Diquat dibromide

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

Study period:

21 Jan 2010 to 29 Jul 2010

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:

January 2000

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: EPA Guideline Series OPPTS 835.1230 (Adsorption/Desorption Batch Equilibrium),

Version / remarks:

October 2008

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:

PRELIMINARY TESTS
- Adsorption equilibrium time and desorption equilibrium time for all four soils: Over a 48h period

DEFINITIVE TEST
- Adsorption equilibrium time: 24 h
- Desorption equilibrium time: 24 h

Matrix no.:

#1

Matrix type:

loam

% Clay:

12

% Silt:

43

% Sand:

45

% Org. carbon:

2.1

pH:

8

CEC:

10.84 meq/100 g soil d.w.

Bulk density (g/cm³):

1.5

Matrix no.:

#2

Matrix type:

sandy clay loam

% Clay:

25

% Silt:

24

% Sand:

51

% Org. carbon:

2.5

pH:

6.9

CEC:

18.94 meq/100 g soil d.w.

Bulk density (g/cm³):

1.5

Matrix no.:

#3

Matrix type:

silty clay

% Clay:

39

% Silt:

56

% Sand:

6

% Org. carbon:

0.9

pH:

8.6

CEC:

12.24 meq/100 g soil d.w.

Bulk density (g/cm³):

1.5

Matrix no.:

#4

Matrix type:

sandy loam

% Clay:

19

% Silt:

11

% Sand:

70

% Org. carbon:

2.85

pH:

8.05

CEC:

18.55 meq/100 g soil d.w.

Bulk density (g/cm³):

1.5

Details on matrix:

TEST SYSTEM
- The four soils used were obtained and supplied by the Sponsor. The soil characteristics are summarised in Table 1 in 'Any other information on materials and methods incl. tables'. The soils were thoroughly mixed and passed through a 2 mm sieve. Prior to use the soils were air-dried and stored in the dark, at room temperature, in loosely tied plastic bags.

SOIL PREPARATION
- Prior to dispensing, the moisture contents of the stored soils were determined at Covance by drying a portion at ca 105 °C. The wet : dry weight ratio was calculated and this allowed the dry weight equivalent of the dispensed soil to be calculated from the wet weight. Dry soil weight = wet soil weight / (wet : dry ratio) All calculations were based upon soil dry weight.

Details on test conditions:

PRELIMINARY TESTS
In the preliminary investigations, experiments were conducted to determine the conditions to be used in the definitive test. A test was performed to determine whether the test substance was soluble at 5 and at 50 µg/mL in 0.01M calcium chloride solution (equivalent cation concentrations are 2.7 and 26.8 µg/mL, respectively). A test was performed to determine whether the test substance adsorbed to vessels from a 0.05 µg/mL test substance solution (equivalent cation concentration is 0.03 µg/mL). The determination of the optimum soil : aqueous ratio for use in the definitive test was conducted using all four soils at a test substance concentration of 0.5 µg/mL (equivalent cation concentration of 0.3 µg/mL). The adsorption equilibrium time and desorption equilibrium time for all four soils were determined over a 48 hours period using a test substance concentration equivalent to 0.5 µg/mL (equivalent cation concentration of 0.3 µg/mL). Stability of the test item during the adsorption time determination was assessed at the 48-hour time point.

DEFINITIVE TEST
Adsorption isotherms were determined on all four soils, at a ratio of 1:100 (soil : solution w/v), over five concentrations of the test substance (0.05, 0.2, 0.5, 2 and 5 µg/mL) (equivalent cation concentrations of 0.03, 0.11, 0.3, 1.1, and 2.7 µg/mL, respectively). All samples were shaken for 24 hours (the adsorption equilibrium time) then centrifuged for 44 minutes at 4750 rpm (ca 4100 g). Weighed aliquots were taken for LSC analysis before removing as much of the adsorption supernatant as possible from each unit into a pre-weighed vessel. The pH value of each adsorption supernatant was determined and are presented in Table 2 in ‘Any other information on materials and methods incl. tables’. The weight of adsorption supernatant removed was replaced by an equal weight of fresh 0.01M calcium chloride solution. Each test vessel was shaken vigorously to break up the soil packed at the bottom of the vessel and to re-mix it with the solution. The samples were, again, shaken for 24 hours (the desorption equilibrium time), centrifuged for 44 minutes at 4750 rpm (ca 4100 g) and radioactivity in the desorption supernatants was determined by LSC.

RADIOCHEMICAL PURITY
The radiochemical purity of the radiolabelled test substance treatment solutions was determined by high performance liquid chromatography (HPLC).

PREPARATION OF CALCIUM CHLORIDE SOLUTION
Several batches of 0.01M calcium chloride solution were used throughout the period of the study. Calcium chloride solution (0.01M) was prepared by dissolving ca 1.47 g calcium chloride dihydrate in 1000 mL water (or ca 7.35 g calcium chloride dehydrate in 5000 mL water).

