Cobalt aluminate blue spinel

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:

2012-04-19 to 2012-09-14

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

`mass balance (%) after completion of the transformation test´ is missing; The 28 d-test was performed at pH 6 and 8, according to OECD 29 a range from pH 5.5 to 8.5 should be covered.; The between-vessel variation on day 14 and 21 was not < 20 % recommended by OECD Series No. 29 in the 28d-full test with a loading of 1mg/L at pH 6. The mean value of Al recovery at pH 8 is out from the range of acceptability following guideline SANCO/3029/99 rev. 4 but considering the precision of the analytical method fixed at 10 % it can be acceptable.

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

Version / remarks:

(ENV/JM/MONO(2001)9): 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

Qualifier:

according to guideline

Guideline:

other: EEC guideline SANCO/3029/99 rev. 4 dated 11/07/00: Working document “Guidance for generating and reporting methods of analysis in support of residue data requirements for Annex II (part A, Section 4) and Annex III (part A, Section 5)

Deviations:

yes

Remarks:

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

GLP compliance:

yes

Type of method:

flask method

Type of test:

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

Mean dissolved conc.:

< 0.5 µg/L

Element analysed:

Co and Al

Loading of aqueous phase:

1 mg/L

Incubation duration:

24 h

Test conditions:

pH 6, 21.1 °C

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:

Co and Al

Loading of aqueous phase:

1 mg/L

Incubation duration:

24 h

Test conditions:

pH 8, 21 °C

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:

Co

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

pH 6, 21.6 °C

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 - < 1 µg/L

Element analysed:

Al

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

pH 6, 21.6 °C

Remarks on result:

other: > LOD, < LOQ

Key result

Type of test:

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

Mean dissolved conc.:

< 0.5 µg/L

Element analysed:

Co

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

pH 8, 21.6 °C

Remarks on result:

other: < LOD

Key result

Type of test:

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

Mean dissolved conc.:

1.9 µg/L

Element analysed:

Al

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

pH 8, 21.6 °C

Remarks on result:

other: S.D.: +/- 0.1 µg Al/L

Key result

Type of test:

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

Mean dissolved conc.:

< 0.5 µg/L

Element analysed:

Co

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

pH 6, 21.5 °C

Remarks on result:

other: < LOD

Key result

Type of test:

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

Mean dissolved conc.:

1.2 µg/L

Element analysed:

Al

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

pH 6, 21.5 °C

Remarks on result:

other: S.D.: +/- 0.2 µg Al/L

Key result

Type of test:

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

Mean dissolved conc.:

< 0.5 µg/L

Element analysed:

Co

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

pH 8, 21.4 °C

Remarks on result:

other: < LOD

Key result

Type of test:

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

Mean dissolved conc.:

2 µg/L

Element analysed:

Al

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

pH 8, 21.4 °C

Remarks on result:

other: S.D.: +/- 0.2 µg Al/L

Details on results:

The analytical method was shown to be suitable for low content determination of cobalt and aluminium in aqueous samples due to the technique ICP-MS. The temperatur of the test vessels were ± 2 °C in the range of 20-25 °C.
The instrumental limit of detection (IDL) defined as the lowest calibration level, was 0.1 µg/L for cobalt and aluminium, respectively.
The limit of quantification (LOQ) of the method was 1 µg/L for cobalt and aluminium, defined as the lowest fortification level.
The limit of detection (LOD) of the method, defined as 50 % of the lowest fortification level, was 0.5 µg/L for cobalt and aluminium.
Concentrations lower than the LOD were classified as not detected (n.d.).
Concentrations higher than the LOD but lower than the LOQ were designated as <1 µg/L for cobalt and aluminium.
From the results of the accuracy test it can be concluded that there was not a matrix effect and contamination (e.g. by the filter procedure) did not occur during sample processing.

Analytical results of the 28d full test at pH 6

Full test 28 days at 1 mg/L		Co (µg/L)	Al (µg/L)
Solution pH 6 T0h	Mean	n.d.	n.d.
	SD	-	-
	RSD (%)	-	-
Solution pH 6 T2h	Mean	n.d.	n.d.
	SD	-	-
	RSD (%)	-	-
Solution pH 6 T6h	Mean	n.d.	n.d.
	SD	-	-
	RSD (%)	-	-
Solution pH 6 T1d	Mean	n.d.	n.d.
	SD	-	-
	RSD (%)	-	-
Solution pH 6 T4d	Mean	n.d.	n.d.
	SD	-	-
	RSD (%)	-	-
Solution pH 6 T7d	Mean	n.d.	<1
	SD	-	-
	RSD (%)	-	-
Solution pH 6 T14d	Mean	n.d.	1.6
	SD	-	0.4
	RSD (%)	-	28.2(**)
Solution pH 6 T21d	Mean	n.d.	1.5
	SD	-	0.4
	RSD (%)	-	25.1(**)
Solution pH 6 T28d	Mean	n.d.	1.2
	SD	-	0.2
	RSD (%)	-	19.3

n.d.: lower than the method Limit of Detection (LOD) (0.5 µg/L for Co and Al).

