N-[[3,5-dichloro-2-fluoro-4-(1,1,2,3,3,3-hexafluoropropoxy)phenyl]carbamoyl]-2,6-difluorobenzamide

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:

21 November 2000 - 4 May 2001

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)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EPA OPPTS 835.1220 (Sediment and Soil Adsorption / Desorption Isotherm)

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: FIFRA N-163-1

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: SETAC Part 1, Section 4

Deviations:

no

GLP compliance:

yes

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Test temperature:

25 °c

Analytical monitoring:

yes

Details on sampling:

TIERS 1, 2 AND 3
Duplicate samples were analysed at 2, 4, 8, 24, and 48 hours after initiation of shaking. The samples were centrifuged and the adsorption solution decanted.

Details on matrix:

Details on the collection and storage and details on the properties of the eight soils used are provided in Tables 1 and 2, respectively.

The soils were screened through a 2 mm sieve and stored at approximately 4 °C in a polyethylene bag stored within a fibre pack. Soil subsamples prior to weighing for each test were stored at room temperature.

Details on test conditions:

CONTAINER SORPTION
The sorption of the test material was evaluated in a 45 mL glass vial, a 2 oz. glass jar, and a 4 oz. glass jar by adding 25, 50, or 100 mL, respectively, of a nominal 0.05 µg/mL solution of ¹⁴C test material in 0.01 M CaCl₂. The samples were shaken overnight (15 hours), then aliquots (0.5 mL) analysed by LSC. Since adsorption to all containers exceeded 5 % of applied radioactivity, the same container types were silanized and the experiment repeated. Non-silanized glassware results were re-verified using the same procedures.

MATRIX INTERFERENCE
Using two of the eight soil types, one with a high clay content and low organic matter content (M590) and one with a low clay content and high organic matter content (M599), the adsorption of ¹⁴C test material to the soil rather than the glassware was evaluated. To the glassware selected from the container sorption test (un-silanized 4 oz. jar) soil (10 g dry weight) and 0.01 M CaCI₂ (to bring total water volume to 45 mL) was added. Two control samples containing calcium chloride but no soil were run concurrently. The samples were shaken for 4 hours and the calcium chloride removed by centrifugation and decantation. The calcium chloride phases were fortified with ¹⁴C test material in acetonitrile to a nominal concentration of 0.04 µg/mL (0.025 mL). Triplicate aliquots (0.5 mL) of the fortified samples were analysed by LSC. Aliquots of the dosed solution for each soil type and control were also analysed by HPLC.

TIER 1 PRELIMINARY TEST
The first preliminary (Tier 1) study evaluated three soil solution ratios using the same two soil types as for the matrix interference test, M590 and M599. Approximately 2 or 5 g (oven dry weight equivalent) moist soil was weighed into the jars with the lowest amount of adsorption from the container adsorption test. Because the test material rapidly sorbs to glassware, 0.01 M CaCl₂ was added first, at a soil/solution ratio of 1:5 (5 g:25 mL), 1:25 (2 g:50 mL), or 1:50 (2 g:100 mL). The ¹⁴C test material was then dosed directly to the calcium chloride at a nominal concentration of 0.05 mg/L (35 or 70 µL). Aliquots (35 µL) of the test material were taken before and after dosing and analysed by LSC to determine application level. Two controls (containing test material but no soil), and two blanks per soil type (containing soil but no test material) were run concurrently. The samples were shaken on a horizontal shaker (approximately 180 excursions per minute) in the dark at 25 °C.
Duplicate samples were analysed at 2, 4, 8, 24, and 48 hours after initiation of shaking. The samples were centrifuged and the adsorption solution decanted. The weight of the calcium chloride phase was recorded, and triplicate aliquots (1.0 mL) removed for LSC analysis. The weight of the soil plus interstitial pore water was also recorded. Blank samples were analysed at the same times and in the same manner except that after aliquots were removed for analysis, the samples were mixed to break the soil pellet and returned to the shaker. Control samples were analysed only at 24 hours. After adsorption, the 24-hour, 1:50 soil:solution soil samples were extracted three times with acetone/0.1 N HCl (80:20, v/v) by shaking for 30 minutes, centrifuging, and decanting. The extracts were pooled and the final volume recorded. Aliquots (1.0 mL) of the extracts were analysed by LSC. Whether extracted or not, the remaining soils were allowed to air dry, and triplicate aliquots (0.2 g) analysed by oxidative combustion to determine mass balance.

