Reaction mass of diiron carbide, diiron phosphide and triiron phosphide

Water solubility

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

transformation / dissolution of metals and inorganic metal compounds

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

2020-11-09 to 2021-06-22

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Qualifier:

equivalent or similar 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

Qualifier:

equivalent or similar to guideline

Guideline:

other: Formal guideline bioelution tests in gastric juice was under development at the time of the study.

Principles of method if other than guideline:

Where possible, the study was conduced in analogy or in adaptation of (i) a bioelution test method on the release of metals from inorganic compounds in artificial gastric juice, and (ii) the so called transformation/dissolution test for inorganic materials under environmental conditions [1]. A formal guideline for the bioelution test in gastric juice was under development at the time of the study [2] and the test principle has also been described in the literature [e.g. 3]. Sample work-up and determination of phosphine release were performed on the basis of the EURL Reference method for determining residue levels of phosphine in/on food items or other consumer goods after fumigation with PH3.


[1] OECD series on testing and assessment 29. July 23rd 2001. “Guidance document on transformation/dissolution of metals and metal compounds in aqueous media”. Document ENV/JM/MONO(2001)9. Organisation de coopération et de développement économiques (OECD), Paris.

[2] ESAC Opinion on the Scientific Validity of the Bioelution Test Method. ESAC Opinion No. 2019-03 of 2 December 2019, doi:10.2760/023005

[3] Henderson et al. 2014: Inter-laboratory validation of bioaccessibility testing for metals. Reg Toxicol Pharmacol 70:170-181. doi:10.1016/j.yrtph.2014.06.021

GLP compliance:

no

Other quality assurance:

ISO/IEC 17025 (General requirements for the competence of testing and calibration laboratories)

Remarks:

Accredited for the analysis of PH3 according to the EURL Reference method for determining residue levels of phosphine in/on food items or other consumer goods after fumigation with PH3. This study was conducted in adaptation of this EURL method.

Type of test:

other: test for release of gaseous PH3 from Fe3P

Element analysed:

PH3 (gas)

Loading of aqueous phase:

400 g/L

Incubation duration:

7 d

Test conditions:

pH=6, 20-25°C

Remarks on result:

other: see "Any other information on results incl. tables"

Artificial gastric juice:

The release of phosphine from Fe3P in artificial gastric juice (hydrochloric acid at pH=1.5 and 37°C) was 3.97, 8.24 and 15.9 mg(PH3)/kg(test item) after 2, 8 or 24 hours, respectively. The loading was 4 g Fe3P/L gastric juice. Based on the phosphorous contained in the test item, less than 0.01% of the contained phosphorus have reacted to PH3.

TDP medium / reconstituted water:

No release of phosphine from Fe3P could be detected in reconstituted water ("transformation/dissolution medium", pH=6, 20-25°C). All measurements after 4, 24 or 168 hours were below the limit of detection (LOD = 0.005 mg(PH3)/kg(test item), corresponding to below 5 ng PH3 absolute). The detection limit is so low that PH3 would have been detected if more than 0.00000085 % of the phosphorus contained in the Fe3P sample would have reacted to PH3, which was not the case.

Reference 2

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2010-08-03 to 2010-11-19

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

EU Method A.6 (Water Solubility)

Deviations:

no

Qualifier:

according to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of method:

column elution method

Specific details on test material used for the study:

Appearance: solid
Storage conditions: room temperature

Water solubility:

<= 1 mg/L

Conc. based on:

test mat. (dissolved fraction)

Loading of aqueous phase:

10 other: % w/w test substance in the loaded support

Temp.:

20 °C

pH:

>= 6.2 - <= 6.9

Details on results:

Column flow rate 0.4 mL/minute; mean water solubility = 1.0 mg/L (mean of five samples)
Column flow rate 0.2 mL/minute; mean water solubility = 0.8 mg/L (mean of six samples)

All collected samples were initially clear and colourless, but it was observed that precipitation occurred from the samples collected at the lower flow rate on standing. A red/brown precipitate, considered likely to be iron oxide, was also noted in the preliminary test sample. These observations, indicative of reaction of Fe3P with water, were a plausible explanation for the poor replication (general decline) of the results at the lower flow rate. For this reason, and also because the measured results may be attributable not only to Fe3P, but also to any soluble degradates (as the analytical technique measures elemental iron following acid digestion), the water solubility will be reported as less than or equal to 1 mg/l. A mean recovery of approximately 70% of Fe3P from fortified control samples was achieved. No significant interference was evident in blank control solutions.

Conclusions:

Fe3P was found to have a water solubility of ≤ 1 mg/l at 20°C.

