2-(2,6-diethyl-4-methyl-phenyl)propanediamide

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption, other

Type of information:

experimental study

Adequacy of study:

key study

Study period:

23 August 2016 to 06 March 2017

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)

Version / remarks:

Dating from 2000

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

no

Test temperature:

20 ± 2 °C

Analytical monitoring:

yes

Details on sampling:

- Concentrations: 0.01, 0.05, 0.1, 0.5 and 1 µg/mL
- Sampling interval: In the preliminary test, the time taken to reach adsorption equilibrium was determined following analysis over a period of 72 hours (analysis after 24, 48 and 72 hours). In the definitive test, a 6-hour adsorption step was used for all soils. Due to suspected lack of stability during the adsorption phase no desorption step was conducted.
- Sample storage before analysis: not specified

Matrix no.:

#1

Matrix type:

loamy sand

% Clay:

4

% Silt:

10

% Sand:

86

% Org. carbon:

0.54

pH:

5.7

CEC:

4.4 meq/100 g soil d.w.

Bulk density (g/cm³):

1.4

Matrix no.:

#2

Matrix type:

sandy clay loam

% Clay:

24

% Silt:

22

% Sand:

54

% Org. carbon:

1.8

pH:

6.4

CEC:

16.7 meq/100 g soil d.w.

Bulk density (g/cm³):

1.17

Matrix no.:

#3

Matrix type:

loam

% Clay:

24

% Silt:

42

% Sand:

34

% Org. carbon:

2.2

pH:

7

CEC:

17.7 meq/100 g soil d.w.

Bulk density (g/cm³):

1.09

Matrix no.:

#4

Matrix type:

silt loam

% Clay:

10

% Silt:

52

% Sand:

38

% Org. carbon:

1.8

pH:

7.4

CEC:

8.4 meq/100 g soil d.w.

Bulk density (g/cm³):

0.97

Matrix no.:

#5

Matrix type:

silty clay

% Clay:

44

% Silt:

42

% Sand:

14

% Org. carbon:

1.1

pH:

8

CEC:

20.1 meq/100 g soil d.w.

Bulk density (g/cm³):

1.18

Details on matrix:

See table 1 under Any other information on materials and methods

Details on test conditions:

Isotherms were determined for each soil, in duplicate at soil:solution ratios of 1:1. All soils were assessed at nominal concentrations of 1, 0.5, 0.1, 0.05 and 0.01 µg/mL. The duration of the adsorption step was 6 hours, and no desorption step was conducted due to the suspected instability of the test substance. Blank controls were also prepared for each soil type.

The supernatants and soil extracts were analysed for all soils, and all samples were used to assess mass balance.

A stock solution at 1000 µg/mL of the test substance was prepared by dissolving circa 10 mg in 10 mL of water/acetonitrile (90/10, v/v) in a flask. This stock solution was used to prepare intermediate solutions at defined lower concentrations, from which the treatment solutions were prepared. These were used to fortify the soil samples.

Replicates of each soil (circa 2 g) in 50 mL polypropylene tubes were equilibrated with 1.8 mL of 0.01M CaCl2 overnight on an end-over-end shaker. An aliquot of 0.2 mL of treatment solutions was added to the samples to give a final solution volume of 2 mL, resulting in 1:1 ratio.

The test temperature was 20 ± 2 °C and the equilibration duration in the adsorption step was 6 hours. No desorption step was performed.

Duration:

6 h

Temp.:

20 °C

Remarks:

Duration of adsorption equilibration for all soils and test concentrations

Remarks:

No desorption testing was performed as the decrease in mass balance after 7 hours shaking time indicated instability of the test substance.

Key result

Sample No.:

#1

Type:

Koc

Value:

8.2 L/kg

pH:

5.35

Temp.:

20 °C

Matrix:

Seven Springs

% Org. carbon:

0.54

Remarks on result:

other: Average over all concentrations

Key result

Sample No.:

#2

Type:

Koc

Value:

25 L/kg

pH:

5.78

Temp.:

20 °C

Matrix:

18 Acres

% Org. carbon:

1.8

Remarks on result:

other: Average over all concentrations

Key result

Sample No.:

#3

Type:

Koc

Value:

28.6 L/kg

pH:

6.23

Temp.:

20 °C

Matrix:

Sarpy

% Org. carbon:

2.2

Remarks on result:

other: Average over all concentrations

Key result

Sample No.:

#4

Type:

Koc

Value:

10.9 L/kg

pH:

7.25

Temp.:

20 °C

Matrix:

Gartenacker

% Org. carbon:

1.8

Remarks on result:

other: Average over all concentrations

Key result

Sample No.:

#5

Type:

Koc

Value:

18.2 L/kg

pH:

7.65

Temp.:

20 °C

Matrix:

Marsillargues

% Org. carbon:

1.1

Remarks on result:

other: Average over all concentrations

Adsorption and desorption constants:

The following Freundlich coefficients were determined:
- Seven Springs: KF = 0.0343, KFOC = 6, 1/n = 0.9169
- 18 Acres: KF = 0.3941, KFOC = 22, 1/n = 0.9535
- Sarpy: KF = 0.4891, KFOC = 22, 1/n = 0.9116
- Gartenacker: KF = 0.2448, KFOC = 14, 1/n = 1.1179
- Marsillargues: KF = 0.1349, KFOC = 12, 1/n = 0.8512

Recovery of test material:

Mean recovery was within 90 to 110%.

Concentration of test substance at end of adsorption equilibration period:

See table in "Any other information on results including tables"

Concentration of test substance at end of desorption equilibration period:

No desorption testing was performed as the decrease in mass balance after 7 hours shaking time indicated instability of the test substance.

Sample no.:

#1

Duration:

6 h

% Adsorption:

108 - 112

Sample no.:

#2

Duration:

6 h

% Adsorption:

103 - 113

Sample no.:

#3

Duration:

6 h

% Adsorption:

97 - 108

Sample no.:

#4

Duration:

6 h

% Adsorption:

104 - 114

Sample no.:

#5

Duration:

6 h

% Adsorption:

102 - 108

Transformation products:

no

Details on results (Batch equilibrium method):

The results are shown under "Any other information on results incl. tables"

Statistics:

Not reported

Table 2: Details on experimental results for partition coefficients

Soil	Nominal rate applied aqueous phase (µg/mL)	Partition coefficients		Freundlich coefficients
		Kd	Koc	KF	KFOC	1/n
7 Springs	0.010	0.04	6.5	0.0343	6	0.9169
	0.050	0.08	13.9
	0.100	0.04	6.5
	0.500	0.06	10.2
	1.000	0.02	3.2
	Average	0.05	8.2
18 Acres	0.010	0.44	24.5	0.3941	22	0.9535
	0.050	0.50	27.8
	0.100	0.48	26.7
	0.500	0.50	27.5
	1.000	0.33	18.4
	Average	0.45	25.0
Sarpy	0.010	0.68	30.7	0.4891	22	0.9116
	0.050	0.79	35.9
	0.100	0.65	29.4
	0.500	0.58	26.1
	1.000	0.46	20.9
	Average	0.63	28.6
Gartenacker	0.010	0.12	6.7	0.2448	14	1.1179
	0.050	0.19	10.3
	0.100	0.23	12.5
	0.500	0.25	13.7
	1.000	0.20	11.1
	Average	0.20	10.9
Marsillargues	0.010	0.25	22.3	0.1349	12	0.8512
	0.050	0.25	22.7
	0.100	0.19	16.8
	0.500	0.22	19.6
	1.000	0.11	9.6
	Average	0.20	18.2

Table 3: Concentrations of the test substance in the supernatant and soil at the end of the adsorption equilibration after 6 hours.

Nominal concentration [µg/mL]	Applied mass [µg]	Seven Springs		18 Acre		Sarpy		Gartenacker		Marsillargues
		Conc. in aqueous supernatant [µg/mL]	Conc. in soil extract [µg/g]	Conc. in aqueous supernatant [µg/mL]	Conc. in soil extract [µg/g]	Conc. in aqueous supernatant [µg/mL]	Conc. in soil extract [µg/g]	Conc. in aqueous supernatant [µg/mL]	Conc. in soil extract [µg/g]	Conc. in aqueous supernatant [µg/mL]	Conc. in soil extract [µg/g]
0.01	0.02	0.010	0.020A	0.007	0.007	0.006	0.008	0.009	0.007	0.008	0.007
		0.010	0.005	0.007	0.008	0.006	0.007	0.009	0.007	0.008	0.006
0.05	0.10	0.047	0.021	0.033	0.038	0.028	0.034	0.041	0.034	0.040	0.029
		0.046	0.026	0.033	0.037	0.028	0.035	0.041	0.033	0.040	0.030
0.10	0.20	0.097	0.046	0.067	0.071	0.061	0.076	0.080	0.071	0.082	0.056
		0.096	0.047	0.067	0.070	0.060	0.077	0.079	0.071	0.085	0.056
0.50	1.00	0.465	0.214	0.339	0.363	0.322	0.378	0.411	0.350	0.399	0.269
		0.479	0.222	0.325	0.350	0.310	0.388	0.378	0.373	0.415	0.288
1.00	2.00	0.972	0.445	0.712	0.747	0.638	0.750	0.794	0.758	0.865	0.579
		0.976	0.464	0.776	0.800	0.721	0.763	0.834	0.767	0.922	0.541
A Suspected contamination or mis-spike. Sample excluded from any further calculations.

