Reaction mass of copper oxide and manganese dioxide

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:

2017-03-20 to 2017-04-13

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

Version / remarks:

2001-07-23

Deviations:

yes

Remarks:

2 mg/L was used as the lowest test item concentration instead of 1 mg/L to ensure saturation of solution - mass fraction of copper in test item ca. 25%, only.

GLP compliance:

yes (incl. QA statement)

Type of method:

flask method

Specific details on test material used for the study:

Homogeneity: homogeneous
Expiry date: 16. Aug. 2021
Storage: Room Temperature: (20 ± 5°C)
The test item was homogenized to fine powder via mortar and pestle, due to a different size of granules: otherwise, no precise weighing of quantities 2 mg and 10 mg would have been possible.

Key result

Type of test:

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

Mean dissolved conc.:

349.9 µg/L

Element analysed:

Copper

Loading of aqueous phase:

100 mg/L

Incubation duration:

7 d

Test conditions:

Loading of 100 mg/L test item, agitation at 21°C and pH 6.0

Type of test:

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

Mean dissolved conc.:

122.5 µg/L

Element analysed:

Copper

Loading of aqueous phase:

10 mg/L

Incubation duration:

7 d

Test conditions:

Loading of 10 mg/L test item, agitation at 21°C and pH 6.0

Type of test:

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

Mean dissolved conc.:

48.3 µg/L

Element analysed:

Copper

Loading of aqueous phase:

2 mg/L

Incubation duration:

7 d

Test conditions:

Loading of 2 mg/L test item, agitation at 21°C and pH 6.0

Type of test:

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

Mean dissolved conc.:

11.6 µg/L

Element analysed:

Manganese

Loading of aqueous phase:

100 mg/L

Incubation duration:

7 d

Test conditions:

Loading of 100 mg/L test item, agitation at 21°C and pH 6.0

Type of test:

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

Mean dissolved conc.:

12.4 µg/L

Element analysed:

Manganese

Loading of aqueous phase:

10 mg/L

Incubation duration:

7 d

Test conditions:

Loading of 10 mg/L test item, agitation at 21°C and pH 6.0

Type of test:

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

Mean dissolved conc.:

9.6 µg/L

Element analysed:

Manganese

Loading of aqueous phase:

2 mg/L

Incubation duration:

7 d

Test conditions:

Loading of 2 mg/L test item, agitation at 21°C and pH 6.0

Details on results:

See below!

Screening Test

Five flasks (2 litres each) with five different pH values (5.5, 6.0, 7.0, 8.0, 8.5, nominal) were prepared with 1 litre of the respective buffer solution each and aerated with air and different percentages of CO2 to achieve the respective pH for 0.5 h. Two samples (volume 5 mL each) were taken from each flask for blank analysis. Then, 100 ± 1 mg of the test item were added to each flask and the closed flasks were shaken vigorously for 24 hours. After this time, the same parameters were measured as at the beginning, two samples are withdrawn from each flask (volume 10 mL each), membrane filtrated, and measured for Cu and Mn. The highest concentration of Cu and Mn was measured in pH 5.5 buffer solution:

Hours	Flask #	Test item added [mg]	T [°C]	pH nominal	pH measured	O2 [mg/L]	Conc.* Cu [µg/L]	Conc.* Mn [µg/L]
0 h	1	100.3	20.0	5.5	5.53	8.08	< 1.9	< 0.5
	2	100.3	20.1	6.0	6.10	7.79	< 1.9	< 0.5
	3	100.3	20.4	7.0	7.01	7.61	< 1.9	< 0.5
	4	100.3	20.0	8.0	7.97	7.43	< 1.9	< 0.5
	5	100.3	20.1	8.5	8.37	7.73	< 1.9	< 0.5
24 h	1	-	21.1	5.5	5.69	7.88	823.9	32.4
	2	-	21.2	6.0	6.15	7.79	231.8	6.6
	3	-	21.4	7.0	6.97	7.68	51.3	1.0
	4	-	21.0	8.0	7.89	8.30	9.5	< 0.5
	5	-	20.9	8.5	8.40	8.03	12.9	< 0.5

*) Conc. = Concentration, mean value of double determination

Reproducibility test

pH 5.5 was chosen for the reproducibility test based on the highest measured concentrations of Cu and Mn in the screening test.

