α-n-butyl-α-(4-chlorophenyl)-1H-1,2,4-triazole-1-propanenitrile

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:

2016-07-18 to 2017-09-26

Reliability:

1 (reliable without restriction)

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Test temperature:

20 ± 2°C.

Analytical monitoring:

yes

Details on sampling:

Nominal test item concentrations of 1.25, 0.625, 0.125, 0.0625 and 0.0125 µg/mL. Duplicate samples were prepared for each soil for analysis at each concentration.

Matrix no.:

#1

Matrix type:

silty clay

% Clay:

42

% Silt:

42

% Sand:

16

% Org. carbon:

1.6

CEC:

16.5 meq/100 g soil d.w.

Matrix no.:

#2

Matrix type:

loam

% Clay:

26

% Silt:

45

% Sand:

29

% Org. carbon:

5

CEC:

18.5 meq/100 g soil d.w.

Matrix no.:

#3

Matrix type:

clay loam

% Clay:

39

% Silt:

21

% Sand:

40

% Org. carbon:

7.6

CEC:

33.1 meq/100 g soil d.w.

Matrix no.:

#4

Matrix type:

loamy sand

% Clay:

7

% Silt:

8

% Sand:

85

% Org. carbon:

1.46

CEC:

5.7 meq/100 g soil d.w.

Matrix no.:

#5

Matrix type:

silt loam

% Clay:

19

% Silt:

50

% Sand:

31

% Org. carbon:

2.85

CEC:

14.8 meq/100 g soil d.w.

Details on matrix:

Soil 1: Fr1, (St Bauzille de la Silve, Herault, France).
Soil 2: E1, (Brierlow, Derbyshire, UK)
Soil 3: J1, (Chapel Hill Farm, Rutland, UK)
Soil 4: A1, (Warsop, Nottinghamshire, UK)
Soil 5: E3, (Kenslow Farm, Derbyshire, UK)

Soil 1 PH in water, in 0.01 M CaCl2: 8.2, 7.7.
Soil 2 PH in water, in 0.01 M CaCl2: 5.9, 5.3.
Soil 3 PH in water, in 0.01 M CaCl2: 8.0, 7.4.
Soil 4 PH in water, in 0.01 M CaCl2: 4.2, 3.7.
Soil 5 PH in water, in 0.01 M CaCl2: 5.7, 5.5.

USDA 1995 textural classification system. Air dried soil, passed through 2 mm sieve prior to use.

Details on test conditions:

SETUP:
The sample tubes used in this study were 50 mL polypropylene conical-based centrifuge tubes. An appropriate amount of the air dried soil was weighed into clean, conical tubes. End-over-end shakers were rotating cylinders to which the centrifuge tubes were attached for the required periods. Equilibration of test item in soil and 0.01 M CaCl2 was carried out in the dark in a temperature controlled room maintained at 20 ± 2°C. Centrifugation and measurement of the supernatants was carried out at ambient temperature under normal laboratory lighting conditions.
Weights of soil (ca 1.75 g for E1, J1, A1 and A3, soils and ca 8.75 g for Fr1 soil, at the optimal soil solution ratio) when referred to in the text as being weighed into the centrifuge tubes, are for air dried soil. For calculation of the adsorption/desorption parameters the moisture content of air dried soils has been corrected for in the calculations and results are expressed on an oven dry basis.

Equilibration solution: 0.01M CaCl2 (31.5 mL).
Control conditions (blank): Soil and 0.01M CaCl2 (no test item); 0.01M CaCl2 and test item (no soil).
Replicates: Blank:1, treated: 2.
Soil to Solution ratio: 1:20 for E1, J1, A1 and A3; 1:4 for Fr1
Centrifugation: 3000 G, 15 minutes, decanting supernatant.

Sample No.:

#1

Duration:

48 h

Temp.:

20 °C

Remarks:

End-ove- end shaker

Sample No.:

#2

Duration:

48 h

Temp.:

20 °C

Remarks:

End-over-end shaker

Sample No.:

#3

Duration:

48 h

Temp.:

20 °C

Remarks:

End-over-end shaker

Sample No.:

#4

Duration:

48 h

Temp.:

20 °C

Remarks:

End-over-end shaker

Sample No.:

#5

Duration:

48 h

Temp.:

20 °C

Remarks:

End-over-end shaker

Sample no.:

#1

Duration:

24 h

Temp.:

20 °C

Remarks:

End-over-end shaker

Sample no.:

#2

Duration:

24 h

Temp.:

20 °C

Remarks:

End-over-end shaker

Sample no.:

#3

Duration:

24 h

Temp.:

20 °C

Remarks:

End-over-end shaker

Sample no.:

#4

Duration:

24 h

Temp.:

20 °C

Remarks:

End-over-end shaker

Sample no.:

#5

Duration:

24 h

Temp.:

20 °C

Remarks:

End-over-end shaker

Key result

Sample No.:

#1

Type:

Koc

Value:

> 410 - < 637 L/kg

pH:

7.7

Temp.:

20 °C

% Org. carbon:

1.6

Remarks on result:

other: Silty Clay

Key result

Sample No.:

#2

Type:

Koc

Value:

> 630 - < 886 L/kg

pH:

5.3

Temp.:

20 °C

% Org. carbon:

5

Remarks on result:

other: Loam

Key result

Sample No.:

#3

Type:

Koc

Value:

> 275 - < 588 L/kg

pH:

7.4

Temp.:

20 °C

% Org. carbon:

7.6

Remarks on result:

other: Clay Loam

Key result

Sample No.:

#4

Type:

Koc

Value:

> 1 070 - < 1 506 L/kg

pH:

3.7

Temp.:

20 °C

% Org. carbon:

1.5

Remarks on result:

other: Loamy Sand

Key result

Sample No.:

#5

Type:

Koc

Value:

> 720 - < 1 020 L/kg

pH:

5.5

Temp.:

20 °C

% Org. carbon:

2.9

Remarks on result:

other: Silt Loam

Key result

Sample No.:

#1

Type:

Kd

Value:

> 6.56 - < 10.2 L/kg

pH:

7.7

Temp.:

20 °C

% Org. carbon:

1.6

Remarks on result:

other: Silty Clay

Key result

Sample No.:

#2

Type:

Kd

Value:

> 31.49 - < 44.29 L/kg

pH:

5.3

Temp.:

20 °C

% Org. carbon:

5

Remarks on result:

other: Loam

Key result

Sample No.:

#3

Type:

Kd

Value:

> 20.9 - < 44.66 L/kg

pH:

7.4

Temp.:

20 °C

% Org. carbon:

7.6

Remarks on result:

other: Clay Loam

Key result

Sample No.:

#4

Type:

Kd

Value:

> 15.62 - < 21.99 L/kg

pH:

3.7

Temp.:

20 °C

% Org. carbon:

1.5

Remarks on result:

other: Loamy Sand

Key result

Sample No.:

#5

Type:

Kd

Value:

> 20.52 - < 30.5 L/kg

pH:

5.5

Temp.:

20 °C

% Org. carbon:

2.9

Remarks on result:

other: Silt Loam

Adsorption and desorption constants:

Please see Table 1 and Table 2 below.

Recovery of test material:

The material balance at each concentration of each test soil was determined. The material
balance at the highest concentration was determined as the sum of the amount of test substance
in the adsorption and desorption phases, soil extracts and extracted soil residues. This procedure
was also carried out for all loamy sand (A1) samples as the initial mass balance results were
below 90% AR. For the remaining samples the mass balance was determined from the sum of
the amount of test substance in the adsorption and desorption phases and soil residues. The
material balances ranged from mean values of 92.9% to 100.5% AR for all soils, which were
within the acceptable guideline range of 90-110% of the applied radioactivity.

Transformation products:

not specified

Details on results (Batch equilibrium method):

SOLUBILITY AND ADDSORPTION TO TEST VESSELS:
The solubility of the test item was measured to determine if the test item was soluble at a concentration of at least 20 µg/mL. Therefore, the highest test solution concentration of 1.25 µg/mL was safely below the aqueous solubility limit.
Adsorption tests showed no adsorption to either polypropylene centrifuge tubes or amber glass
jars.

ADSORPTION:
The values for the adsorption coefficients, Kd and Koc were calculated for all five soils at each of the five test solution concentrations. The values for the Freundlich adsorption isotherm parameters, KF, KFoc and 1/n were derived from the linear form of the Freundlich equation for all five test systems. The values of Koc from the adsorption isotherms indicate that [14C]-myclobutanil has a medium to low mobility in soil. The results of the values of 1/n for each of the systems (ca > 0.9, except J1 Clay Loam) indicates that adsorption is linear over the range of concentrations tested. The random variation in Kd values with respect to soil organic carbon and pH indicates that there is no correlation between adsorption and the organic carbon content or pH of the test system.

DESORPTION:
The values for the desorption coefficients, Kdes and Koc,des were calculated for all five soils at each of the five test solution concentrations. The values for the Freundlich desorption isotherm parameters, KF,des, KFoc,des and 1/n were derived from the linear form of the Freundlich equation for all five test systems. The results from the desorption isotherms indicate that desorption is linear over the range of concentrations tested., with the value of 1/n for each of the systems ca > 0.9 (except J1, Clay Loam). The range of Koc,des / KFoc,des values indicates that there is not a strong correlation between desorption and the organic carbon content of the test system.

Table 1: Adsorption coefficients

Soil	Kd (mL/g)	Koc (mL/g)	KF	KFOC	1/n
Fr1, Silty Clay	6.56-10.20	410-637	6.18	386	0.909
E1, Loam	31.49-44.29	630-886	29.65	593	0.925
J1, Clay Loam	20.90-44.66	275-588	18.32	241	0.853
A1, Loamy Sand	15.62-21.99	1070-1506	15.35	1051	0.917
E3, Silt Loam	20.52-30.50	720-1070	20.28	711	0.913

Table 2: Desportion coefficients

Soil	Kdes (mL/g)	Koc,des (mL/g)	KF,des	KFOC, des	1/n
Fr1, Silty Clay	10.77-15.65	673-978	7.87	492	0.916
E1, Loam	47.00-64.72	940-1294	38.19	764	0.928
J1, Clay Loam	32.76-62.10	431-817	23.12	304	0.859
A1, Loamy Sand	26.03-33.43	1735-2229	27.29	1869	0.996
E3, Silt Loam	34.16-55.37	1178-1909	26.49	929	0.901

 

Conclusions:

The arithmetic mean of the Koc-value of myclobutanil was calculated to be 774 at 20°C.