Reference 3

Endpoint:

transformation / dissolution of metals and inorganic metal compounds

Type of information:

experimental study

Adequacy of study:

supporting study

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:

yes

Remarks:

Note: analyses were carried out according to ISO 17025 standard rather than GLP Principles.

Type of method:

other: transformation /dissolution

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

12 µg/L

Element analysed:

Fe

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Remarks on result:

other: see details below

Details on results:

Refer to measured concentrations in table 1, below. It should be noted that for all three species (Fe, P and o-PO4) the measured concentrations were below the typical reporting limits, and as such very large coefficients of variation were oberved.

Table 1: Measured concentrations of Fe, P, and orthophosphate (o-PO₄) after 7 or 28 days.

Loading (mg/L)	Time (days)	[Fe] (µg/L)	[P] (µg/L)	[o-PO4] (µg/L)
1	7	4	16	7
	28	12	47	31
10	7	12	33	11

Conclusions:

Over 7 days at a loading of 10 mg/L and over 28 days at a loading of 1 mg/L in aqueous medium (adjusted to pH6), Fe3P was found to evolve minimal concentrations of Iron, Phosporous, and orthophosphate; the concentrations of each of these species observed would not be expected to have any significance to the aquatic environment.

Description of key information

Fe3P was found to have a water solubility of ≤ 1 mg/l at 20°C (OECD Method 105).

A transformation / dissolution test was conducted according to OECD Test Guideline 29. Using a loading of 1 mg/L Fe3P in pH6 aqueous media, very small quantities of iron, phosphorous, and orthophosphate were measured in the test medium; after 28 days the concentrations of Iron, Phosphorous, and orthophosphate measured were 12µg/L, 47µg/L, and 31µg/L respectively.

The release (evolution) of gaseous phosphine (PH3) from Fe3P was studied in artificial gastric juice (HCl at pH=1.5, 37°C, tested at 2, 8 and 24 hours) and simulated environmental conditions (transformation/dissolution medium at pH=6, up to 168 hours). Less than 0.01% of the phosphorous contained in Fe3P reacted to PH3 in artificial gastric juice. No release of phosphine from Fe3P could be detected in reconstituted water ("transformation/dissolution medium", pH=6, 20-25°C). All measurements after 4, 24 or 168 hours were below the limit of detection (LOD = 0.005 mg(PH3)/kg(test item), corresponding to below 5 ng PH3 absolute). The detection limit is so low that PH3 would have been detected if more than 0.00000085 % of the phosphorus contained in the Fe3P sample would have reacted to PH3, which was not the case.

 

 

Additional information

A water solubility determination was performed as part of a set of tests for physico-chemical properties (Huntingdon Life Sciences, 2011, Study FGE0002). The water solubility was determined according to OECD Method 105 and EU Method A6, and the study was conducted in compliance with GLP. Fe3P was found to have a water solubility of ≤ 1 mg/l at 20°C.

On the basis of the low water solubility determined in the OECD105 test, a transformation / dissolution test was conducted according to OECD Test Guideline 29 (ECTX, 2013). Using a loading of 1 mg/L Fe3P in pH6 aqueous media, very small quantities of iron, phosphorous, and orthophosphate were measured in the test medium; after 28 days the concentrations of Iron, Phosphorous, and orthophosphate measured were 12µg/L, 47µg/L, and 31µg/L respectively. It was considered that because these are all naturally-occuring species, and because the concentrations measured over 28 days were extremely low, that the environmental impact of Fe3P in water would be negligible.

In a further study by Klimmek and Schneider (2021) the possible release of the toxic gas phosphine ("phosphane", PH3) from Fe3P was tested in artificial gastric juice and in reconstituted water ("transformation dissolution medium"): The release of phosphine from Fe3P in artificial gastric juice (hydrochloric acid at pH=1.5 and 37°C) was 3.97, 8.24 and 15.9 mg(PH3)/kg(test item) after 2, 8 or 24 hours, respectively. The loading was 4 g Fe3P/L gastric juice. Based on the phosphorous contained in the test item, less than 0.01% of the contained phosphorus have reacted to PH3 under these conditions. No release of phosphine from Fe3P could be detected in reconstituted water ("transformation/dissolution medium", pH=6, 20-25°C). All measurements after 4, 24 or 168 hours were below the limit of detection (LOD = 0.005 mg(PH3)/kg(test item), corresponding to below 5 ng PH3 absolute). The detection limit is so low that PH3 would have been detected if more than 0.00000085 % of the phosphorus contained in the Fe3P sample would have reacted to PH3, which was not the case.