PREPARATION OF SOIL SLURRIES PRIOR TO TREATMENT
Duplicate units were prepared by dispensing ca 1 g (dry weight equivalent, accurately weighed) of each soil into pre-weighed centrifuge tubes. Dispensed soils were then pre-equilibrated by shaking with 0.01M calcium chloride solution (90 mL) overnight before the day of the experiment.

PREPARATION OF TREATMENT SOLUTIONS
Application solutions of radiolabelled test substance in calcium chloride solution (named stock solutions 3 to 12) were prepared, when required, from the stock solutions. Aliquots of the stock solution were transferred to pre-weighed fresh glass vessels and the solvent evaporated under a stream of nitrogen. A volume of 0.01M calcium chloride was added to achieve the required nominal concentration and the resulting solution was sonicated to ensure mixing. The radiochemical purity of the test item in the application solutions prepared for the definitive test was checked by HPLC. The preparation details of each application solution used are described in each test.

TREATMENT OF SLURRIES
Stock solutions of the radiolabelled test substance in 0.01M calcium chloride with nominal concentrations of 0.5, 2, 5, 20 and 50 µg/mL were prepared for the isotherm test (equivalent cation concentrations of 0.3, 1.1, 2.7, 11, and 27 µg/mL, respectively). The appropriate stock solutions (10 mL) were pipetted into the equilibrated units to achieve final nominal concentrations of 0.05, 0.2, 0.5, 2 and 5 µg/mL test substance equivalent to cation concentrations of 0.03, 0.11, 0.3, 1.1, and 2.7 µg/mL, respectively.

ANALYSIS

AQUEOUS PHASE
Supernatants were radio assayed with LSC. For stability determination, the test item was quantified in selected adsorption and desorption supernatants via reversed phase HPLC with radio-detection. The samples analysed were: One replicate from each concentration of the North Dakota soil. The North Dakota soil was the soil with the highest Kd value. One replicate of the samples of the other three soils at the highest concentration only.

STABILITY OF THE TEST SUBSTANCE DURING THE ISOTHERM TEST
Residual radioactivity in the soil from the same representative samples (after the removal of the desorption supernatant) was extracted and analysed by HPLC. All soil samples were extracted by refluxing twice with 6M sulphuric acid (60 mL) for 5 hours, followed by shaking with acetone (10 mL) to aid drying of the residue. Duplicate aliquots were removed from the extracts for analysis by LSC. Adsorption supernatants, desorption supernatants and soil extracts were analysed by HPLC, where appropriate.

MASS BALANCE
Mass balance was determined on each soil at the highest concentration and at all concentrations for North Dakota soil. The samples used were those that had been used for the stability test. Extracted soils were combusted to determine radioactivity remaining in soil.

EXPRESSION OF RESULTS
All values in tables have been computer generated and data values displayed are rounded values of those held in memory. As a result of this, calculation of mean and total values from individual data presented in the report will, in some instances, yield a minor variation to the value shown. Data was derived and calculations made using the cation. Whenever results are available from more than one replicate at a timepoint, values quoted in the text of the report are rounded mean values, unless otherwise stated and percent values are expressed as a percent of applied radioactivity. Volumes taken for LSC referred to in the methods section are approximate volumes only. The aliquots were, however, weighed and the weight of the total sample was determined. Centrifugation speeds (rpm) and forces (g) are approximate values.

Duration:

24 h

Initial conc. measured:

>= 0.5 - <= 50 other: µg/mL

Temp.:

20 °C

Remarks:

for all soils

Duration:

24 h

Temp.:

20 °C

Remarks:

for all soils

Key result

Sample No.:

#1

Type:

Koc

Remarks:

Freundlich Coefficients

Value:

6 857 L/kg

pH:

8

Temp.:

20 °C

Matrix:

Loam

% Org. carbon:

2.1

Key result

Sample No.:

#2

Type:

Koc

Remarks:

Freundlich Coefficients

Value:

360 446 L/kg

pH:

6.9

Temp.:

20 °C

Matrix:

Sandy clay loam

% Org. carbon:

2.5

Key result

Sample No.:

#3

Type:

Koc

Remarks:

Freundlich Coefficients

Value:

1 436 850 L/kg

pH:

8.6

Temp.:

20 °C

Matrix:

Silty clay

% Org. carbon:

0.9

Key result

Sample No.:

#4

Type:

Koc

Remarks:

Freundlich Coefficients

Value:

2 511 015 L/kg

pH:

8

Temp.:

20 °C

Matrix:

Sandy loam

% Org. carbon:

2.8

Sample No.:

#1

Phase system:

solids-water in soil

Type:

other: Koc - Desorption Freundlich Coefficients

Value:

7 343 L/kg

Temp.:

20 °C

pH:

8

Matrix:

Loam

% Org. carbon:

2.1

Sample No.:

#2

Phase system:

solids-water in soil

Type:

other: Koc - Desorption Freundlich Coefficients

Value:

766 809 L/kg

Temp.:

20 °C

pH:

6.9

Matrix:

Sandy clay loam

% Org. carbon:

2.5

Sample No.:

#3

Phase system:

solids-water in soil

Type:

other: Koc - Desorption Freundlich Coefficients

Value:

8 482 799 L/kg

Temp.:

20 °C

pH:

8.6

Matrix:

Silty clay

% Org. carbon:

0.9

Sample No.:

#4

Phase system:

solids-water in soil

Type:

other: Koc - Desorption Freundlich Coefficients

Value:

2 732 954 L/kg

Temp.:

20 °C

pH:

8

Matrix:

Sandy loam

% Org. carbon:

2.8

Details on results (HPLC method):

Not applicable

Adsorption and desorption constants:

Mean values for adsorption partition coefficients (Kd) per soil were in the range 869 to 44605 L/kg and (KOC) values were in the range 41404 to 2380784 L/kg. Freundlich adsorption coefficients (KfOC) were in the range 6857 to 2511015 L/kg. Mean values for desorption partition coefficients (Kd) per soil were in the range 1410 to 81326 L/kg and (KOC) values were in the range 67121 to 5109808 L/kg. Freundlich desorption coefficients (KfOC) were in the range 7343 to 8482799 L/kg. Adsorption and desorption Kd values are summarised in Tables 8 and 9 in ‘Any other information on results incl. tables’, respectively.

Recovery of test material:

A summary of the radioactivity recovered following a 24 hour adsorption phase and a 24 hour desorption phase is shown in Table 2 in ‘Any other information on results incl. tables’. Extracts of soil and supernatant were analysed by HPLC and the recovery of applied radioactivity as [14C]-substance in all samples was ≥ 94% (Table 3 in ‘Any other information on results incl. tables’).

Concentration of test substance at end of adsorption equilibration period:

See Table 4 in 'Any other information on results incl. tables'.

Concentration of test substance at end of desorption equilibration period:

See Table 4 in 'Any other information on results incl. tables'.

Sample no.:

#1

Duration:

24 h

% Adsorption:

40.1

Remarks on result:

other: Recovery of radioactivity at the adsorption supernatant

Sample no.:

#2

Duration:

24 h

% Adsorption:

0.7

Remarks on result:

other: Recovery of radioactivity at the adsorption supernatant

Sample no.:

#3

Duration:

24 h

% Adsorption:

0.4

Remarks on result:

other: Recovery of radioactivity at the adsorption supernatant

Sample no.:

#4

Duration:

24 h

% Adsorption:

0.225

Remarks on result:

other: Mean recovery of radioactivity at the adsorption supernatant

Sample no.:

#1

Duration:

24 h

% Desorption:

17.9

Remarks on result:

other: Recovery of radioactivity at the desorption supernatant

Sample no.:

#2

Duration:

24 h

% Desorption:

0.4

Remarks on result:

other: Recovery of radioactivity at the desorption supernatant

Sample no.:

#3

Duration:

24 h

% Desorption:

0.2

Remarks on result:

other: Recovery of radioactivity at the desorption supernatant

Sample no.:

#4

Duration:

24 h

% Desorption:

0.1

Remarks on result:

other: Mean recovery of radioactivity at the desorption supernatant

Transformation products:

no

Details on results (Batch equilibrium method):

SOIL CHARACTERISATION
A summary of characteristics is presented in Table 1 in ‘Any other information on materials and methods incl. tables‘.

RADIOCHEMICAL PURITY
he radiochemical purity of the radiolabelled test substance treatment solutions (adsorption equilibrium time test and main isotherms test), was determined by high performance liquid chromatography (HPLC). The radiochemical purity was found to be > 95%.

PRELIMINARY TESTS
Preliminary investigations were conducted to determine the conditions to be used in the definitive study. A summary of these tests is presented in Table 1 in ‘Any other information on results incl. tables‘.

DEFINITIVE TEST
TREATMENT RATES
Five application solutions were prepared and diluted with calcium chloride such that the application to the units was determined to be: 0.05, 0.21, 0.50, 2.04 and 4.57 µg/mL test substance (0.03, 0.11, 0.27, 1.09 and 2.45 µg/mL of cation).

ISOTHERMS
The soil to aqueous phase ratio of 1:100 w/v, 24 hour adsorption equilibrium period and 24 hour desorption equilibrium period were based upon the results of the preliminary tests. A summary of test conditions is presented in section 3.6.1.2. Measurements of pH made on the adsorption supernatants are presented in Table 2 in ‘Any other information on materials and methods incl. tables‘. Concentrations of [14C]-cation in the adsorption supernatants and adsorbed to the soil are shown in Tables 4 to 7 in ‘Any other information on results incl. tables ‘. The proportions of [14C]-cation that were adsorbed and desorbed are also shown in these tables. Mean values for adsorption partition coefficients (Kd) per soil were in the range 869 to 44605 L/kg and (KOC) values were in the range 41404 to 2380784 L/kg. Freundlich adsorption coefficients (KFOC) were in the range 6857 to 2511015 L/kg. Mean values for desorption partition coefficients (Kd) per soil were in the range 1410 to 81326 L/kg and (KOC) values were in the range 67121 to 5109808 L/kg. Freundlich desorption coefficients (KFOC) were in the range 7343 to 8482799 L/kg. Adsorption and desorption Kd values are summarised in Tables 8 and 9 in ‘Any other information on results incl. tables‘, respectively.

