Aluminium tris(dihydrogen phosphate)

Water solubility

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Study period:

January 2015 - March 2015

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP - 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:

yes (incl. QA statement)

Remarks:

Ministerium für Arbeit, Integration und Soziales des Landes Nordrhein-Westfalen

Type of method:

flask method

Water solubility:

16.293 µg/L

Temp.:

21.6 °C

pH:

8

Remarks on result:

other: Dissolved aluminium concentrations at loading of 100 mg/L of test item after 24 h (1d)

Water solubility:

5 535.5 µg/L

Temp.:

21.6

pH:

6

Remarks on result:

other: Dissolved aluminium concentrations at loading of 100 mg/L of test item after 24 h (1d)

Method validation summary (ICP-OES)

validation parameter	results	Comment
selectivity	selective wavelength of 167.019 nm for detection and evaluation of Al	no interferences observed
linearity	applied calibration functions were linear	correlation factor at least 0.999899
limit of detection	0.114 – 0.515 μg Al/L
limit of quantification	0.344 – 1.54 μg Al/L
accuracy and precision, reproducibility	mean recovery for diluted CRM TMDA-53.3 (121 μg Al/L): 103 ± 3 % (n = 4)	for concentration range
accuracy and precision, reproducibility	mean recovery for diluted CRM TMDA-53.3 (181.5 μg Al/L): 105 ± 4 % (n = 7)	for concentration range
accuracy and precision, reproducibility	mean recovery for diluted CRM TM-15.2 (22.6 μg Al/L): 105 ± <1 % (n = 5)	for concentration range
accuracy and precision, reproducibility	mean recovery for multi element standard IV (500 μg Al/L): 102 ± 1 % (n = 5)	for low concentration range
accuracy and precision, reproducibility	mean recovery for multi element standard IV (250 μg Al/L): 100 ± 2 % (n = 5)	for low concentration range
trueness	mean recovery for multi element standard IV (100 μg Al/L): 100 ± 3 % (n = 4)	for concentration range

 

Test

The results of ICP-OES measurements of Al concentrations of solutions and the blank methods are presented in the following tables (100 mg/L loading).

Data for within- and between-vessel variation and difference of mean Al concentrations between sampling intervals are reported in Table 8 – Table 9. The vessel variations were obtained by calculation of the variation coefficient, i.e. standard deviation is divided by the mean measured Al concentration and multiplied by 100.

  

 

sample name and day	target pH	Al conc. [µg/L]	mean Al conc. Per vessel [µg/L]	SD Al conc. per vessel [µg/L]	within vessel variation [%]	mean Al conc. All samples [µg/L]	SD Al conc. All samples [µg/L]	between vessel variation [µg/L]
1 a d 1	8	9.4980
1 b d 1	8	8.40072	8.9526	0.7713	8.6
2a d1	8	17.899
2b d1	8	18.529	18.214	0.445	2.4
3a d1	8	17.510
3b d1	8	25.916	21.713	5.944	27.4	7.420	16.293	38.2
4a d1	6	5732.9
4b d1	6	5687.9	5710.4	31.8	0.6
5a d1	6	5559.8
5b d1	6	5543.6	5551.7	11.4	0.2
6a d1	6	5351.8
6b d1	6	5336.9	5344.3	10.6	0.2	46.40	5535.5	3.0

 

The observed variations within and between test vessels for the aluminium concentrations with a loading of 100 mg test item/L at pH 6 and 8 are mostly in compliance with the test guideline after one day of testing, except within-vessel variation at pH 8 for vessel 3 (27.4 %) and between-vessel variation at pH 8 (38.2 %).

