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Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Study period:

From 20 March 2019 to 17 May 2019

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

Qualifier:

according to guideline

Guideline:

EU Method C.19 (Estimation of the Adsorption Coefficient (KOC) on Soil and Sewage Sludge Using High Performance Liquid Chromatography (HPLC))

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

Inspection dates: 29-30-31 May 2018 / Signature date: 15 November 2018

Type of method:

HPLC estimation method

Media:

soil/sewage sludge

Specific details on test material used for the study:

- pKa: based on chemical structure (ketone), no ionisation anticipated in environmentally relevant pH range
- Storage conditions: Refrigerated (2-8°C) under nitrogen

Radiolabelling:

no

Test temperature:

The temperature variations of the oven containing the HPLC column were included in the range 29.3°C - 30.0 °C.

Details on study design: HPLC method:

EQUIPMENT
- HPLC-DAD: WATERS 996
- LC column: Roc Cyano (4.6 x 150 mm, 5 μm), RESTEK
- Injection volume: 50 μL
- Column flow: 1 mL/min
- Column temperature: 30 ± 1 °C
- Detection wavelength: Test item 200 nm; Reference substances 200 nm (except pyrazophos: 245 nm)
- Duration: 25 minutes

MOBILE PHASES
- Type: Methanol 55 % / H2O 45 %
- pH: The pH value measured in the ultrapure water used for the mobile phase was 6.77.

PREPARATION OF THE TEST ITEM SOLUTION
A stock solution of the test item was prepared at a concentration of 9.88 g/L in acetone. A diluted solution at 98.8 mg/L was prepared in the HPLC mobile phase. Sodium nitrate at 1 mg/L was added to this solution. These concentrations were adjusted depending on the response intensity of the compound on the system.

REFERENCE SUBSTANCES
- Identity: phenol, atrazine, isoproturon, aniline, triazoxide, naphtalene, 1,2,3-trichlorobenzene, pyrazophos, diclofop-methyl, DDT
- Preparation of the reference substances solutions: A stock solution of each reference substance was prepared at a concentration of approximately 1 g/L in acetone. These solutions were kept at 1 - 5 °C for 6 months. Two diluted reference solutions (Mix1 and Mix2) containing all the reference substances were prepared in the HPLC mobile phase. The concentrations were adjusted depending on the response intensity of each compound on the system according to the table 3. Sodium nitrate at 1 mg/L was added to these mixes.
MIX1: phenol, isoproturon, triazoxide, 1,2,3-trichlorobenzene, pyrazophos, DDT
MIX2: atrazine, aniline, naphtalene, phenanthrene, diclofop-methyl

DETERMINATION OF DEAD TIME
The dead time t0 was measured by using a non-retained organic compound (sodium nitrate) which was present in the reference items mixes and in the test item solution.

PRELIMINARY TEST
A preliminary study was carried out in order to check the retention times and the signal areas of the test and the reference items.
A solution of the test item was prepared at a concentration of approximately 100 mg/L in a methanol/ultrapure water (55/45 v/v) solution with 1 mg/L of sodium nitrate. Individual solutions of eleven reference items were also prepared in a methanol/ultrapure water solution with 1 mg/L of sodium nitrate. These solutions were injected in the chromatographic system. The same analytical conditions described for the main test were used.
For the test item, one peak was observed with a retention time of 4.82 min. The dead time t0, determined with the peak of sodium nitrate, was 1.09 min.
A linear regression of log k versus log KOC for the reference items was carried out and the following equation was obtained: log KOC = 4.1600 log k + 0.6648 with R = 0.9935 and R² = 0.9871. The log KOC value of the test item was then deduced from the previous equation: log KOC = 2.87.
The coefficient of determination obtained with the reference solutions is higher than 0.95 and the retention time of the test item is included in the range of the retention times of the reference items. Therefore, these reference items will be used for the main test.

