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Physical & Chemical properties

Water solubility

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Endpoint:
water solubility
Type of information:
experimental study
Adequacy of study:
key study
Study period:
from 17 May 2012 to 19 June 2012
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Reason / purpose:
reference to same study
Qualifier:
according to
Guideline:
OECD Guideline 105 (Water Solubility)
Qualifier:
according to
Guideline:
EU Method A.6 (Water Solubility)
GLP compliance:
yes (incl. certificate)
Type of method:
flask method
Key result
Water solubility:
> 59.3 - < 61.9 other: weight%
Conc. based on:
test mat.
Temp.:
20 °C
pH:
< 0
Remarks on result:
other: Result expressed as w/w% ((mass test item/(mass test item+mass water)) x100).
Key result
Water solubility:
> 919 - < 1 020 g/L
Conc. based on:
test mat.
Temp.:
20 °C
pH:
< 0
Remarks on result:
other: Result recalculated from w/w% to w/v in g/L
Details on results:
In the preliminary test the low ratio samples were observed to be amber solutions containing no undissolved test item, while the high ratio samples did contain undissolved test item. The water solubiliy was estimated to be in the range of 59.3 to 68.8% (w/w). Temperature was 20°C; pH was measured to be generally "less than 0". The pH was in all samples overruled and no significant effect of initial pH was observed. It was furthermore indicated that the test item might interact with the pH 7 "Tris" buffer.

In the definitive test all samples were observed to be clear dark orange solutions containing excess undissolved test item. Solution pH was all "less than 0".

The water solubiliy was estimated from both the preliminary and definitive test to be in the range of 59.3 to 61.9% (w/w) at 20°C.
Recalculating the w/w% to w/v, applying a density of water of 1 g/mL and of the test item of 2.49 g/mL, results in a water solubility in the range of 0.919 to 1.02 kg/L.

It was noticed that rare earth hydroxides could form at much lower loading rates, due to the more neutral to alkaline solution pH's, and that these hydroxides will have a much lower solubility in water. However, this process can be slow and will be variable for different metal cations. Adding an alkali would increase the pH and form more rare earth hydroxides, dropping the pH until all of the rare earth metal has been precipitated as the hydroxides. Following the above rationale, it was concluded that measuring the water solubility at increased pH is technically not feasible.

Conclusions:
The maximum solubility of cerium ammonium nitrate in water was estimated to be in the range of 59.3 to 61.9% (w/w) (equals 0.919 to 1.02 kg/L) at 20°C and a pH < 0. The buffering capacity of buffer solutions at pH 4, 7 and 9 was overruled and therefore the influence of pH on the solubility of the substance in water at the strength tested could not be evaluated.
Endpoint:
water solubility
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
GLP compliance:
no
Type of method:
other: dissolution study
Water solubility:
150 µg/L
Conc. based on:
test mat.
Remarks:
(NH4)2Ce(NO3)6
Loading of aqueous phase:
0.46 other: µM Ce
Incubation duration:
28 d
pH:
4
Water solubility:
>= 1 - < 5 µg/L
Conc. based on:
test mat.
Remarks:
(NH4)2Ce(NO3)6
Loading of aqueous phase:
0.46 other: µM Ce
Incubation duration:
28 d
pH:
>= 7 - <= 9
Details on results:
The solubility of Ce4+ appears to be higher at acidic pH which is anticipated to be at least partly explained by the low solubility of Ce hydroxides. Furthermore, an increase in solubility in time was observed which could be attributed to the reduction of Ce4+ to the more water soluble form Ce3+.
In the presence of NaCl, the concentration at pH 4 test conditions increased over time from approximately 10% of nominal to approximately 60% of nominal Ce concentration (no plateau value observed); at higher pH values initial concentrations were at or below the limit of detection (not further specified) and below the limit of detection at day 14 and 28.
In the presence of artificial soil, significantly higher solubilities are noted, at pH 4 from initially 10% of nominal to approximately 100% on day 28. At pH 7 the increase in time was up to 30% of nominal on day 28 while at pH 9 no significant amount of Ce was detected over time. The higher solubilities in the presence of artificial soil are related to the formation of ion pairs (Ce4+ with chloride and sulphate).

Temperature of measurement was not reported; ambient conditions are anticipated.

It is thus postulated that the solubility of Ce4+ is closely related to the pH and the solution matrix which determines the formation of ion pairs.

Based on available data it is estimated that the water solubility of (NH4)2Ce(NO3)6 in the presence of sodium chloride, is approximately 150 μg/L at pH 4. At pH 7 and 9 concentrations were mostly not detectable; although no limit of detection of the analytical method was provided, available data suggest that the water solubilty under these conditions could be in the range of 1-5 μg/L, or below.
Conclusions:
In a dissolution test over 28 days and in the presence of sodium chloride, the water solubility of (NH4)2Ce(NO3)6 is estimated to be approximately 150 μg/L at pH 4. At pH 7 and 9 concentrations were mostly not detectable; although no limit of detection of the analytical method was provided, available data suggest that the water solubilty under these conditions could be in the range of 1-5 μg/L, or below.

Description of key information

The water solubility of cerium ammonium nitrate was determined in a GLP study following the test design as specified in test method EC A.6 (Walker, 2012). The maximum water solubility was estimated to be in the range of 59.3 to 61.9% (w/w) (equals 0.919 to 1.02 kg/L) at 20°C and a pH < 0. Buffer solution capacity (pH 4, 7 and 9) was overruled and therefore the influence of pH on the solubility of the substance in water at the strength tested could not be evaluated.

Key value for chemical safety assessment

Water solubility:
1 020 g/L
at the temperature of:
20 °C

Additional information

The substance is miscible with water up to a 1:1 ratio, at a pH < 0. The bounded value of 100 g/L is used as the key value for chemical safety assessment, being the maximum value for water solubility as defined in the EUSES program.

Buffer solution capacity at pH 4, 7 and 9 was overruled. Resulting pH values were comparable to pH values of the non-buffered solution (< 0) and initial pH did not influence water solubility.

In a supporting dissolution study (Cornelis et al., 2011) performed over 28 days and in the presence of sodium chloride, the water solubility of (NH4)2Ce(NO3)6 is estimated to be approximately 150 μg/L at pH 4. At pH 7 and 9 concentrations were mostly not detectable; although no limit of detection of the analytical method was provided, available data suggest that the water solubility under these conditions could be in the range of 1-5 μg/L, or below.