TIER 2 PRELIMINARY TEST
Using the soil:solution ratio of 1:50 selected from the Tier 1 Preliminary test, an adsorption kinetics test was conducted on the remaining six soils. Approximately 2 g (oven dry weight equivalent) moist soil was weighed into the jars with the lowest amount of adsorption from the container adsorption test. As for the Tier 1 Preliminary test, 0.01 M CaCl₂ (100 mL) was added, at a soil:solution ratio of 1:50. The ¹⁴C test material was then dosed directly to the calcium chloride solution at a nominal concentration of 0.05 mg/L (65 µL). Aliquots (65 µL) of the test material were taken before and after dosing and analysed by LSC to determine application level. Two blanks per soil type (containing soil but no test material) were run concurrently. The samples were shaken on a horizontal shaker (approximately 180 excursions per minute) in the dark at 25 °C.
Duplicate samples were analysed at 2, 4, 8, 24, and 48 hours after initiation of shaking. The samples were centrifuged and the adsorption solution decanted. The weight of the calcium chloride phase was recorded, and triplicate aliquots (1.0 mL) removed for LSC analysis. The weight of the soil plus interstitial pore water was also recorded. Blank samples were analysed at the same times and in the same manner except that after aliquots were removed for analysis, the samples were mixed to break the soil pellet and returned to the shaker. After adsorption, one of the 48 hour samples per each soil type was extracted three times with acetone/0.1 N HCl (80:20, v/v) by shaking for 30 minutes, centrifugation, and decantation, pooling the extracts. Aliquots (1.0 mL) of the extracts were analysed by LSC. Whether extracted or not, the remaining soils were allowed to air dry, and triplicate aliquots (0.2 g) analysed by oxidative combustion to determine mass balance.

TIER 3 DESORPTION KINETICS PRELIMINARY TEST
Once the adsorption equilibration time was determined from the Tiers 1 and 2 Preliminary tests, all eight soils were evaluated for desorption kinetics. Approximately 2 g (oven dry weight equivalent) moist soil was weighed into jars, 0.01 M CaCl₂ (100 mL) added, ¹⁴C test material was applied at a nominal concentration of 0.05 mg/L (65 µL) and the samples shaken overnight (16 hours) in the dark at 25 °C. The adsorption solutions were removed and analysed. A volume of fresh 0.01 M CaCl₂ (98 mL) was added, approximately equal to the amount of adsorption solution removed. Two blanks per soil type (containing soil but no test material) and duplicate controls (containing test material but no soil) were run concurrently. The samples were shaken on a horizontal shaker (approximately 180 excursions per minute) in the dark at 25 °C.
Duplicate samples were analysed at 2, 4, 8, 24, and 48 hours after initiation of shaking. The samples were centrifuged and the desorption solution decanted. The weight of the desorption calcium chloride phase was recorded, and triplicate aliquots (1.0 mL) were removed for LSC analysis. The weight of the soil plus interstitial pore water was also recorded. Blank samples were analysed at the same times and in the same manner except that after aliquots were removed for analysis, the samples were mixed to break the soil pellet and returned to the shaker. Control samples were analysed only at 24 hours. Following desorption, one of the 48 hour samples per each soil type was extracted three times with acetone/0.1 N HCI (80:20, v/v) by shaking for 30 minutes, centrifugation, and decantation, pooling the extracts. Aliquots (1.0 mL) of the extracts were analysed by LSC. Whether extracted or not, the remaining soils were allowed to air dry, and triplicate aliquots (0.2 g) analysed by oxidative combustion to determine mass balance.