Five vessels were prepared with 1 L of pH 5.5 buffer solutions each and aerated with air and CO2 to achieve the pH 5.5 ± 0.2 for 0.5 h. Two samples (volume 5 mL each) were taken from each flask for blank analysis; then, the flasks were aerated again with air and CO2 for 15 min. because pH values had slightly increased and lay at the highest range of pH 5.5 ± 0.2.

100 ± 1 mg of the test item were added to each flask and the closed flasks were shaken vigorously for 24 hours. After 4.5 hours the pH values were measured and adjusted to 5.5 ± 0.2 (aeration with air and CO2 for 15 min.). After 24 h, the same parameters were measured as at the beginning, 20 mL were with-drawn from each flask (whole volume), membrane filtrated, and three samples measured for Cu and Mn:

Concentration and RSD in Reproducibility Test**

Flask #	Replicate #	Conc. Cu [µg/L]		RSD Cu [%]	RSD Cu [%] (between vessel variation)	Conc. Mn [µg/L]		RSD Mn [%]	RSD Mn [%] (between vessel variation)
		0 h*	24 h			0 h*	24 h
1	1	< 1.9	719.7	0.3	3.9	< 0.5	27.5	0.2	3.6
	2	< 1.9	716.9			< 0.5	27.5
	3	-	721.3			-	27.6
2	1	< 1.9	700.3	0.7		< 0.5	26.5	0.3
	2	< 1.9	710.1			< 0.5	26.5
	3	-	706.9			-	26.4
3	1	< 1.9	704.8	0.3		< 0.5	25.6	0.6
	2	< 1.9	708.2			< 0.5	25.9
	3	-	704.3			-	25.9
4	1	< 1.9	729.8	0.6		< 0.5	26.9	0.9
	2	< 1.9	727.1			< 0.5	26.5
	3	-	721.4			-	26.5
5	1	< 1.9	656.9	0.9		< 0.5	24.6	0.7
	2	< 1.9	644.8			< 0.5	24.9
	3	-	652.6			-	25.0

*two replicates per flask were prepared and measured

**rounding error is possible as the calculation was performed with at least three decimal places

In OECD guidance document No. 29, a within-vessel variation of max. 10% and a be-tween-vessel variation of max. 20% is demanded. These conditions were fulfilled.

Therefore, for the main test three flasks per concentration with double determination were used.

Main test

 Preparation

According to OECD 29, the main test may either be performed as a long-term test (28 days) at a single low (1 mg/L) concentration at the pH showing highest dissolution within the screening test (pH 5.5), the low pH chosen to take account of long-term effects in acidic lakes. Alternatively, a 7 -day test may be performed with three different concentration levels at the appropriate pH based on screening test results, but not below pH 6.0. Because already at pH 6.0 considerable dissolution especially of copper but also Mn was observed in the screening test within 24 hours, the information gain was considered to be higher if the 7d-test was performed at three different concentrations. Further, pH 6.0 is more often found in environmental waters, while pH 5.5 is more characteristic for acidic lakes of the northern hemisphere. In conclusion, the 7 day main test was chosen and performed at pH 6.0. Deviating from the OECD 29 guideline, 2 mg/L was used as the lowest test item concentration instead of 1 mg/L. Reasoning: the mass fraction of copper is around 25%, only. With reference to OECD SIDS initial assessment profile for copper and copper compounds (2014), OECD 29 Transformation / dissolution test with nominal 1 mg/L CuO produced a soluble copper concentration of 210 µg/L at pH 6.0 after 28 days. As such, the lowest default concentration for the 7 days test, 1 mg/L test item, may not be sufficient to produce a saturated solution.

Eleven flasks (nominal volume two litres) were used. The flasks were filled with 1 litre medium (pH 6.0, nominal) and aerated with air and CO₂ for 45 min. until pH 6.0 ± 0.2 was reached.