A reason for the observed increased between-vessel variation might be a wide particle size distribution of the test item. Therefore, the particle size distribution of each loading replicate may differ resulting in differing overall surface areas. Furthermore, as the surface area affects transformation and dissolution of sparingly soluble metals, increased between-vessel variations may be observed in tests of materials with wider particle size distributions. According to the guidance document “[…]it is [only] reasonable to anticipate that for a constant loading of a substance, tested in a narrow particle size (e.g., 37 - 44 μm) and total surface area range, the within-vessel variation in transformation data should be less than 10 % and the between-vessel variation should be less than 20 %.” It can be assumed that the test item has wider particle size distribution. Therefore, the percentage is not within the limits of 20 %. At the pH of 8 only 16.29 ± 6.22 μg Al/L were quantified and therefore the above described particle size has a much more increased effect on the between-vessel variation than at pH 6 (5536 ± 164 μg Al/L).

Conclusions:

Interpretation of results (migrated information): slightly soluble (0.1-100 mg/L)

Reference 2

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

06 October - 23 November 2009.

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

The study has reliabilty 2 due to guideline deviations and insufficient quality. The test substance demonstrated strongly acidic characteristics on dissolution (the pH-value decreases with increasing loadings). The solubility of the test item at a neutral pH-value (pH 7) was not determined.

Qualifier:

according to guideline

Guideline:

EU Method A.6 (Water Solubility)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

UK GLP standards (Schedule 1, Good Laboratory Practice Regulations 1999 (SI 1999/3106 as amended by SI 2004/0994)). These Regulations are in accordance with GLP standards published as OECD Principles on Good Laboratory Practice.

Type of method:

flask method

Water solubility:

> 294 g/L

Temp.:

20 °C

pH:

2.1

Remarks on result:

other: However the solubility of the test material was demonstrated to be extremely sensitive to the initial nominal loading concentration of the solution as demonstrated by the results in the attachment - summary

Details on results:

Please see section Remarks on results including tables and figures.

Results

Preliminary test

Un-buffered glass double-distilled water preliminary test 1

The preliminary estimate of water solubility, as equivalent test material concentration, was 14.3 g/l, with a final sample solution pH of 2.3.

pH 4 buffer solution

The preliminary estimate of water solubility, as equivalent test material concentration, was 67.1 g/l, with a final sample solution pH of 2.1.

pH 9 buffer solution

The preliminary estimate of water solubility, as equivalent test material concentration, was 65.1 g/l, with a final sample solution pH of 2.0. 

Un-buffered glass double-distilled water preliminary test 2

The preliminary estimate of water solubility, as equivalent test material concentration, was 63.0 g/l, with a final sample solution pH of 2.1.

Un-buffered glass double-distilled water preliminary test 3

The preliminary estimate of water solubility, as equivalent test material concentration, was 127 g/l, with a final sample solution pH of 2.0.

Definitive test

The mean phosphate peak areas relating to the standard and sample solutions are shown in the following table:

Solution	Area
Standard 50.1 mg/l	3.536
Standard 50.2 mg/l	3.825
Matrix blank	none detected
Sample 1A	1.494
Sample 1B	1.499
Sample 2A	1.883
Sample 2B	1.873
Sample 3A	1.597
Sample 3B	5.000
Standard 50.1 mg/l	3.638
Standard 50.2 mg/l	3.857
Sample 4A	5.152
Sample 4B	5.468
Sample 5A	2.678
Sample 5B	3.883
Sample 6A	3.316
Sample 6B	3.165

 

The equivalent concentration (g/l) of test material in the sample solutions is shown in the following tables:

Un-buffered glass double-distilled water

Sample  Number	Time Shaken at ~ 30ºC (hours)	Equilibration Time at 20°C (hours)	Equivalent Test Material Concentration (g/l)	Solution pH
1	24	24	6.92	2.5
2	24	24	17.4	2.4
3	24	24	46.3[1]	2.3
4	24	24	96.5	2.2
5	24	24	176*	2.1
6	24	24	294	2.1

[*]Calculated using duplicate dilution B only, see discussion.

The relationship between nominal loading concentration (g/l) and the resulting analysed equivalent test material concentration (g/l) is shown in attachment "nominal loading concentration".