DEFINITIVE ISOTHERM TEST
Once the adsorption and desorption equilibration times were determined from the Tiers 1, 2, and 3 Preliminary tests, all eight soils were evaluated via the definitive isotherm test. Approximately 2 g (oven dry weight equivalent) moist soil was weighed into jars, 0.01 M CaCI₂ (100 mL) added, ¹⁴C test material was applied at nominal concentration of 0.009, 0.025, 0.050, and 0.095 mg/L (65 µL). The samples were shaken overnight (16 hours) in the dark at 25 °C, and the adsorption solution removed as described in Tiers 1 and 2, and analysed by LSC. Study design conditions for the adsorption phase are shown in Table 3. Approximately the amount of 0.01 M CaCl₂ removed in the adsorption phase was added for the desorption phase (98 mL). The samples were shaken for 3 hours in the dark at 25 °C, and the desorption solution removed as described in Tier 3, and analysed by LSC. The U.S. soils only (M555, M588, M590, M599) were subjected to a second desorption following the same procedure as the first desorption. Study conditions for the desorption phases are summarised in Table 4. Following the last desorption, the soils were allowed to air-dry, and triplicate aliquots (0.2 g) removed for oxidative combustion to determine mass balance. Adsorption and desorption Kd, Koc, and Kf values were calculated.

Duration:

16 h

Temp.:

25

Duration:

3 h

Temp.:

25

Key result

Type:

Kd

Value:

>= 1 475 - <= 3 115 L/kg

pH:

7.9

Temp.:

25 °C

Matrix:

Silt loam (Greece)

% Org. carbon:

1

Key result

Type:

Koc

Value:

>= 98 315 - <= 207 641 L/kg

pH:

7.9

Temp.:

25 °C

Matrix:

Silt loam (Greece)

% Org. carbon:

1

Key result

Type:

Kd

Value:

>= 1 351 - <= 2 897 L/kg

pH:

6.3

Temp.:

25 °C

Matrix:

Silty clay loam (France)

% Org. carbon:

1.1

Key result

Type:

Koc

Value:

>= 32 162 - <= 68 981 L/kg

pH:

6.3

Temp.:

25 °C

Matrix:

Silty clay loam (France)

% Org. carbon:

1.1

Key result

Type:

Kd

Value:

>= 1 614 - <= 1 994 L/kg

pH:

5.2

Temp.:

25 °C

Matrix:

Loam (Indiana USA)

% Org. carbon:

1.1

Key result

Type:

Koc

Value:

>= 159 776 - <= 197 432 L/kg

pH:

5.2

Temp.:

25 °C

Matrix:

Loam (Indiana, USA)

% Org. carbon:

1.1

Key result

Type:

Kd

Value:

>= 2 137 - <= 3 275 L/kg

pH:

6

Temp.:

25 °C

Matrix:

Sand (UK)

% Org. carbon:

1.6

Key result

Type:

Koc

Value:

>= 199 721 - <= 306 050 L/kg

pH:

6

Temp.:

25 °C

Matrix:

Sand (UK)

% Org. carbon:

1.6

Key result

Type:

Kd

Value:

>= 2 545 - <= 3 425 L/kg

pH:

7.7

Temp.:

25 °C

Matrix:

Sandy clay loam (UK)

% Org. carbon:

1.9

Key result

Type:

Koc

Value:

>= 231 330 - <= 292 166

pH:

7.7

Temp.:

25 °C

Matrix:

Sandy clay loam (UK)

% Org. carbon:

1.9

Key result

Type:

Kd

Value:

>= 859 - <= 1 437

pH:

6.4

Temp.:

25 °C

Matrix:

Sand (North Carolina, USA)

% Org. carbon:

0.8

Key result

Type:

Koc

Value:

>= 53 673 - <= 89 783 L/kg

pH:

6.4

Temp.:

25 °C

Matrix:

Sand (North Carolina, USA)

% Org. carbon:

0.8

Key result

Type:

Kd

Value:

>= 4 013 - <= 7 828 L/kg

pH:

4.7

Temp.:

25 °C

Matrix:

Loam (North Dakota, USA)

% Org. carbon:

4.2

Key result

Type:

Koc

Value:

>= 211 143 - <= 412 004 L/kg

pH:

4.7

Temp.:

25 °C

Matrix:

Loam (North Dakota, USA)

% Org. carbon:

4.2

Key result

Type:

Kd

Value:

>= 3 008 - <= 3 755 L/kg

pH:

7.2

Temp.:

25 °C

Matrix:

Clay (Mississippi USA)

% Org. carbon:

1.5

Key result

Type:

Koc

Value:

>= 376 061 - <= 469 335 L/kg

pH:

7.2

Temp.:

25 °C

Matrix:

Clay (Mississippi USA)

% Org. carbon:

1.5

Adsorption and desorption constants:

Adsorption and desorption constants are provided in Table 5. The adsorption Kd ranged from 859 to 7828 mL/g, while the adsorption Koc ranged from 32 162 to 412 004 mL/g; in all cases, indicated an extremely low potential to leach. In the same way the desorption constants indicated an extremely low potential for the test material to leach, with desorption Kd values ranging from 858 to 12 514 mL/g and desorption Koc values ranging from 53 618 to 738 634 mL/g. Generally the adsorption Kd values were higher than the desorption constants.

FREUNDLICH CONSTANTS
Adsorption and desorption Freundlich constants were calculated for each soil, with results shown in Table 5. Adsorption Kf values ranged from 557 to 5840 mL/g, averaging 2280 ± 1651 mL/g. The linear correlation coefficients (R²) ranged from 0.976 to 0.996. The 1/n values ranged from 0.82 to 1.11, indicating some non-proportional dependence upon concentration, but this may be exaggerated due to the low levels of radioactivity measured in the adsorption solutions.
First desorption isotherms were similar to the adsorption results but with more variability, with Kf values ranging from 616 to 16 457 mL/g. The linear correlation coefficients ranged from 0.973 to 0.996. The 1/n values ranged from 0.75 to 1.37, again indicating non-proportional dependence upon concentration, but may also be exaggerated due to the low levels of radioactivity measured in the desorption solutions.

Details on results (Batch equilibrium method):

MATRIX INTERFERENCE PRELIMINARY TEST
For the M590 soil, 61 and 81 % of the applied radioactivity was detected in the solution, for soil M599, 64 and 76 % of the applied radioactivity was detected in solution, and for the controls, 81 and 82 % of the applied radioactivity was in solution. One sample for each soil type and control was analysed by HPLC and shown to contain at least 98 % test material. Therefore, there was no matrix interference noted.

PRELIMINARY TEST TO DETERMINE SOIL:SOLUTION RATIO AND ADSORPTION EQUILIBRATION TIME (TIER I TEST)
All blank soil samples contained radioactivity at less than the limit of quantification. Equilibration was rapid, with less than 2.2 % of the applied radioactivity remaining in solution after only two hours. Mass balance was acceptable, generally greater than 90 % of applied radioactivity.
As expected, the soil:solution ratio of 1:50 yielded higher concentrations of the test material in solution at the various time points. At no soil:solution ratio was adsorption less than 85 % of applied. Soil:solution ratios of 1:100 and 1:250 were briefly evaluated using similar procedures, but resulted in similar amounts of test material adsorbed to the soil (98 - 106 % based upon combustion of the soil pellet). Therefore, the soil:solution ratio of 1:50 was selected for the remainder of the tests.
The soils remaining after adsorption (soil:solution ratio 1:50) were extracted. Both the adsorption phase and organic extract were concentrated and separately analysed by HPLC. Concentration recoveries for the adsorption solutions were low, 57 - 87 %, most likely due to the low total amount of radioactivity. Results showed that there was up to 22 % degradation of the test material in the adsorption solution (up to 0.2 % of applied radioactivity) but not in the organic extract. Overall, 90 - 91 % of the applied radioactivity remained as test material. In comparison, there was no degradation of test material in the adsorption solutions of the control samples (at least 98 % parent by HPLC), however, there was significant sorption to the container, 67 - 81 %, resulting in 16 - 26 % of applied parent detected in the control samples.