2 x 5 mL samples were taken from each flask as blanks for analysis of Cu and Mn via ICP-OES. After that, the following amounts of the test item were added to the flasks (three flasks for each loading):

Flasks 3 – 5:          2 mg each

Flasks 6 – 8:          10 mg each

Flasks 9 – 11:        100 mg each.

Two flasks (1 and 2) were prepared as blanks without addition of the test item.

After addition of the test item, the flasks were closed using screw-caps and shaken for 7 days on an orbital shaker at 100 rpm. After 24 hours, 45 mL medium and after 4 d, 15 mL medium were added to each flask (replenishing as demanded in the guideline).

Sampling

After 2 h, 6 h, 1 d, 4 d and 7 d, respectively, samples of 15 mL (5 and 10 mL) were taken from the flasks and pH, oxygen and temperature were measured at each sampling point. The samples were membrane filtrated (0.2 µm, nylon), prepared for analysis (50 µL HNO₃(65%) for 5 mL test solution) and measured via ICP-OES.

Results of the main test:

pH, temperature and oxygen concentration measurements

	pH*	T [°C]	O2[mg/L]
Minimum (0 h)	5.86	20.90	7.83
Maximum (0 h)	5.99	21.70	8.08
Mean (0 h)	5.93	21.40	7.96
Minimum (2 h)	5.92	20.90	7.86
Maximum (2 h)	6.00	21.80	8.18
Mean (2 h)	5.96	21.39	8.03
Minimum (6 h)	5.85	20.30	7.82
Maximum (6 h)	5.92	21.40	8.20
Mean (6 h)	5.89	20.85	8.01
Minimum (1 d)	5.91	20.90	8.00
Maximum (1 d)	6.06	21.90	8.21
Mean (1 d)	5.97	21.53	8.12
Minimum (4 d)	5.96	21.00	8.23
Maximum (4 d)	6.11	21.90	8.33
Mean (4 d)	6.05	21.58	8.30
Minimum (7 d)	6.00	21.00	8.10
Maximum (7 d)	6.13	21.90	8.31
Mean (7 d)	6.07	21.50	8.18

*) values of pH given after pH adjustment performed for flasks 9, 10, and 11 at day 3 and for all flasks at day 4

Analysis Data for Copper

Analysis data for copper, 2 mg/L nominal concentration (flasks 3 to 5):

Flask #	Conc.after 2 h [µg/L]	Conc.after 6 h [µg/L]	Conc.after 1 d [µg/L]	Conc.after 4 d [µg/L]	Conc.after 7 d [µg/L]
3	12.5	20.0	30.5	36.9	38.2
4	12.5	20.8	39.3	50.9	57.3
5	13.7	23.6	35.5	46.9	49.4
Mean	12.9	21.5	35.1	44.9	48.3
RSD [%]	4.9 %	8.0 %	11.2 %	14.4 %	17.8 %

Dependency of measured concentrations on time was nearly linear in the first 24 hours only. Rate constants given below are based on linear regression between 0 h and 24 h:

Flask #	Linear Rate Constant [µg/L / h]	Linear Rate Constant Mean[µg/L / h]	RSD [%]
3	0.7	0.9	22.4
4	1.2
5	0.9

Analysis data for copper, 10 mg/L nominal concentration (flasks 6 to 8):

Flask #	Conc.after 2 h [µg/L]	Conc.after 6 h [µg/L]	Conc.after 1 d [µg/L]	Conc.after 4 d [µg/L]	Conc.after 7 d [µg/L]
6	39.8	55.5	76.7	105.9	111.8
7	30.8	49.4	80.2	113.6	129.5
8	34.3	49.5	84.6	106.3	126.1
Mean	35.0	51.5	80.5	108.6	122.5
RSD [%]	11.7 %	6.1 %	4.4 %	3.6 %	6.9 %

Dependency of measured concentrations on time was nearly linear in the first 24 hours only. Rate constants given below are based on linear regression between 0 h and 24 h:

Flask #	Linear Rate Constant [µg/L / h]	Linear Rate Constant Mean [µg/L / h]	RSD [%]
6	1.5	1.9	18.3
7	2.1
8	2.2

Analysis data for copper, 100 mg/L nominal concentration (flasks 9 to 11):

