Chromium iron oxide

Water solubility

Link to relevant study record(s)

Reference

Endpoint:

transformation / dissolution of metals and inorganic metal compounds

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2009-09-07 to 2010-02-10

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

deviations from the guideline, which do not effect the validity of the study (a) The 28-day test with a loading of 1 mg/L was conducted at pH 6 instead of 5.5 (b)`mass balance (%) after completion of the transformation test´ is missing

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:

yes

Remarks:

please refer to the field "Rationale for reliability incl. deficiencies" above

GLP compliance:

yes (incl. QA statement)

Remarks:

signed 2009-06-19

Type of method:

flask method

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

< 0.5 µg/L

Element analysed:

Cr

Loading of aqueous phase:

100 mg/L

Incubation duration:

24 h

Test conditions:

T = 22.4 - 22.5 °C ; pH = 6.06 - 6.13

Remarks on result:

other: < LOD

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

< 0.5 µg/L

Element analysed:

Fe

Loading of aqueous phase:

100 mg/L

Incubation duration:

24 h

Test conditions:

T = 22.4 - 22.5 °C, pH = 6.06 - 6.13

Remarks on result:

other: < LOD

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

< 0.5 µg/L

Element analysed:

Cr

Loading of aqueous phase:

100 mg/L

Incubation duration:

24 h

Test conditions:

T = 22.4 - 22.5 °C, pH = 8.02 - 8.11

Remarks on result:

other: < LOD

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

< 0.5 µg/L

Element analysed:

Fe

Loading of aqueous phase:

100 mg/L

Incubation duration:

24 h

Test conditions:

T = 22.4 - 22.5 °C, pH = 8.02 - 8.11

Remarks on result:

other: < LOD

Type of test:

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

Mean dissolved conc.:

< 0.5 µg/L

Element analysed:

Cr

Loading of aqueous phase:

100 mg/L

Incubation duration:

7 d

Test conditions:

T = 22.4 - 22.5 °C, pH = 6.02 - 6.1 (6.9 in one sample at 0 h)

Remarks on result:

other: < LOD

Type of test:

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

Mean dissolved conc.:

< 0.5 µg/L

Element analysed:

Fe

Loading of aqueous phase:

100 mg/L

Incubation duration:

7 d

Test conditions:

T = 22.4 - 22.5 °C, pH = 6.02 - 6.1 (6.9 in one sample at 0 h)

Remarks on result:

other: < LOD

Type of test:

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

Mean dissolved conc.:

< 0.5 µg/L

Element analysed:

Cr, Fe

Loading of aqueous phase:

1 mg/L

Incubation duration:

24 h

Test conditions:

T = 22.6 °C, pH = 6.05

Remarks on result:

other: < LOD

Key result

Type of test:

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

Mean dissolved conc.:

< 0.5 µg/L

Element analysed:

Cr, Fe

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

T = 22.4 °C, pH = 6.04 - 6.09

Remarks on result:

other: < LOD

Key result

Type of test:

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

Mean dissolved conc.:

< 0.5 µg/L

Element analysed:

Cr, Fe

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

T = 22.5 °C, pH = 6.04 - 6.08

Remarks on result:

other: < LOD

Details on results:

The instrumental limit of detection (I.D.L.) defined as the lowest calibration level, was 0.1 µg/L for Cr and Fe, respectively.
The limit of quantification (L.O.Q.) of the method was 1 µg/L for Cr and Fe, defined as the lowest fortification level.
The limit of detection (L.O.D.) of the method, defined as 50 % of the lowest fortification level, was 0.5 µg/L for either metal.
Concentrations lower than the L.O.D. were classified as not detected (n.d.).
Concentrations higher than the limit of detection but less than the limit of quantification were designated as <1 µg/L for Cr and Fe.
If metal concentrations were higher than 10 µg/L for Cr and Fe, respectively, solution were suitably diluted in volumetric flasks.

Repeatability (Precision) and Accuracy (Recovery)
The test was performed by spiking each of the test media (using three replicates) with known amounts of Cr and Fe at two fortification levels (1 µg/L for the low level and 10 µg/L for the high level) using the SS 2 and SS 1 solution of 1 mg/L and 10 mg/L, respectively.
Each spiked test media was shaken for 24 hours and then sampled and analyzed according to the procedure described above.

