Olivine, cobalt silicate blue

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:

2018-01-15 to 2018-04-04

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 (incl. QA statement)

Remarks:

signed 2016-05-31

Type of method:

flask method

Key result

Type of test:

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

Mean dissolved conc.:

185 µg/L

Element analysed:

Co

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

pH 6, separation of aqueous phase by filtration 0.2 µm

Remarks on result:

other: LOQ = 0.572 µg/L

Key result

Type of test:

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

Mean dissolved conc.:

52.2 µg/L

Element analysed:

Co

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

pH 8, separation of aqueous phase by filtration 0.2 µm

Remarks on result:

other: LOQ = 0.572 µg/L, data background corrected

Key result

Type of test:

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

Mean dissolved conc.:

139 µg/L

Element analysed:

Co

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

pH 6, separation of aqueous phase by filtration 0.2 µm

Remarks on result:

other: LOQ = 1.29 µg/L

Key result

Type of test:

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

Mean dissolved conc.:

44 µg/L

Element analysed:

Co

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

pH 8, separation of aqueous phase by filtration 0.2 µm

Remarks on result:

other: LOQ = 1.29 µg/L

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

82.3 µg/L

Element analysed:

Co

Loading of aqueous phase:

1 mg/L

Incubation duration:

24 h

Test conditions:

pH 6, separation of aqueous phase by filtration 0.2 µm

Remarks on result:

other: LOQ = 0.268 µg/L

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

30.4 µg/L

Element analysed:

Co

Loading of aqueous phase:

1 mg/L

Incubation duration:

24 h

Test conditions:

pH 8, separation of aqueous phase by filtration 0.2 µm

Remarks on result:

other: LOQ = 0.268 µg/L

Details on results:

In case a detectable Co background concentration was measured on the respective sampling day, the shown data is background corrected.

Solution pH, oxygen concentrations, temperature:
Mean temperature was 20.0 ± 0.1 °C during the over 28-d. The solution pH for the pH 8 treatment shows a decrease of the pH during the test in the method blanks as well as in the sample vessels. In the test item vessels the pH was in the range of 7.55 – 7.75 and in method blank vessels the pH was in the range of 7.59 – 7.79. Oxygen levels in all test vessels pH 8 were in the range recommended by the OECD Test Guidance 29 during the test: above 70 % of oxygen saturation at 8.5 mg/L (70 % of 8.5 mg/L = 6 mg/L). Therefore, an influence on the test item can be excluded.

Variation of analytical measurements:
For all samples and sampling points the observed variations are in the necessary range of 20 % (between-vessel) and 10 % (withinvessel).

Validation experiments regarding applicability of filtration method:
Validation experiments were performed to show that dissolved cobalt (applied as standard solution) was not retained by the 0.2 µm filters. The respective recoveries of dissolved cobalt from the filters ranged from 101 to 109 %. Therefore, the 0.2 µm filtration step does not interfere with Co measurements.

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: 0.089 -0.430 µg Co/ L.

Limits of quantification (LOQ) within all measurement series: 0.268-1.29 µg Co / L.

Correlation coefficients (r) within all measurement series: > 0.999906

 

Method validation summary

Mean recovery of fortified samples (n = 10): 98.2 - 102 %

Mean recoveries for certified reference material CRM TMDA-70.2 and TMDA-52.4 (concentration range 63.5 - 97 µg Co / L, n = 26): 98.5 -107 %

Mean recoveries for quality control standard (concentration range 250 – 750 µg Co/ L, n = 26): 97.4 - 106 %

Mean recoveries for internal standard (concentration 500 µg Co/ L, n = 15): 98.6 - 102 %

Conclusions:

The transformation/dissolution test (OECD Series on Testing and Assessment Number 29, 2001) of the inorganic Pigment Olivine, cobalt silicate blue (sample IPC-2013-006-07) at a loading of 1 mg/L at pH 6 resulted in mean cobalt concentrations of 139 µg/L and 185 µg/L after 7 and 28 days, respectively. At a pH of 8, mean Co release after 7 and 28 days was lower and resulted in concentrations of 44 µg/L and 52.2 µg/L, respectively. Thus, the extent to which the inorganic Pigment Olivine, cobalt silicate blue can produce soluble available ionic and other metal-bearing species in aqueous media, is limited.

Description of key information

The solubility of Olivine, cobalt silicate blue is ~15-20 wt% at a 1mg/L loading. A full transformation/dissolution test with a loading of 1 mg/L in two artificial media (pH 6 and pH 8) over 28 days at room temperature was conducted. The test revealed a higher solubility at pH 6. The dissolved cobalt concentrations at a loading of 1 mg/L at pH 6 after 7 and 28 days were 139 µg Co/L and 185 µg Co/L, respectively. (Knopf, 2018).

The particle size of the tested sample (BET surface area 2.3 m2/g) is representative for the particle size on the market. Thus, the extent to which "Olivine, cobalt silicate blue" can produce soluble available ionic and other metal-bearing species in aqueous media is limited.