Iron orthophosphate

Water solubility

Link to relevant study record(s)

Reference

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

30 September 2009 to 31 October 2009

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method A.6 (Water Solubility)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of method:

flask method

Water solubility:

0.083 g/L

Temp.:

20 °C

pH:

>= 3.3 - <= 3.4

Details on results:

Please see section Remarks on results including tables and figures.

Results

Preliminary test

The preliminary estimate of water solubility was 6.44 x 10^-2g/L.

Definitive test

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

Table 5.

Solution	Mean peak area*
Standard 30.0 mg/L	2.785
Standard 30.6 mg/L	3.175
Sample 7A	2.671
Standard 30.0 mg/L	3.252
Standard 30.6 mg/L	3.510
Sample 7B	2.762
Sample 6A	2.908
Sample 6B	2.889
Standard 30.0 mg/L	3.720
Standard 30.6 mg/L	3.846
Sample 1A	3.256
Sample 1B	3.267
Standard 30.0 mg/L	3.746
Standard 30.6 mg/L	3.872
Sample 3A	3.009
Sample 3B	2.978
Sample 2A	3.093
Sample 2B	3.079
Standard 30.0 mg/L	3.777
Standard 30.6 mg/L	3.904
Sample 4A	7.479
Sample 4B	7.472
Sample 5A	3.291
Sample 5B	3.288

* corrected for the relevant blank

The concentration (g/L) of test material in the sample solutions is shown in the following table:

Table 6.

Sample Number	Time shaken at ~ 30ºC (hours)	Time equilibrated at 20ºC (hours)	Concentration (g/L)	Solution pH
1	72	24	8.29 x 10^-2	3.3
6	48	24	8.25 x 10^-2	3.4
7	24	24	8.24 x 10^-2	3.3
2	72	24 (30°C)	7.79 x 10^-2	3.3
3	72	24 (10°C)	7.56 x 10^-2	3.3
4	72	24	≤0.187*	3.8
5	72	24	≤8.24 x 10^-2*	6.6

* Please see section titled Definitive Test in the other Materials and Methods section.

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 orthophosphate anion). This was satisfactory with a correlation coefficient of 1.000 being obtained. This work was performed as part of Harlan Laboratories Ltd Project Number 2920/0020.

Conclusions:

The water solubility of the test material has been determined to be 0.0826 g/L at 20.0±0.5°C, resulting in a sample pH of 3.3 - 3.4.

Description of key information

Water solubility:  21.10 ± 0.587 μg test item/L (OECD 105, GLP). 

Key value for chemical safety assessment

Water solubility:

21.1 µg/L

at the temperature of:

20 °C

Additional information

Key study, Klawonn T (2015)

The water solubility of iron orthophosphate was deterimed according to OECD 105 (flask method), EU method A.6 and GLP.

Iron analysis was carried out via ICP-OES. The samples were measured in duplicate. A preliminary test (non-GLP) resulted in a water solubility of 8.937 ± 0.086 μg Fe/L at room temperature after 24 h of stirring. This corresponds to a calculated solubility of 24.83 ± 0.240 μg test item/L. In the main tests, 250 mg of the test substance were added into 500 mL of ultrapure water (250.4 mg/500 mL and 250.1 mg/500 mL were weighed into vessel 1 and 2, respectively). This applied loading (500.8 mg test substance/L and 500.2 mg test substance/L) corresponded to at least five times the quantity of the solved test item as requested in the guideline and observed in the preliminary test. To enable the possibility to observe insoluble material within the test vessel this high excess was applied. An insoluble powder (probably the test item) was observed in the water in test vessels throughout the test.Constant iron concentrations could be measured during the testing (days 1 – 3). The mean concentration was calculated.