Based on the results of the study [14C]-myclobutanil was shown to have medium to low mobility in the soils tested. The 1/n values for both adsorption and desorption indicated that both adsorption and desorption were linear over the range of concentrations tested. No correlation was observed between the pH or organic carbon content of the test system and the Kd values.

Executive summary:

The study was designed to investigate the adsorption and desorption properties of [14C]-myclobutanil in 5 soil types. The experiment was conducted in accordance with the OECD Guidelines for testing of chemicals, OECD Guideline 106: Adsorption-Desorption Using a Batch Equilibrium Test (January 2000).

The adsorption and desorption properties of [14C]-myclobutanil were investigated in the current study to assess its potential mobility in soils. The adsorption coefficients (K_d and K_oc), the desorption coefficients (K_des and K_oc,des), the Freundlich adsorption isotherm parameters (K_F, K_Foc and 1/n) and the Freundlich desorption isotherm parameters (K_F,des, K_Foc,des, and 1/n) were calculated.
The texture (USDA) of the soils included silty clay (Fr1), loam (E1), clay loam (J1), loamy sand (A1) and silt loam (E3). The percent organic matter of the soils ranged from 2.7% to 13.1% (1.6% to 7.6% organic carbon). The pH ranged from 3.7 to 7.7 as measured in 1:1 soil:0.01 M CaCl2.

Adsorption and desorption isotherm experiments were performed using the batch equilibration method on all soils with five nominal concentrations (1.25, 0.625, 0.125, 0.0625 and 0.0125 μg/mL) of the test substance in aqueous 0.01 M CaCl2. A desorption cycle was performed on all samples at all concentrations. A 1:20 (w/w) soil-to-solution ratio was used for all soils except Fr1 (S1013) which was tested at a 1:4 (w/w) ratio. 

The sorption coefficients K_d and K_OC were calculated for each soil at each concentration of the test substance. The values for the Freundlich adsorption isotherm parameters K_F, K_Foc, and 1/n were derived from the linear form of the Freundlich equation and summarised below.

 

Soil Type	OC %	Soil pH	Kd (mL/g)	Kdoc (mL/g)	KF (mL/g)	KFoc (mL/g)	1/n
Fr1, Silty Clay	1.6	7.7	6.56-10.20	410-637	6.18	386	0.909
E1, Loam	5.0	5.3	31.49-44.29	630-886	29.65	593	0.925
J1, Clay Loam	7.6	7.4	20.90-44.66	275-588	18.32	241	0.853
A1, Loamy Sand	1.5	3.7	15.62-21.99	1070-1506	15.35	1051	0.917
E3, Silt Loam	2.9	5.5	20.52-30.50	720-1070	20.28	711	0.913
Geometric mean			NA	NA	16.0	528	NA
Arithmetic mean			23.9	774	18.0	596	0.903
Maximum			44.66	1506	29.65	1051	0.925
Minimum			6.56	275	6.18	241	0.853
pH dependence			No

The desorption coefficients, K_des and K_des,oc, were calculated for each soil at the highest test concentration. The values for the Freundlich desorption isotherm parameters K_F, K_Foc, and 1/n were derived from the linear form of the Freundlich equation. A summary of the desorption results for each soil is given in the following table.

Soil Type	OC %	Soil pH	Kdes (mL/g)	K oc,des (mL/g)	KF,des (mL/g)	KFoc,des (mL/g)	1/n
Fr1, Silty Clay	1.6	7.7	10.77-15.65	673-978	7.87	492	0.916
E1, Loam	5	5.3	47.00-64.72	940-1294	38.19	764	0.928
J1, Clay Loam	7.6	7.4	32.76-62.10	431- 817	23.12	304	0.859
A1, Loamy Sand	1.5	3.7	26.03-33.43	1735-2229	27.29	1869	0.996
E3, Silt Loam	2.9	5.5	34.16-55.37	1178-1909	26.49	929	0.901
Geometric mean			NA	NA	21.9	724	NA
Arithmetic mean			36.5	1181	24.6	872	0.900
Maximum			64.72	2229	38.2	1869	0.996
Minimum			10.77	431	7.87	304	0.859
pH dependence			No

Based on the results of the study [14C]-myclobutanil was shown to have medium to low mobility in the soils tested. The Kd values for both adsorption and desorption were slightly higher at lower test item concentrations. No correlation was observed between the organic carbon content or pH of the test system and the Kd values.

Description of key information

In a GLP-study performed according to OECD TG 106, the arithmetic mean of the Koc-value of myclobutanil was calculated to be 774 at 20°C.

Key value for chemical safety assessment

Koc at 20 °C:

774