Thiram

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:

28 April 1995 - 23 May 1995

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

Degradation products of 14C-labelled Thiram were not described in the study.

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

Guideline:

other: EPA 540/9-82-021, Subdivision N; Section 163-1; October 1982

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Analytical monitoring:

yes

Details on matrix:

Details on table below

Details on test conditions:

Aqueous solvent:
0.01 M CaCl2 solution was used as the aqueous solvent phase.
Preparation of the stock solution:
Approximately 1 mg of the radiolabelled test item was dissolved in 1 ml of acetone and afterwards an aliquot of 10 µL was filled up to 10 mL with the same solvent as given above. After measurement by LSC (liquid scintillation counting) the content of 14C-THIRAM in the stock solution was determined to be 1.39 mg/mL.
Application solutions:
Application solution no. 1:
0.2 mL of the stock solution (0.278 mg of radiolabelled THIRAM) was mixed with 0.05 mL of a solution of unlabelled test item in acetone in concentration of 5.51 mg/mL. The resulting solution was dissolved in 0.01 M CaCl2 to a volume of 550 mL. The actual concentration of THIRAM was determined by LSC to be 1.069 mg/L.
Application solution 2, 3, 4:
Appropriate volumes of the application solution 1 were diluted with 0.01 M CaCl2 solution to a volume of 300 mL to obtain the application solutions no. 2, 3 and 4 in concentration of 0.201 mg, 0.041 mg and 0.010 mg THIRAM per litre, respectively.
Stability of the test item during application:
The stability of the radiolabelled test item in the application solution was determined by high-pressure liquid chromatography (HPLC) before and after (about 30 min.) the start of the adsorption test.
Additionally, the application solution in aqueous CaCl2 phase (1 mg/mL) in two control tubes without soil (control samples) was checked for parent compound by HPLC after 12 hours of shaking (adsorption step for four hours and two desorption steps, each for 4 hours).
Soil preparation:
The air dried soil samples were equilibrated by shaking with 0.01 M CaCl2 solution (2:1, vol : mass) overnight, then centrifuged at about 2000 g for 10 minutes. Afterwards the supernatant was discarded and the solution remaining in soil gravimetrically determined.
Blank test per soil with the same amount of soil and total volume of CaCl2 solution was subjected to the same test procedure. This served as a background control during the analysis to detect interfering compounds or contaminated soils.
Two replicates per test soil and one replicate per control and blank sample were prepared for the main test.

Sample No.:

#1

Duration:

4 h

Initial conc. measured:

>= 0.01 - <= 1 other: mg/L

pH:

6.7

Temp.:

20 °C

Sample No.:

#2

Duration:

4 h

Initial conc. measured:

>= 0.01 - <= 1 other: mg/L

pH:

4.8

Temp.:

20 °C

Sample No.:

#3

Duration:

4 h

Initial conc. measured:

>= 0.01 - <= 1 other: mg/L

pH:

6.7

Temp.:

20 °C

Sample No.:

#4

Duration:

4 h

Initial conc. measured:

>= 0.01 - <= 1 other: mg/L

pH:

7.3

Temp.:

20 °C

Sample No.:

#1

Type:

Koc

Value:

2 245 L/kg

pH:

6.7

Temp.:

20 °C

% Org. carbon:

2.41

Remarks on result:

other: Soil I

Sample No.:

#2

Type:

Koc

Value:

24 526 L/kg

pH:

4.8

Temp.:

20 °C

% Org. carbon:

0.61

Remarks on result:

other: Soil II

Sample No.:

#3

Type:

Koc

Value:

6 359 L/kg

pH:

6.7

Temp.:

20 °C

% Org. carbon:

1.06

Remarks on result:

other: Soil III

Sample No.:

#4

Type:

Koc

Value:

12 899 L/kg

pH:

7.3

Temp.:

20 °C

% Org. carbon:

2.04

Remarks on result:

other: Soil IV

Sample No.:

#1

Type:

log Koc

Value:

3.3 L/kg

pH:

6.7

Temp.:

20 °C

% Org. carbon:

2.41

Remarks on result:

other: Soil I

Sample No.:

#2

Type:

log Koc

Value:

4.4 L/kg

pH:

4.8

Temp.:

20 °C

% Org. carbon:

0.61

Remarks on result:

other: Soil II

Sample No.:

#3

Type:

log Koc

Value:

3.8 L/kg

pH:

6.7

Temp.:

20 °C

% Org. carbon:

1.06

Remarks on result:

other: Soil III

Sample No.:

#4

Type:

log Koc

Value:

4.1 L/kg

pH:

7.3

Temp.:

20 °C

% Org. carbon:

2.04

Remarks on result:

other: Soil IV

Transformation products:

not specified

Adsorption and desorption of THIRAM in soils I to IV as a function of time from the pre-test (values in percent of applied radioactivity).