For precision, the SANCO/3029/99 rev. 4 guideline requires a RSD % lower than 20 % for each fortification level; therefore the precision of the analytical method at low and high fortification levels can be considered acceptable.
The precision of the analytical method has been fixed at 10 % taking into account the results obtained.

For accuracy, the SANCO/3029/99 rev. 4 guideline requires individual recovery values in the range from 70 to 110 % with mean value between 80 to 100 % at each fortification level, therefore the accuracy of the analytical method can be considered acceptable.
Considering the low concentrations tested (low fortification level 1 µg/L and high fortification level 10 µg/L), the precision of the analytical method fixed at 10 % and the complexity of the aqueous matrices tested the accuracy of the analytical method can be considered acceptable.

From the data and results of the accuracy test it can be concluded that no matrix effect was observed and no contribution of the filter procedure was observed.

Screening Test at 0.1 g/L		^52Cr (µg/L)	^56Fe (µg/L)
AA76579 pH 6 T24 h	Mean	n.d.	n.d.
	S.D.	-	-
	RSD %	-	-
AA76579 pH 8 T24 h	Mean	n.d.	n.d.
	S.D.	-	-
	RSD %	-	-

Conclusion of the screening test:

Dissolved Fe or Cr concentrations were below the LOD at both pH levels. Therefore, pH 6 was selected for the full test assuming that the dissolution of metal oxides (i.e. this pigment) is maximized at the lower pH (in acidic medium).

Full Test 7 days at 0.1 g/L pH6		^52Cr (µg/L)	^56Fe (µg/L)
AA76579 T1 day	Mean	n.d.	n.d.
	S.D.	-	-
	RSD %	-	-
AA76579 T4 days	Mean	n.d.	n.d.
	S.D.	-	-
	RSD %	-	-
AA76579 T7 days	Mean	n.d.	n.d.
	S.D.	-	-
	RSD %	-	-

Full Test 28 days at 1 mg/L pH6		^52Cr (µg/L)	^56Fe (µg/L)
AA76579 T1 day	Mean	n.d.	n.d.
	S.D.	-	-
	RSD %	-	-
AA76579 T7 days	Mean	n.d.	n.d.
	S.D.	-	-
	RSD %	-	-
AA76579 T14 days	Mean	n.d.	n.d.
	S.D.	-	-
	RSD %	-	-
AA76579 T28 days	Mean	n.d.	n.d.
	S.D.	-	-
	RSD %	-	-

Test conditions

- The pH was inside of the acceptable range (pH 6 + 0.2 units) in a range of 6.02 to 6.12

- The temperature was inside of the acceptable range (20 -25 +/- 2) in a range of 22.4 to 22.6

- The O2 -concentration was always above the accaptable limit of 70 % in a range of 79.8 % to 81.6 %

- The within-vessel values and the between-vessel values could not be determined, because the concentrations of Cr and Fe were below the LOD (0.5 µg/L for Cr and Fe).

Conclusions:

Transformation/dissolution of chromium iron oxide (24-screening test according to OECD Series 28, loading of 100 mg/L, pH 6 and 8) resulted in metal concentrations that are below the respective LODs for iron and chromium (< 0.5 µg/L). Dissolved metal concentrations were also below the respective LODs after the 7-d test with 100 mg/L at pH 6 and after the 28-d test with 1 mg/L at pH 6. Thus, chromium iron oxide is considered to be environmentally inert.

Description of key information

The solubility of Chromium iron oxide in environmental media is low. Transformation/dissolution of chromium iron oxide (according to OECD Series 28: (i) 24 h, loading of 100 mg/L, pH 6 and 8; (ii) 7 d, loading of 100 mg/L, pH 6; and (iii) 28 d, loading of 1 mg/L, pH 6) resulted in metal concentrations below the respective LODs for iron and chromium (< 0.5 µg/L). Thus, the extent to which "Chromium iron oxide" can produce soluble available ionic and other metal-bearing species in aqueous media is limited.