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Reference
Endpoint:
adsorption / desorption, other
Type of information:
experimental study
Adequacy of study:
key study
Study period:
15 January 2016 to 07 December 2017
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
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. QA statement)
Type of method:
HPLC estimation method
Radiolabelling:
no
Details on study design: HPLC method:
EQUIPMENT
Column: Zorbax CN 250 × 4.6 mm, 5 µm
Temperature: 25 °C
Flowrate: 1 mL/min
Injection volume: 25 µL
Detection: 205 nm
Run time: 10 minutes (formamide and acetanilide) to 60 minutes (DDT)

MOBILE PHASES
- Mobile Phase: Methanol (55 %) and water (45 %), isocratic

REFERENCE SUBSTANCES
- Three standards; formamide (for void volume), acetanilide (the lowest standard, log Koc of 1.25) and DDT (the highest standard, log Koc of 5.63) were used. One run was performed.

- Test material solutions were prepared at concentrations of 100 and 200 µg/mL.

Key result
Type:
log Koc
Remarks:
Free acid
Value:
3.966 dimensionless
Matrix:
KOCWIN-MCI method
Remarks on result:
other: KOCWIN-MCI method
Key result
Type:
log Koc
Remarks:
Free acid
Value:
2.838 dimensionless
Matrix:
LKOW method
Remarks on result:
other: LKOW method
Key result
Type:
log Koc
Remarks:
Monoester
Value:
2.358 dimensionless
Matrix:
KOCWIN-MCI method
Remarks on result:
other: KOCWIN-MCI method
Key result
Type:
log Koc
Remarks:
Monoester
Value:
2.538 dimensionless
Matrix:
LKOW method
Remarks on result:
other: LKOW method
Key result
Type:
log Koc
Remarks:
Diester
Value:
7.174 dimensionless
Matrix:
KOCWIN-MCI method
Remarks on result:
other: KOCWIN-MCI method
Key result
Type:
log Koc
Remarks:
Diester
Value:
6.076 dimensionless
Matrix:
LKOW method
Remarks on result:
other: LKOW method
Details on results (HPLC method):
- It was concluded that the adsorption coefficient could not be estimated practically. Based on this it was decided calculate adsorption coefficient values using the Estimation Program Interface EPI ver. 4.1.

CALCULATED VALUES
- Calculated values for the log Koc were determined for each of the specified constituents of the test material stated in information provided by the Sponsor.
The EPI ver 4.1 software used two different methods for calculating the adsorption coefficient, the KOCWIN-MCI and LKOW methods. The calculated values for log Koc from these two methods were as follows:

- KOCWIN-MCI calculated values:
The acid: Low sorption to soil/sediment, predicted log Koc 3.9662.
The monoester: Low sorption to soil/sediment, predicted log Koc 2.3584.
The diester: Very strong sorption to soil/sediment, predicted log Koc 7.1744.

- LKOW calculated values:
The acid: Low sorption to soil/sediment, predicted log Koc 2.8384.
The monoester: Low sorption to soil/sediment, predicted log Koc 2.5384.
The diester: Very strong sorption to soil/sediment, predicted log Koc 6.0758.

-Note that the Koc of all the constituents is pH dependent (soil adsorption decreases as ionisation increases).
Validity criteria fulfilled:
not applicable
Conclusions:
The calculated adsorption coefficient Koc values of the test material were:
Using the KOCWIN-MCI method: Free acid: 3.9662, monoester: 2.3584 and diester: 7.1744.
Using the LKOW method: Free acid: 2.8384, monoester: 2.5384 and diester: 6.0758.
Executive summary:

The adsorption coefficient of the test material was investigated in accordance with the standardised guideline OECD 121, under GLP conditions.

A feasibility study was conducted to assess whether or not the HPLC simulation method could be used, as the test material exhibited a strong UV absorbance, albeit at 205 nm. Solutions of the test material at 100 and 200 µg/mL were injected and gave a group of poorly separated peaks with retention times between 2.7 and 4.5 minutes. A solution of formamide, as the void volume marker, and standard solutions of acetanilide and DDT were also injected. The combined peaks of the test material covered a range from before the retention time of formamide (2.955 minutes) to just beyond the retention time of acetanilide (4.180 minutes).

It was concluded that on this basis the adsorption coefficient could not be estimated practically. Based on this the adsorption coefficient Koc values of the test material were calculated:

Using the KOCWIN-MCI method: Free acid: 3.9662, monoester: 2.3584 and diester: 7.1744.

Using the LKOW method: Free acid: 2.8384, monoester: 2.5384 and diester: 6.0758.

Description of key information

For the chemical safety assessment, a Koc of 94.8 L/kg was derived based on the weighted average log Kow of 1.84. It was considered this was the most robust way to determine Koc as the value obtained is calculated through EUSES based on the experimental log Kow.

Key value for chemical safety assessment

Koc at 20 °C:
94.8

Additional information

The adsorption coefficient of the test material was investigated in accordance with the standardised guideline OECD 121, under GLP conditions.

A feasibility study was conducted to assess whether or not the HPLC simulation method could be used, as the test material exhibited a strong UV absorbance, albeit at 205 nm. Solutions of the test material at 100 and 200 µg/mL were injected and gave a group of poorly separated peaks with retention times between 2.7 and 4.5 minutes. A solution of formamide, as the void volume marker, and standard solutions of acetanilide and DDT were also injected. The combined peaks of the test material covered a range from before the retention time of formamide (2.955 minutes) to just beyond the retention time of acetanilide (4.180 minutes).

It was concluded that on this basis the adsorption coefficient could not be estimated practically. Based on this the adsorption coefficient values were calculated using the Estimation Program Interface EPI ver. 4.1.

The calculated adsorption coefficient Koc values of the test material were:

Using the KOCWIN-MCI method: Free acid: 3.9662, monoester: 2.3584 and diester: 7.1744.

Using the KOW method: Free acid: 2.8384, monoester: 2.5384 and diester: 6.0758.

As these values were based on individual constituents obtained using a QSAR estimation programme, for the chemical safety assessment, a Koc of 94.8 L/kg was derived from Kow based on the weighted average of the components from their proportion in the substance. The weighted average Log Kow of 1.84 was used for the CSA to determine the Koc.