Validity criteria fulfilled:

yes

Conclusions:

The adsorption potential of the test substance was tested in a guideline-compliant GLP batch equilibrium test. Five soils were used in the study and the Koc was found to range from 8.2 to 28.6 across all soils. Following the McCall Classification scale, the mobility in soil of the test substance is classified as "very high".

Executive summary:

The adsorption characteristics of the test substance were studied in five different soils using a standard batch equilibrium method at 20 °C under GLP and in accordance with OECD Test Guideline 106. The five soils were: Seven Springs (loamy sand, USA), 18 Acres (sandy clay loam, UK), Sarpy (loam, USA), Gartenacker (silt loam, Switzerland) and Marsillargues (silty clay, France). The chemical was added to a mixture of soil and aqueous slurries resulting in a final nominal composition of 2 g of soil and 2 mL aqueous 0.01M CaCl2 solution for all soils. Five nominal test concentrations were applied for each soil (0.01, 0.05, 0.1, 0.5 and 1.0 µg/mL). The soil adsorption coefficients Kd and KOC together with the Freundlich adsorption constants KF and KFOC were determined for each soil.

Only the adsorption phase was assessed. Preliminary testing indicated a lack of stability after a period of about 7 hours, and therefore testing of desorption would not have been accurate. The 6 hour time point was chosen for the definite isotherm test. Mass balances of the applied test substance concentrations were determined at all concentrations by LC/MSMS.

For all soils the recovery was quantitative and mass balances ranged from 96% to 116% for all five soils at all concentrations. The mass balance data confirmed that the test substance was stable over the 6 -hour duration of the definite test. The calculated Freundlich coefficients (KF) ranged from 0.0343 to 0.4891, while the 1/n values ranged from 0.8512 to 1.1179. When corrected for the organic matter content of the soils, the resultant KFOC values ranged from 6 to 22. The partition coefficients Kd ranged from 0.05 to 0.63 with the corresponding Koc values ranging from 8.2 to 28.6. These data indicate that the test substance was very weakly adsorbed to the soils studied.

Description of key information

The adsorption potential of the test substance was tested in a guideline-compliant GLP batch equilibrium test. Five soils were used in the study and the Koc was found to range from 8.2 to 28.6 across all soils.

Key value for chemical safety assessment

Koc at 20 °C:

28.6

Additional information

The adsorption characteristics of the test substance were studied in five different soils using a standard batch equilibrium method at 20 °C under GLP and in accordance with OECD Test Guideline 106. The five soils were: Seven Springs (loamy sand, USA), 18 Acres (sandy clay loam, UK), Sarpy (loam, USA), Gartenacker (silt loam, Switzerland) and Marsillargues (silty clay, France). The chemical was added to a mixture of soil and aqueous slurries resulting in a final nominal composition of 2 g of soil and 2 mL aqueous 0.01M CaCl2 solution for all soils. Five nominal test concentrations were applied for each soil (0.01, 0.05, 0.1, 0.5 and 1.0 µg/mL). The soil adsorption coefficients Kd and KOC together with the Freundlich adsorption constants KF and KFOC were determined for each soil.

Only the adsorption phase was assessed. Preliminary testing indicated a lack of stability after a period of about 7 hours, and therefore testing of desorption would not have been accurate. The 6 hour time point was chosen for the definite test. For all soils the mass balances ranged from 96% to 116% for all five soils at all concentrations. The Koc values ranged from 8.2 to 28.6. These data indicate that the test substance was very weakly adsorbed to the soils studied. Following the McCall Classification scale, the mobility in soil of the test substance is classified as "very high".

The adsorption coefficient of the test material was determined in accordance with standardised guideline OECD 121 using a High Performance Liquid Chromatography (HPLC) method. The dead time of the HPLC system was determined by the use of a suitable inert substance that was not retained by the column. The capacity factors (k’) for the test material and reference substances were then calculated and the log k’ values were plotted against their adsorption coefficient values (log Koc) to construct a calibration curve. The calibration curve was used to estimate the adsorption coefficient of the test item using its experimentally determined k’. The estimated log Koc for the test material was 1.80 (Koc = 63). The guidelines suggested the use of reference compound that were structurally similar to the test material. A calibration curve was constructed using only the reference compounds that were structurally similar to the test material and the Koc estimated using this curve. The estimated log Koc was 1.94 (Koc = 87). The potential mobility of the test material as according to the McCall classification was high.