thiamethoxam (ISO); 3-(2-chloro-thiazol-5-ylmethyl)-5-methyl[1,3,5]oxadiazinan-4-ylidene-N-nitroamine

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption, other

Remarks:

Batch equilibrium method

Type of information:

experimental study

Adequacy of study:

key study

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:

May 1981

GLP compliance:

yes

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Remarks:

14C-labelled at position 2 of thiazole ring

Test temperature:

20 °C

Analytical monitoring:

yes

Details on sampling:

- Adsorption phase: After the adsorption phase the flasks were centrifuged and 50 mL of the supernatant taken from each flask (whole volume was utilized for mass balance).
- Desorption phase: For the 1st desorption phase the 50 mL supernatant removed from each flask after the adsorption step was replaced with 50 mL untreated 0.01 M CaCl2 solution, and same procedure as before was carried out. For the 2nd desorption step all supernatant was removed; therefore 100 mL of untreated 0.01 M CaCl2 was added per flask.

Matrix no.:

#1

Matrix type:

loam

% Clay:

11.9

% Silt:

48

% Sand:

40.1

% Org. carbon:

2

pH:

7.1

CEC:

12.7 meq/100 g soil d.w.

Matrix no.:

#2

Matrix type:

silt loam

% Clay:

23.3

% Silt:

58.5

% Sand:

18.2

% Org. carbon:

4.7

pH:

7.2

CEC:

28.1 meq/100 g soil d.w.

Matrix no.:

#3

Matrix type:

other: Humic soil

% Org. carbon:

19.8

pH:

6.7

CEC:

102.8 meq/100 g soil d.w.

Details on matrix:

For a full listing of test soil specifics, see the data table at 'Any other information on materials and methods incl. tables'.

Details on test conditions:

ADSORPTION PHASE
- Soil sample weight: ~ 30 g, 15 g and 30 g (dry weight) for Gartenacker, lllarsaz and Vetroz respectively
- Equilibration solution: 0.01M CaCl2
- Control conditions: No soil (test item in 0.01M CaCl2 only)
- Test apparatus: glass flasks and caps
- Number of replicates of control: 1
- Number of replicates of treatment: 1
- Solvent used: Test substance dosed in 0.01M CaCl2 (test substance dissolved in acetonitrile)
- Volume of test solution used/treatment: ~100 mL for all soils
- Application method: Graduated cylinder
- Evaporation of application solvent: No
- Nominal application rates: 0 (control), 0.10, 0.20, 0.5, 1.00 and 2.00 µg a.s./mL for all soils
- Indication of test material adsorbing to walls of test apparatus: The adsorption of the test substance to the glass surfaces was tested by radioassaying tubes containing only test solution during the adsorption phase of the preliminary trial. No significant adsorption to glass was observed.
- Time to equilibrate: 24h
- Continuous darkness: Yes
- Shaking method: Reciprocating shaker
- Method of separation of supernatant: Centrifugation (3500 rpm for 3 min) and decanting

DESORPTION PHASE
- Soil samples from adsorption phase used: Yes
- Number of desorption cycles: 2 for all dose rates
- Equilibration solution: 0.01 M CaCl2 (50ml or 100ml)
- Control conditions: Not performed
- Number of replicates (treated samples): 1(at each concentration and soil); 2 (Vetroz soil))
- Time to equilibrate: 24h
- Continuous darkness: Yes
- Shaking method: Reciprocating shaker
- Method of separation of supernatant: Centrifugation (2500 rpm for 3 min) and decanting

Duration:

24 h

Temp.:

20 °C

Remarks:

duration of adsorption-equilibration for all 3 soils and test concentrations.

Duration:

24 h

Temp.:

20 °C

Remarks:

duration of desorption-equilibration for all 3 soils and test concentrations.

Sample No.:

#1

Type:

other: Freundlich Koc

Value:

33 L/kg

pH:

7.1

Temp.:

20 °C

Matrix:

Loam (Gartenacker)

% Org. carbon:

2

Remarks on result:

other: For a full list of adsorption and desorption coefficients, see 'Any other information on results incl. tables'

Sample No.:

#2

Type:

other: Freundlich Koc

Value:

32.5 L/kg

pH:

7.2

Temp.:

20 °C

Matrix:

Silt loam (Vetroz)

% Org. carbon:

4.7

Remarks on result:

other: Performed with duplicate samples. The Freundlich Koc is the mean of the two values.