Flask #	Conc.after 2 h [µg/L]	Conc.after 6 h [µg/L]	Conc.after 1 d [µg/L]	Conc.after 4 d [µg/L]	Conc.after 7 d [µg/L]
9	130.5	181.5	354.8	332.3	354.6
10	131.1	188.8	331.2	306.4	341.0
11	129.9	187.9	345.1	330.4	354.1
Mean	130.5	186.1	343.7	323.0	349.9
RSD [%]	0.5 %	1.9 %	3.1 %	4.0 %	2.0 %

Dependency of measured concentrations on time was linear in the first 24 hours. Equilibration was achieved after 24 hours.

During the test, 45 mL medium were added to each flask after 24 hours and 15 mL medium were added after 4 d (replenishing as demanded in guideline). Therefore, the measured concentrations of Copper after 4 d were slightly lower than after 1 d. Rate constants given below are based on linear regression between 0 h and 24 h:

Flask #	Linear Rate Constant [µg/L / h]	Linear Rate Constant Mean [µg/L / h]	RSD [%]
9	10.0	9.4	6.9
10	8.7
11	9.5

Conclusions:

A transformation / dissolution test according to OECD 29 (2001) was performed compliant with GLP (RL 1) on the reaction mass of copper oxide and manganese dioxide (Hopcalite) via measurement of copper (Cu) and manganese (Mn) per ICP-OES in aqueous media.
The following concentrations of Cu and Mn were determined at pH 6.0 after 7 days of agitation at 21 °C:

2 mg/L nominal: 48.3 µg/L Cu 9.6 µg/L Mn
10 mg/L nominal: 122.5 µg/L Cu 12.4 µg/L Mn
100 mg/L nominal: 349.9 µg/L Cu 11.6 µg/L Mn

Executive summary:

A transformation / dissolution test according to OECD 29 (2001) was performed compliant with GLP (RL 1) on the reaction mass of copper oxide and manganese dioxide (Hopcalite) via measurement of copper (Cu) and manganese (Mn) per ICP-OES in aqueous media.

Metals and sparingly soluble metal compounds can produce soluble available ionic and other metal-bearing species in aqueous media under a set of standard laboratory conditions representative of those generally occurring in the environment. In this study maximum concentration of total dissolved metals at different test item concentrations over time was determined in order to characterize the dissolution / transformation potential of the test item leading to freely available metal ions with a potential for ecotoxicity.

In the screening test, the highest concentration of Copper and Manganese was measured in pH 5.5 buffer solution. Therefore, this buffer was used in the reproducibility test. Five flasks with one loading (100 mg/L) were tested and concentrations of Copper and Manganese were determined in triplicate. Both conditions RSD < 10 % (within-vessel) and < 20 % (between-vessel) were fulfilled for Copper and Manganese.

According to OECD 29, the main test may either be performed as a long-term test (28 days) at a single low (1 mg/L) concentration at the pH showing highest dissolution within the screening test (pH 5.5), the low pH chosen to take account of long-term effects in acidic lakes. Alternatively, a 7 -day test may be performed with three different concentration levels at the appropriate pH based on screening test results, but not below pH 6.0. Because already at pH 6.0 considerable dissolution especially of copper but also Mn was observed in the screening test within 24 hours, the information gain was considered to be higher if the 7d-test was performed at three different concentrations. Further, pH 6.0 is more often found in environmental waters, while pH 5.5 is more characteristic for acidic lakes of the northern hemisphere. In conclusion, the 7 day main test was chosen and performed at pH 6.0. Deviating from the OECD 29 guideline, 2 mg/L was used as the lowest test item concentration instead of 1 mg/L, because the mass fraction of copper in the test item is around 25%, only. With reference to OECD SIDS initial assessment profile for copper and copper compounds (2014), OECD 29 Transformation / dissolution test with nominal 1 mg/L CuO produced a soluble copper concentration of 210 µg/L at pH 6.0 after 28 days. As such, the lowest default concentration for the 7 days test, 1 mg/L test item, possibly would not have been sufficient to produce a saturated solution.

