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Water solubility

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Reference
Endpoint:
transformation / dissolution of metals and inorganic metal compounds
Type of information:
experimental study
Adequacy of study:
key study
Study period:
29 Nov 2019 - 10 Feb 2020
Reliability:
1 (reliable without restriction)
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
GLP compliance:
yes
Type of method:
other: This study was performed in order to determine the transformation and/or dissolution of Sulphide Precipitate via measurement of Zink (Zn) per ICP-OES in aqueous media.
Specific details on test material used for the study:
Name Lead Sulphate
Batch no. 20170505
Appearance grey granules of different sizes
Composition 1.2 % Cu; 4.2 % Zn; 0.8 % Fe; 59.5 % Pb; 0.1 % Cd; 1.7 % As; 0.2 % Sb; 4.0 % Sn; 0.5 % Bi; 0.1 % Br; 0.7 % Cl; 0.3 % F
CAS No. unknown
EC-No. 951-962-1
Molecular formula not stated
Molecular weight not stated
Purity 100 % (UVCB)
Homogeneity homogeneous
Vapour pressure not stated
Stability in solvents H2O: not stated; EtOH: not stated; acetone: not stated; CH3CN: not stated; DMSO: not stated
Solubility in solvents H2O: not stated; EtOH: not stated; acetone: not stated; CH3CN: not stated; DMSO: not stated
Production date not stated
Expiry date 31. Dec. 2025
Storage room temperature (20 ± 5 °C)
Stability stable under storage conditions

Key result
Type of test:
full transformation/dissolution test - metals and sparingly soluble metal compounds
Mean dissolved conc.:
492 µg/L
Element analysed:
Pb
Loading of aqueous phase:
1 mg/L
Incubation duration:
4 d
Key result
Type of test:
full transformation/dissolution test - metals and sparingly soluble metal compounds
Mean dissolved conc.:
5 090 µg/L
Element analysed:
Pb
Loading of aqueous phase:
10 mg/L
Incubation duration:
7 d
Key result
Type of test:
full transformation/dissolution test - metals and sparingly soluble metal compounds
Mean dissolved conc.:
20 700 µg/L
Element analysed:
Pb
Loading of aqueous phase:
100 mg/L
Incubation duration:
7 d
Details on results:
The following mean vales and RSD were calculated:
Analysis Data for Zn (Flasks 3 – 5, 1 mg/L)
Analysis Data for Pb (Flasks 3 – 5, 1 mg/L)
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]
3 161.6 211.5 281.5 441.7 371.6
4 215.2 293.9 366.4 485.0 423.8
5 243.9 319.0 391.7 548.1 479.0
Mean 206.9 274.8 346.5 491.6 424.8
RSD [%] 20.2 20.5 16.7 10.9 12.6

Analysis Data for Pb (Flasks 6 – 8, 10 mg/L)
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 1499 1976 2753 3890 4552
7 1835 2384 3246 4394 5243
8 1892 2415 3485 4936 5475
Mean 1742 2258 3162 4409 5090
RSD [%] 12.2 10.9 11.8 11.9 9.4


Analysis Data for Pb (Flasks 9 – 11, 100 mg/L)
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 8390 10648 15313 18956 21642
10 8427 9950 13653 17291 20580
11 9186 10539 13862 18310 19878
Mean 8668 10379 14276 18186 20700
RSD [%] 5.2 3.6 6.3 4.6 4.3

A duplicate determination was performed from each flask. Measurement data for Pb are presented in the following table

                    

Fl.

Content

Conc. Pb in µg/L at following sampling points

0 h1

2 h

6 h

1 d

4 d

7 d

1

blank

< 10

< 10

< 10

< 10

12.27

13.03

< 10

< 10

16.872

< 10

14.21

< 10

2

blank

< 10

< 10

< 10

< 10

14.40

13.17

< 10

< 10

< 10

< 10

12.28

13.20

3

1.0 mg/L

< 10

165.4

207.6

299.9

419.1

363.13

< 10

157.7

215.4

263.2

464.2

380.13

4

1.0 mg/L

< 10

215.8

290.4

377.9

488.4

424.93

< 10

214.5

297.4

355.0

481.7

422.83

5

1.0 mg/L

< 10

247.2

315.4

394.6

558.9

476.83

< 10

240.6

322.6

388.7

537.3

481.13

6

10 mg/L

< 10

1467

1998

2708

3840

4409

< 10

1532

1953

2798

3939

4695

7

10 mg/L

< 10

1854

2442

3173

4305

5136

< 10

1815

2327

3320

4483

5350

8

10 mg/L

< 10

1882

2394

3450

4948

5591

< 10

1902

2436

3521

4925

5359

9

100 mg/L

< 10

8280

10459

15321

19477

22888

< 10

8500

10837

15304

18436

20395

10

100 mg/L

< 10

8225

9962

13918

17150

20411

< 10

8630

9937

13388

17432

20749

11

100 mg/L

< 10

8994

10320

14000

19310

20491

< 10

9378

10758

13723

17310

19264

1the LOQ of Pb is 10 µg/L

2possible contamination, the repetition of the measurement showed the value 17.16

3repetition of determination as an error was assumed during the first sample preparation

Conclusions:
The following concentrations of Pb were stated on day 4 (1 mg/L) and 7 (10 and 100 mg/L):
1 mg/L nominal: 491.6 µg/L Pb;
10 mg/L nominal: 5090 µg/L Pb;
100 mg/L nominal: 20700 µg/L Pb.

