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Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2017.07.14 to 2017-09-29
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Reason / purpose for cross-reference:
reference to same study
Qualifier:
according to guideline
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Version / remarks:
13. Apr. 2004
Qualifier:
according to guideline
Guideline:
other: EU method A.6 ("Water solubility“), Council Regulation (EC) No 440/2008
Qualifier:
according to guideline
Guideline:
other: OECD Guideline for the testing of chemicals, 105 "Water Solubility“, dated 27. Jul. 1995
Version / remarks:
27. Jul. 1995
Principles of method if other than guideline:
Water solubility and hydrolysis of the test item were assessed in a combined conduct.
Due to the properties of the test item (e. g. rapid hydrolysis in contact with water), these standard test guidelines were not generally applicable and substantial modifications were necessary. Detailed information on the methods used are given in the following sections.
GLP compliance:
yes (incl. QA statement)
Specific details on test material used for the study:
Storage: in freezer (-25 °C to -15 °C)
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
Sample Order: Rinse solution 1 and 2 were analysed before and after each measurement of a sample or calibration solution to ensure a clean system and to avoid carry over effects.
Buffers:
pH 4, citrate buffer (c = 0.5 mol/L)
pH 7, phosphate buffer (c = 0.5 mol/L)
pH 9, borate buffer (c = 0.5 mol/L)
Details on test conditions:
TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: volumetric flasks with stoppers
- Details on test procedure for unstable compounds: The untreated test item was handled in an inert and anhydrous atmosphere (glove bag under nitrogen). Moreover, the test item was weighed into previously dried volumetric flasks with stoppers.
- If no traps were used, is the test system closed (volumetric flask with stoppers)

TEST MEDIUM
- Preparation of test medium: a stock solution was prepared as follows
Stock solution II (as named in the report): The test item was exactly weighed (individual weights are given in Table 1) into a tared 50.0 mL volumetric flask. Then, approx. 30 mL buffer was added whilst agitating with a magnetic stirrer and cooling in a water bath with frozen thermal packs for about 30 minutes. Thereafter, the solution was ultrasonicated for five minutes, allowed to equilibrate to room temperature and filled to volume with buffer solution. The turbid solution was transferred into a 50 mL centrifuge tube and centrifuged for 10 min with rcfmin ≈ 550. The supernatant was membrane-filtrated (0.45 µm, PTFE).

- Dilutions of the stock solutions were prepared as follows:
* Test Item in Buffer Solution - Dilution VII (as named in the report): 5 mL of the filtrate of the stock solution ll was pipetted into a 25.0 mL volumetric flask which was previously filled with 2.5 mL stabiliser solution. Approx. 10 mL of water was added and the solution was mixed. Subsequently,
2.5 mL of reference item no. 2 (i.e., the internal Tantalum ICP Standard) was added and the flask was filled to volume with water, resulting in a dilution factor of 5.
* Test Item in Buffer Solution - Dilution VIII (as named in the report): 100 µL of dilution VII was mixed in a plastic tube with 9.9 mL diluent, resulting in an overall dilution factor of 500.
* Test Item in Buffer Solution - Dilution IX (as named in the report): 100 µL of dilution VIII was mixed in a plastic tube with 9.9 mL diluent, resulting in an overall dilution factor of 50 000.
The solution was used for analysis via ICP-MS.

OTHER TEST CONDITIONS
- Adjustment of pH: no pH adjustment in the buffer solutions necessary
Duration:
1 h
pH:
4
Temp.:
25 °C
Initial conc. measured:
> 49.8 - < 66 µg/L
Remarks:
nominal concentration of tungsten in sample solution
Duration:
1 h
pH:
7
Temp.:
25 °C
Initial conc. measured:
> 53.9 - < 62.2 µg/L
Remarks:
nominal concentration of tungsten in sample solution
Duration:
1 h
pH:
9
Temp.:
25 °C
Initial conc. measured:
> 52.2 - < 63.2 µg/L
Remarks:
nominal concentration of tungsten in sample solution
Number of replicates:
5
Positive controls:
no
Negative controls:
no
Preliminary study:
In a pre-test tungsten hexachloride showed a rapid hydrolysis in contact with aqueous solutions. A temperature rise during the addition of aqueous solutions was observed due to the exothermic reaction. The dispersion of the tungsten hexachloride with water was acidic (pH-value 2 to 3) and an insoluble residue sedimented on the ground.
Transformation products:
yes
Remarks:
partially
No.:
#1
Details on hydrolysis and appearance of transformation product(s):
- Rapid hydrolysis in contact with buffer solutions (pH 4, 7, 9)
- Temperature rise during the addition of aqueous solutions
- In buffered solutions the test item was completely dissolved (in pure water an insoluble residue occured, also after adjustment of pH to 4, 7, and 9).
% Recovery:
ca. 96.9
St. dev.:
8.1
pH:
4
Temp.:
25 °C
Duration:
< 1 h
Remarks on result:
other: in buffer solution
% Recovery:
ca. 88.9
St. dev.:
6.1
pH:
7
Temp.:
25 °C
Duration:
< 1 h
Remarks on result:
other: in buffer solution
% Recovery:
ca. 94.3
St. dev.:
1.1
pH:
9
Temp.:
25 °C
Duration:
< 1 h
Remarks on result:
other: in buffer solution
pH:
4
Temp.:
25 °C
DT50:
< 1 h
Remarks on result:
not determinable because of methodological limitations
Remarks:
hydrolysed completely within 1 hour
pH:
7
Temp.:
25 °C
DT50:
< 1 h
Remarks on result:
not determinable because of methodological limitations
Remarks:
hydrolysed completely within 1 hour
pH:
9
Temp.:
25 °C
DT50:
< 1 h
Remarks on result:
not determinable because of methodological limitations
Remarks:
hydrolysed completely within 1 hour
Details on results:
TEST CONDITIONS
- pH, sterility, temperature, and other experimental conditions maintained throughout the study: pH was stabilized in buffered solutions, temperature was in a range of 20 to 25 °C (deviation from OECD 111 demanding a range of 20.0 ± 0.5 °C); conditions of sterility are not mentioned, as well as light conditions
- Anomalies or problems encountered (if yes): The test item showed a rapid hydrolysis in contact with aqueous solutions. A temperature rise during the addition of aqueous solutions was observed due to the exothermic reaction. The dispersion of the WCl6 test item with water was acidic (pH-value 2 - 3) and an insoluble residue sedimented on the ground. In the buffered solution no precipitation was observed.