Sample No.:

#3

Type:

other: Freundlich Koc

Value:

35 L/kg

pH:

6.7

Temp.:

20 °C

Matrix:

Humic soil (Illarsaz)

% Org. carbon:

19.8

Recovery of test material:

The mass balance ranged between 98.43 and 99.54 % recovery of the applied dose for the three soils tested. Analysis of the acetone soil extracts after the adsorption step showed that the adsorbed radioactivity consisted entirely of parent compound.
Total recovery (as sum of % not adsorbed + % desorbed with acetone + % not extractable):
- Soil #1 (Gartenacker): 98.81 - 98.47%
- Soil #2 (Vetroz): 98.43 - 98.89%
- Soil #3 (Illarsaz): 98.64 - 99.54%
A complete overview of the recovery of radioactivity following a 24h adsorption phase for the highest application rate (2.00 mg/L) are presented in 'Any other information on materials and methods incl. tables'.

Concentration of test substance at end of adsorption equilibration period:

Concentrations of radiolabelled test substance (in the adsorption and desorption supernatants and adsorbed to the soil at the end of the adsorption and desorption phase are presented in 'Any other information on results incl. tables'.

Concentration of test substance at end of desorption equilibration period:

Concentrations of radiolabelled test substance (in the adsorption and desorption supernatants and adsorbed to the soil at the end of the adsorption and desorption phase are presented in 'Any other information on results incl. tables'.

Remarks on result:

other: see 'Any other information on results incl. tables'.

Remarks on result:

other: see 'Any other information on results incl. tables'.

Transformation products:

no

Details on results (Batch equilibrium method):

The results are tabulated in detail in 'Any other information on results incl. tables'.

Statistics:

Not reported

Table: Soil adsorption constants

Parameter	Gartenacker	Vetroz		Illarsaz
Soil number	#1	#2		#3
Texture	Loam	Silt loam		Humic soil
Adsorption
Experiment	A	C	D	B
Kf	0.66	1.50	1.56	6.94
KfOC	33	32	33	35
1/n	0.9126	0.8907	0.9190	0.9323
r2	0.9967	0.9993	0.9990	0.9998
1^stDesorption
Experiment	A	C	D	B
Kf	0.84	1.48	1.55	7.74
KfOC	42	31	33	39
1/n	0.9646	0.8744	0.9086	0.9596
r2	0.9943	0.9976	0.9983	0.9997
2^ndDesorption
Experiment	A	C	D	B
Kf	1.73	1.60	1.92	9.48
KfOC	87	34	41	48
1/n	1.0726	0.8658	0.9482	0.9799
r2	0.9819	0.9939	0.9950	0.9995

Table: Mass balance after adsorption (concentration: 2.00 mg/l)

Soil	Sample	% Not adsorbed*	% Desorbed with acetone**	% Not extractable	Total Recovery (%)
Gartenacker Soil #1	B1	85.04	11.05	2.72	98.81
	B2	84.25	11.40	2.82	98.47
Vetroz Soil #2	B1	51.51	41.30	6.08	98.89
	B2	51.20	41.21	6.02	98.43
Illarsaz Soil #3	B1	71.33	23.27	4.94	99.54
	B2	71.03	22.98	4.63	98.64

* In water phase after the adsorption step

**Consisted entirely of parent compound

Table: Concentration of the radiolabelled test substance in the supernatant and soil at the end of adsorption and desorption equilibration period in Gartenacker Soil (Soil #1)

Nominal dose level (µg/mL)	Adsorption		1st Desorption		2nd Desorption
	Conc. in solution (µg/mL)	Conc. in soil (µg/g)	Conc. in solution (µg/mL)	Conc. in soil (µg/g)	Conc. in solution (µg/mL)	Conc. in soil (µg/g)
0.25	0.2080	0.1470	0.1174	0.0965	0.0339	0.0383
0.50	0.4079	0.3223	0.2285	0.2283	0.0645	0.1179
1.0	0.8354	0.5476	0.4519	0.4105	0.1264	0.1991
1.5	1.2646	0.7962	0.6918	0.5637	0.1911	0.2649
2.0	1.6808	1.0499	0.9183	0.7431	0.2420	0.3644