DETERMINATION OF THE LOG KOC OF THE TEST ITEM
Two vials were filled for the two reference items mixes, and two others with the test item solution. The items were injected in the following order:
- reference items Mix1 (x 1)
- reference items Mix2 (x 1)
- test item (x 2)
- reference items Mix1 (x 1)
- reference items Mix2 (x 1)
A blank solution was injected between each item in order to check that no signal was observed from contamination or interfering compounds.

EVALUATION
- Calculation of capacity factors k': The capacity factor k for every peak was calculated using the following equation: k = (tR - t0) / t0; where tR is the HPLC retention time of test or reference substance (min); t0 is the HPLC dead-time = retention time of sodium nitrate (min).
- Determination of the log Koc value: The calibration function was drawn up from the two measurements of the capacity factors of each reference item. The corresponding logarithms of the adsorption coefficient, log KOC, were plotted as a function of log k. A linear regression was performed and a calibration function was obtained. The partition coefficient of the test substance was obtained for the two measurements by interpolation of the calculated capacity factor on the calibration graph. Mean and standard deviations of the log KOC were calculated.

Key result

Sample No.:

#1

Type:

log Koc

Value:

3.05 dimensionless

pH:

6.77

Remarks on result:

other: Temperature range: 29.3°C - 30.0 °C.

Key result

Sample No.:

#2

Type:

log Koc

Value:

3.05 dimensionless

pH:

6.77

Remarks on result:

other: Temperature range: 29.3°C - 30.0 °C.

Details on results (HPLC method):

- Retention times of reference substances used for calibration: See table 5.4.1/1 in "Any other information on results incl. tables". The equilibrium state of the system is declared valid since the difference of the reference items retention times (ΔtR / tR mean) did not exceed 5 % between two analyses.
- Dead times recorded for the reference mixes: First injection, t0 = 1.10 min (Mix1) and 1.09 min (Mix 2); Second injection, t0 = 1.10 min (Mix 1) and 1.08 min (Mix 2).
- Details of fitted regression line (log k' vs. log Koc): See table 5.4.1/2 in "Any other information on results incl. tables"
- Graph of regression line attached
- Average retention data for test substance: See tables 5.4.1/3-4 in "Any other information on results incl. tables"

Table 5.4.1/1: Retention times of the reference items

Compound	tR1 (min)	tR2 (min)	ΔtR(min)	tRmean (min)	ΔtR/ tRmean	Equilibrium ?
phenol	2.74	2.74	0.00	2.74	0.00%	YES
atrazine	2.67	2.67	0.00	2.67	0.00%	YES
isoproturon	3.25	3.25	0.00	3.25	0.00%	YES
aniline	3.01	3.01	0.00	3.01	0.00%	YES
triazoxide	4.02	4.02	0.00	4.02	0.00%	YES
naphtalene	4.50	4.50	0.00	4.50	0.00%	YES
1,2,3-trichlorobenzene	5.50	5.51	0.01	5.51	0.18%	YES
pyrazophos	7.68	7.68	0.00	7.68	0.00%	YES
phenanthrene	7.48	7.49	0.01	7.49	0.13%	YES
diclofop-methyl	9.11	9.13	0.02	9.12	0.22%	YES
DDT	18.39	18.34	0.05	18.37	0.27%	YES

with t_R: retention time; Δt_R: absolute value of the retention times difference

Table 5.4.1/2: log Koc and log k values for the reference items

Compound	log KOC	k1	k2	k mean	log (k mean)
phenol	1.32	1.49	1.49	1.49	0.17
atrazine	1.81	1.45	1.47	1.46	0.16
isoproturon	1.86	1.95	1.95	1.95	0.29
aniline	2.07	1.76	1.79	1.78	0.25
triazoxide	2.44	2.65	2.65	2.65	0.42
naphtalene	2.75	3.13	3.17	3.15	0.50
1,2,3-trichlorobenzene	3.16	4.00	4.01	4.01	0.60
pyrazophos	3.65	5.98	5.98	5.98	0.78
phenanthrene	4.09	5.86	5.94	5.90	0.77
diclofop-methyl	4.20	7.36	7.45	7.41	0.87
DDT	5.63	15.72	15.67	15.70	1.20