PRELIMINARY TEST TO DETERMINE ADSORPTION EQUILIBRATION TIME (TIER 2 TEST)
All blank soil samples contained radioactivity at less than the limit of quantitation.
Adsorption equilibrium was achieved in the preliminary Tiers 1 and 2 tests within 24 hours. The radioactive components rapidly sorbed to the soil, with generally less than 5 % of the applied radioactivity recovered in the adsorption solution. Mass balance was generally acceptable at the later time points. There may have been sorption to the glassware at the early time points, but over time the radioactivity appeared to preferentially bind to the soil. However, soils M579 and M588 consistently yielded low recoveries, 66.7 - 100 % of applied. Both M579 and M588 are sandy soils, from the UK and North Carolina (USA), respectively. The recoveries were acceptable when one set of the 48 hour samples was extracted with organic solvent, even for M579 and M588 soils. Therefore, the test material adsorbed to the glass rather than the soil.

One replicate of the 48 hour adsorption solutions was concentrated using C₁₈ SPE and analysed by HPLC. Radioactivity recovered in the phase analysed by SPE ranged from 72 - 86 %. The amount of parent remaining in the adsorption solution was 63.3 - 92.7 % of the radioactivity in solution (1.3 - 6.4 % of the applied radioactivity), with up to 31.4 % urea metabolite formed (0.4 - 0.7 % of applied radioactivity), plus up to 6 % polar components or amine metabolite (up to 0.2 % of applied radioactivity), similar to the M599 soil analysed in Tier 1. The organic extracts from the 48 hour samples were also concentrated and analysed by HPLC, but showed no degradation (greater than 98 % test material by HPLC, 81 - 104 % of the applied radioactivity remained as test material), similar to the Tier 1 results. Therefore, any radioactivity on the soil or container was considered to be test material with no degradation. Overall, 82.5 - 110 % of the applied radioactivity was determined to be test material.
From the preliminary Tiers 1 and 2 tests, an adsorption equilibration period of approximately 16 hours (overnight) was chosen to allow equilibrium yet minimise degradation.

PRELIMINARY TEST TO DETERMINE DESORPTION EQUILIBRATION TIME (TIER 3 DESORPTION KINETICS TEST)
All blank soil samples contained radioactivity at less than the limit of quantification. Desorption equilibration was achieved very rapidly, within two hours, for seven of the eight soils. Generally less than 5 % of the applied radioactivity remained in the adsorption solution, and generally less than 3 % was removed in the desorption solution. Mass balance was generally good, except for soils M579 and M588 (also observed in the Tier 2 test). Because recoveries for all soils were good when extracted with organic solvent, it was assumed that a small portion of the radioactivity sorbed to the container. The 48 hour M599 sample, which was extracted with organic solvent, yielded an extremely high recovery, 177 %. It is believed that this sample was inadvertently dosed twice. If the data for this sample are divided in half, the adsorption solution, desorption solution, organic extract, soil pellet, and total recovery would be 1.7, 1.2, 85.0, 0.6, and 88.6 %, respectively.
As the adsorption solutions had previously been characterised, the adsorption solutions from the tier 3 desorption kinetics were not analysed by HPLC. One replicate of the 48 hour desorption solutions was concentrated using C₁₈ SPE and analysed by HPLC. The radioactivity recovered in the phase analysed by SPE ranged from 68 - 151 %. The amount of parent remaining in the desorption solution was greater than 99 % for the control (no soil) sample, although only 23 - 30 % of the applied radioactivity was desorbed, resulting in 37 % of the applied radioactivity as parent (high recovery from SPE). In the soil samples, degradation in the desorption solutions was greater, with 47 - 90 % parent (0.5 - 2.5 % of applied radioactivity) and up to 52.8 % urea metabolite formed (up to 1.0 % of applied radioactivity).
The soils remaining after a 16 hour adsorption and 48 hour desorption were subsequently extracted with organic solvent. Results indicated that 81 - 103 % of the radioactivity remaining on the soil was extracted with the organic solvent. The extracts were concentrated and analysed by HPLC. The HPLC results showed that 97 - 100 % of the radioactivity in the organic extract had the same retention time as the test material (82 - 102 % of the applied radioactivity), with 2.4 % of the applied radioactivity determined to be urea metabolite in the M585 soil only. The identity of the test material was confirmed using normal phase TLC. Overall, 83 - 104 % of the applied radioactivity was recovered as parent.
From the preliminary Tier 3 desorption kinetics test, a desorption equilibration period of at least two hours was chosen to allow equilibrium yet minimise degradation.

