Dimolybdenum trizinc nonaoxide

Water solubility

Link to relevant study record(s)

Reference

Endpoint:

transformation / dissolution of metals and inorganic metal compounds

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 Series on Testing and Assessment No. 29 (23-Jul-2001): Guidance document on transformation/dissolution of metals and metal compounds in aqueous media

Deviations:

yes

Remarks:

Minor deviations in relation to temperature, media carbon content and pH.

GLP compliance:

yes (incl. QA statement)

Type of method:

other: Transformation/dissolution test

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

>= 9.84 - <= 11.2 mg/L

Element analysed:

Zinc

Loading of aqueous phase:

100 mg/L

Incubation duration:

24 h

Test conditions:

The screening test was performed across the pH range 5.5 to 8.5 to ensure that the concentration of the dissolved metal ions in solution is maximized. This test served as a preliminary screening to assess the pH that maximizes the transformation/dissolution for the full test.

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

>= 12.6 - <= 16.9 mg/L

Element analysed:

Molybdenum

Loading of aqueous phase:

100 mg/L

Incubation duration:

24 h

Test conditions:

The screening test was performed across the pH range 5.5 to 8.5 to ensure that the concentration of the dissolved metal ions in solution is maximized. This test served as a preliminary screening to assess the pH that maximizes the transformation/dissolution for the full test.

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

0.14 mg/L

Element analysed:

Zinc

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

The vessels were stoppered and shaken at approximately 100 rpm for the specified times at 25 °C ± 2°C in the dark.

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

1.86 mg/L

Element analysed:

Zinc

Loading of aqueous phase:

10 mg/L

Incubation duration:

7 d

Test conditions:

The vessels were stoppered and shaken at approximately 100 rpm for the specified times at 25 °C ± 2°C in the dark.

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

13.4 mg/L

Element analysed:

Zinc

Loading of aqueous phase:

100 mg/L

Incubation duration:

7 d

Test conditions:

The vessels were stoppered and shaken at approximately 100 rpm for the specified times at 25 °C ± 2°C in the dark.

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

0.23 mg/L

Element analysed:

Zinc

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

The vessels were stoppered and shaken at approximately 100 rpm for the specified times at 25 °C ± 2°C in the dark.

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

0.36 mg/L

Element analysed:

Molybdenum

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

The vessels were stoppered and shaken at approximately 100 rpm for the specified times at 25 °C ± 2°C in the dark.

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

3.47 mg/L

Element analysed:

Molybdenum

Loading of aqueous phase:

10 mg/L

Incubation duration:

7 d

Test conditions:

The vessels were stoppered and shaken at approximately 100 rpm for the specified times at 25 °C ± 2°C in the dark.

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

31.1 mg/L

Element analysed:

Molybdenum

Loading of aqueous phase:

100 mg/L

Incubation duration:

7 d

Test conditions:

The vessels were stoppered and shaken at approximately 100 rpm for the specified times at 25 °C ± 2°C in the dark.

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

0.35 mg/L

Element analysed:

Molybdenum

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

The vessels were stoppered and shaken at approximately 100 rpm for the specified times at 25 °C ± 2°C in the dark.

Details on results:

Screening test:
It was observed that there was variance in the zinc and molybdenum concentrations in the test solutions. However it was not considered significant and there was no obvious trend. In addition the actual pH of the test solutions after addition of the test item were all approximately neutral and in the pH range of 6.3 to 7.2.
It was therefore considered appropriate to perform the main test using ISO 6341 aqueous media unadjusted (nominal pH 8).

Validation:
The calibration curves for the analyses were second order. The concentrations of each analyte in the sample solutions were interpolated from the respective calibration curve for each analysis.

Reproducibility data obtained for the zinc and molybdenum analyses were acceptable using the pH 6 aqueous media. This demonstrated that inter-vessel variation is <10% for both zinc and molybdenum, indicating that duplicate samples from triplicate vessels is sufficient to give a representative result for the main test.

Discussion:

The ISO 6341 aqueous media used in the main test was analyzed for total organic carbon. It was determined to be greater than the limit specified in the test guidelines (2.0 mg/L). However, it was not considered to interfere with the analysis of zinc or molybdenum and therefore was not considered to have a significant impact on the performance of the test. The dissolved oxygen level in all the test solutions was greater than 70% saturation (>6.0 mg/L) and thus satisfied the guidelines.

The specified test temperature was 25 ± 2 °C. In the screening test , a maximum temperature of 28.0 °C was observed and several flasks were greater than 27 °C. The flasks were shaken in an controlled environment set at a nominal 25 °C; those flasks at temperatures >27 °C were shaken on flat-bed shakers which may have increased the temperature over a period of time. However, sampling was performed at ambient laboratory temperature, allowing the test

solutions to equilibrate prior to filtration; therefore the small rise in test temperature was not considered to have had a significant effect. In main test, air shakers set at 25 °C were used and the temperature remained constant (± 1 °C) over the duration of the test.

The ISO 6341 aqueous media for the screening tests at pH 5.5, 6.0, 7.0 and 8.5 were prepared at lower concentrations than are specified in the guidelines. The results indicated that there was no significant effect of pH on concentration levels over the range tested. Since there was no observed pH effect, the main test was performed using ISO 6341 aqueous media (pH unadjusted) at a nominal pH 8.

The pH of the main test solutions (7 day and 28 day) were observed to decrease. The guidelines state that the pH should be stable to <0.2 pH unit although variations in pH may be expected at higher loading rates. Since the concentrations of dissolved zinc an molybdenum were not considered to be affected by pH, the decrease in pH over the test period was not deemed significant.

The rates of increasing concentration of zinc and molybdenum in the aqueous media were observed to decrease over the 7 day testing period. However, the kinetics of the transformation/dissolution could not be calculated accurately as the results indicated that the mechanism did not follow a simple relationship. The final mean concentration of zinc and molybdenum at the end of the specified testing period has been reported.

The transformation/dissolution of the test item in terms of solubility was demonstrated to be loading rate dependent.

Conclusions:

The transformation/dissolution of the test substance in terms of solubility was demonstrated to be loading rate dependant. The results for Zinc in the short-term test ranged from 0.14 to 13.4 mg/L and for Molybdenum 0.36 to 31.1 mg/L. In the long term test this was 0.23 and 0.35 mg/L, for Zinc and Molybdenum, respectively.

Description of key information

The transformation/dissolution of the test substance in terms of solubility was demonstrated to be loading rate dependant. The results for Zinc in the short-term test ranged from 0.14 to 13.4 mg/L and for Molybdenum 0.36 to 31.1 mg/L. In the long term test this was 0.23 and 0.35 mg/L, for Zinc and Molybdenum, respectively.

As the parameter of water solubility is less relevant for an inorganic substance and as various values were obtained under different conditions, no value is selected as the key value for chemical safety assessment.