MAJOR TRANSFORMATION PRODUCTS
At pH 4, 7 and 9: soluble tungsten ions

For further details on results see table 1 below.

Table 1: The following table represents the results obtained from each analysis of the fivefold preparation of the test item in three different buffer solutions.

Preparation #

pH value

Sample mass [mg]

Nominal concentration of tungsten in sample solution [µg/L]

Actual concentration of tungsten in sample solution [µg/L]

Recovery of tungsten in sample solution [%]

1

4

334

62.0

65.3

105.4

2

349

64.8

62.4

96.3

3

356

66.0

66.5

100.8

4

268

49.8

41.7

83.8

5

354

65.6

64.4

98.3

 

 

 

 

 

 

 

 

 

 

Mean

96.9

 

 

 

 

SD

8.1

 

 

 

 

RSD [%]

8.4

 

 

 

 

 

 

 

 

 

 

 

 

 

1

7

291

53.9

43.3

80.4

2

316

58.5

52.0

88.7

3

296

54.9

47.2

86.0

4

300

55.6

52.2

94.0

5

335

62.2

59.4

95.5

 

 

 

 

 

 

 

 

 

 

Mean

88.9

 

 

 

 

SD

6.1

 

 

 

 

RSD [%]

6.9

 

 

 

 

 

 

 

 

 

 

 

 

 

1

9

305

56.6

53.2

94.0

2

311

57.6

54.8

95.1

3

291

54.0

51.6

95.6

4

341

63.2

58.7

92.9

5

282

52.2

48.9

93.7

 

 

 

 

 

 

 

 

 

 

Mean

94.3

 

 

 

 

SD

1.1

 

 

 

 

RSD [%]

1.2

Validity criteria fulfilled:
not specified
Conclusions:
Tungsten hexachloride reacts strongly with water. Hydrolysis takes place immediately, hence no exact dissipation half-life or degradation time was determined.
Executive summary:

Hydrolysis of tungsten hexachloride at nominal concentrations of 49.8 to 66.0 µg/L was studied at 20 to 25 ºC in aqueous buffered solutions at pH 4 (citrate buffer, c = 0.5 mol/L), pH 7 (phosphate buffer, c = 0.5 mol/L) and pH 9 (borate buffer, c = 0.5 mol/L). The GLP experiment was conducted in a combined approach, investigating water solubility of the test item (acc. to OECD 105) and hydrolysis in dependence of pH (acc. to OECD 111). Samples were analysed immediately after dissolution of the test item in buffer solutions and subsequent ICP-MS analysis.

The determined concentrations of tungsten in the sample solution after preparation of the test item in citrate buffer (pH 4) ranged from 41.7 µg/L to 66.5 µg/L, corresponding to a mean recovery of 96.9 ± 8.1 %. The determined concentrations of tungsten in the sample solution after preparation of the test item in phosphate buffer (pH 7) varied between 43.3 to 59.4 µg/L, corresponding to a mean recovery of 88.9 ± 6.1 %. The determined concentrations of tungsten in the sample solution after preparation of the test item in borate buffer (pH 9) ranged between 48.9 to 58.7 µg/L, corresponding to a mean recovery of 94.3 ± 1.1 %.

In summary tungsten hexachloride shows a rapid hydrolysis in contact with aqueous solutions. This exothermic reaction results in a temperature rise of the test solutions. Tungsten hexachloride was almost completely dissolved in the three buffer solutions at pH 4, 7 and 9.

 

This study is classified acceptable and satisfies the guideline requirement for hydrolysis study.

 

Description of key information

A study on hydrolysis which was conducted according to the OECD guideline 111 is available. Results from a pre-test showed that tungsten hexachloride reacts exothermic with water and a pH shift (2 to 3) occurs upon dissolution. The main test was conducted with tungsten hexachloride in buffered solutions with concentrations of tungsten at 49.8 to 66.0 µg a.i./L was at 20 to 25 ºC: pH 4 (citrate buffer, c = 0.5 mol/L), pH 7 (phosphate buffer, c = 0.5 mol/L) and pH 9 (borate buffer, c = 0.5 mol/L) for less than an hour. Samples were analysed immediately after dissolution of the test item in buffer solutions by diluting the solution and directly injecting it to ICP-MS. ICP-MS identified tungsten (VI) oxide as main transformation product.

As hydrolysis takes place immediately, hence no dissipation half-life or degradation time was determined.

Key value for chemical safety assessment

Additional information