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Water solubility

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Reference
Endpoint:
transformation / dissolution of metals and inorganic metal compounds
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2013-09-25 to 2014-06-16
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:
no
GLP compliance:
no
Type of method:
flask method
Specific details on test material used for the study:
Substance name: Zirconium carbide
CAS-Number: 12070-14-3
Molecular formula: ZrC
Molecular weight: 103.24 g/mol
Appearance: dark-grey powder
Batch Number: 25051/13
Purity: 97. 3 % Zr + Hf 99.8 %
Hf 2.0 %
C total 11.4 %
C bound 11.2 %
C free 0.2 %
Expiry date: not applicable
Storage: Keep substance dry in tightly sealed container.
Type of test:
screening transformation/dissolution test - sparingly soluble metal compounds
Mean dissolved conc.:
0.272 µg/L
Element analysed:
Zirconium
Loading of aqueous phase:
100 mg/L
Incubation duration:
24 h
Test conditions:
pH 8
Type of test:
screening transformation/dissolution test - sparingly soluble metal compounds
Mean dissolved conc.:
0.008 µg/L
Element analysed:
Zirconium
Loading of aqueous phase:
100 mg/L
Incubation duration:
24 h
Test conditions:
pH 6
Type of test:
full transformation/dissolution test - metals and sparingly soluble metal compounds
Mean dissolved conc.:
0.232 µg/L
Element analysed:
Zirconium
Loading of aqueous phase:
1 mg/L
Incubation duration:
28 d
Test conditions:
pH 8
Type of test:
full transformation/dissolution test - metals and sparingly soluble metal compounds
Mean dissolved conc.:
0.289 µg/L
Element analysed:
Zirconium
Loading of aqueous phase:
1 mg/L
Incubation duration:
7 d
Test conditions:
pH 8
Type of test:
full transformation/dissolution test - metals and sparingly soluble metal compounds
Mean dissolved conc.:
0.368 µg/L
Element analysed:
Zirconium
Loading of aqueous phase:
10 mg/L
Incubation duration:
7 d
Test conditions:
pH 8
Type of test:
full transformation/dissolution test - metals and sparingly soluble metal compounds
Mean dissolved conc.:
0.368 µg/L
Element analysed:
Zirconium
Loading of aqueous phase:
100 mg/L
Incubation duration:
7 d
Test conditions:
pH 8

The screening test started on September 25, 2013 and the full test on January 13, 2014. The test was performed in triplicate. All flasks were agitated on laboratory shakers (Gerhardt, Laboshake RO 500, Königswinter, Germany and Sartorius Certomat SII, Sartorius AG, Goettingen, Germany) at 100 rpm at 21.5 ± 1.5°C with samplings after 2h, 6h, 24h, 96h (4 d) and 168h (7 d) for loadings of 1 mg/L, 10 mg/L and 100 mg/L. Test vessels with the loading of 1 mg/L were additionally sampled after 336h (14 d), 504h (21 d) and 672h (28 d). Only one sampling point after 24 h is required for the screening test (loading 100 mg/L). Samples (2 x 20 mL for determination of dissolved zirconium by ICP-MS) were collected from each test vessel at every sampling point. According to the guidance document the withdrawn solution was replenished with respective media (120 mL after 24 h and then 40 mL after each additional sampling, except after last samplings).

Screening test:

 sample  target pH

 mean per vessel

Zr conc. µg/l

SD per vessel

Zr. conc. µg/l

 mean all Zr. conc. µg/l  SD all Zr conc. µg/l
 1 24 h  8

 0.305

 0.007        0.272        0.051
 2 24 h  8  0.305  0.002
 3 24 h  8  0.206  0.001
           
 4 24 h  6  0.015  0.002        0.008        0.005
 5 24 h  6  0.008  0.001
 6 24 h  6  0.003  <0.001

The OECD guidance document 29 requests the performance of the test at a pH which maximizes the dissolution. Therefore, prior to the full test a screening over 24 h (agitation at 100 rpm, 21.5 ± 1.5 °C, loadings of 100 mg/L) was conducted in test media at pH 6 and pH 8 in triplicate vessels and duplicate samples per vessel.

After 24 h the dissolved zirconium concentrations were quantified by ICP-MS:

Mean concentrations pH 8:

Zr (after 24h): 0.272 ± 0.051 μg Zr/L

Mean concentrations pH 6:

Zr (after 24h): 0.008 ± 0.005 μg Zr/L

Based on these results the full test was performed in test media at a target pH of 8.

Conclusions:
The results showed that zirconium carbide can be considered as insoluble (< 0.1 mg/L) in aquoeus solution in this study according to OECD 29.
Executive summary:

A transformation/dissolution (T/D) test, according to OECD 29, was carried out to study the potential of zirconium carbide to release metal to the environment.

A 24 hour screening test to determine the pH of maximum zirconium release was performed at pH 6 and 8 with a loading rate of 100 mg/l. The pH screening test showed zirconium releases of 0.272 ± 0.051 µg Zr/L at pH 8, while the mean release of Nb at pH 6 was 0.008 ± 0.005 μg Zr/L.

The full T/D test was conducted at pH 8. The acute endpoint (7 days), was performed at sample loadings of 1, 10 and 100 mg/L; the chronic endpoint was determined from the extension of the 1 mg/L loading test to 28 days. The results of the study documented zirconium release measurements as follows:

- 1 mg/l loading after 7 days: 0.289 ± 0.010 µg Zr/L,

- 1 mg/l loading after 28 days: 0.232 ± 0.002 μg Zr/L

- 10 mg/L loading after 7 days: 0.368 ± 0.037 μg Zr/L

- 100 mg/L loading after 7 days: 0.368 ± 0.052 μg Zr/L

Therefore, zirconium carbide is considered to be highly insoluble in water.

Description of key information

The results showed that zirconium carbide can be considered as insoluble (< 0.1 mg/L) in aqueous solution in this study according to OECD 29.

Key value for chemical safety assessment

Water solubility:
0.368 µg/L
at the temperature of:
22 °C

Additional information

A transformation/dissolution (T/D) test, according to OECD 29, was carried out to study the potential of zirconium carbide to release metal to the environment.

A 24 hour screening test to determine the pH of maximum zirconium release was performed at pH 6 and 8 with a loading rate of 100 mg/l. The pH screening test showed zirconium releases of 0.272 ± 0.051 µg Zr/L at pH 8, while the mean release of Nb at pH 6 was 0.008 ± 0.005 μg Zr/L.

The full T/D test was conducted at pH 8. The acute endpoint (7 days), was performed at sample loadings of 1, 10 and 100 mg/L; the chronic endpoint was determined from the extension of the 1 mg/L loading test to 28 days. The results of the study documented zirconium release measurements as follows:

- 1 mg/l loading after 7 days: 0.289 ± 0.010 µg Zr/L,

- 1 mg/l loading after 28 days:0.232 ± 0.002 μg Zr/L

- 10 mg/L loading after 7 days:0.368 ± 0.037 μg Zr/L

- 100 mg/L loading after 7 days:0.368 ± 0.052 μg Zr/L

Therefore, zirconium carbide is considered to be highly insoluble in water.

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