<1: lower than the method Limit of Quantification (LOQ) (1 µg/L for Al) but higher than the method Limit of Detection (LOD) (0.5 µg/L for Al).

(**)The between-vessel variation was not less than 20% recommended by OECD Series No. 29.

Analytical results of the 28d full test at pH 8

Full test 28 days at 1 mg/L		Co (µg/L)	Al (µg/L)
Solution pH 8 T0h	Mean	n.d.	n.d.
	SD	-	-
	RSD (%)	-	-
Solution pH 8 T2h	Mean	n.d.	n.d.
	SD	-	-
	RSD (%)	-	-
Solution pH 8 T6h	Mean	n.d.	n.d.
	SD	-	-
	RSD (%)	-	-
Solution pH 8 T1d	Mean	n.d.	n.d.
	SD	-	-
	RSD (%)	-	-
Solution pH 8 T4d	Mean	n.d.	1.1
	SD	-	0.02
	RSD (%)	-	1.6
Solution pH 8 T7d	Mean	n.d.	1.9
	SD	-	0.1
	RSD (%)	-	4.2
Solution pH 8 T14d	Mean	n.d.	2.0
	SD	-	0.1
	RSD (%)	-	3.1
Solution pH 8 T21d	Mean	n.d.	1.9
	SD	-	0.1
	RSD (%)	-	5.5
Solution pH 8 T28d	Mean	n.d.	2.0
	SD	-	0.2
	RSD (%)	-	9.7

n.d.: lower than the method Limit of Detection (LOD) (0.5 µg/L for Co and Al).

Parameters of the linear calibration for the Co analysis of solutions from the 28 d-full test

m (slope): 1.1753

q (intercept): 0.0020

R² (correlation): 0.9999

Parameters of linear calibration for Al analysis of solutions from the 28 d-full test:

m (slope): 0.0177

q (intercept): 0.0290

R² (correlation): 0.9997

Analytical method (Inductively-Coupled-Plasma Mass-Spectrometry ICP-MS)

Specificity

Cobalt and aluminium concentrations of blanks from each test medium were analyzed. Cobalt concentrations in blanks of the respective media were below the method LOD, while aluminium concentrations in blanks of the respective media were higher than the method LOD.

Linearity and System Precision

The analysed range of Co and Al concentrations, from 0.1 µg/L to 200 µg/L,was found to be linear (correlation coefficient > 0.99 for metal).

Since the fortification levels for the recovery test were 1 mg/L and 10 mg/L, the linear calibration performed for recovery quantification ranged from 0.1 µg/L to 50 µg/L.

Parameters of the linear calibration for the Co analysis of solutions from the recovery test

m (slope): 1.1959

q (intercept): 0.0012

R² (correlation): 0.9994

Parameters of the linear calibration for the Al analysis of solutions from the recovery test

m (slope): 0.0260

q (intercept): 0.0662

R² (correlation): 0.9992

 

Repeatability (Precision) and Accuracy (Recovery)  

For precision, the SANCO/3029/99 rev. 4 guideline requires an RSD to be lower than 20 % for each fortification level.

For accuracy, the SANCO/3029/99 rev. 4 guideline requires mean recovery values for each fortification level in the range from 70 to 110 %, ideally with the mean in the range 80 to 100 %.

Recovery (Co)

Test   Medium	Spike add	Mean Found	RSD (%)	Recovery  Mean
pH 6	1 µg/L	0.9 µg/L	1.0	93.3 %
	10 µg/L	9.2 µg/L	0.9	91.8 %
pH 8	1 µg/L	0.9 µg/L	1.9	90.3 %
	10 µg/L	8.9 µg/L	1.8	89.1 %

Recovery (Al)

Test Medium	Spike add	Mean Found	RSD (%)	Recovery Mean
pH 6	1 µg/L	1.1 µg/L	3.7	107.3 %
	10 µg/L	10.9 µg/L	2.3	108.9 %
pH 8	1 µg/L	1.0 µg/L	1.7	102.6 %
	10 µg/L	11.5 µg/L	2.4	115.1 %(*)

(*)Out value from the range of acceptability following guideline SANCO3029/99 rev.4 but considering the precision of the analytical method fixed at 10 % it can be acceptable.