Table 1. Preliminary studies results

Solubility test Solubility at 5 and 50 µg/mL (2.7 and 27 µg/mL ion) in 0.01M CaCl2 solution Adsorption to containers test (0.5 µg/mL (0.3 µg/mL cation) in 0.01M CaCl2 solution).	The compound was soluble at both concentrations tested. The compound adsorbed to Telfon® vessels but did not adsorb to polypropylene or Nalgene® vessels. Therefore Nalgene® tubes were selcted for the definitive test.
Ratio of soil to aqueous test at 0.5 µg/mL test item concentration 1:10 ratio 1g soil : 10 mL 0.01M CaCl2 solution 1:50 ratio 1g soil : 50 mL 0.01M CaCl2 solution 1:100 ratio 1g soil : 100 mL 0.01M CaCl2 solution.	The test item adsorbed very strongly (> 80%) to the soil at all ratios tested. A ratio of 1:100 w/v was selected for use in the definitive test.
Time to adsorption equilibrium Tested using 1:100 w/v soil ratio at 0.5 µg/mL (0.3 µg/mL cation) test item concentration in the aqueous phase incubated for 0.5, 2, 4, 6, 24 and 48 hours.	Adsorption equilibrium was reached within 24 hours for all soils. Therefore, this was selected as the adsorption equilibrium time in the definitive test.
Time to desorption equilibrium Tested using 1:100 w/v soil ratio at 0.5 µg/mL (0.3 µg/mL ion) test item concentration in the aqueous phase incubated for 0.5, 2, 4, 6, 24 and 48 hours.	Desorption equilibrium was reached within 24 hours for all soils. Therefore, this was selected as the desorption equilibrium time in the definitive test.
Stability during equilibrium time determination One replicate per soil after 48 hours equilibrium in the time to adsorption equilibrium test.	Recovery of applied radioactivity as [14C]-substance was in the range 93 to 96%

  

Table 2. Recovery of Radioactivity Following a 24 Hour Adsorption Phase and a 24 Hour Desorption Phase

Soil	Concentration of cation (µg/mL)	Recovery of radioactivity (%)					Total recovery (%)
		Adsorption supernatant	Desorption supernatant	Soil extract (sulphuric acid)	Soil extract (Acetone)	Unextracted from soil
Gartenacker	2.7	40.1	17.9	40.6	0.1	0.1	98.8
18 Acres	2.7	0.7	0.4	97.2	0.2	0.0	98.5
Marsillargues	2.7	0.4	0.2	95.2	0.3	0.1	96.2
North Dakota	2.7	0.2	0.1	98.5	0.4	0.1	99.3
North Dakota	1.1	0.3	0.1	99.9	0.3	0.3	100.9
North Dakota	0.3	0.2	0.1	97.6	0.4	0.4	98.7
North Dakota	0.11	0.2	ND	97.2	0.8	0.3	98.5
North Dakota	0.03	ND	ND	100.0	0.4	0.5	100.9

ND = Not Detected or < 0.1%

Table 3. Purity of [14C]-substance in the isotherm supernatants and soil extracts

Soil	Concentration of catiion (µg/mL)	% Recovery of radioactivity present as substance			% Total radioactivity as extractable substance
		Adsorption supernatant 1	Desorption supernatant 1	Soil extract 1
Gartenacker	2.7	40.0	17.8	40.5	98.2
18 Acres	2.7	NA	NA	96.8	96.8
Marsillargues	2.7	NA	NA	94.5	94.5
North Dakota	2.7	NA	NA	97.8	97.8
North Dakota	1.1	NA	NA	99.0	99.0
North Dakota	0.3	NA	NA	97.2	97.2
North Dakota	0.11	NA	NA	96.2	96.2
North Dakota	0.03	NA	NA	97.4	97.4

1 Mean value of two injections

NA = Not analysed due to extract < 1% applied radioactivity

 

Table 4. Concentrations of Substance Ion Equivalents for the Adsorption and Desorption Isotherms for Gartenacker Soil

