potassium (oxido-NNO-azoxy)cyclohexane; cyclohexylhydroxydiazene 1-oxide, potassium salt; [K-HDO]

Adsorption / desorption

Administrative data

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Experiments: 28.11.2005 - 12/13.12.2005

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2006

Report date:

2006

Materials and methods

Test guideline

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

Test material

Test material information

Constituent 1

Reference substance name:

Cyclohexylhydroxydiazene 1-oxide, potassium salt

EC Number:

613-953-8

Cas Number:

66603-10-9

Molecular formula:

C6H11KN2O2

IUPAC Name:

Cyclohexylhydroxydiazene 1-oxide, potassium salt

Test material form:

solid: particulate/powder

Details on test material:

Test item: (N-Cyclohexyl-diazeniumdioxy)-potassium
IUPAC name: Cyclohexylhydroxydiazene 1-oxide, potassium salt
Chemical name: Cyclohexylhydroxydiazene 1-oxide, potassium salt; synonyma: (N-Cyclohexyl-diazeniumdioxy)-potassium, K-HDO, K-NCH, Xyligen K powder, Xyligen K
Molecular formula: C6 H11 K N2 O2
Molecular mass: 182.27

Specific details on test material used for the study:

See table below

Radiolabelling:

no

Study design

Test temperature:

Mean room temperature of 22.94 ± 0.46 °C.

HPLC method

Details on study design: HPLC method:

The HPLC - Instrument parameters and the chromatographic conditions are given in the table below.

1.1. HPLC - MEASUREMENTS:
1.1. Calibration:
The calibration of the analytical method was performed in three calibration ranges:
High calibration range: 10 - 130 µg/mL
Mid calibration range: 1 - 13.0 µg/mL
Low calibration range: 0.1 - 1.3 µg/mL
All calibration lines were measured with 7 calibration points in duplicate. The calibration function and the correlation coefficient were calculated.
To eliminate some variations in detector response during the test, three recalibration standards with concentrations corresponding to the calibration ranges were analyzed before and after each sample group.

All measured concentrations were multiplied with the corresponding recalibration factor. The applied recalibration factors were in the range of 0.88 to 1.050, i.e. the change in detector response was less or equal 20 % over the test duration of about 5 weeks.

For the measurements of Tier 3 desorption complete new calibration lines were measured.

1.2. System validation:
To determine the system suitability a system validation procedure was developed. The system validation test contained:
Injection test: Injection volume of the auto sampler varied from 1 to 100 µl
Linearity test 1: Standard solutions I - IV (concentration range 107.9 - 0.1079 µg/mL)
Linearity test 2: Test item solutions I - III (concentration range 100.5 - 1.005 µg/mL)
Reproducibility: 7-fold injections of standards (calibration range High, Mid, Low)

1.3. Sample measurement:
The samples were measured with the HPLC-conditions described in the table "HPLC - Instrument parameters". A set of recalibration standards, which include the three calibration ranges, were measured before and after a sample set.

Batch equilibrium or other method

Analytical monitoring:

yes

Details on sampling:

See above

Details on matrix:

COLLECTION AND STORAGE
Soils were derived from LUFA "Landwirtschaftliche Untersuchungs- und Forschungsanstalt", Agricultural Investigation and Development Institute, Speyer, Germany
PROPERTIES
see table "Soil information"

Details on test conditions:

TEST CONDITIONS
The adsorption /desorption characteristics of K-HDO were investigated according to the OECD Guideline No. 106 (OECD Guideline for Testing of Chemicals "Determination of Soil Adsorption/Desorption, using a Batch Equilibrium Method" , 2000). The laboratory study was performed with five certified soils.
The test comprises three tiers. The tier 1 is the preliminary study, the tier 2 is the screening test (in 5 soils) and the tier 3 is the determination of Freundlich adsorption isotherms or the study of desorption by means of desorption kinetics/Freundlich desorption isotherms, as appropriate.

TEST SYSTEM
- Water filtered (i.e. yes/no; type of size of filter used, if any):
- Amount of soil per treatment: To prepare the blank recovery samples, 2 x 2.0 g soil (calculated as dry matter) was fortified with 1.0 mL of the blank solution, mixed well and equilibrated for 2 hours without shaking.
To prepare the high range recovery samples, 2.0 g soil (calculated as dry matter) was fortified with 1.0 mL of the test item stock solution, mixed well and equilibrated for 2 hours without shaking.
To prepare the low range recovery samples, 2.0 g soil (calculated as dry matter) was fortified with 0.1 mL of the test item stock solution and 0.9 ml of 0.01 m CaCl2 solution, mixed well and equilibrated for 2 hours without shaking.
- Measuring equipment:
- Test performed in closed vessels due to significant volatility of test substance: no
- Test performed in open system: yes
- Method of preparation of test solution: see table below

Results and discussion

Adsorption coefficient

Key result

Type:

other: Freundlich adsorption constants KFads for all soils

Value:

>= 20.5 dimensionless

Results: Batch equilibrium or other method

Adsorption and desorption constants:

The determined Freundlich adsorption constants KFads for all soils were between 20.5 (soil Bruch West) and 223.8 (Soil LUFA 2.2), the respective organic carbon content normalized values (KF,oc ads) between 10606 and 805.
The determined Freundlich desorption constant KFdes for all soils was between 27.0 (soil Bruch West) and 343.8 (soil LUFA 2.2).

