Diiron trioxide

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:

2018-03-19 to 2018-06-15

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Deviations:

yes

Remarks:

Please refer to "Principles of method if other than guideline"

Qualifier:

according to guideline

Guideline:

EU Method A.6 (Water Solubility)

Version / remarks:

2008

Principles of method if other than guideline:

The water solubility of nano-sized diiron trioxide was assessed according to the OECD-Guideline for Testing of Chemicals No. 105, Water Solubility (flask method) with the following modifications:
- Two vessels were set up in a parallel design at 20.0 ± 1.0 °C, each vessel was sampled several times instead of sampling one single vessel at each point in time
- The study was performed under exclusion of atmospheric oxygen and carbon dioxide under inert gas (argon)

GLP compliance:

yes (incl. QA statement)

Remarks:

signed 2016-05-31

Type of method:

flask method

Key result

Water solubility:

1.77 µg/L

Conc. based on:

test mat. (dissolved fraction)

Loading of aqueous phase:

200 mg/L

Incubation duration:

>= 1 - <= 25 d

Temp.:

20 °C

pH:

>= 6.1 - <= 7.1

Remarks on result:

other:

Remarks:

Filtration through a 0.2 µm membrane and centrifugal filtration (3kDa), Mean of Vessel 1 and 2

Water solubility:

1.22 µg/L

Conc. based on:

element (dissolved fraction)

Loading of aqueous phase:

200 mg/L

Incubation duration:

>= 1 - <= 25 d

Temp.:

20 °C

pH:

>= 6.1 - <= 7.1

Remarks on result:

other:

Remarks:

Filtration through a 0.2 µm membrane and centrifugal filtration (3kDa), Mean of Vessel 1 and 2

Water solubility:

3.11 µg/L

Conc. based on:

test mat.

Remarks:

dissolved and dispersed < 0.2 µm

Loading of aqueous phase:

200 mg/L

Incubation duration:

>= 1 - <= 25 d

Temp.:

20 °C

pH:

>= 6.1 - <= 7.1

Remarks on result:

other:

Remarks:

Filtration through a 0.2 µm membrane, Mean of Vessel 1 and 2

Water solubility:

2.15 µg/L

Conc. based on:

element

Remarks:

dissolved and dispersed < 0.2 µm

Loading of aqueous phase:

200 mg/L

Incubation duration:

>= 1 - <= 25 d

Temp.:

20 °C

pH:

>= 6.1 - <= 7.1

Remarks on result:

other:

Remarks:

Filtration through a 0.2 µm membrane, Mean of Vessel 1 and 2

Details on results:

The iron concentrations of solutions containing nano-sized diiron trioxide did not appear to increase during the test, and the majority of concentrations was below the LOD or LOQ. Thus, the overall mean iron concentration during the test was calculated based on iron concentrations from day1 to day25, i.e. 2.15 ± 0.47 µg Fe/L for the dissolved/dispersed fraction (0.2 µm filtration), corresponding to 3.11 ± 0.68 µg/L test item. Iron concentrations in the dissolved phase (filtered through a 0.2 µm filter and centrifugally filtered samples) were determined with 1.22 ± 0.19 µg Fe/L, corresponding to 1.77 ± 0.28 µg/L diiron trioxide (Sicovit red 30 E172).

Observations

During the study, the respective test items were homogenously distributed in solution. After sampling and filtering, the samples were clear.

 

Temperature

The mean temperature was 20.6 ± 0.4 °C.

 

Oxygen concentrations

The oxygen concentration was measured over the period of sampling time inside the acrylic glass box with anMicro IC oxygen sensor (Gfg, Dortmund, Germany). No oxygen was measurable.

pH measurements

Table 1: pH of solutions containing the test item and method blanks

Tes titem/sample	Solution pH (min-max)
	1d,2dand3d	8dand9d	23d,24d and25d
MethodBlanks	5.7–6.0	5.9–6.2	5.7–5.9
SICOVIT®Red30E172	6.5–6.7	6.7–6.9	6.0–  6.6

 

Turbidity measurement

The turbidity of filtered samples from day 1, 2 and 3 was immediately measured after filtering (centrifugal filtration) with a TURB 550 IR (WTW, Weilheim, Germany) to confirm that measured iron concentrations correspond to the dissolved fraction.

