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Adsorption / desorption

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Reference
Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Reference:
Composition 0
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:
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:
2008
Deviations:
no
GLP compliance:
yes (incl. certificate)
Type of method:
HPLC estimation method
Media:
soil/sewage sludge
Test material information:
Composition 1
Radiolabelling:
no
Test temperature:
25°C
Details on study design: HPLC method:
EQUIPMENT
- Apparatus: A high performance liquid chromatograph with an UV-VIS detector was used. The detection wavelength depended on the characteristics of the test item and the reference items.
- Type, material and dimension of analytical (guard) column: LiChrospher 100 CN (250*4 mm, 5 μm)
- Detection system: UV-Detector, 220 nm

MOBILE PHASES
- Type: The mobile phase was 55% methanol / 45% pure water.

DETERMINATION OF DEAD TIME
- Method: By inert substance sodium nitrate which is not retained by the column. Sodium nitrate was used as inert substance (not retained by the column) to determine the dead time. A stock solution of the compound was prepared by dissolution in pure water (1000 mg/L). This stock solution was diluted with solvent mixture of methanol/pure water (55%:45%, v:v) and was injected to determine the dead time t0 (t0 = retention time of the unretarded component).

REFERENCE SUBSTANCES
- Identity: Six chemicals for which log Koc has been reported were used to calibrate the elution time in units of log Koc. Structurally heterogeneous reference items were chosen.
Methylbenzoate (log Koc = 1.8)
Pyrazophos (log Koc = 3.65)
Acetanilide (log Koc = 1.25)
Linuron (log Koc = 2.59)
1,2,3 Trichlorobenzene (log Koc = 3.16)
Diclofop-methyl (log Koc = 4.2)
Sodium nitrate (inert reference substance)

DETERMINATION OF RETENTION TIMES
- Quantity of test substance introduced in the column: 50 mg dissolved in methanol, made up to 50 mL Stock solution), then diluted in methanol to obtain standard solution at the concentration of 100 mg/L for application.
- Quantity of reference substances: A stock solution of each reference compound was prepared by dissolution of the reference item in methanol. Appropriate volumes of the stock solutions were diluted using solvent mixture of methanol/pure water (55%:45%, v:v) to prepare standard solutions of these compounds at concentration of 50 mg/L. In addition, defined volumes of each of the stock solutions were diluted to prepare a reference item mixture.

REPETITIONS
- Number of determinations: Each reference item was injected separately to the HPLC system to determine the individual retention time of the compounds under test conditions. Subsequently a mixed solution of the reference items was injected three times and the inert compound was injected three times. Thereafter, the test item was injected at least in triplicate. After the analysis of the test item solution the mixed solution of the reference compounds was injected once again.

EVALUATION
- Calculation of capacity factors k': The capacity factor was calculated from the retention of the substance concerned (tr) and the unretarded component (t0):
k' = (tr-t0)/t0, where
tr = retention time of the test item [min]
t0 = time a non-sorbed chemical needs to pass the column (dead time) [min]
k' = capacity factor
- Calculation of retention times: Each reference item was injected separately to the HPLC system to determine the individual retention time of the compounds under test conditions.
- Determination of the log Koc value: The log Koc of the test item was estimated using HPLC method. Based on calibration curves obtained by correlation of the retention time of heterogeneous reference items with their known adsorption coefficient, the log Koc of the test was estimated.
Key result
Type:
log Koc
Value:
> 4.2 dimensionless
Temp.:
25 °C
Remarks on result:
other: no information on pH available
Validity criteria fulfilled:
yes
Conclusions:
The Adsorption Coefficient (Koc) was determined according to OECD 121 and EU method C.19 under GLP on the registered substance itself, so there is no reason to conclude that the results are not reliable. The study was assessed to be of high quality and testing is expected to be reasonably performed; results can be considered as reliable. The log Koc of the test was estimated to be above 4.2.
Executive summary:

The log Koc of the test item was estimated in a GLP study according to OECD 121 und EU Method C.19 using HPLC method. Based on calibration curves obtained by correlation of the retention time of heterogeneous reference items with their known adsorption coefficient, the log Koc of the test was estimated.

The adsorption coefficient Koc was determined based on a calibration curve using 6 reference items. The calibration curve was obtained from data generated by HPLC-UV detection. Calibration curve:

y = 0.1778* x - 0.05446, regression coefficient r² = 0.9931

The linearity of the method was proven in the log Koc-range from 1.25 to 4.20.

Based on the retention times the system independent capacity factors were calculated. Based on the capacity factor and on the calibration curved obtained by HPLC analysis, the log Koc of the test item was calculated; log Koc (estimated): > 4.2 and hence, the substance has to be considered as strongly adsorbing/binding substance (logKoc > 3).

Description of key information

Log Koc (estimated): > 4.2 and hence, the substance has to be considered as strongly adsorbing/binding substance (logKoc > 3) (OECD 121)

Key value for chemical safety assessment

Koc at 20 °C:
15 849

Additional information

The chosen endpoint is the only available study. It was conducted under GLP according to OECD guideline 121 and EU Method C.19 on the registered substance itself, so there is no reason to conclude that the results are not reliable. The study was assessed to be of high quality and testing is expected to be reasonably performed; results can be considered as reliable. The log Koc of the test was estimated to be above 4.2 using the HPLC method; the substance has to be considered as strongly adsorbing/binding substance (logKoc > 3).

[LogKoc: 4.2]