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Environmental fate & pathways

Adsorption / desorption

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Reference
Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
key study
Study period:
29-09-2011 till 07-10-2011
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Well conducted study under GLP, according to OECD guideline 121 without modifications. Certificate of analysis included in the report in the amendment.
Qualifier:
according to
Guideline:
OECD Guideline 121 (Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC))
Deviations:
no
GLP compliance:
yes (incl. certificate)
Type of method:
HPLC estimation method
Radiolabelling:
no
Details on study design: HPLC method:
The Koc was determined by applying the HPLC method. This method was performed on an analytical column packed with a commercially available cyanopropyl solid phase containing lipophilic and polar moieties. A moderately polar stationary phase based on a silica matrix was used. While passing through the column along with the mobile phase the test substance interacted with the stationary phase. As a result of partitioning between the mobile phase and stationary phase the test substance was retarded. The dual composition of the stationary phase having polar and non-polar sites allowed for interaction of polar and non-polar groups of a molecule in a similar way as in the case for organic matter in soil or sewage sludge matrices. This enabled the relationship between the retention time on the column and the adsorption coefficient on organic matter to be established.
Computational methods:
The partition coefficient was deduced from the capacity factor k, given by the expression:

  k=(tR- t0)/ t0

The capacity factor k for each reference substance was calculated from the average measured retention time tR of the substance and the average retention time of sodium nitrate (= t0 is the dead time, i.e. the average time a solvent molecule needed to pass the column).
The adsorption coefficient (Koc) was deduced from the capacity factor (k) using a calibration plot of Log Koc versus Log k of the selected reference substances.
Type:
log Koc
Value:
4.7
Remarks on result:
other: by HPLC method
Details on results (HPLC method):
See table below

Results of net retention times of reference and test substance

Substance

Log Koctheor.

Average net
retention time
(min)

Average
Log k

Sodium nitrate

 

0

 

Aniline

2.07

1.24

0.06

Methylbenzoate

1.80

1.87

0.24

1,2,3-Trichlorobenzene

3.16

3.64

0.53

Naphtalene

2.75

3.69

0.53

Phenantrene

4.09

9.09

0.93

4,4’-DDT

5.63

20.03

1.27

1,1,3,3-tetramethylbutyl peroxyneodecanoate

 

11.89

1.04

The graphs are uploaded in the attachment.

Figure 1 in the attachment displays the graph of the theoretical values of Log Kocand the average Log k of the reference substances. Figure 2 shows an example of a HPLC-chromatogram from the analysis performed according to the test set up.

The average measured Log Kocvalue for 1,1,3,3-tetramethylbutyl peroxyneodecanoate was calculated with the retention time from two injections usingthe calibration plot of Log Kocversus Log k of the selected reference substances.

The result was calculated to be 4.7; therefore 1,1,3,3-tetramethylbutyl peroxyneodecanoate had a Kocof 4.5E+04.

Amendment to study plan

The reference substances were dissolved in mobile phase because dissolving in methanol, as originally mentioned in the study plan, caused severe tailing of the response peaks in the HPLC chromatogram which made an unambiguous identification difficult. The test substance could not be dissolved in the mobile phase as it is very poorly water soluble. Due to this it was not possible to prepare mixtures of reference and test substances together. Mixtures of only reference substances were still possible.

Deviation from study plan

For practical reasons the stock solutions of the reference substances were dissolved in methanol. The diluted solutions of the reference substances, injected into the HPLC, were finally dissolved in mobile phase.

Validity criteria fulfilled:
yes
Conclusions:
The average measured log Koc value for 1,1,3,3-tetramethylbutyl peroxyneodecanoate as calculated from the test was 4.7.
Executive summary:

The adsorption coefficient (Koc) of 1,1,3,3-tetramethylbutyl peroxyneodecanoatewas estimated using the High Performance Liquid Chromatography (HPLC) method. The Koctest was performed in accordance with the OECD guideline 121 withoutmodification.The data on Koccan be used to predict the potential of the test substance to partition to soil, sediment or sewage sludge.

The average measured log Koc value for 1,1,3,3-tetramethylbutyl peroxyneodecanoate as calculated from the test was 4.7.

Description of key information

The average measured log Koc value for 1,1,3,3-tetramethylbutyl peroxyneodecanoate as calculated from the test was 4.7. 1,1,3,3-tetramethylbutyl peroxyneodecanoate may therefore be considered to have a high potential to partition to soil, sediment or sewage sludge. The limitations of this data should be considered when concluding potential environmental risk due to the short half life of 1,1,3,3-tetramethylbutyl peroxyneodecanoate when considering both hydrolytic and thermal degradation endpoints. In reality the properties of the main degradation product  2,2,4-trimethylpentanol are of greater relevance when considering transport and distribution and particularly potential chronic effects. The low  log Koc predictions of 2,2,4-trimethylpentanol (1.9) and the relatively high water 
solubility indicate a likely partitioning to the water phase.

Key value for chemical safety assessment

Koc at 20 °C:
50 119

Other adsorption coefficients

Type:
other: Predicted Log Koc of main degradation product
Value in L/kg:
1.96

Additional information

[LogKoc: 4.7]