The turbidity was below 0.02 NTU, indicating the absence of particles. Due to the limited volume of test solution, turbidity was measured only on day 1, 2 and 3.

Method validation summary (ICP-OES)

Limits of detection (LODs), limits of quantification (LOQs) and correlation coefficients (r)

Limits of detection (LOD) within all measurement series: < 0.938 µg Fe/ L.

Limits of quantification (LOQ) within all measurement series: < 2.81 µg Fe/ L.

Correlation coefficients (r) within all measurement series: >0.99993

Mean recoveries for certified reference materialTMDA-52.4 (concentration range 16.6 – 66.4 µg Fe/L, n=8): 98.4-100%

Mean recoveries for quality control standard (5 µg Fe/ L, n = 4): 99.4 %

Mean recoveries for internal standard (10 µg / L, n = 4): 97.7 %

Mean recovery of fortified samples (n = 20): 98.6 - 104 %

Conclusions:

Under the conditions of this test (flask method; loading of 200 mg/L), iron concentrations of solutions containing nano-sized diiron trioxide did not appear to increase during the test (25d), indicating solubility equilibrium. Mean dissolved Fe concentrations after filtration through a 0.2 µm membrane and centrifugal filtration were determined with 1.22 ± 0.19 µg Fe/L, corresponding to 1.77 ± 0.28 µg/L test item in solution.

Reference 2

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Deviations:

yes

Remarks:

standard water pH 8 ISO 6341 OECD TGD 29

GLP compliance:

yes (incl. QA statement)

Type of method:

flask method

Water solubility:

< 1 µg/L

Temp.:

20 °C

pH:

8

Concentration of Fe < 1 µg/L

Conclusions:

insoluble (< 0.1 mg/L)
A very low water solubility was determined according to OECD Guideline 105. With a loading of 1 and 10 g/L diiron trioxide to water at pH 8 the dissolved iron was determined to be < 1µg/l.

Executive summary:

A very low water solubility of diiron trioxide was determined according to OECD Guideline 105. With a loading of 1 and 10 g/L diiron trioxide to water at pH 8 the dissolved iron was determined to be < 1µg/l.

The loading was performed at two different concentrations (1 and 10 g/L). The concentration of iron in water was measured in blank samples and in samples after loading with diiron trioxide with graphite furnace atomic absorption spectrometry (GFAAS) using the standard addition method.

Description of key information

Very low water solubility of diiron trioxide was determined according to OECD Guideline 105. With a loading of 10 g/l diiron trioxide to water at pH8 the dissolved iron was determined to be < 1µg/l.

Furthermore, Iron concentrations of solutions containing a loading of 200mg/L diiron trioxide (Sicovite red 30 E172) did not appear to increase during the test (25d), indicating solubility equilibrium. Mean dissolved Fe concentrations after filtration through a 0.2 µm membrane and centrifugal filtration were determined for Sicovite red 30 E172 with 1.22 ± 0.19 µg Fe/L, corresponding to 1.77 ± 0.28 µg/L test item in solution.

Key value for chemical safety assessment

Water solubility:

1 µg/L

Additional information

Very low water solubility was determined according to OECD Guideline 105. With a loading of 1 and 10 g/L diiron trioxide to water at pH 8 the dissolved iron was determined to be < 1µg/l.

The loading was performed at two different concentrations (1 and 10 g/L). The concentration of iron in water was measured in blank samples and in samples after loading with diiron trioxide with graphite furnace atomic absorption spectrometry (GFAAS) using the standard addition method.