	Soil I New York		Soil II Illinois 1A		Soil III Illinois site 1		Soil IV IOWA 1A
	Radioactivity in % applied:
Time (hours)	Adsorbed RA	Desorbed RA	Adsorbed RA	Desorbed RA	Adsorbed RA	Desorbed RA	Adsorbed RA	Desorbed RA
0	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0
1	60.9	3.5	42.9	1.5	51.0	4.9	71.0	3.9
2	76.5	3.9	66.3	1.7	65.4	5.3	79.8	4.8
3	84.4	4.1	82.2	1.8	73.6	5.6	84.1	5.4
4	88.1	4.3	91.1	1.8	79.4	5.8	88.3	6.1
5	89.7	4.5	94.8	1.9	82.7	5.8	88.5	6.5
6	90.5	4.7	96.0	2.0	84.6	6.2	88.1	6.8

Freundlich adsorption / desorption constants calculated for four soils used in the study

Soil type	Organic carbon [%]	Clay content [%]	Freundlich adsorption				Freundlich desorption
			Ka [mL/g]	Koc [mL/g]	R	1/n	Kd [ml/g]	Koc [ml/g]	1/n	R
I: sandy loam	2.41	14.8	54.1	2245	0.9955	1.036	781.2	32414	1.271	0.9963
II: loamy sand	0.61	7.5	149.6	24526	0.9964	1.149	1762.1	288869	1.264	0.9995
III: silt loam	1.06	16.8	67.4	6359	0.9974	1.104	841.4	79381	1.225	0.9976
IV: loam	2.04	25.2	263.1	12899	0.9891	1.126	1679.7	82340	1.156	0.9935

Ka: Adsorption constant,
Kd: desorption constant,
Koc(a): adsorption constant as a function of the organic content,
Koc(d): desorption constant as a function of the organic content,
1/n: slope of the adsorption / desorption isotherm,
R: correlation coefficient

Balance of the applied radioactivity in the soil-water systems treated with ¹⁴C-THIRAM at a concentration of 1mg/L

	Sample	Soil I: sandy loam		Soil II: loamy sand		Soil III: silt loam		Soil IV: loam
		µg*	%**	µg*	%**	µg*	%**	µg*	%**
Aqueous phase (W)	A B Mean SD***	2.83 2.94 2.88 0.054	10.58 10.98 10.78 0.200	1.78 1.82 1.80 0.019	6.65 6.79 6.72 0.072	4.39 4.36 4.38 0.016	16.44 16.32 16.38 0.059	3.36 3.34 3.35 0.009	12.58 12.51 12.54 0.034
Soil Extract	A B Mean SD***	15.57 15.63 15.60 0.028	58.26 58.47 58.36 0.103	14.15 13.63 13.89 0.259	52.92 50.98 51.95 0.970	11.74 11.84 11.79 0.047	43.92 44.28 44.10 0.177	12.67 12.80 12.74 0.066	47.41 47.90 47.65 0.248
Soil Combustion	A B Mean SD***	7.40 7.00 7.20 0.200	27.68 26.19 26.94 0.747	10.14 10.19 10.17 0.023	37.94 38.12 38.03 0.087	9.23 8.76 9.00 0.236	34.53 32.77 33.65 0.883	9.12 9.01 9.06 0.052	34.10 33.71 33.91 0.194
TOTAL		25.68	96.08	25.85	96.70	25.16	94.13	25.16	94.10

Calculation was performed by means of EXCEL 4.0 using not rounded values.
*= Values expressed as parent equivalents in micrograms.
**= Values in % of the applied radioactivity (RA).
*** = Standard deviation.

Adsorption and Desorption of parent radioactivity (RA) from soil sediments (soils I to IV) after equilibration with ¹⁴C-THIRAM at various initial concentrations Ci

