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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Koc values are in the range of 33.7 to 246.7 mL/g.

Depending on the soil type the mobility of 2-{2-chloro-4-mesyl-3-[(tetrahydrofuran-2-ylmethoxy)methyl]benzoyl}cyclohexane-1,3-dione can be classified from mobile to low mobility in the tested soils.

Key value for chemical safety assessment

Additional information

The adsorption/desorption characteristics of 2-{2-chloro-4-mesyl-3-[(tetrahydrofuran-2-ylmethoxy)methyl]benzoyl}cyclohexane-1,3-dione were studied in five soils (#1: Wurmwiese, sandy loam, pH 5.1, 2.0% organic carbon, Germany; #2: Höfchen am Hohenseh 4a, silt loam, pH 6.3, 2.9% organic carbon, Germany; #3: Dollendorf II, loam, pH 7.3, 4.4% organic carbon, Germany; #4: Laacher Hof AXXa, loamy sand, pH 5.9, 2.0% organic carbon, Germany; #5: Hanscheider Hof, silt loam, pH 5.2, 2.9% organic carbon, Germany) in batch equilibrium experiments (M-442744-01-1; 2012), M-442744-02-1 (Hein, 2012)). The pH values were determined in aqueous CaCl2 solution for characterization of the soils.

The experiments were conducted in accordance to OECD Guideline 106, the US EPA OPPTS 835.1220, and in compliance with GLP.

The adsorption phase of the study (Definitive Test) was carried out using pre-equilibrated air-dried soil with the test item at concentrations of nominal 1, 0.3, 0.1, 0.03, and 0.01 mg/L in the dark at 20 °C ± 2 °C for 24 hours. The equilibration solution used was 0.01 M aqueous CaCl2 solution.

Following soil to solution ratios were defined to the soils: #1 and #5 (1:8) and #2 to #4 (1:2). Desorption phase of the study was carried out by supplying pre-adsorbed soil specimens with fresh 0.01 M aqueous CaCl2 solution for one desorption cycle.

The aqueous supernatant after adsorption and desorption was separated by centrifugation. The test item residues in the supernatant were analyzed by liquid scintillation counting (LSC). The adsorption parameters were calculated using the Freundlich adsorption isotherm.

Test systems without soil were used as control in preliminary test and did not show adsorption to the vessels or degradation.

For all soils the Parental Mass Balance after 72 h showed that >90% of applied test item could be recovered. This demonstrates that the test item was sufficiently stable for the test.

The mass balance of the soils was determined by LSC of the supernatants after adsorption and desorption and by combustion of the remaining soils. The overall material balance for all concentrations for individual specimens was in the range of 96.3-98.9%, 89.1-93.3%, 91.0- 100.9%, 88.6-96.9%, and 97.3-99.4% of the applied radioactivity in soils #1 to #5, respectively.

In the definitive adsorption test 38.4-54.6%, 51.0-66.7%, 44.6-64.2%,49.6-65.9%, and 37.2- 55.5% of the applied test material was adsorbed in soils #1 to #5, respectively.

The calculated adsorption constants KF(ads)of the FREUNDLICH isotherms for the five test soils ranged from 1.5 mL/g to 5.1 mL/g. The FREUNDLICH exponents 1/n were in the range of 0.8515 to 0.8740, indicating that the concentration of the test item did affect the adsorption behavior.

At the end of one adsorption and one desorption phase, 29.3 - 46.9%, 14.4 - 27.3%, 13.6 - 27.7%, 16.1 - 33,4% and 27.7 - 45.1% of the initially adsorbed amount were desorbed in soils #1 to #5, respectively.

The mean desorption KF(des)ranged from 1.7 - 6.1 mL/g and and the normalized KF,OC(des)ranged from 38.3 - 285.9 mL/g.

The following table summarizes the key soil properties and results from the study:

Soil origin

#1

#2

#3

#4

#5

Soil type (USDA)

Sandy loam

Silt loam

Loam

Loamy sand

Silt loam

pH (0.01MCaCl2)

5.1

6.3

7.3

5.9

5.2

Organic carbon [%]

2.0

2.9

4.4

2.0

2.9

KF(ads)[mL/g]

4.9

1.9

1.5

1.8

5.1

1/n

0.8740

0.8700

0.8515

0.8678

0.8681

KF,OC(ads)[mL/g]

246.7

66.4

33.7

63.5

175.0

 

Mean KF,OC(ads): 117 mL/g

According to Briggs (1973; A simple relationship between soil adsorption of organic chemicals and their octanol/water partition coefficients. Proc. 7th British Insecticide and Fungicide Conference, Nottingham/UK, 83-86) the test item can be classified from mobile to low mobility in the tested soils.