Repeatability and Recovery test: Test medium at pH 6

Elution medium pH 6	Co (µg/L) (1)	Co Recovery (%)	Al (µg/L) (1)	Al Recovery (%)
Solution blank	n.d.	-	n.d.	-
Spike L1	0.92	92.29	1.11	111.15
Spike L2	0.94	94.14	1.07	107.35
Spike L3	0.93	93.42	1.03	103.29
Mean value:	0.9	93.3	1.1	107.3
Standard deviation (SD):	0.01	0.93	0.04	3.93
Relative Standard deviation (RSD (%)):	1.0	1.0	3.7	3.7
Elution medium pH 6	Co (µg/L) (1)	Co Recovery (%)	Al (µg/L) (1)	Al Recovery (%)
Solution blank	n.d.	-	n.d.	-
Spike H1	9.12	91.22	10.61	106.10
Spike H2	9.28	92.81	11.03	110.32
Spike H3	9.15	91.51	11.04	110.40
Mean value:	9.2	91.8	10.9	108.9
Standard deviation (SD):	0.08	0.85	0.25	2.46
Relative Standard deviation (RSD (%)):	0.9	0.9	2.3	2.3

(1) Mean of two determinations

n.d.: lower than the method Limit of Detection (LOD) (0.5 µg/L for Co and Al).

Repeatability and Recovery test: Test medium at pH 8

Elution medium pH 8	Co (µg/L) (1)	Co Recovery (%)	Al (µg/L) (1)	Al Recovery (%)
Solution blank	n.d.	-	n.d.	-
Spike L1	0.91	91.47	1.04	103.51
Spike L2	0.91	91.05	1.01	100.56
Spike L3	0.88	88.25	1.04	103.79
Mean value:	0.9	90.3	1.0	102.6
Standard deviation (SD):	0.02	1.75	0.02	1.79
Relative Standard deviation (RSD (%)):	1.9	1.9	1.7	1.7
Elution medium pH 8	Co (µg/L) (1)	Co Recovery (%)	Al (µg/L) (1)	Al Recovery (%)
Solution blank	n.d.	-	n.d.	-
Spike H1	8.74	87.39	11.23	112.32
Spike H2	9.05	90.46	11.52	115.24
Spike H3	8.95	89.47	11.78	117.83
Mean value (µg/L):	8.9	89.1	11.5	115.1(*)
Standard deviation (SD):	0.16	1.57	0.28	2.75
Relative Standard deviation (RSD (%)):	1.8	1.8	2.4	2.4

(1) Mean of two determinations.

n.d.: lower than the method Limit of Detection (LOD) (0.5 µg/L for Co and Al).

(*) Out value from the range of acceptability following guideline SANCO/3029/99 rev. 4 but considering the precision of the analytical method fixed at 10 % it can be acceptable.

Repeatability and Recovery test: Certified Reference Material analysis

	Ratio Co/Ge	Co (µg/L)	Ratio Al/Ge	Al (µg/L)
Certified Reference Material A	18.7878	15.71	0.9601	34.38
Certified Reference Material B	17.9231	14.99	0.9314	33.28
Mean value (µg/L):	15.35		33.83
Standard deviation (SD):	0.51		0.78
Relative Standard deviation (RSD (%)):	3.3		2.3

Conclusions:

The transformation/dissolution of cobalt aluminate blue spinel was measured according to the method OECD test series No. 29 (Guidance document on transformation/dissolution of metals and metal compounds in aqueous media).
Under the described conditions of this test, the following dissolved concentrations were measured at the respective loading, exposure and solution pH:

Full test 7 days at 1 mg/L and pH 6: <0.5 µg Co/L and <1 µg Al/L
Full test 7 days at 1 mg/L and pH 8: <0.5 µg Co/L and 1.9 µg Al/L

Full test 28 days at 1 mg/L and pH 6: <0.5 µg Co/L and 1.2 µg Al/L
Full test 28 days at 1 mg/L and pH 8: <0.5 µg Co/L and 2.0 µg Al/L

The dissolved Co and Al concentrations were below 2.5 µg/L after 7 and 28 days at a loading of 1 mg/L, referring to a total solubility of < 0.25wt %.
Thus, the extent to which the pigment can produce soluble available ionic and other metal-bearing species in aqueous media is limited.

Description of key information

The solubility of cobalt aluminate blue spinel is < 0.25 wt% at a 1mg/L loading at pH 6 and 8. A GLP-conform transformation/dissolution test with a loading of 1 mg/L at pH 6 and pH 8 over 28 days, revealed higher dissolution of aluminium at pH 8.

Transformation/dissolution at a loading of 1 mg/L at pH 6 and 8 after 7 and 28 days resulted in dissolved cobalt concentrations below LOD. The dissolved aluminium concentrations at pH 8 were of 1.9 µg/L and 2.0 µg/L after 7 and 28 days, respectively (Pardo Martinez, 2013).

The particle size of the tested sample (BET surface area 9.1 m2/g) is representative for the particle size on the market. Thus, the extent to which "cobalt aluminate blue spinel" can produce soluble available ionic and other metal-bearing species in aqueous media is limited.