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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
Study period:
20 November 2012
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
Type of method:
HPLC estimation method
Radiolabelling:
no
Test temperature:
The temperature was maintained at approximately 30 °C
Details on study design: HPLC method:
TEST MATERIAL
A 10.0 mg/mL test material stock solution was prepared by placing 0.5031 g of the test material (0.5016 g as active ingredient) in a 50.0-mL volumetric flask and bringing it to volume with acetonitrile. This stock solution was divided into separate aliquots and stored refrigerated until injected on the instrument.

REFERENCE SUBSTANCES
- Identity: a 10.0 mg/mL primary formamide reference standard stock solution was prepared by placing 0.2507 g of formamide (0.2504 g as active ingredient) in a 25.0-mL volumetric flask and bringing it to volume with acetonitrile. This 10.0 mg/mL stock solution was used to determine the dead time (t0) of the instrument, and was stored in a freezer until injected. See Table 1 in "Any other information on materials and methods incl. tables" for information on the other reference substances used.

BUFFER PREPARATION
A 0.01 M sodium phosphate solution was prepared by combining 800 mL of a sodium phosphate monobasic solution (2.4987 g of sodium phosphate monobasic dissolved and brought to volume with 1000 mL of purified reagent water) with 1200 mL of a sodium phosphate dibasic solution (5.7928 g of sodium phosphate dibasic dissolved and brought to volume with 2000 mL of purified reagent water) and bringing it to a final volume of 4000 mL with purified reagent water. The pH of the resulting solution was adjusted to 7.00 by the addition of approximately 10 mL of 0.1 M of hydrochloric acid.

Samples were analysed by high performance liquid chromatographic system equipped with refractive index detection (HPLC/RI). The following instrumental conditions were used:
- Apparatus: Hewlett Packard quaternary solvent pump Series 1100 equipped with an Agilent degasser Series 1200 and autosampler Series 1100, a Hewlett Packard refractive index detector Series 1100 and Agilent Version B.04.02 for data acquisition.
- Column: Agilent Zorbax SB-CN, 5-µm, 250 mm x 4.6 mm
- Column temperature: 30 ºC
- Mobile Phase: A: 0.01 M sodium phosphate buffer (pH 7.0)/100% ACN 40/60 v/v
Isocratic analysis
- Flow Rate: 1.00 mL/minute
- Injection Volume: 10.0 µL
- Run time: 30 min
- Retention Times: approximately 9.4 minutes for the test substance (see table 1 for reference substance retention times)

DETERMINATION OF DEAD TIME
- Method: the dead time (t0) of the system was determined by making duplicate injections of formamide. Each remaining reference substance was analysed in duplicate. A calibration graph was determined by plotting the log k’ versus corresponding log Koc for the reference substances.

The test material was analysed in duplicate. The retention factor and log k’ was calculated and the log Koc determined from the calibration curve. The values of the log Koc from the duplicate measurement are considered acceptable when they fall within a range of ± 0.25 log units.

DATA HANDLING
The retention factors (k’) for each reference standard compound with a known Koc value were determined by the equation:

k' = (tR - t0) / t0

where
tR = the retention time of the test material
t0 = the dead time (the average time a solvent molecule needs to pass through the column

A calibration curve was constructed by plotting the logarithm of the partition coefficient (log Koc) of the reference standards (log Koc values taken directly from the OECD 121 guideline) against the logarithm of the retention factor (log k’) of the reference standards. The equation of the line (equation 1) was algebraically manipulated to give equation 2. The log Koc of the test material was then determined from the slope and intercept of the regression analysis, and the logarithm of the retention factor (k’) of the test material using equation 2.

(1) y = mx + b

(2) x = (y - b) / m

where
x = log Koc
y = log k'
b = y-intercept from the regression analysis
m = slope from the regression analysis
Type:
Koc
Value:
1 320 000
Temp.:
30 °C
Type:
log Koc
Value:
6.12
Temp.:
30 °C
Details on results (HPLC method):
The pH of the aqueous mobile phase was 7.00. The temperature during the Koc determination was maintained at approximately 30 °C via the HPLC column heater.

The mean Koc for the test material was determined to be greater than the Koc for DDT (log Koc = 5.63) and was therefore extrapolated above the standard curve to be 1,320,000 (log Koc = 6.12 ± 0.0250). The duplicate values of the log Koc for the test material were considered acceptable since they fell within a range of ± 0.25 log units. The retention time of the test material for each sample was 9.423 and 9.424 minutes.
Statistics:
Student's t-two-tailed value (95 % confidence): 2.22814
Validity criteria fulfilled:
yes
Conclusions:
Under the conditions of the study, the Koc for the test material was determined to be 1,320,000 while the log Koc was determined to be 6.12 ± 0.0250.
Executive summary:

The adsorption coefficient of the test material was determined in a GLP study which was conducted in accordance with the standardised guideline OECD 121 using a High Performance Liquid Chromatography (HPLC) method. During the study, a series of chemicals with well characterised partition coefficients were injected onto the analytical column which was then followed by an injection of the test material. The retention of each chemical injected onto such a column is in proportion to the adsorption coefficient of each chemical, with water soluble chemicals eluting first and oil-soluble chemicals last. The adsorption coefficient of the test material was deduced from the capacity factor k’, using a calibration plot of log k’ versus log Koc of the reference compounds.

 

Under the conditions of the study the pH of the aqueous mobile phase was 7.00. The temperature during the Koc determination was maintained at approximately 30 °C via the HPLC column heater. The mean Koc for the test material was determined to be greater than the Koc for DDT (log Koc = 5.63) and was therefore extrapolated above the standard curve to be 1,320,000 (log Koc = 6.12 ± 0.0250). The duplicate values of the log Koc for the test material were considered acceptable since they fell within a range of ± 0.25 log units. The retention time of the test material for each sample was 9.423 and 9.424 minutes.

Description of key information

The study was conducted to recognised testing guidelines with GLP certificaiton.

Key value for chemical safety assessment

Koc at 20 °C:
1 320 000

Additional information

The adsorption coefficient of the test material was determined in a GLP study which was conducted in accordance with the standardised guideline OECD 121 using a High Performance Liquid Chromatography (HPLC) method. During the study, a series of chemicals with well characterised partition coefficients were injected onto the analytical column which was then followed by an injection of the test material. The retention of each chemical injected onto such a column is in proportion to the adsorption coefficient of each chemical, with water soluble chemicals eluting first and oil-soluble chemicals last. The adsorption coefficient of the test material was deduced from the capacity factor k’, using a calibration plot of log k’ versus log Koc of the reference compounds.

 

Under the conditions of the study the pH of the aqueous mobile phase was 7.00. The temperature during the Koc determination was maintained at approximately 30 °C via the HPLC column heater. The mean Koc for the test material was determined to be greater than the Koc for DDT (log Koc = 5.63) and was therefore extrapolated above the standard curve to be 1,320,000 (log Koc = 6.12 ± 0.0250). The duplicate values of the log Koc for the test material were considered acceptable since they fell within a range of ± 0.25 log units. The retention time of the test material for each sample was 9.423 and 9.424 minutes.

The study was performed in line with GLP and an accepted standardised guideline with a high standard of reporting. The study was assigned a reliability score of 1 and considered suitable for assessment as an accurate reflection of the substance.

The available data are considered to be complete and the result determined, Koc 1,320,000 at 30 °C, was taken forward for risk assessment.

It is considered unnecessary to undertake additional testing to further investigate this endpoint.

[LogKoc: 6.12]

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