Table: Concentration of the radiolabelled test substance in the supernatant and soil at the end of adsorption and desorption equilibration period in Vetroz Soil (Soil #2)

Nominal dose level (µg/mL)	Replicate	Adsorption		1st Desorption		2nd Desorption
		Conc. in solution (µg/mL)	Conc. in soil (µg/g)	Conc. in solution (µg/mL)	Conc. in soil (µg/g)	Conc. in solution (µg/mL)	Conc. in soil (µg/g)
0.25	C	0.1624	0.2952	0.1066	0.2053	0.0439	0.1063
	D	0.1610	0.2964	0.1059	0.2065	0.0445	0.1053
0.50	C	0.3234	0.5537	0.2073	0.3914	0.0858	0.1995
	D	0.3248	0.5471	0.2112	0.3735	0.0861	0.1823
1.0	C	0.6663	1.0190	0.4332	0.6642	0.1681	0.3091
	D	0.6612	1.0274	0.4311	0.6713	0.1683	0.3129
1.5	C	1.0051	1.5712	0.6447	1.0648	0.2496	0.5357
	D	0.9873	1.6244	0.6450	1.0876	0.2519	0.5534
2.0	C	1.3494	1.9079	0.8541	1.2669	0.3258	0.5861
	D	1.3265	2.0004	0.8460	1.3499	0.3236	0.6797

Concentration of the radiolabelled test substance in the supernatant and soil at the end of adsorption and desorption equilibration period in Illarsaz Soil (Soil #3)

Nominal dose level (µg/mL)	Adsorption		1st Desorption		2nd Desorption
	Conc. in solution (µg/mL)	Conc. in soil (µg/g)	Conc. in solution (µg/mL)	Conc. in soil (µg/g)	Conc. in solution (µg/mL)	Conc. in soil (µg/g)
0.25	0.1149	0.9466	0.0849	0.7255	0.0460	0.4639
0.50	0.2274	1.7670	0.1660	1.4022	0.0891	0.9030
1.0	0.4681	3.3861	0.3388	2.6567	0.1779	1.6709
1.5	0.7127	5.1782	0.5092	4.1149	0.2672	2.6390
2.0	0.9730	6.6627	0.6761	5.3364	0.3491	3.4144

Validity criteria fulfilled:

not specified

Conclusions:

Adsorption/Desorption isotherms of the test substance were determined using three soils. Adsorption Kfoc values ranged from 32 to 35 mL/g. These Kfoc values predict that the test substance can be classified as mobile.

Executive summary:

The adsorption/desorption characteristics of the substance was studied in a standard batch equilibrium method according to OECD TG 106 and in compliance with GLP criteria. In this study, radiolabelled test item at nominal application rates of 0.25, 0.50, 1.00, 1.50 and 2.00 mg/L prepared in 0.01M CaCl2 was added to 3 different soils with varying properties (i.e. texture, organic matter- and carbon-content, pH etc.) and equilibrated at 20 °C in the dark. The soils that were used were a loam type soil ('Gartenacker'), a silty loam type soil ('Vetroz') and a humic soil ('Illarsaz'). For the preliminary test 5 soils were used, but only those that adsorbed more than 10% of the test substance were used in the definitive test. The soil:solution ratio (g/mL) used was different for each soil (~ 30:100, 15:100 and 30:100 for 'Gartenacker', 'lllarsaz' and 'Vetroz', respectively). The equilibrium time for adsorption and desorption experiments was set to 24 hours.

Supernatants were radioassayed with LSC by triplicate. For the determination of the stability, the test item in the supernatant was quantified and identified using TLC.  The extracted soils were analyzed by combustion and LSC and the extracts by TLC. The total recovery of the radioactivity (as sum of % not adsorbed + % desorbed with acetone + % not extractable) was determined by radioassay for all soils at the highest concentration tested. Based on the results, the soil adsorption coefficients Kd and Koc, together with the Freundlich adsorption constants Kf and KFoc, were determined for each soil.