Ci (µg/ ml)	Sam-ple	Soil I			Soil II			Soil III			Soil IV
		RA ads	RA des		RA ads	RA des		RA ads	RA des		RA ads	RA des
		[%]*	D1 [%]	[%]	[%]*	D1 [%]	[%]	[%]*	D1 [%]	[%]	[%]*	D1 [%]	[%]
1.07	A B Mean	88.50 84.42 86.46	1.15 1.23 1.19	1.67 1.80 1.74	93.31 92.11 92.71	0.76 0.75 0.76	1.17 1.15 1.16	82.87 83.16 83.01	1.00 1.01 1.00	1.48 1.47 1.47	86.30 85.84 86.07	0.45 0.29 0.37	0.60 0.43 0.51
0.20	A B Mean	84.39 84.11 84.25	2.26 2.44 2.40	3.44 3.53 3.48	93.48 93.51 93.49	1.10 1.05 1.07	1.62 1.54 1.58	81.82 82.17 81.99	1.94 1.43 1.68	2.77 2.30 2.54	74.68 74.67 74.67	0.58 1.06 0.82	0.68 1.34 1.01
0.04	A B Mean	79.58 79.99 79.79	3.36 3.30 3.33	4.67 4.56 4.61	89.74 90.16 89.95	1.46 1.54 1.50	2.18 2.20 2.19	74.55 74.27 74.41	2.43 2.41 2.42	3.35 3.25 3.30	72.80 71.97 72.39	0.85 0.53 0.69	1.12 0.65 0.89
0.01	A B Mean	84.56 85.78 85.17	3.78 3.61 3.70	5.12 5.03 5.08	87.42 88.37 87.89	2.31 2.19 2.25	3.22 2.96 3.09	78.47 76.03 77.25	2.46 2.58 2.52	3.44 3.45 3.44	77.30 76.52 76.91	0.75 1.12 0.93	0.89 1.40 1.14

Calculation was performed by means of EXCEL 4.0 using not rounded values.
RA ads = Radioactivity adsorbed.
RA des = Radioactivity desorbed
D₁ = Amount of radioactivity (RA) desorbed after the first desorption step.
D_total = Total radioactivity desorbed during both desorption steps: D1 + D2.
* = Percentage from the radioactivity totally applied to the system.

Validity criteria fulfilled:

yes

Conclusions:

Based on the range of the Koc values it can be concluded that THIRAM is strongly adsorbed by soil components.
According to the scheme introduced by McCall (1980, mobility classes of pesticides) as well as Briggs (Proc. 7th British Insecticide and Fungicide Conference, Nottingham, UK, 83 86, 1973), the mobility of the test item can be classified as very low mobile to immobile for all soils used in the study

Executive summary:

Materials and methods: The adsorption and desorption of THIRAM was investigated in four different soils (soil I: sandy loam, soil II: loamy sand, soil III: silt loam and soil IV: loam) varying in clay content, organic carbon content and pH value using the ¹⁴C-labelled test item.

The analysis was performed in accordance with OECD Guidelines for Testing of Chemicals, No. 106.

The radioactivity in all samples was determined on a Packard liquid scintillation counter. Furthermore the stock solution, application solutions as well as aqueous phases and organic soil extracts were analysed by HPLC.

Results and discussion: The adsorption experiment showed that the adsorption of ¹⁴C-THIRAM reached equilibrium after about four hours.

The equilibrium concentrations of total radioactivity found for soils I to IV (mass balance) in the aqueous phase after adsorption were 10.8%, 6.7%, 16.4% and 12.5%, respectively. The corresponding values for the amount adsorbed onto the soils were 85.3%, 90.0%, 77.8% and 81.6% of the radioactivity initially applied.

The radioactivity in the aqueous phases after the adsorption step consisted of THIRAM as well as of degradation products, whereas the soil extracts contained mainly the parent compound.

The total recoveries ranged from 94.1% for soil IV to 96.7% for soil II with a mean value for the four soils of 95.3%.

The adsorption tests indicated very high adsorption levels of ¹⁴C-THIRAM onto the four soils analysed, whereas the amounts adsorbed did not depend on the organic carbon content and on the concentration level of test item.
The maximum amounts adsorbed were 86.5%, 93.5% 83.0% and 86.1% of the applied radioactivity for soil I to IV, respectively. For the same soils the maximum amounts desorbed as ¹⁴C-THIRAM in a first desorption step were 3.7 %, 2.3 %, 2.5 % and 0.9 %, only.

The results indicate that THIRAM was bound to the chosen soils specifically.

Description of key information

Koc: 2245 - 24526 L/kg (log Koc: 3.3 - 4.4 at 20 °C, OECD 106)

Additional information

The adsorption/desorption potential of tetramethylthiuram disulfide (CAS No. 137-26-8) was investigated in a study using radiolabeled test material. This test was conducted according to OECD Guideline No.106: Adsorption/Desorption using a Batch Equilibrium Method (2000) and EPA’s Pesticide Assessment Guidelines, CFR 40, Subdivision 163-1 (1982) under GLP conditions. 14C-thiram was tested in 4 soil types (sandy loam, loamy sand, silt loam, loam) obtaining adsorption constants related to the organic carbon content (Koc) of 2245 (pH 6.7), 24526 (pH 4.8), 6359 (pH 6.7) and 12899 (pH 7.3) L/kg (corresponding to log Koc values of 3.3, 4.4, 3.8 and 4.1).

 

Considering this information, it can be concluded that tetramethylthiuram disulfide shows potential for adsorption to soil.