incubation duration:

>= 1 - <= 3 d

Temp.:

20.8 °C

pH:

>= 7.1 - <= 7.7

Water solubility:

18.43 mg/L

Conc. based on:

element

Remarks:

molybdenum

Loading of aqueous phase:

1 000 mg/L

Incubation duration:

>= 1 - <= 3 d

Temp.:

20.8 °C

pH:

>= 7.1 - <= 7.7

Details on results:

Observations
During the study, undissolved test material was observed in the test vessels. To verify the reliability of the filtration step and thus that only dissolved metal concentrations would get measured, turbidity was measured in a filtered sample directly after sampling.

Temperature
The temperature was monitored using a Testo Data Logger. The mean temperature was 20.8 ± 0.3 °C.
Solution pH
Solution pH in samples containing the test item were at 7.1 - 7.7 while the pH in method blanks ranged from 6.1 to 6.3.

Turbidity
The turbidity was measured after filtration to verify that only dissolved metal concentrations would get measured. The turbidity was always <<1 NTU, indicating that there was not any undissolved material after the filtration step.

Dissolved metal concentrations
Due to low limits of quantification and a potential cross-contamination by the electrodes for pH measurements, calcium levels in method blanks were above the limits of quantification (LOQ = 0.418 - 0.572 µg Ca/L) but well below concentrations in samples containing the test item (<< 1 %). Molybdenum concentrations in method blanks were below the respective limits of detection (LOD = 1.133– 1.379 µg Mo/L). Test samples containing the test item were diluted (dilution factor 100) so that the respective metal concentrations would be in the calibrated range of the ICP-OES instrument.

Method validation summary

validation parameter	results	comment
selectivity	similar data with at least two different molybdenum and calcium wavelengths for ICP-OES method	matrix effects were not observed
linearity	applied calibration functions were linear	correlation coefficient at least 0.999806
limits of detection (LOD)	1.133 – 1.379 µg Mo/L 0.139 – 0.191 µg Ca/L
limits of quantification (LOQ)	3.399 –4.137 µg Mo/L 0.418 - 0.572 µg Ca/L
concentrations in method blanks	Ca: above LOQ but far below concentrations in samples containing the test item (<< 1 %) Mo: < LODs (<3.399 –4.137 µg Mo/L)	-
accuracy and precision, repeatability	mean recovery for TMDA-53.3 reference material: Mo: (dilution factor 10, 25.5 µg Mo/L): 98.3 ± 5.3 % (n = 5)	for concentration range of diluted samples and for fortification and method blanks
accuracy and precision, repeatability	mean recovery for Quality Control Standard Mo: (50 µg Mo/L): 97.2 ± 1.6 % (n = 5)	for concentration range of diluted samples and for fortification and method blanks
accuracy and precision	mean recovery for Quality Control Standard Ca: (50 µg Ca/L): 108 ± <1 % (n = 2)	for concentration range of diluted samples and for fortification and method blanks
accuracy and precision, repeatability	mean recovery for recalibration Mo: (10 µg Mo/L): 101.3 ± 10.1 % (n = 4) Ca: (10 µg Mo/L): 104.2 ± 6.2 % (n = 5)	for concentration range of diluted samples and for fortification and method blanks
trueness	recovery from fortification of samples: Mo: 98.1 - 102.4 % (n = 6) Ca: 98.2 - 102.9 % (n = 6)

Results

The mean dissolved molybdenum concentrations of solutions sampled on day 1, day 2 and day 3 were calculated. Mean dissolved Mo concentrations day 1 – day 3:

Vessel 1: 18.16 ± 0.42 mg/L

Vessel 2: 18.70 ± 0.45 mg/L

Mean for both vessels: 18.43 ± 0.5 mg/L

The amount of dissolved calcium molybdate was calculated based on the molybdenum content of the test substance as follows:

= mean of measured Mo concentration * 100 % / 46.58 % [Mo content of test item, as per certificate of analysis provided by the sample producer]

mean calculated water solubility of calcium molybdate (based on dissolved Mo) , day 1 – day 3:

Vessel 1: 38.99 ± 0.90 mg/L

Vessel 2: 40.16 ± 0.96 mg/L

Mean for both vessels: 39.57 ± 1.08 mg/L

Dissolved measured Ca concentrations were lower than expected and correspondingly the calculated solubility of the test item was approx. 27% lower when based on analysed dissolved Ca than when based on analysed dissolved Mo (waters solubility = 39.57 mg/L based on Mo, compared 28.77 mg/L based on Ca). It is assumed that this is due to the formation of poorly soluble, possibly colloidal calcium species (such as calcium carbonate), that have not passed the filter before analysis. Using the analysed dissolved Mo to calculate the solubility of the test item calcium molybdate provides the higher final solubility figure. Since this is also the more conservative figure in a regulatory context, it is taken forward as the final result.

Final results

Under the conditions of this test flask method; loadings of 1000.2 mg/L in vessel 1 and 2, respectively), a solubility equilibrium was reached during the first three days of testing. The mean measured amount of dissolved Mo on day 1, day 2 and day 3 at 20.0 ± 1.0°C is 18.43 ± 0.50 mg/L (determined as dissolved Mo, separated by filtration from undissolved test item). This corresponds to a water solubility of calcium molybdate of 39.57 ± 1.08 mg/L, calculated based on a molybdenum content of 46.58 %. Solution pH in samples containing the test item were at 7.1 - 7.7 while the pH in method blanks ranged from 6.1 to 6.3.

Conclusions:

Interpretation of results: slightly soluble (0.1-100 mg/L)
The water solubility of calcium molybdate is 39.57 mg/L at 20.8 °C (pH 7.1 - 7.7 in the saturated solution)

Description of key information

The water solubility of calcium molybdate has been determined experimentally (OECD TG 105 study, GLP)  to be 39.6 mg/L at 20 °C.  The pH of the saturated solution was 7.1 - 7.7.

In addition to the standard OECD TG 105 water solubility study, the substance has also been tested in a bioelution study (in vitro bioaccessibility) in artificial gastric juice. This test and the results are described in the stand-alone document „MoCon read-across concept (human health)“, which is attached to the technical dossier in IUCLID section 13.

 

Key value for chemical safety assessment

Water solubility:

39.6 mg/L

at the temperature of:

20 °C