Mean dissolved iron concentration day 1 – day 3:

Vessel 1: 7.705 ± 0.284 μg Fe/L

Vessel 2: 7.484 ± 0.321μg Fe/L

The calculated amount of iron(III) orthophosphate dissolved was calculated by: = mean of measured values * 100 % / 36 %

Mean calculated iron(III) orthophosphate dissolved day 1 – day 3:

Vessel 1: 21.40 ± 0.789 μg/L

Vessel 2: 20.79 ± 0.891 μg/L

Under the conditions of this test (flask method; loadings of 500.8 mg test item/L and 500.2 mg test item/L in vessel 1 and 2, respectively), a solubility equilibrium was observed during the testing (days 1 – 3). The mean amount of dissolved iron, during the test at 20.0 ± 1.0°C is 7.595 ± 0.211 μg Fe/L (determined as dissolved iron, separated by centrifugation followed by filtration from undissolved test item). This corresponds to calculated dissolved iron(III) orthophosphate of 21.10 ± 0.587 μg test item/L. The pH in test item loaded vessels was in the range of 4.1 – 4.3, whereas the pH in method blanks

ranged from 5.6 – 5.8.

Key study, Klawoon T (2016)

The study to determine the transformation/dissolution of the test items iron(lll)orthophosphate anhydrous (CAS 10045-86-0) and iron (III) orthophosphate dihydrate (CAS 14567-75-0) was conducted according to the OECD guidance document 29 (2001) and GLP.

The OECD guidance document 29 requests the performance of the test to maximize the dissolution. Therefore, it was decided to perform the test with both test items at pH 6 and 8 to cover acidic as well as basic conditions in environment. As requested the test was conducted with a loading of 100 mg/L of both test items over 24 hours and one sampling after one day.

The maximum amount of iron in the screening test was quantified at pH 6 applying iron(lll)orthophosphate (CAS 10045-86-0 [anhydrous]).

Therefore, the full test had been subsequently conducted with iron(lll)orthophosphate (CAS 10045-86-0) at pH 6.

Solution pH, oxygen concentrations and total dissolved iron concentrations were measured at each sampling time.

lron(lll)orthophosphate (CAS 10045-86-0 [anhydrous]) at pH 6 exhibited the highest dissolved Fe concentration in the screening after 24 h with 11.229 ± 4.544 µg Fe/L.

The mean dissolved amount of Fe after 168 h of testing at pH 6 with a loading of 100 mg/L was 21.062 ± 9.214 µg Fe/L. This corresponds to a calculated solubility of 58.506 ± 25.594 µg test item/L

The mean dissolved amount of Fe after 168 h of testing at pH 6 with a loading of 10 mg/L was 0.884 ± 0.242 µg Fe/L. This corresponds to a calculated solubility of 2.456 ± 0.672 µg test item/L.

At the loadings of 10 and 100 mg test item/L the dissolved Fe concentrations decreases over time. This is probably due to formation of hydroxides and subsequent precipitation.

Supporting study, Walker J (2009)

The water solubility of the test material has been determined according to EU method A.6 and GLP . The results are shown in the following table:

Test temperature	Water solubility (g/l)	Typical solution pH
30.0±0.5°C	7.79 x 10^-2	3.3
20.0±0.5°C	8.26 x 10^-2	3.3 - 3.4
10.0±0.5°C	7.56 x 10^-2	3.3

Overall, the effect of temperature over the range 10 to 30°C has been considered not to have had a significant influence on the solubility of the test material.

An assessment of the solubility of the test material over the environmentally relevant pH range of 4 to 9 was carried out; however, the resulting samples could not be cleaned-up fully in order to remove all of the excess undissolved test material. Consequently, the analysed solubilities for these samples may have somewhat over-estimated the actual solubilities. However, the increase in colour between the unbuffered water samples and the buffered sample (at a solution pH of 3.8) suggests that more test material had actually dissolved in that sample.

The water solubility of iron orthophosphate was determined to be 0.0826 g/L at 20°C.

Disregarded literature, Lidre DR (1989)

The study indicates that the substance is very soluble 670.000 mg/L, however the study was performed at a temperature that is not considered to be environmentally relevant (100°C).

The literature data is disregarded, as the study was performed at a temperature that is not considered to be environmentally relevant (100°C) and as sufficient information on the material & methods used is not available.