Recovery of test material:

The recovery rate of CaCl2-soluble K-HDO was determined to be 95.6 % for the 0.1 mg/L level and 100.8 % for the 10 mg/L level.
The recovery rate of Methanol/Eluent-extract soluble K-HDO was determined to be 80.5 % for the 50 mg/kg concentration level and 89.1 % for the 500 mg/kg level.
All determined recovery rates met the validation criteria requested to be between 70 and 110 %.

Transformation products:

no

Details on results (Batch equilibrium method):

See tables below

Statistics:

Mean, standard deviation and relative standard deviation were calculated.

Any other information on results incl. tables

LoD and LoQ of the determination of K-HDO:

	CaCl2- Extract	CaCl2- Extract	Methanol / Eluent - Extract*	Methanol / Eluent- Extract
	mg/L extract	mg/kg soil	mg/L extract	mg/kg soil
Limit of detection LoD	0.05	1.2	0.05	0.6
Limit of quantification LoD	0.1	10	4	50

Results of preliminary test:

Test substance	K-HDO
Sample purity	100 % as (N-Cyclohexyldiazeniumdioxy)-potassium monohydrate
Weighed soil	2 g soil
Volume of CaCl2solution	49-50 mL CaCl2extraction solution
Nominal concentration of a.s. final solution	Analytically verified concentrations used
Analytical concentration final of a.s. solution	Was determined for each solution and used for calculation
Concentration of the test solution (show calculation)	Analytically verified concentrations used
Details of the analytical method used:	Determination of the K-HDO content was performed by analysis of K-HDO using HPLC and UV/VIS detection. The method was calibrated in the range from 0.1-130 µg/mL K-HDO and validated.
Method	HPLC-UV/VIS
Recovery rate (CaCl2-soluble K-HDO recovery rate)	95.6 % at 0.1 mg/L level 100.8 % at the 10 mg/L level
Detection limit	0.05 mg/L CaCl2extract

Results of test - adsorption:

	Bruch West	LUFA 2.1	LUFA 2.2	LUFA 2.3	LUFA 6S
Concentration of test material [mg/L]	0.8-201	0.8-201	0.8-201	0.8-201	0.8-201
After contact of 24 hours with soil	0.387-175.8	0.176-126	0.079-35	0.28-146.9	0.142-124.6
Correction for blank with soil	0	0	0	0	0
Correction for blank without soil	0	0	0	0	0
Final corrected concentration [mg/L]	0.387-175.8	0.176-126	0.079-35	0.28-146.9	0.142-124.6
Initial concentration of test solution [mg/L]	0.8-201	0.8-201	0.8-201	0.8-201	0.8-201
Decrease in concentration [mg/L]	0.413-26.2	0.624-75	0.72-166	0.52-54.1	0.658-76.4
Quantity adsorbed [mg]	20.8-1259.6	31.4-3750.8	36.2-8300	26-2705	33.1-3819
Quantity of soil [g of oven-dried equivalent]	2	2	2	2	2
Quantity adsorbed [mg] per gram of soil	10.4-628.5	15.7-1872.8	18.1-4142.5	13-1351	16.5-1909
Test material adsorbed [%]	51.8-12.5	78.1-37.1	90.1-82.6	64.8-26.9	82.3-38
Temperature [°C]	22.9	22.9	22.9	22.9	22.9
Distribution coefficient at adsorption equilibrium Kd	26.88-3.58	89.4-14.9	289-118.2	45.9-9.2	149-15.3
Organic carbon normalized adsorption coefficient	1058-140.7	14186-2358.7	10796-5602	4499-902	6339-822
Freundlich adsorption coefficient	20.5	66.3	223.8	38.1	79.8
Organic carbon normalized Freundlich adsorption coefficient	805	10518	10606	3739	4360
PH-value of the aqueous phase at adsorption equilibrium	7.2-7.4	5.9-6.7	5.5-6.3	6.75-7	6.9-7.2

Results of test - desorption:

