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Partition coefficient

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Reference
Endpoint:
partition coefficient
Type of information:
experimental study
Adequacy of study:
key study
Study period:
Experimental starting date: 05 November 2016 Experimental completion date: 10 July 2017
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
EU Method A.8 (Partition Coefficient - Shake Flask Method)
Deviations:
no
Qualifier:
according to
Guideline:
OECD Guideline 107 (Partition Coefficient (n-octanol / water), Shake Flask Method)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Type of method:
flask method
Partition coefficient type:
octanol-water
Specific details on test material used for the study:
Identification: Dichlorobis(η-cyclopentadienyl)titanium
(CAS# 1271-19-8)
Appearance/physical state: red powder
Batch: 07088501022
Purity: 99.8%
Expiry date: 04 March 2019
Storage conditions: room temperature, in the dark
Analytical method:
photometric method
Key result
Type:
log Pow
Partition coefficient:
-1.35
Temp.:
20 °C
pH:
< 7
Details on results:
Discussion
The test item was demonstrated to be insoluble in n-octanol at a nominal concentration of 1.0 g/L. It was therefore necessary to prepare the stock solution in the aqueous phase (n octanol saturated water). However, from available literature, the test item was expected to hydrolyze very rapidly on contact with water and dissolution may in fact be directly linked to this hydrolysis process. However, as the test item demonstrated significant solubility in water, testing continued to quantify the partitioning characteristics of the resulting products, irrespective of the final species in solution.
Standard solutions were also prepared directly in matrices containing at least a proportion of aqueous media, such that quantification was performed on the test item in the same form as the partitioned sample solutions, and thus allowing calculation of concentrations relative to the parent test item.
Due to the potential complexity of the test item chemistry in the environment, the inherent acidity of aqueous test item solutions due to the liberation of hydrochloric acid and observed insolubility of the test item in aqueous buffer solutions, no manipulation of the test systems’ pH was performed and the determination was carried out at the natural pH achieved on dissolution of the test item.
Quantification of the partition coefficient of the test item hydrolysis products was performed using absorbance at a wavelength of 330 nm, which monitored a characteristic shoulder on the spectrum profile of the solubilized products. This allowed determination of the stock and the individual phase concentrations, working within the linear response range of the instrument, without having to employ the extreme dilution factor as was needed for the water solubility determination.
On evaluation of the relevant aqueous phase standard solutions, the diluted stock sample solutions and the diluted aqueous phase sample solutions, essentially identical spectra were generated, both with respect to the profile and the magnitude of absorbance, indicating the hydrolysis products generated as being highly hydrophilic and predominantly retained in the aqueous phase. Analyzed aqueous phase concentrations were in the range 94.6 to 97.2% of the mean analyzed stock solution concentration.
Evaluating the spectra originating from the organic phase analysis; standard solution spectra were similar to that observed for the aqueous phase analysis, with some minor differences expected due to the possible matrix specific absorbance characteristics of the hydrolysis product complexes. However, significant differences were observed between standard and sample solution spectra; indicating that the species that did partition into the organic phase were extremely limited. For example the absorbance maxima observed at approximately 250 nm in the standard solutions was not replicated in the organic phase sample solutions. The region of absorbance that was used for quantification however was dominant in the organic phase sample solutions and therefore allowed for presentation of a worst case scenario for lipophilic behaviour, although this still remained negligible.

Definitive Test

The mean peak absorbances obtained for the standard, stock and sample solutions are shown in the following two tables:

Solution

Absorbance

Standard 5.02 mg/L

0.0275

Standard 10.0 mg/L

0.0458

Standard 20.1 mg/L

0.0951

Standard 20.1 mg/L

0.0804

Standard 40.2 mg/L

0.1675

Organic phase matrix blank

no significant response

Sample 1

0.0978

Sample 2

0.1031

Sample 3

0.0469

Sample 4

0.0697

Sample 5

0.1631

Sample 6

0.1671

Aqueous Phase

Solution

Absorbance

Standard 25.1 mg/L

0.2359

Standard 50.2 mg/L

0.4595

Standard 50.3 mg/L

0.4515

Standard 75.3 mg/L

0.6968

Standard 100 mg/L

0.9561

Aqueous phase matrix blank

no significant response

Sample 1

0.4769

Sample 2

0.4640

Sample 3

0.4688

Sample 4

0.4699

Sample 5

0.4676

Sample 6

0.4724

Stock solution A

0.4911

Stock solution B

0.4913

The total weights (mg) and analyzed concentration (mg/L) of the respective phases are shown in the following table:

Sample number

Total weight (mg)[1]

Organic phase

Aqueous phase

% recovery

Analyzed concentration (mg/L)

Weight (mg)[2]

Analyzed concentration (mg/L)

Weight

(mg)[2]

pH

1

95.6

45.4

4.09

1.03 x 103

92.9

2.5

101

2

95.6

48.1

4.33

1.01 x 103

90.5

2.5

99.2

3

68.0

20.0

2.56

1.02 x 103

65.0

2.5

99.3

4

59.5

31.4

3.51

1.02 x 103

57.0

2.5

102

5

127

78.0

4.68

1.01 x 103

122

2.5

99.1

6

119

80.0

4.48

1.02 x 103

115

2.5

100

Mean stock solution concentration:   1.06 x 103mg/L

pH of stock solution:                        2.5
Temperature:                                    20.0 ± 0.5 °C

[1]From analysis of the stock solution

[2]From analysis of the respective phase

The partition coefficient determined for each sample is shown in the following table:

Sample number

Organic/aqueous volume ratio

Partition coefficient

Log10Pow

Mean partition coefficient

1

1:1

4.40 x 10-2

-1.36

4.59 x 10-2

2

4.78 x 10-2

-1.32

3

2:1

1.97 x 10-2

-1.71

2.53 x 10-2

4

3.08 x 10-2

-1.51

5

1:2

7.70 x 10-2

-1.11

7.76 x 10-2

6

7.82 x 10-2

-1.11

Mean Pow : 4.96 x 10-2           log10Pow: -1.35          Powstandard deviation : 2.39 x 10-2

Conclusions:
The partition coefficient of the test item has been determined to be 4.96 x 10-2 at 20.0 ± 0.5 °C, log10 Pow -1.35, monitoring responses attributed to test item hydrolysis products, reflective of the species expected to form rapidly on accidental release into the environment.
Executive summary:

4.96 x 10-2at 20.0±0.5 °C, log10Pow-1.35,monitoring responses attributed to test item hydrolysis products, reflective of the species expected to form rapidly on accidental release into the environment. Testing used ashake-flask method designed to be compatible with Method A.8 Partition Coefficient of Commission Regulation (EC) No 440/2008 of 30 May 2008andMethod 107 of the OECD Guidelines for Testing of Chemicals, 27 July 1995. 

Description of key information

The endpoint is waived as the substance is hydrolytically unstable

Key value for chemical safety assessment

Log Kow (Log Pow):
-1.35
at the temperature of:
20 °C

Additional information

The substance is hydrolytically unstable. The measured log Kow is attributed to hydrolysis byproducts.