thiourea; thiocarbamide

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:

no data

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

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

Deviations:

yes

Remarks:

1981 version. Test solutions were added to soil instead of vice-versa as indicated in the guideline. Agitation was continuous and sufficient to maintain the soil in suspension but breakdown of the soil structure could not be prevented.

GLP compliance:

not specified

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

not specified

Analytical monitoring:

yes

Details on sampling:

- Concentrations: No data
- Sampling interval: 16 h
- Sample storage before analysis: No data

Details on matrix:

COLLECTION AND STORAGE
- Geographic location: Germany, Frankfurt area
- Collection procedures: not reported
- Sampling depth (cm): not reported
- Storage conditions: not reported
- Storage length: not reported
- Soil preparation: not reported

PROPERTIES - Alfisol (neutral loamy soil)
- Soil texture
- % sand: 12.9
- % silt: 64.3
- % clay: 19.6
- pH: 7.45
- Organic carbon (%): 0.76
- Carbonate as CaCO3: 0.75 %

PROPERTIES - Spodosol (acidic sandy soil)
- Soil texture
- % sand: 81.5
- % silt: 10.0
- % clay: 7.2
- pH: 3.88
- Organic carbon (%): 3.56

PROPERTIES - Entisol (slightly basic loamy soil)
- Soil texture
- % sand: 8.5
- % silt: 68.3
- % clay: 20.6
- pH: 7.9
- Organic carbon (%): 1.11
- Carbonate as CaCO3: 5.55 %

Details on test conditions:

TEST CONDITIONS
- Buffer: CaCl2

TEST PROCEDURE
- Soil-water ratio: 1:5
- 20 ml 0.01 M CaCl2 were added to 10 g soil and subsequently equilibrated for 24 h by slight agitation in a shaking machine.
- After that the test substance dissolved in in 0.01 M CaCl2 was added to the test vessels and the samples were vigorously shaken for 16 h to achieve adsorption.
- After 16h the samples were centrifuged and the supernatant was decantet and the volume was measured.
- Desorption, 1st step; duration: 16 h:
The amount of liquid that has been removed was replaced by the same amount of 0.01 M CaCl2. The same test procedure was repeated as for adsorption (vigorous shaking for 16 h; centrifuging and decanting of the supernatant).
- Desorption, 2nd step; duration: 16 h: excatly the same procedure was repeated as for desoprtion step 1

TEST SYSTEM
- Type, size and further details on reaction vessel: all experiments (adsorption as well as desorption) were conducted in centrifuge tubes equipped with shortened stoppers NS45
- Water filtered: not specified
- Amount of soil and water per treatment: 10 g soil and 20 mL 0.01M CacCl2 -> subsequently equilibrated for 24h in shaking machine and slightly agitated. After that the test substance was added to the test vessels in 0.01 M CaCl2
- Number of reaction vessels/concentration: 2 replicates per soil
- One blank sample per soil (soil without test chemical)
- One control containing thiourea in 0.01 M CaCl2 (sample without soil) for the determination of the initial test substance concentration.

Sample No.:

#1

Duration:

16 h

Computational methods:

No details reported.

Sample No.:

#1

Type:

Koc

Remarks:

Alfisol

Value:

28 dimensionless

% Org. carbon:

0.76

Remarks on result:

other: Temperature during test not reported.

Sample No.:

#2

Type:

Koc

Remarks:

Spodosol

Value:

26.13 dimensionless

% Org. carbon:

3.56

Remarks on result:

other: Temperature during test not reported.

Key result

Sample No.:

#3

Type:

Koc

Remarks:

Entisol

Value:

36.49 dimensionless

% Org. carbon:

1.11

Remarks on result:

other: Temperature during test not reported.

Adsorption and desorption constants:

- Adsorption coefficient (Kd):
* Alfisol: K = 0.22
* Spodosol: K = 0.93
* Entisol: K = 0.41
- Adsorption coefficient per organic carbon (Koc):
* Alfisol: Koc = 28.95
* Spodosol: Koc = 26.13
* Entisol: Koc = 36.49

Recovery of test material:

No details reported.

Concentration of test substance at end of adsorption equilibration period:

No details reported.

Concentration of test substance at end of desorption equilibration period:

No details reported.

Transformation products:

not measured

Details on results (Batch equilibrium method):

No further details reported.

Statistics:

No details reported.

Validity criteria fulfilled:

not applicable

Conclusions:

The Koc values determined in this test (OECD 106) for thiourea adsorption to Alfisol, Spodosol and Entisol are 28.95, 26.13 and 36.49.

Executive summary:

The adsorption/desorption of thiourea was determined in a test that was conducted according to OECD Guideline 106 (May 12, 1981). In this test three different kind of soil were used having the following characteristics:

 

Soil type	Sand [%]	Silt [%]	Clay [%]	organic carbon [%]	[%] carbonat as CaCO3	pH
Alfisol	12.9	64.3	19.6	0.76	0.75	7.45
Spodosol	81.5	10.0	7.2	3.56	/	3.88
Entisol	8.5	68.3	20.6	1.11	5.55	7.9

 

Thiourea was added to the soils in 0.01 M CaCl2. Soil and test substance were equilibrated for 16 h. Afterwards thiourea was extracted and analytically determined (GC, UV). (No further details on test substance concentration, and analytical methods were reported.) The results for thiourea adsorption to soil are as follows:

 

Soil type	Adsorption [%]	K	Koc
Alfisol	5.00	0.22	28.95
Spodosol	17.80	0.93	26.13
Entisol	8.45	0.41	36.49

 

The authors report difficulties regarding the determination of thiourea desorption from the soils as the substance was reported to biodegrade in the test (extent of biodegradation was not reported).

 

Because of the observed biodegradation of the substance in soil, the "advanced test" proposed by the guideline was not conducted as the authors did not expect to obtain valid test results on adsorption.

Description of key information

Experimental Koc values for thiourea in three soils were determined to be 28.95, 26.13. and 36.49.

The mean value (Koc = 30.5) is carried forward to the risk assessment.

Key value for chemical safety assessment

Koc at 20 °C:

30.5

Additional information

The adsorption and desorption of thiourea was determined in a test according to OECD guideline 106 (May 12, 1981). In this test three different soil types with the following characteristics were used:

 

Soil type	Sand [%]	Silt [%]	Clay [%]	Organic carbon [%]	Carbonate as CaCO3 [%]	pH
Alfisol	12.9	64.3	19.6	0.76	0.75	7.45
Spodosol	81.5	10.0	7.2	3.56	-	3.88
Entisol	8.5	68.3	20.6	1.11	5.55	7.9

 

The results for thiourea adsorption to soil are as follows:

 

Soil type	Adsorption [%]	K	Koc
Alfisol	5.00	0.22	28.95
Spodosol	17.80	0.93	26.13
Entisol	8.45	0.41	36.49

 

The determined K values for thiourea are dependent on soil texture characteristics, pH and content of organic carbon. The mean Koc from the three soil types is carried forward to the risk assessment of thiourea.