Executive summary:

In this study, the maximum concentration of total dissolved Lead was determined in order to identify compounds of Lead Sulphate which undergo either dissolution or rapid transformation.

The calibration was performed using a certified Pb stock solution (1000 mg/L nominal each). All validation conditions for the range of 10 – 100 µg/L Pb in pH 5.5 buffer solution were fulfilled.During the study the calibration was performed four times as the recovery rate of QC sample lay outside the range of 100±15% %.

The correlation coefficient r was > 0.99 of each calibration.The back calculated concentrations of the calibration standards layin the demanded ranges 100 ± 15 % and 100±20 % (low concentration) of the nominal values of each calibration. The accuracy in pH 7.0 buffer solution was given (value lay in the range of 100±5 %). For the determination of Pb in pH 8.5 buffer solution the recovery rate 87.7 % was taken into account in the calculation of Pb concentration in the screening test.

After the screening test, pH 5.5 was chosen for the reproducibility and full test based on the highest measured concentrations of Pb.

The reproducibility test was performed with 100 mg/L test item (nominal) in pH 5.5 buffer solution over a period of 24 hours. Five vessels were prepared; each flask was measured in triplicate. A within-vessel variation of max. 10% and a between-vessel variation of max. 20% is demanded. These conditions were fulfilled. Therefore, for the full test three flasks per concentration with double determination were used.

The full test was performed with three different concentrations of the test item (nominal loads 1, 10 and 100 mg/L, three replicates each) over a period of 7 days with samplings after 2 h, 6 h, 1 d, 4 d and 7 d. Two flasks were prepared as blanks without addition of test item.

No linear dependency of measured concentrations on time was observed for each nominal load. Furthermore, the concentration of Pb on day 7 in the flasks 3 – 5 (1 mg/L nominal load) was lower than on day 4. Either an error during the sample preparation or precipitation of Pb on day 7 are the possible reasons for this behaviour. Therefore, the values on day 7 were not used for evaluation. The conditions RSD < 10 % (within-vessel)and < 20 % (between-vessel) were fulfilled in all flasks at each sampling point of full test except the RSD between 3 – 5 flasks after 2 and 6 h. This was considered as uncritical as the result of dissolution of Pb with 1 mg/L nominal load was stated from day 4 with RSD of 10.9 %.

As no linear dependency of measured concentrations on time was observed, the first order model was used for the determination of kinetic. The first order constant “k” (slope of linear function) was calculated as 0.379 1/d (mean value of all flasks).

The mass balance lay in the range of 92.6 – 99.8 %.

Description of key information

The following concentrations of Pb were stated on day 4 (1 mg/L) and 7 (10 and 100 mg/L):

1 mg/L nominal:              491.6 µg/L Pb;

10 mg/L nominal:              5090 µg/L Pb;

100 mg/L nominal:              20700 µg/L Pb.

Key value for chemical safety assessment

Water solubility:
491 µg/L
at the temperature of:
21 °C

Additional information

In this study, the maximum concentration of total dissolved Lead was determined in order to identify compounds of Lead Sulphate which undergo either dissolution or rapid transformation.

The calibration was performed using a certified Pb stock solution (1000 mg/L nominal each). All validation conditions for the range of 10 – 100 µg/L Pb in pH 5.5 buffer solution were fulfilled.During the study the calibration was performed four times as the recovery rate of QC sample lay outside the range of 100±15% %.

The correlation coefficient r was > 0.99 of each calibration.The back calculated concentrations of the calibration standards layin the demanded ranges 100 ± 15 % and 100±20 % (low concentration) of the nominal values of each calibration. The accuracy in pH 7.0 buffer solution was given (value lay in the range of 100±5 %). For the determination of Pb in pH 8.5 buffer solution the recovery rate 87.7 % was taken into account in the calculation of Pb concentration in the screening test.

After the screening test, pH 5.5 was chosen for the reproducibility and full test based on the highest measured concentrations of Pb.

The reproducibility test was performed with 100 mg/L test item (nominal) in pH 5.5 buffer solution over a period of 24 hours. Five vessels were prepared; each flask was measured in triplicate. A within-vessel variation of max. 10% and a between-vessel variation of max. 20% is demanded. These conditions were fulfilled. Therefore, for the full test three flasks per concentration with double determination were used.

The full test was performed with three different concentrations of the test item (nominal loads 1, 10 and 100 mg/L, three replicates each) over a period of 7 days with samplings after 2 h, 6 h, 1 d, 4 d and 7 d. Two flasks were prepared as blanks without addition of test item.

No linear dependency of measured concentrations on time was observed for each nominal load. Furthermore, the concentration of Pb on day 7 in the flasks 3 – 5 (1 mg/L nominal load) was lower than on day 4. Either an error during the sample preparation or precipitation of Pb on day 7 are the possible reasons for this behaviour. Therefore, the values on day 7 were not used for evaluation. The conditions RSD < 10 % (within-vessel)and < 20 % (between-vessel) were fulfilled in all flasks at each sampling point of full test except the RSD between 3 – 5 flasks after 2 and 6 h. This was considered as uncritical as the result of dissolution of Pb with 1 mg/L nominal load was stated from day 4 with RSD of 10.9 %.

As no linear dependency of measured concentrations on time was observed, the first order model was used for the determination of kinetic. The first order constant “k” (slope of linear function) was calculated as 0.379 1/d (mean value of all flasks).

The mass balance lay in the range of 92.6 – 99.8 %.