It should be noted that as the nominal 50 g/l and 200 g/l loading concentration results have been taken from only single and not duplicate dilution values, these points have been excluded from calculation of the second order line fitted to the plot. However in each case, the remaining value plots with a very strong correlation to the relationship determined.

Overall result: the water solubility of the test material has been determined to be at least 294 g/l, although observed solubility was extremely sensitive to loading rate.

Validation

The linearity of the detector response with respect to concentration was assessed over the nominal concentration range of 0 to 100 mg/l as the phosphate anion. This was satisfactory with a correlation coefficient of 1.000 being obtained. The linearity was performed under Harlan Laboratories Ltd project number 2920/0020.

Conclusions:

Interpretation of results (migrated information): very soluble (> 10000 mg/L)
The ion chromatography method applied directly quantified the dissolved phosphate content of each sample solution and these have been corrected to equivalent test material concentrations based on the theoretical phosphate content of the test material. The water solubility of the test material has been determined to be at least 294 g/l of solution at 20.0 ± 0.5°C in un-buffered glass double-distilled water. However the solubility of the test material was demonstrated to be extremely sensitive to the initial nominal loading concentration of the solution as demonstrated by the results in the following table:

Nominal Loading Equivalent Test Material Solution pH
Concentration (g/l) Concentration (g/L)
10 6.92 2.5
25 17.4 2.4
50 46.3 2.3
100 96.5 2.2
200 176 2.1
400 294 2.1

A possible reason for this relationship was the influence of the final solution pH’s which bracket a known dissociation constant for the parent phosphoric acid (pKa = 2.16). Thus solubility characteristics of the test material may change as there would be a significant shift in the degree of ionisation of the phosphate ion over this narrow pH range.
Investigation into the influence of the pH range 4 to 9 on the solubility of the test material was performed but in each case the test material demonstrated strongly acidic characteristics on dissolution, overwhelming the capacity of the buffer solutions to give solution pH’s approximately equal to those observed in un-buffered water. Therefore, as the buffering capacity of the solutions used were considered to exceed that of the environment, the solubility of the test material was considered to be independent of the initial pH range 4 to 9, resulting in a consistent highly acidic solution capable of overwhelming any weak to moderate buffering capacities present.
Finally, as the influence of loading concentration on the observed solubility was anticipated to greatly exceed any influence of temperature, and as the definitive test experimental design needed amending to accommodate this, no further testing was performed to investigate the influence of temperature; especially in the absence of a definitive saturation concentration at 20°C with which to compare the results with.

Description of key information

Dissolved aluminium concentrations at 20°C (EU Method A.6, GLP):
294 g/L at pH 2, 20°C 
Dissolved aluminium concentrations at 21.6 °C  after 24 h with a loading of 100 mg/L test item (OECD 29):
16.293 µg Al/L at pH 8 
5535.5 µg Al/L at pH 6

Key value for chemical safety assessment

Water solubility:

294 g/L

at the temperature of:

20 °C

Additional information

The water solubility of aluminium tris(dihydrogen phosphate) was determined using the flask method in a study conducted according to EU Method A.6 under GLP conditions (O’Connor and Woolley, 2010). The water solubility of the test material has been determined to be at least 294 g/l at 20.0 ± 0.5°C in un-buffered glass double-distilled water (final pH solution 2). However the solubility of the test material was demonstrated to be extremely sensitive to the initial nominal loading concentration of the solution and the media pH. The test substance reacts strongly acidic with water (the pH-value decreases with increasing loadings) and the solubility of the test item at a neutral pH-value was not determined.

Therefore, a solubility test of the test item in media simulating environmental conditions (OECD 29) was also performed (Klawonn 2015). Under these conditions and an loading of 100 mg/L test item, aluminium tris(dihydrogen phosphate) shows a solubility of 6.293 µg Al/L at pH 8 and a solubility of 5535.5 μg Al/L at pH 6 after 24 h (1 d).