Nominal dose level as cation (µg/mL)	Replicate	Adsorption			Desorption
		Ce*(µg/mL)	X/m*(µg/g)	% adsorbed (a)	C1*(µg/mL)	X1/m*(µg/g)	% desorbed (b)
2.7	1	0.9920	144.4443	59.3	0.4420	101.7971	29.5
	2	1.0200	144.1727	58.9	0.4520	100.9645	30.0
	Mean	1.0060	144.3085	59.1	0.4470	101.3808	29.7
1.1	1	0.3200	76.7272	70.8	0.1760	59.8190	22.0
	2	0.3170	76.2410	71.3	0.1780	59.3588	22.1
	Mean	0.3185	76.4841	71.0	0.1770	59.5889	22.1
0.3	1	0.0433	22.1324	84.1	0.0268	19.6085	11.4
	2	0.0428	22.1031	84.2	0.0267	19.5762	11.4
	Mean	0.0431	22.1177	84.2	0.0268	19.5923	11.4
0.11	1	0.0115	10.0128	90.0	0.0068	9.3744	6.4
	2	0.0115	10.0799	90.0	0.0068	9.4376	6.4
	Mean	0.0115	10.0463	90.0	0.0068	9.4060	6.4
0.03	1	0.0009	2.5975	96.6	0.0006	2.5381	2.3
	2	0.0011	2.6301	96.1	0.0006	2.5770	2.0
	Mean	0.0010	2.6138	96.3	0.0006	2.5576	2.2

*Expressed as substance ion

(a) % adsorbed as the % of the applied.

(b) as % of the adsorbed

 

Table 5. Concentrations of Substance Ion Equivalents for the Adsorption and Desorption Isotherms for 18 Acres Soil

Nominal dose level as cation (µg/mL)	Replicate	Adsorption			Desorption
		Ce*(µg/mL)	X/m*(µg/g)	% adsorbed (a)	C1*(µg/mL)	X1/m*(µg/g)	% desorbed (b)
2.7	1	0.0166	240.9443	99.3	0.0096	240.0223	0.4
	2	0.0160	242.0283	99.4	0.0083	241.2322	0.3
	Mean	0.0163	241.4863	99.3	0.0089	240.6272	0.4
1.1	1	0.0081	106.1489	99.3	0.0038	105.7972	0.3
	2	0.0081	108.7527	99.3	0.0040	108.3681	0.4
	Mean	0.0081	107.4508	99.3	0.0039	107.0826	0.3
0.3	1	0.0013	26.4813	99.5	0.0012	26.3669	0.4
	2	0.0014	26.5127	99.5	0.0005	26.4636	0.2
	Mean	0.0014	26.4970	99.5	0.0009	26.4152	0.3
0.11	1	0.0004	11.1655	99.6	0.0002	11.1493	0.1
	2	0.0005	11.1023	99.5	0.0002	11.0857	0.2
	Mean	0.0005	11.1339	99.6	0.0002	11.1175	0.1
0.03	1	0.0001	2.7379	99.5	0.0001	2.7262	0.4
	2	0.0001	2.6923	99.6	0.0002	2.6738	0.7
	Mean	0.0001	2.7151	99.5	0.0002	2.7000	0.6

*Expressed as substance ion

(a) % adsorbed as the % of the applied.

(b) as % of the adsorbed

 

Table 6. Concentrations of Substance Ion Equivalents for the Adsorption and Desorption Isotherms for Marsillargues Soil

Nominal dose level as cation (µg/mL)	Replicate	Adsorption			Desorption
		Ce*(µg/mL)	X/m*(µg/g)	% adsorbed (a)	C1*(µg/mL)	X1/m*(µg/g)	% desorbed (b)
2.7	1	0.0098	240.1286	99.6	0.0044	239.7181	0.2
	2	0.0103	238.3245	99.6	0.0045	237.9022	0.2
	Mean	0.0101	239.2266	99.6	0.0044	238.8102	0.2
1.1	1	0.0077	107.9695	99.3	0.0028	107.7099	0.2
	2	0.0080	108.2684	99.3	0.0030	107.9867	0.3
	Mean	0.0078	108.1190	99.3	0.0029	107.8483	0.3
0.3	1	0.0013	26.4945	99.5	0.0005	26.4459	0.2
	2	0.0013	26.4137	99.5	0.0005	26.3696	0.2
	Mean	0.0013	26.4541	99.5	0.0005	26.4077	0.2
0.11	1	0.0006	11.2210	99.5	0.0002	11.2049	0.1
	2	0.0004	10.9837	99.7	0.0002	10.9681	0.1
	Mean	0.0005	11.1024	99.6	0.0002	11.0865	0.1
0.03	1	0.0001	2.7241	99.5	0.0001	2.7115	0.5
	2	0.0001	2.7309	99.7	0.0002	2.7158	0.6
	Mean	0.0001	2.7275	99.6	0.0001	2.7137	0.5

*Expressed as substance ion

(a) % adsorbed as the % of the applied.