The Freundlich adsorption coefficient varied between 0.66 mL/g for the loam soil to 6.94 mL/g for the humic soil. An average Kfoc value of 33 mL/g was calculated. The slopes 1/n for the adsorption isotherms ranged between 0.8907 (silty loam) and 0.9323 (humic soil). Desorption of the test substance from the soils was nearly equal to adsorption as shown by the very similar desorption coefficients (kf= 0.84 to 7.74 mL/g) calculated after the first desorption step. The values after the second desorption step were in the same order of magnitude. The mass balance ranged between 98.43 and 99.54 % recovery of the applied dose for the three soils tested. Analysis of the acetone soil extracts after the adsorption step showed that the adsorbed radioactivity consisted entirely of parent compound.

Description of key information

Kfoc-ads of 32.5 - 35, batch equilibrium method, OECD TG 106, Keller 1996.

The geometric mean of all reliable adsorption data is used as key value for chemical safety assessment.

Key value for chemical safety assessment

Koc at 20 °C:

53.04

Additional information

The adsorption coefficient of the substance in a broad range of soils has been investigated in valid and reliable GLP studies conducted to the relevant test guidelines (OECD TG 106, EPA 163-1). The geometric mean value of all experimental Koc values (n = 25) was calculated and used as a representative value for use in the chemical safety assessment.

Table: Overview of reliable data on adsorption / desorption of the test item 

Method			Guideline / GLP	Endpoint	Value (mL/g)	Reference
Test medium	pH	%OC
Silt loam (Gartenacker, CH)	7.1	2.00	OECD TG 106 / GLP	Kfoc-Ads	33	Keller, 1996
Silt loam (Vetrox, CH)	7.2	4.70		Kfoc-Ads	32.5
Humic silt loam (Illarsaz, CH)	6.7	19.80		Kfoc-Ads	35
Sandy clay loam (Carman, Manitoba, USA)	6.2	3.0	EPA 163-1 / GLP	Kfoc-Ads	77.2	Concha, 1998
Loam (Plattsville, Ontario, USA)	6.2	3.0		Kfoc-Ads	53.1
Sandy loam (Sanger, California, USA)	7.6	0.4		Kfoc-Ads	176.7
Sand (Andersonville, Georgia, USA)	5.4	0.5		Kfoc-Ads	43.0
Loam (Niagara, New York, USA)	7.2	1.7		Kfoc-Ads	38.3
Silty clay loam (Niagara, New York, USA)	6.5	2.4		Kfoc-Ads	33.1
Loamy sand (Birkenheide, D)	6.0	0.9	OECD TG 106 / GLP	Kfoc-Ads	33	Hein, 2001
Loamy sand (Three Rivers, Michigan, USA)	6.9	0.70	EPA 163-1 / GLP	Kfoc-Ads	45.1	McKillan 2006
Loamy sand (Three Rivers, Michigan, USA)	6.9	0.70		Kfoc-Ads	24.5
Sand (Americus, Georgia, USA)	7.2	0.52	EPA 163-1 / GLP	Kfoc-Ads	54.8	Moore 2007
Sand(Americus, Georgia, USA)	7.2	0.52		Kfoc-Ads	59.4
Sandy clay loam (Argissolo) (Eldorado do Sul, BR)	5.4 (H2O)	2.2		Kfoc-Ads	36	Monego, 2008
Clay (Latossolo) (Nova Prata, BR)	4.9 (H2O)	1.9		Kfoc-Ads	40
Sand (Neossolo) (Osorio, BR)	5.9 (H2O)	1.0		Kfoc-Ads	31
Sandy loam (Gleissolo) (Viamão, BR)	4.3 (H2O)	4.9		Kfoc-Ads	237
Sandy loam (Belle Gade, Florida, USA)	7.2	28.3	OECD TG 106 / GLP	Kfoc-Ads	88	Crabtree, 2015
Clay loam (Coalinga, California, USA)	7.6	0.6		Kfoc-Ads	80
Loam (Conklin, Michigan, USA)	7.3	1.2		Kfoc-Ads	35
Silty clay loam (Dewey, Illinois, USA)	6.9	1.9		Kfoc-Ads	81
Sand (Oviedo, Florida, USA)	6.7	0.3		Kfoc-Ads	32
Loamy sand (Wilson, North Carolina, USA)	6.3	0.7		Kfoc-Ads	64
Silt loam / loam (Winterville, Mississippi, USA)	5.4	0.4		Kfoc-Ads	171
Geometric mean (n=25)					53.04