Thus, the main test was performed with three different loadings of the test item (2 mg/L (flasks 3 – 5), 10 (flasks 6 – 8) and 100 mg/L (flasks 9 – 11)) over a period of 7 days with samplings after 2 h, 6 h, 1 d, 4 d and 7 d. Two flasks (1 – 2) without addition of test item were tested in parallel as blanks.

The following mean results were determined for copper:

Analysis Data for Copper

nominal test item concentration	Cu after 2 h [µg/L]	Cu after 6 h [µg/L]	Cu after 1 d [µg/L]	Cu after 4 d [µg/L]	Cu after 7 d [µg/L]
2 mg/L	12.9	21.5	35.1	44.9	48.3
10 mg/L	35.0	51.5	80.5	108.6	122.5
100 mg/L	130.5	186.1	343.7	323.0	349.9

 

The equilibrium for Copper in 100 mg/L test item solution was achieved after 24 hours as the measured concentration from sampling after 1, 4 and 7 d lay in the same range. At lower concentrations of the test item (2 and 10 mg/L) the equilibrium was obviously not achieved after 7 days.

Dependency of measured concentrations on time was nearly linear in the first 24 hours only:

Linear Rate Constants Cu

nominal test item concentration	Linear Rate Constant [µg/L / h]
2 mg/L	0.9
10 mg/L	1.9
100 mg/L	9.4

 

 

For manganese, the followin mean results were obtained:

Analysis Data for Manganese

nominal test item concentration	Mn after 2 h [µg/L]	Mn after 6 h [µg/L]	Mn after 1 d [µg/L]	Mn after 4 d [µg/L]	Mn after 7 d [µg/L]
3 – 5 (2 mg/L)	1.3	2.4	4.1	7.3	9.6
6 – 8 (10 mg/L)	2.6	4.0	5.9	9.6	12.4
9 – 11 (100 mg/L)	4.0	5.8	9.1	9.0	11.6

 

An upward tendency of Mn concentrations was observed at each nominal load. Similar concentrations of Mn were observed in all flasks with different load of the test item after 7 days.

Dependency of measured concentrations on time was nearly linear in the first 24 hours and in the whole test.

Linear Rate Constants Mn:

nominal test item concentration	Linear Rate Constant [µg/L / h]
	0 – 24 h	0 – 7 d
2 mg/L	0.12	0.04
10 mg/L	0.14	0.06
100 mg/L	0.22	-*

*linear dependency was not observed

 

Validity criteria of OECD 29 RSD < 10 % (within-vessel)and RSD < 20 % (between-vessel) were fulfilled for Copper and Manganese in all flasks at each sampling point.

Description of key information

A transformation / dissolution test according to OECD 29 (2001) was performed compliant with GLP (RL 1) on the reaction mass of copper oxide and manganese dioxide (Hopcalite) via measurement of copper (Cu) and manganese (Mn) per ICP-OES in aqueous media (Affolter, 2017).

The following concentrations of Cu and Mn were determined at pH 6.0 after 7 days of agitation at 21 °C:

 

2 mg/L nominal:             48.3 µg/L Cu         9.6 µg/L Mn

10 mg/L nominal:           122.5 µg/L Cu       12.4 µg/L Mn

100 mg/Lnominal:          349.9 µg/L Cu       11.6 µg/L Mn

Key value for chemical safety assessment

Water solubility:

350 µg/L

at the temperature of:

21 °C

Additional information

A transformation / dissolution test according to OECD 29 (2001) was performed compliant with GLP (RL 1) on the reaction mass of copper oxide and manganese dioxide (Hopcalite) via measurement of copper (Cu) and manganese (Mn) per ICP-OES in aqueous media.

Metals and sparingly soluble metal compounds can produce soluble available ionic and other metal-bearing species in aqueous media under a set of standard laboratory conditions representative of those generally occurring in the environment. In this study maximum concentration of total dissolved metals at different test item concentrations over time was determined in order to characterize the dissolution / transformation potential of the test item leading to freely available metal ions with a potential for ecotoxicity.