(b) as % of the adsorbed

 

Table 7. Concentrations of Substance Ion Equivalents for the Adsorption and Desorption Isotherms for North Dakota Soil

Nominal dose level as cation (µg/mL)	Replicate	Adsorption			Desorption
		Ce*(µg/mL)	X/m*(µg/g)	% adsorbed (a)	C1*(µg/mL)	X1/m*(µg/g)	% desorbed (b)
2.7	1	0.0038	237.7585	99.8	0.0028	237.4981	0.1
	2	0.0043	244.8437	99.8	0.0050	244.3524	0.2
	Mean	0.0041	241.3011	99.8	0.0039	240.9252	0.2
1.1	1	0.0029	109.2548	99.7	0.0013	109.1288	0.1
	2	0.0029	109.1119	99.7	0.0015	108.9682	0.1
	Mean	0.0029	109.1834	99.7	0.0014	109.0485	0.1
0.3	1	0.0006	26.6311	99.8	0.0003	26.6093	0.1
	2	0.0006	26.5011	99.8	0.0003	26.4756	0.1
	Mean	0.0006	26.5661	99.8	0.0003	26.5424	0.1
0.11	1	0.0003	11.2213	99.8	0.0001	11.2113	0.1
	2	0.0003	11.1942	99.8	0.0000	NAc	NA (c)
	Mean	0.0003	11.2077	99.8	0.0001	11.2113	0.1
0.03	1	0.0001	2.7193	99.7	0.0000	2.7155	0.1
	2	0.0001	2.7306	99.8	0.0001	2.7225	0.3
	Mean	0.0001	2.7249	99.7	0.0001	2.7190	0.2

*Expressed as substance ion

(a) % adsorbed as the % of the applied.

(b) as % of the adsorbed

(c) Sample lost in desorption step, therefore value from one replicate used.

 

Table 8. Summary of Kd, KOC, KF, KFOC and 1/n Values from the Adsorption Step

Soil	Nominal rate applied aqueous phase as cation (µg/mL)	Partition coefficients		Freundlich coefficients
		Kd	KOC	KF	KFOC	1/n
Gartenacker	2.7	143.48	6832	144.00	6857	0.5867
	1.1	240.14	11435
	0.3	513.78	24466
	0.11	873.59	41600
	0.03	2576.45	122688
	Overall average:	869.49	41404
18 Acres	2.7	14820.74	592830	9011.16	360446	0.8925
	1.1	13281.92	531277
	0.3	19161.19	766448
	0.11	23559.35	942374
	0.03	21304.48	852179
	Overall average:	18425.54	737022
Marsillargues	2.7	23820.61	2646735	12931.65	1436850	0.9272
	1.1	13831.35	1536817
	0.3	20672.82	2296980
	0.11	23757.69	2639744
	0.03	25052.82	2783646
	Overall average:	21427.06	2380784
North Dakota	2.7	59311.91	2118283	70308.42	2511015	1.0649
	1.1	37456.82	1337744
	0.3	47697.77	1703492
	0.11	41746.70	1490954
	0.03	36813.45	1314766
	Overall average:	44605.33	1593048

All values are in terms of substance ion

 

Table 9. Summary of Kd, KOC, KF, KFOC and 1/n Values from the Desorption Step

Soil	Nominal rate applied aqueous phase as substance ion (µg/mL)	Partition coefficients		Freundlich coefficients
		Kd	KOC	KF	KFOC	1/n
Gartenacker	2.7	226.84	10802	154.20	7343	0.5555
	1.1	336.68	16032
	0.3	732.43	34877
	0.11	1393.48	66356
	0.03	4358.30	207538
	Overall average:	1409.55	67121
18 Acres	2.7	27046.25	1081850	19170.24	766809	0.9315
	1.1	27581.00	1103240
	0.3	36520.68	1460827
	0.11	64107.36	2564294
	0.03	18099.79	723991
	Overall average:	34671.02	1386840
Marsillargues	2.7	53916.67	5990741	76345.19	8482799	1.0809
	1.1	37310.29	4145587
	0.3	54230.98	6025665
	0.11	65212.92	7245880
	0.03	19270.52	2141169
	Overall average:	45988.28	5109808
North Dakota	2.7	67607.75	2414562	76522.70	2732954	1.0048
	1.1	78539.12	2804969
	0.3	103125.79	3683064
	0.11	106774.00	3813357
	0.03	50581.71	1806490
	Overall average:	81325.67	2904488

All values are in terms of substance ion

Validity criteria fulfilled:

not specified

Conclusions:

The adsorption/desorption properties of the radiolabelled test substance were studied in Swiss Gartenacker soil, British 18 Acres soil, French Marsillargues soil and US American North Dakota soil. Mean values for adsorption partition coefficients (Kd) per soil were in the range 869 to 44605 L/kg and (KOC) values were in the range 41404 to 2380784 L/kg. Freundlich adsorption coefficients (KFOC) were in the range 6857 to 2511015 L/kg. Mean values for desorption partition coefficients (Kd) per soil were in the range 1410 to 81326 L/kg and (KOC) values were in the range 67121 to 5109808 L/kg. Freundlich desorption coefficients (KFOC) were in the range 7343 to 8482799 L/kg. Using the McCall Classification scale to assess the potential mobility of a chemical in soil (based on KFOC), the test substance can be classified as being “immobile” in the four soils studied.

