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Environmental fate & pathways

Adsorption / desorption

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Reference
Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
key study
Study period:
From 4 July 2016 to 14 July 2016
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)
Version / remarks:
Tier 1 (preliminary study) and Tier 2 (screening test)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.18 (Adsorption / Desorption Using a Batch Equilibrium Method)
Version / remarks:
Tier 1 (preliminary study) and Tier 2 (screening test)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Type of method:
batch equilibrium method
Media:
soil
Radiolabelling:
no
Test temperature:
25°C
Details on study design: HPLC method:
not applicable
Analytical monitoring:
yes
Details on sampling:
- Concentrations: 400.0 mg of the test item were mixed with 400 mL of the CaCl2 solution (0.01 M). The re-sulting mixture (Lot. 20160705), with a nominal concentration of 1000 mg/L, was shaken vigorously for 23 hours and filtrated with Nylon filters 0.45 µm pore size. The resulting so-lution with nominal concentration 1000 mg/L was used as test solution for Tier 1and Tier 2.
- Sampling interval: Tier: Samples of 0.3 mL were taken at 4 hours, 8 hours, 24 hours and 48 hours and measured directly after centrifugation. Tier 2: Samples of 0.3 mL were taken at 2, 4, 6, 8, 24 and 48 hours for soil 1 and at 2, 4, 6, 24, 29 and 48 hours for soils 3 and 4 and measured directly after centrifugation. Different sam-pling times were chosen for the soils for organizational reasons.
Details on matrix:
to be added
Details on test conditions:
TEST CONDITIONS
- pH: From 5.63 to 6.61 (Tier 2).

TEST SYSTEM
- Type, size and further details on reaction vessel: not specified
- Water filtered (i.e. yes/no; type of size of filter used, if any): not specified
- Soil-water ratio (if simulation test): Tier 1: from 1:1 to 1:3.1. Tier 2: 1:1.
- Number of reaction vessels/concentration: not specified
- Measuring equipment: HPLC Ultimate3000
- Test performed in closed vessels due to significant volatility of test substance: not specified
- Test performed in open system: not specified
- Method of preparation of test solution: 400.0 mg of the test item were mixed with 400 mL of the CaCl2 solution (0.01 M). The re-sulting mixture (Lot. 20160705), with a nominal concentration of 1000 mg/L, was shaken vigorously for 23 hours and filtrated with Nylon filters 0.45 µm pore size. The resulting so-lution with nominal concentration 1000 mg/L was used as test solution for Tier 1and Tier 2.
- Are the residues from the adsorption phase used for desorption: no
Computational methods:
- Adsorption and desorption coefficients (Kd): no computational method used
- Adsorption coefficient per organic carbon (Koc): no computational method used
Sample No.:
#1
Type:
Kd
Value:
>= 0.54 - <= 0.62 L/kg
pH:
6.94
Temp.:
25 °C
Matrix:
Lufa 6S
% Org. carbon:
1.78
Sample No.:
#2
Type:
Kd
Value:
>= 19.08 - <= 22.79 L/kg
pH:
2.96
Temp.:
25 °C
Matrix:
Eurosoil 5
% Org. carbon:
5.94
Sample No.:
#3
Type:
Kd
Value:
0.54 L/kg
pH:
6.56
Temp.:
25 °C
Matrix:
Soil LUFA 2.2
% Org. carbon:
1.61
Sample No.:
#4
Type:
Kd
Value:
1.61 L/kg
pH:
6.29
Temp.:
25 °C
Matrix:
Soil Refesol 03-G
% Org. carbon:
3.1
Sample No.:
#5
Type:
Kd
Value:
4.96 L/kg
pH:
5.66
Temp.:
25 °C
Matrix:
Soil Eurosoil 1
% Org. carbon:
3.74
Adsorption and desorption constants:
Because the hydrolysed Chlorendic Anhydride, Chlorendic Acid is a polar organic substance, the KOC should not be applied when assessing the adsorption behaviour of the test item.
Recovery of test material:
Recoveries were between 90% and 110%. Only two values were outside the range (respectively 110.2% and 111.7%).
Transformation products:
yes
No.:
#1
Details on results (Batch equilibrium method):
PRELIMINARY TEST
- Sample purity: 95.3 %
- Weighed soil: see attached background material
- Volume of CaCl2 solution: see attached background material
- Initial test substance concentration: 1000 mg/l
- Test substance concentration in final solution: not applicable (study was performed on degradation product chlorendic acid)
- Analytical test substance concentration in final solution: not applicable (study was performed on degradation product chlorendic acid)