DEFINITIVE ISOTHERM TEST
MASS BALANCE AND DEGRADATION OF PARENT
The average mass balance for all samples was 88.5 %, which, given the compound’s natural tendency to sorb to glassware, should be considered acceptable. Mass balance decreased with increased dose concentration, once again indicating that a portion of the radioactive test material may have sorbed to the container. From low to high dosing concentration, average mass balance over all of the soils decreased from 95 - 88 to 87 - 84 %. As noted in the preliminary studies, mass balance for the M588 samples was consistently low, independent of dose concentration. In the earlier tests, extraction of the samples with organic solvent yielded higher mass balance results. Since none of the isotherm samples were extracted, the radioactivity sorbed to glass was not measured, accounting for the lower mass balance results observed in the isotherm test.
An average of 2.3 % (0.7 - 5.1 %) of the applied radioactivity remained in the adsorption solution, while an average of 1.4 % (0.4 - 3.8 %) was recovered in the first desorption solution. An additional 1.6 % (0.4 - 3.8 %) of the applied radioactivity was recovered in the second desorption solution (US soils only). An average of 84 % (61.4 - 105 %) of the applied radioactivity remained in the soil pellet, as determined by oxidative combustion.
The duplicate adsorption solutions dosed at the highest concentration were concentrated using C₁₈ SPE and analysed by HPLC. The radioactivity recovered in the adsorption phase analysed by SPE ranged from 34 - 149 %. The amount of parent remaining in the adsorption solution was 0.8 - 2.6 % of the applied radioactivity with up to 0.3 % urea metabolite by HPLC. The presence of the test material and urea metabolite was confirmed using normal phase TLC.
The radioactivity recovered in the desorption phase analysed by SPE ranged from 62 - 97 %. The amount of parent remaining in the desorption solution was greater than 70 % by HPLC, accounting for 0.4 - 1.5 % of the applied radioactivity. Therefore, the shorter shaking time for the definitive desorption solutions resulted in less degradation of parent than detected in the desorption kinetics test.
As stability of the test material in soil was demonstrated after a 48 hour desorption, the stability of the test material in the remaining soil was assumed for the isotherm samples, which were subjected to only a 3 hour desorption and for four of the soils an additional 2 hour second desorption. Therefore, the soil remaining after desorption was not extracted with organic solvent.

Table 5: Adsorption and Desorption Constants

Soil	Adsorption					Desorption
	Kf (mL/g)	1/n	R²	Kd (mL/g)	Koc (mL/g)	Kf (mL/g)	1/n	R²	Kd (mL/g)	Koc (mL/g)
M546	708	0.85	0.995	1475 to 3115	98 315 to 207 641	1108	0.88	0.994	2455 to 3366	163 652 to 224 369
M547	557	0.82	0.990	1351 to 2897	32 162 to 68 981	3888	1.02	0.983	3099 to 3642	73 780 to 86 713
M555	2356	1.05	0.994	1614 to 1994	159 776 to 197 432	2763	1.02	0.974	2032 to 2833	201 207 to 280 494
M579	1805	0.94	0.992	2137 to 3275	199 721 to 306 050	616	0.75	0.992	3416 to 7903	319 278 to 738 634
M585	3014	1.02	0.996	2545 to 3425	231 330 to 311 353	1922	0.93	0.976	2432 to 3904	221 070 to 354 898
M588	2086	1.11	0.976	859 to 1437	53 673 to 89 783	16 457	1.37	0.973	858 to 1853	53 618 to 115 827
M590	1872	0.88	0.989	4013 to 7828	211 237 to 412 004	1342	0.78	0.996	6079 to 12 514	319 951 to 658 639
M599	5840	1.08	0.995	3008 to 3755	376 061 to 469 335	2972	0.96	0.992	3752 to 4797	469 017 to 599 390

Validity criteria fulfilled:

yes

Conclusions:

The sorptive behaviour of the test material may be characterised as immobile for all soil types. Adsorption is rapid, with equilibrium reached in less than 16 hours, resulting in adsorption Kd values above 850 mL/g and Koc values above 32 000 mL/g. The sorption is nearly irreversible, with desorption Kd values above 850 mL/g and Koc values above 53 000 mL/g.