Executive summary:

The adsorption/desorption characteristics of the radiolabelled test substance cation were studied under GLP using a standard batch equilibrium methodaccording to OECD TG 106 using Swiss Gartenacker soil (loam), British 18 Acres soil (sandy clay loam), French Marsillargues soil (silty clay) and US American North Dakota soil (sandy loam).

The definitive adsorption and desorption assessments were conducted in the dark at 20 ± 2°C. Soil samples (1 g dry weight equivalent) were pre-equilibrated with 0.01M calcium chloride solution (90 mL) overnightand then treated with solutions of radiolabelled test substance (10 mL) to produce duplicate samples per soil. Concentrations of the test substance in the aqueous phase were initially 0.05, 0.2, 0.5, 2 and 5 µg/mL (equivalent cation concentrations were 0.03, 0.11, 0.3, 1.1, and 2.7 µg/mL, respectively). The adsorption phase was followed by a single desorption phase to determine the reversibility of adsorption. The recovery of radioactivity was established in all four soils using the highest test concentration only.

North Dakota soil only was selected to determine the recovery of radioactivity at all remaining concentrations. This recovery was established by radioassay of the adsorption supernatants, desorption supernatants and soil extracts and by combustion of the soil residues to determine the mass balance. Stability was verified by HPLC analyses of selected pooled adsorption and desorption supernatants and soil extracts. The soil adsorption coefficients Kd and Koc, together with the Freundlich adsorption constants Kf and Kfoc, were determined for each soil based on the cation. One replicate sample at each concentration from the North Dakota soil (the soil with the highest Kd) and one replicate sample from the remaining soils (the highest concentration only) were analysed for the stability test and mass balance.

 

No significant degradation was observed in supernatants or soil extracts with overall recoveries of applied radioactivity in the selected samples being in the range 96.2 to 100.9%. Mean values for adsorption partition coefficients (Kd) per soil were in the range 869 to 44605 L/kg and (Koc) values were in the range 41404 to 2380784 L/kg. Freundlich adsorption coefficients (Kfoc) were in the range 6857 to 2511015 L/kg. These data were derived using cation concentrations. Mean values for desorption partition coefficients (Kd) per soil were in the range 1410 to 81326 L/kg and (Koc) values were in the range 67121 to 5109808 L/kg. The calculated Freundlich desorption coefficients (Kfoc) were in the range 7343 to 8482799 L/kg. The desorption constants of the test substance were higher than the adsorption constants thus demonstrating that adsorption was not fully reversible. Using the McCall Classification scale to assess the potential mobility of a chemical in soil (based on Kfoc) the test substance can be classified as being “immobile” in the four soils studied.

Description of key information

Kfoc-ads of 7343 to 8482799 L/kg, batch equilibrium method, OECD TG 106, Dixon 2012

Several other studies have been conducted investigating the adsorption potential of the test substance. These have not been included in the dossier as robust study summaries. However, 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:

1 696 600

Additional information

Table: all reliable adsorption data of the test substance used for the derivation of the key value for chemical safety assessment