In the screening test, the highest concentration of Copper and Manganese was measured in pH 5.5 buffer solution. Therefore, this buffer was used in the reproducibility test. Five flasks with one loading (100 mg/L) were tested and concentrations of Copper and Manganese were determined in triplicate. Both conditions RSD < 10 % (within-vessel) and < 20 % (between-vessel) were fulfilled for Copper and Manganese.

According to OECD 29, the main test may either be performed as a long-term test (28 days) at a single low (1 mg/L) concentration at the pH showing highest dissolution within the screening test (pH 5.5), the low pH chosen to take account of long-term effects in acidic lakes. Alternatively, a 7 -day test may be performed with three different concentration levels at the appropriate pH based on screening test results, but not below pH 6.0. Because already at pH 6.0 considerable dissolution especially of copper but also Mn was observed in the screening test within 24 hours, the information gain was considered to be higher if the 7d-test was performed at three different concentrations. Further, pH 6.0 is more often found in environmental waters, while pH 5.5 is more characteristic for acidic lakes of the northern hemisphere. In conclusion, the 7 day main test was chosen and performed at pH 6.0. Deviating from the OECD 29 guideline, 2 mg/L was used as the lowest test item concentration instead of 1 mg/L, because the mass fraction of copper in the test item is around 25%, only. With reference to OECD SIDS initial assessment profile for copper and copper compounds (2014), OECD 29 Transformation / dissolution test with nominal 1 mg/L CuO produced a soluble copper concentration of 210 µg/L at pH 6.0 after 28 days. As such, the lowest default concentration for the 7 days test, 1 mg/L test item, possibly would not have been sufficient to produce a saturated solution.

Thus, the main test was performed with three different loadings of the test item (2 mg/L (flasks 3 – 5), 10 (flasks 6 – 8) and 100 mg/L (flasks 9 – 11)) over a period of 7 days with samplings after 2 h, 6 h, 1 d, 4 d and 7 d. Two flasks (1 – 2) without addition of test item were tested in parallel as blanks.

 

The following mean results were determined for copper:

Analysis Data for Copper

nominal test item concentration	Cu after 2 h [µg/L]	Cu after 6 h [µg/L]	Cu after 1 d [µg/L]	Cu after 4 d [µg/L]	Cu after 7 d [µg/L]
2 mg/L	12.9	21.5	35.1	44.9	48.3
10 mg/L	35.0	51.5	80.5	108.6	122.5
100 mg/L	130.5	186.1	343.7	323.0	349.9

 

The equilibrium for Copper in 100 mg/L test item solution was achieved after 24 hours as the measured concentration from sampling after 1, 4 and 7 d lay in the same range. At lower concentrations of the test item (2 and 10 mg/L) the equilibrium was obviously not achieved after 7 days.

Dependency of measured concentrations on time was nearly linear in the first 24 hours only:

Linear Rate Constants Cu

nominal test item concentration	Linear Rate Constant [µg/L / h]
2 mg/L	0.9
10 mg/L	1.9
100 mg/L	9.4

 

 

For manganese results are summarised in the tables below:

Analysis Data for Manganese

nominal test item concentration	Mn after 2 h [µg/L]	Mn after 6 h [µg/L]	Mn after 1 d [µg/L]	Mn after 4 d [µg/L]	Mn after 7 d [µg/L]
3 – 5 (2 mg/L)	1.3	2.4	4.1	7.3	9.6
6 – 8 (10 mg/L)	2.6	4.0	5.9	9.6	12.4
9 – 11 (100 mg/L)	4.0	5.8	9.1	9.0	11.6

 

An upward tendency of Mn concentrations was observed at each nominal load.Similar concentrations of Mn were observed in all flasks with different load of the test item after 7 days.

Dependency of measured concentrations on time was nearly linear in the first 24 hours and in the whole test:

Linear Rate Constants Mn:

nominal test item concentration	Linear Rate Constant [µg/L / h]
	0 – 24 h	0 – 7 d
2 mg/L	0.12	0.04
10 mg/L	0.14	0.06
100 mg/L	0.22	-*

*linear dependency was not observed

 

Validity criteria of OECD 29 RSD < 10 % (within-vessel)and RSD < 20 % (between-vessel) were fulfilled for Copper and Manganese in all flasks at each sampling point.