Executive summary:

The adsorption/desorption characteristics of the test material were investigated in a batch equilibrium study. The experiment was conducted in accordance with the standardised guidelines OECD 106, FIFRA N-163-1, SETAC Part 1 Section 4, and OPPTS 835.1220 under GLP conditions.

The study was conducted using eight soils: a clay (pH 7.2, organic carbon 1.5 %) from Mississippi (USA); a loam (pH 4.7, organic carbon 4.2 %) from North Dakota (USA); a silt loam (pH 7.9, organic carbon 1.0 %) from Greece; a silty clay loam (pH 6.3, organic carbon 1.1 %) from France; a loam (pH 5.2, organic carbon 1,1 %) from Indiana (USA); a sand (pH 6.0, organic carbon 1.6 %) from the United Kingdom; a sandy clay loam (pH 7.7, organic carbon 1.9%) from the United Kingdom; and a sand (pH 6.4, organic carbon 0.8 %) from North Carolina (USA).

Following preliminary testing, the adsorption phase of the definitive isotherm study was carried out by equilibrating fresh soil with ¹⁴C-test material at 0, 0.010, 0.024, 0.052, and 0.097 mg a.i./kg soil in the dark at 25 °C for 16 hours. The equilibrating solution used was 0.01 M CaCl₂, with a soil:solution ratio of 1:50. The desorption phase of the study was carried out by adding approximately the amount of 0.01 M CaCl₂ removed for adsorption and equilibrating in the dark at 25 °C for three hours. Half of the soils were desorbed a second time after equilibrating in the dark at 25 °C for two hours.

The supernatant after adsorption and desorption was separated by centrifugation, concentrated using SPE, and analysed directly by HPLC-fraction collection. The ¹⁴C residue remaining in the soil was determined by oxidative combustion. The adsorption parameters were calculated using the Freundlich adsorption isotherm.

The stability of the test material during the adsorption phase of the study, and the stability during the desorption phase averaged 86.0 ± 6.2 % in the adsorption solution (isotherm test, highest concentration only). The mass balance at the end of the adsorption phase of the study averaged 92.7 ± 9.7 % of that applied in all of the soils (preliminary, tier 1 and 2 tests, 24 hour equilibrium, soil/solution ratio of 1/50). The mass balance at the end of the desorption phase averaged 88.0 ± 6.4 % of that applied in all of the soils (preliminary tier 3 desorption test, 4 hour equilibrium).

After 16 hours of equilibration, an average of 97.8 ± 1.2 % of the applied test material adsorbed to all of the soils. The adsorption Kd values were 859 - 7828 mL/g, with an average of 2706 ± 1285 mL/g. Adsorption Koc values were 32 162 - 469 335 mL/g, with an average of 209 900 ± 119 596 mL/g. At the end of the desorption, 0.4 - 3.8 % of the adsorbed radioactivity was desorbed. The desorption Kd values were 858 - 12 514 mL/g, with an average of 3982 ± 2448 mL/g. The desorption Koc values were 53 618 - 738 634 mL/g with an average of 299 818 ± 183 961 mL/g. The desorption Kd values were slightly higher than those obtained for adsorption.

The sorptive behaviour of the test material may be characterised as immobile for all soil types. Adsorption is rapid, with equilibrium reached in less than 16 hours, resulting in adsorption Kd values above 850 mL/g and Koc values above 32 000 mL/g. The sorption is nearly irreversible, with desorption Kd values above 850 mL/g and Koc values above 53 000 mL/g.