Parent
USDA	Name / Origin	OC*	pH	Kd/Kf*	Koc*	1/n	Author / Year /
Course Sand	RG1, DK	2.8	5.9	5000	180000	-	Ferguson et al., 1994
Sand	RG2, DK	4.9	5.8	1200	32000	-
Peat	RG3, DK	31.6	5	17000	54000	-
Very fine sand	RG4, DK	1.3	6.5	8500	640000	-
Loamy fine sand	RG5, DK	1.7	6.7	16000	920000	-
Course sand	RG5A, DK	3.7	6.1	3500	96000	-
Sand	RG6, DK	2.4	6.3	5000	210000	-
Sand	RG7, DK	2.3	6.4	4500	200000	-
Fine sandy loam	RG8, DK	1	8	42000	4200000	-
Loamy fine sand	RG9, DK	0.9	7.4	22000	2400000	-
Loamy fine sand	RG10, DK	1.3	7.3	20000	1500000	-
Loamy fine sand	RG11, DK	1.6	5.5	7000	450000	-
Loamy fine sand	RG12, DK	1.5	5.5	27000	1900000	-
Loamy sand	RG13, DK	1.4	7.1	38000	2700000	-
Loamy fine sand	RG14, DK	1.2	5	37000	3000000	-
Loamy fine sand	RG15, DK	1.8	5.9	31000	1700000	-
Loamy sand	RG16, DK	1.1	6.4	43000	3900000	-
Loamy sand	RG17, DK	2	6.1	14000	690000	-
Loamy fine sand	RG18, DK	1.6	4.9	12000	740000	-
Coarse sand	RG19, DK	0.8	6.2	6000	740000	-
Loamy sand	RG20, DK	0.7	6.3	25000	3600000	-
Loamy sand	RG21, DK	1	7.3	16000	1500000	-
Loamy sand	RG22, DK	1.2	7.1	92000	7900000	-
Loamy sand	RG23, DK	1.5	6.6	53000	3600000	-
Loamy fine sand	RG24, DK	1.5	6.9	14000	960000	-
Fine sandy loam	RG25, DK	1.1	8.2	28000	2500000	-
Loamy fine sand	RG26, DK	1	7.2	47000	4800000	-
Loamy sand	RG27, DK	1.2	7.1	43000	3500000	-
Sandy loam	RG28, DK	1.4	7.1	57000	4100000	-
Fine sandy loam	RG29, DK	1.1	7.8	49000	4400000	-
Loamy fine sand	RG30, DK	1.7	7.7	25000	1400000	-
Sandy loam	RG30A, DK	1.1	7.9	60000	5400000	-
Sand	Ocoee, Florida, USA	1.8	7.2	36	2000	0.4	Pack, 1987
Sand	Ocoee, Florida, USA	1.9	6.7	42	2211	0.45
Sandy clay loam	Stephenville, Texas, USA	0.6	7	4895	815833	0.94
Loam	Greenville, Mississippi, USA	1.5	5.5	10740	716000	1
Sandy loam	Greenville, Mississippi, USA	1	7.1	1882	188200	0.75
Sandy clay loam	Argissolo, Eldorado do Sul, BR	2.3	4.8	507	22025	0.558	Monego, 2005
Clay	Latossolo, Nova Prata, BR	2.7	4.7	1519	56272	0.693
Sand	Neossolo, Osorio, BR	0.3	5.2	910	303477	0.678
Sandy loam	Gleissolo, Viamao, BR	3.5	3.7	484	13834	0.588
Loam	Gartenacker, CH	2.1	7.4	144	6857	0.5867	Dixon, 2012
Sandy clay loam	18 Acres, UK	2.5	6.1	9011	360446	0.8925
Silty clay	Marsillargues, FR	0.9	7.8	12932	1436850	0.9272
Sandy loam	North Dakota, USA	2.8	7.4	70308	2511015	1.0649
Arithmetic mean / median Koc					1696600 / 920000	0.7329 / 0.6930
pH dependence (yes / no)	No

 

Dixon 2012

The adsorption/desorption characteristics of the radiolabelled test substance cation were studied under GLP using a standard batch equilibrium methodaccording to OECD TG 106 using Swiss Gartenacker soil (loam), British 18 Acres soil (sandy clay loam), French Marsillargues soil (silty clay) and US American North Dakota soil (sandy loam).

The definitive adsorption and desorption assessments were conducted in the dark at 20 ± 2°C. Soil samples (1 g dry weight equivalent) were pre-equilibrated with 0.01M calcium chloride solution (90 mL) overnightand then treated with solutions of radiolabelled test substance (10 mL) to produce duplicate samples per soil. Concentrations of the test substance in the aqueous phase were initially 0.05, 0.2, 0.5, 2 and 5 µg/mL (equivalent cation concentrations were 0.03, 0.11, 0.3, 1.1, and 2.7 µg/mL, respectively). The adsorption phase was followed by a single desorption phase to determine the reversibility of adsorption. The recovery of radioactivity was established in all four soils using the highest test concentration only.

North Dakota soil only was selected to determine the recovery of radioactivity at all remaining concentrations. This recovery was established by radioassay of the adsorption supernatants, desorption supernatants and soil extracts and by combustion of the soil residues to determine the mass balance. Stability was verified by HPLC analyses of selected pooled adsorption and desorption supernatants and soil extracts. The soil adsorption coefficients Kd and Koc, together with the Freundlich adsorption constants Kf and Kfoc, were determined for each soil based on the cation. One replicate sample at each concentration from the North Dakota soil (the soil with the highest Kd) and one replicate sample from the remaining soils (the highest concentration only) were analysed for the stability test and mass balance.

 

No significant degradation was observed in supernatants or soil extracts with overall recoveries of applied radioactivity in the selected samples being in the range 96.2 to 100.9%. Mean values for adsorption partition coefficients (Kd) per soil were in the range 869 to 44605 L/kg and (Koc) values were in the range 41404 to 2380784 L/kg. Freundlich adsorption coefficients (Kfoc) were in the range 6857 to 2511015 L/kg. This data was derived using cation concentrations. Mean values for desorption partition coefficients (Kd) per soil were in the range 1410 to 81326 L/kg and (Koc) values were in the range 67121 to 5109808 L/kg. The calculated Freundlich desorption coefficients (Kfoc) were in the range 7343 to 8482799 L/kg. The desorption constants of the test substance were higher than the adsorption constants thus demonstrating that adsorption was not fully reversible. Using the McCall Classification scale to assess the potential mobility of a chemical in soil (based on Kfoc) the test substance can be classified as being “immobile” in the four soils studied.