	Bruch West	LUFA 2.1	LUFA 2.2	LUFA 2.3	LUFA 6S
Temperature [°C]	22.1	22.1	22.1	22.1	22.1
Evaluated concentration range [µg/g]	20-5015	20-5015	20-5015	20-5015	20-5015
Freundlich desorption coefficient	27	103.3	343.8	53.7	93.5
Organic carbon normalized Freundlich desorption coefficient	1064	15472	16293	5261	5112
[%] of desorbed test material	34-55	17-24	4-9	23-39	14-35
Correlation coefficient R²	0.964	0.998	0.976	0.972	0.985

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Conclusions:

The adsorption in all soils exceeded 25 %.
The recovery rates of the CaCl2-soluble K-HDO recovery test were calculated to be 95.6 % for the 0.1 mg/I concentration level and 100.8%for the 10 mg/I level.
The recovery rates of the Methanol/Eluent-extraction of K-HDO from soil were calculated to be 80.5 % for the 50 mg/kg concentration level and 89.1% for the 500 mg/kg level.
The recovery rate of the mass balance experiment was calculated to be 90.2%.The mass balance, considering the aqueous and the soil phase (by extraction with methanol/eluent) was> 90%, indicating the stability of the compound during the test.

Taking the adsorption behaviour of the test item into account, the adsorption equilibration time was 24 hours. Since adsorption may continue by longer agitation due to diffusion, slow degradation or the formation of bound residues, the obtained adsorption data represent worst case values. The organic carbon normalized Freundlich adsorption coefficient KF,ocadsvalues are considerable and in the range from 805 to 10606.
The maximal desorption was reached after 8 hours of agitation for all soils.The resulting organic carbon normalized Freundlich desorption coefficient KF,ocdeswere in the range from 1064 to 16394 and therefore significantly 1.4 fold higher than the corresponding adsorption values, indicating irreversible adsorption

Executive summary:

The adsorption /desorption characteristics of K-HDO were investigated according to the OECDGuideline No. 106 (OECD Guideline for Testing of Chemicals "Determination of Soil Adsorption/Desorption, using a Batch Equilibrium Method" , 2000).

The laboratory study was performed with five certified soils.

1.     An analytical method was adapted and validated to determine K-HDO in extraction solvents from an adsorption/desorption study. The validation parameters confirm the suitability of the method for the adsorption/desorption study.

2.     The performance of the study shows different adsorption behaviours of K-HDO towards the soils used with the present concentrations. The soil LUF A 2.2 shows the strongest adsorption of all the investigated soils, followed by the soils LUF A 2.1, and LUFA 6S. The adsorption of the soils Bruch West and LUFA 2.3 is lower.

3.     The adsorption equilibrium time was reached at 24 h. After this time, only a slight adsorption increase was observed so that the adsorption values obtained represent worst case values.

4.     The determined Freundlich adsorption constants KFads for all soils were between 20.5 (soil Bruch West) and 223.8 (Soil LUFA 2.2), the respective organic carbon content normalized values (KF,oc ads) between 10606 and 805.

5.     The desorption equilibrium time was reached at 8 h.

6.     The desorption behaviour of K-HDO corresponds to the adsorption on the soils.

7.     The determined Freundlich desorption constant KFdes for all soils was between 27.0 (soil Bruch West) and 343.8 (soil LUFA 2.2).

8.     For all the soils the organic carbon normalized Freundlich adsorption constant KF,ocads and the organic carbon normalized Freundlich desorption constant KF,ocdes were calculated.

9.     The Freundlich desorption coefficient KFdes is higher than the corresponding Freundlich adsorption coefficient KFads by the reversibility factor 1.4 (averaged over all the soils). The test item K-HDO is practically irreversibly adsorbed on the soils.

The parameters of Freundlich adsorption/desorption equation were summarized in the following table:

Parameter	Soil	Bruch West	LUFA 2.1	LUFA 2.2	LUFA 2.3	LUFA 6S	Mean
Freundlich adsorption coefficient	KF^ads	20.5	66.3	223.8	38.1	79.8	85.7
exponent	n	1.498	1.404	1.105	1.373	1.555
inverse exponent	1/n	0.6677	0.7138	0.9100	0.7281	0.6433
organic carbon normalized Freundlich adsorption coefficient	KF,OC^ads	805	10518	10606	3739	4360	6007
Freundlich desorption coefficient	KF^des	27.0	97.5	343.8	53.7	93.5	123.1
exponent	n	1.048	1.059	0.959	0.989	1.257
inverse exponent	1/n	0.9542	0.9445	1.0434	1.0113	0.7955
organic carbon normalized Freundlich desorption coefficient	KF,OC^des	1064.2	15472.1	16292.6	5261.1	5111.9	8640
Reversibility factor	KF^des/KF^a ds	1.321	1.171	1.536	1.407	1.172	1.381