Description of key information

The sorptive behaviour of the test material may be characterised as immobile for all soil types. Adsorption is rapid, with equilibrium reached in less than 16 hours, resulting in adsorption Kd values above 850 mL/g and Koc values above 32 000 mL/g. The sorption is nearly irreversible, with desorption Kd values above 850 mL/g and Koc values above 53 000 mL/g.

Key value for chemical safety assessment

Koc at 20 °C:

209 900

Additional information

The adsorption/desorption characteristics of the test material were investigated in a batch equilibrium study. The experiment was conducted in accordance with the standardised guidelines OECD 106, FIFRA N-163-1, SETAC Part 1 Section 4, and OPPTS 835.1220 under GLP conditions. The study was awarded a reliability score of 1 in accordance with the criteria set forth by Klimisch et al. (1997).

The study was conducted using eight soils: a clay (pH 7.2, organic carbon 1.5 %) from Mississippi (USA); a loam (pH 4.7, organic carbon 4.2 %) from North Dakota (USA); a silt loam (pH 7.9, organic carbon 1.0 %) from Greece; a silty clay loam (pH 6.3, organic carbon 1.1 %) from France; a loam (pH 5.2, organic carbon 1,1 %) from Indiana (USA); a sand (pH 6.0, organic carbon 1.6 %) from the United Kingdom; a sandy clay loam (pH 7.7, organic carbon 1.9%) from the United Kingdom; and a sand (pH 6.4, organic carbon 0.8 %) from North Carolina (USA).

Following preliminary testing, the adsorption phase of the definitive isotherm study was carried out by equilibrating fresh soil with ¹⁴C-test material at 0, 0.010, 0.024, 0.052, and 0.097 mg a.i./kg soil in the dark at 25 °C for 16 hours. The equilibrating solution used was 0.01 M CaCl₂, with a soil:solution ratio of 1:50. The desorption phase of the study was carried out by adding approximately the amount of 0.01 M CaCl₂ removed for adsorption and equilibrating in the dark at 25 °C for three hours. Half of the soils were desorbed a second time after equilibrating in the dark at 25 °C for two hours.

The supernatant after adsorption and desorption was separated by centrifugation, concentrated using SPE, and analysed directly by HPLC-fraction collection. The ¹⁴C residue remaining in the soil was determined by oxidative combustion. The adsorption parameters were calculated using the Freundlich adsorption isotherm.

The stability of the test material during the adsorption phase of the study, and the stability during the desorption phase averaged 86.0 ± 6.2 % in the adsorption solution (isotherm test, highest concentration only). The mass balance at the end of the adsorption phase of the study averaged 92.7 ± 9.7 % of that applied in all of the soils (preliminary, tier 1 and 2 tests, 24 hour equilibrium, soil/solution ratio of 1/50). The mass balance at the end of the desorption phase averaged 88.0 ± 6.4 % of that applied in all of the soils (preliminary tier 3 desorption test, 4 hour equilibrium).

After 16 hours of equilibration, an average of 97.8 ± 1.2 % of the applied test material adsorbed to all of the soils. The adsorption Kd values were 859 - 7828 mL/g, with an average of 2706 ± 1285 mL/g. Adsorption Koc values were 32 162 - 469 335 mL/g, with an average of 209 900 ± 119 596 mL/g. At the end of the desorption, 0.4 - 3.8 % of the adsorbed radioactivity was desorbed. The desorption Kd values were 858 - 12 514 mL/g, with an average of 3982 ± 2448 mL/g. The desorption Koc values were 53 618 - 738 634 mL/g with an average of 299 818 ± 183 961 mL/g. The desorption Kd values were slightly higher than those obtained for adsorption.

The sorptive behaviour of the test material may be characterised as immobile for all soil types. Adsorption is rapid, with equilibrium reached in less than 16 hours, resulting in adsorption Kd values above 850 mL/g and Koc values above 32 000 mL/g. The sorption is nearly irreversible, with desorption Kd values above 850 mL/g and Koc values above 53 000 mL/g.

[LogKoc: 5.3]