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Reference
Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2018-02-19 - 2018-10-24
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
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))
Version / remarks:
22 January 2001
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.19 (Estimation of the Adsorption Coefficient (KOC) on Soil and Sewage Sludge Using High Performance Liquid Chromatography (HPLC))
Version / remarks:
30 May 2008
Deviations:
no
GLP compliance:
yes (incl. certificate)
Type of method:
HPLC estimation method
Media:
soil/sewage sludge
Radiolabelling:
no
Test temperature:
25 ± 0.5 °C
Details on study design: HPLC method:
EQUIPMENT
HPLC_7 (Thermo Ultimate)
Components: Solvent Rack; Pump LPG-3400SD; Autosampler; Column Compartment TCC 3200 with 6-fold column switch valve; UV-Detector DAD-3000
Manufacturer: Thermo Fisher Scientific
Software: CHROMELEON 6.80 SR15b Build 4981
Method Parameters
HPLC column: Reprosil Pur 120 CN 3 pm 125x4.6 mm with pre-column Phenomenex SecurityGuard CN, 4x3 mm
Eluent: isocratic methanol/water 55/45 (% v/v), degassed
Flow rate: 0.8 mL/min
Injection volume: 10 pL
Column temperature: 25 ± 0.5 °C
Wavelength for evaluation: 200 nm (reference item mix); 289 nm (test item)

MOBILE PHASES
An eluent of 55% methanol and 45% water, isocratic, was used. The mobile phase was produced by the mixture of 550 mL methanol and 450 mL water. pH of the eluent was approx. 5 - 6 (estimated with pH indicator paper). The temperature was held constant at 25 ± 0.5 °C by use of a HPLC column oven.

DETERMINATION OF DEAD TIME
The dead time t0 was measured by using an unretained compound (sodium nitrate) which was included in the mix of the reference items.

REFERENCE SUBSTANCES
Sodium nitrate, Phenol, Acetanilide, Methylbenzoate, Naphtalene, 1,2,3-Trichlorobenzene, Phenanthrene, 4,4'-DDT

DETERMINATION OF RETENTION TIMES
Pre-Tests
In a preliminary test, a solution of the test item with a concentration of 2 mL/L was injected in order to check retention time and the signal height. The solution gave one peak at 2.9 min.
Based on this result, a suitable mix of reference items was chosen (with 4,4-DDT as substance with the highest log KOC and a retention time of approx. 24.1 minutes and with Acetanilide with the lowest log KOC and a retention time of 2.8 minutes). The test item solution with concentration 2 mL/L was used for the determination of the log Koc of the test item.

Determination of the Log Koc of the Test Item
One vial was filled with the reference item mix and one vial with the test item solution. The vials were analysed using HPLC with the program described above. Three injections were measured from the reference item mix, three injections from the test item solution and again three injections from the reference item mix.
The data was saved, the retention times of the seven peaks of the reference item mix and the retention time of the peak of the test item were used for further calculations.

REPETITIONS
Three different measurements were done.

EVALUATION
Calculation of capacity factors k': k' = (tr - t0) / t0, with tr = retention time and t0 = dead time (retention time of sodium nitrate)
Calibration log k' vs. log Koc: The calibration function was drawn up from the six measurements of the capacity factors of the reference items. By plotting the (known) log Koc values of the reference items against the mean log capacity factors and performing linear regression, a calibration function was obtained.
Determination of the log Koc value: With the calculated capacity factors for the test item, each log KOC from the three determinations was calculated. Finally, mean and standard deviation of the log KOC were calculated.
Key result
Type:
log Koc
Value:
1.51 dimensionless
pH:
5.5
Temp.:
25 °C
Details on results (HPLC method):
Retention times of reference substances used for calibration: Sodium nitrate (1.050 min); Acetanilid (2.808 min); Methylbenzoate (3.308 min); Napthalene (4.893 min); 1,2,3-Trichlorobenzene (5.614 min); Phenanthrene (8.540 min); 4,4'-DDT (24.061 min)
Details of fitted regression line (log k' vs. log Koc): log k' = 0.2519 * log KOC - 0.1256, with a coefficient of determination r2 = 0.991
Average retention data for test substance: 2.933 min.

Due to an error the following deviation from the study plan was observed:

No separate thermometer was used during this study. The used thermometer is part of the HPLC. This is stated as uncritical, because the description was at the wrong place only.

The deviation was assessed and stated by the study director on 15. Nov. 2018.

Validity criteria fulfilled:
yes
Conclusions:
Using the correlation log k' / log Koc, the log Koc of the peak of the test item was calculated as 1.51 ± 0.00 (mean ± standard deviation).
Executive summary:

The study was performed under GLP-conditions and according to OECD guideline 121 and EU method C.19 using a HPLC with a cyanopropyl chemical bound resin on a silica base column. Six reference items with different retention times and sodium nitrate for the determination of the dead time were used to produce a calibration curve, since retention time on cyanopropyl columns and KOC are correlated. The reference items were chosen on behalf of the results of the pre-test.

A solvent blank followed by three injections of a solution of the reference items were analysed with HPLC, then three injections of a solution of the test item; and finally three injections of the solution with the reference items, in total ten runs.

For each reference item, the capacity factor k' was calculated from the retention time of sodium nitrate and the retention time of the respective reference item. A calibration function was set up using the literature values for KOC of the reference items and the mean capacity factor of the six determinations. In the graph log k' versus log KOC, linear regression was performed, giving r2 = 0.991 and r = 0.996.

The chromatogram of the test item gave one peak (mean RT = 2.933 min). With the calibration function log k' versus log KOC, the corresponding log KOC was calculated as

1.51 ± 0.00. This value is the mean ± standard deviation of three independent determinations. The validity criteria specified in the respective guideline were all fulfilled.

Description of key information

The study was performed under GLP-conditions and according to OECD guideline 121 and EU method C.19 using a HPLC with a cyanopropyl chemical bound resin on a silica base column. Six reference items with different retention times and sodium nitrate for the determination of the dead time were used to produce a calibration curve, since retention time on cyanopropyl columns and KOCare correlated. The reference items were chosen on behalf of the results of the pre-test.

A solvent blank followed by three injections of a solution of the reference items were analysed with HPLC, then three injections of a solution of the test item; and finally three injections of the solution with the reference items, in total ten runs.

For each reference item, the capacity factor k' was calculated from the retention time of sodium nitrate and the retention time of the respective reference item. A calibration function was set up using the literature values for KOC of the reference items and the mean capacity factor of the six determinations. In the graph log k' versus log KOC, linear regression was performed, giving r2= 0.991 and r = 0.996.

The chromatogram of the test item gave one peak (mean RT = 2.933 min). With the calibration function log k' versus log KOC, the corresponding log KOCwas calculated as

1.51 ± 0.00. This value is the mean ± standard deviation of three independent determinations. The validity criteria specified in the respective guideline were all fulfilled.

Key value for chemical safety assessment

Koc at 20 °C:
32.359

Additional information

Temperature stated in the study report is 25 °C. Nevertheless the determinded KOC value at this temperature can be also assumed for a temperature of 20 °C (as stated for the CSA) because of the low difference.