MAIN TEST: PERFORMANCE
- Test material stability during adsorption/desorption phase: no signs of instability were observed
- Experimental conditions maintained throughout the study: Yes
- Buffer/test substance interactions affecting sorption: not specified
- Further chemical interactions: none
- Buffer-catalyzed degradation of test substance: none
- Anomalies or problems encountered (if yes): none


TRANSFORMATION PRODUCTS
- Range of maximum concentrations in % of the applied amount: not applicable (study was performed on degradation product chlorendic acid)

RESIDUES
- Total unidentified radioactivity (range) of applied amount: not applicable
- Extractable residues (% of applied amount at end of study period): not specified
- Non-extractable residues (% of applied amount at end of study period): not specified

VOLATILIZATION
- % of the applied radioactivity present as volatile organics at end of study: not applicable

Statistics:
not applicable

Results Tier 1

 Soil        Lufa 6S        Eurosoil 5
 Organic Carbon 1.78%  1.78%  1.78%  5.94%  5.94%  5.94%
  Soil/Solution ratio  1:1.1  1:1.6  1:3.1  1:1.1  1:1.5  1:3.1
 Ads (eq)  34.1%  26.5%  16.4%  95.7%  93.4%  86.1%
 Kd (cm3/g)  0.54  0.57  0.62  22.79  21.74  19.08
 Koc (cm3/g)  30.45  31.81  34.78  383.59  365.92  321.10

Results Tier 2

Soil designation   Soil LUFA 2.2  Soil Refesol 03 -G  Soil Eurosoil 1
 Organic carbon 1.16%   3.1%  3.74%
 Soil/Solution ratio  1:1.0  1:1.0  1:1.1
 Ads (2h)  26.2%  49.3%  69.6%
 Ads (4h)  27.9%  52.6%  74.9%
 Ads (6h)  28.7%  54.0%  77.1%
 Ads (8h)  30.6%  -  -
 Ads (24h)  33.1%  58.2%  81.6%
 Ads (29h)  -  59.5%  82.7%
 Ads (48h)  34.7%  60.8%  82.4%
 Kd (cm3/g)  0.54  1.61  4.96
 Koc (cm3/g)  33.63  51.78  132.68
Validity criteria fulfilled:
yes
Conclusions:
The determination of the absorption of chlorendic acid on soil using five different soils reported a mean Kd of 5.78 cm3/g and a log(mean Kd) of 0.76 cm3/g at 25°C.
Executive summary:

A determination of the absorption of chlorendic anhydride on soil was performed according to the OECD Testing Guideline 106. As chlorendic anhydride forms chlorendic acid in aqueous medium, the degradation product was actually tested.

During Tier 1, ratios of 1:1 to 1:31 were selected to be tested on Eurosoil 5 and Soil Lufa 6S. From the results in Tier 1, it was decided to use a ratio of 1:1 in Tier 2 on Soil LUFA 2.2, Soil Refesol 03-G, and Soil Eurosoil 1. Because the same concentrations were used in Tier 1 and Tier 2, Tier 2 was performed on three soils instead of five, and the results on the two soils tested during Tier 1 are used in complement to obtain the five soils required by the OECD Testing Guideline 106.

Because chlorendic acid is a polar organic substance, the KOC should not be applied when assessing the adsorption behaviour of the test item. The distribution coefficient Kd of the test item shows dependence of the pH, measured in the aqueous solution after final sampling. At lower pH, the carboxylate-group of the test item was probably protonated, making the test item less polar and increasing the adsorption.

The determination of the absorption of chlorendic acid allowed to determine a mean Kd of 5.78 cm3/g and a log(mean Kd) of 0.76 cm3/g at 25°C.

Description of key information

Chlorendic anhydride rapidly hydrolyses to chlorendic acid, therefore the adsorption/desorption values for the acid are used for the anhydride also. As chlorendic acid is an ionisable substance, the batch equilibrium method to calculate Kd was used. Five soils were tested and the average value used for the assessment. The logKp was derived from this experimental value.

Key value for chemical safety assessment

Other adsorption coefficients

Type:
log Kp (solids-water in soil)
Value in L/kg:
0.76
at the temperature of:
25 °C

Additional information