The logarithms of the adsorption coefficients, log K_OC, are plotted as a function of the mean capacity factors, log k. The linear regression obtained with the reference items is presented in the graph (see "illustration") with the representation of the confidence interval (in orange) calculated with a 98 % confidence level. The determination coefficient R² observed is 0.9790 and the correlation coefficient R is 0.9895. According to the guideline, a typical correlation coefficient for the relationship between log K_OCand log k for a set of test substances is around 0.95. Therefore, the obtained coefficients are satisfactory.

The equation of the line issued from this linear regression will be used for the test item log K_OCcalculation.

Table 5.4.1/3: Retention times of the test item

	Injection 1 tR(min)	Injection 2 tR(min)	tRmean (min)	Relative standard deviation
Dead time t0	1.08	1.08	1.08	0.0%
Test item	4.98	4.98	4.98	0.0%

Table 5.4.1/4: Calculated values of log Koc for the test item

	Test item
Measurement No.	k	log k	log KOC
1	3.61	0.56	3.05
2	3.61	0.56	3.05
log KOCmean			3.05
Standard deviation			0.000

log Koc is calculated using the regression equation obtained from the reference items: log K_oc= 3.8600 x log k + 0.8892

Validity criteria fulfilled:

yes

Conclusions:

Using the HPLC method, the following adsorption coefficient was determined for the test item: log KOC = 3.05.
This value is the mean of two independent measurements.

Executive summary:

A study was performed to estimate the Adsorption Coefficient (log K_OC) on Soil and Sewage Sludge of the test item using HPLC (High Performance Liquid Chromatography). The method followed was designed to be compliant with the OECD Guideline for Testing of Chemicals No. 121.

This study was performed using the HPLC method. Eleven reference items with different retention times were used to produce the calibration curve. They were chosen in relation with the expected retention time of the test item. For each reference item, two determinations were performed. The capacity factor k was calculated from the retention time of sodium nitrate (dead time) and the retention time of the respective reference item. A calibration function (log K_OCversus log k, linear fit) was determined based on literature values of K_OCfor the reference items.

The following adsorption coefficient was determined for the test item: log KOC = 3.05.

This value is the mean of two independent measurements.

Description of key information

OECD Guideline 121, EU Method C.19, GLP, key study, validity 1:

log Koc = 3.05; Koc = 1122

Low mobile in soils (according to P.J. McCall et al., 1980)

Key value for chemical safety assessment

Koc at 20 °C:

1 122

Additional information

One experimental study is available to assess the adsorption coefficient on soil and sewage sludge of the registered substance. This study was performed according to OECD Guideline 121 and EU Method C.19 with GLP compliance. The test utilized a high performance liquid chromatograph. Eleven reference items with different retention times were used to produce the calibration curve. They were chosen in relation with the expected retention time of the test item. For each reference item, two determinations were performed. The capacity factor (k) was calculated from the retention time of sodium nitrate (dead time) and the retention time of the respective reference item. A calibration function (log Koc versus log k, linear fit) was determined based on literature values of Koc for the reference items. All validity criteria were fulfilled. The substance was determined to have a log Koc value of 3.05 (equivalent to Koc = 1122). This value is the mean of two independent measurements and indicates that the registered substance is low mobile in soils (according to P.J. McCall et al., 1980¹).

¹McCall P.J., Swann RL, Laskowski D.A., Unger SM, Vrona SA and Dishburger H.J., (1980), “Estimation of chemical mobility in soil from liquid chromatographic retention times”, Bull Environ Contam Toxicol 24 (2) 190 -5.

Mobility classification scheme:

Range of Koc	Mobility class
0 - 50	Very high
50 - 150	High
150 - 500	Medium
500 - 2000	Low
2000 - 5000	Slightly
> 5000	Immobile