Iodomethane

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:

17 January 2001 to 26 March 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)

GLP compliance:

yes

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Test temperature:

20 °C

Analytical monitoring:

yes

Details on sampling:

- Samples were taken at the start and the end of the experiment
- All samples were stored in a refrigerator at approximately 4 °C prior to and after analysis.

Details on matrix:

COLLECTION AND STORAGE
- Test soils acquired by Ricera or supplied by the sponsor.
- Geographic location: The soils were a sandy loam soil from Bezirks Verband AIRS, Speyer, Germany (German); a sandy loam soil from Plant Sciences, Inc., Watsonville, California (California); a clay loam soil from Painesville Township, Ohio (Ohio); a loam soil from AgroLab AG. Switzerland (Swiss); and a silt loam soil from Collins Agricultural Consultants, Hillsboro, Oregon (Oregon).
- Soil preparation: Prior to use, the test soils were air-dried and sieved through a No. 10 sieve (2-mm mesh). The moisture content of each soil was determined in triplicate by drying the soils at 110 °C for a minimum of three hours. The dry weight equivalent was then determined for each soil using the following equation. % Moisture= [(wet soil weight/dry soil weight)-1] x 100. An appropriate amount of the air-dried soil was weighed into clean glass screw-cap centrifuge tubes to give 1.0, 2.0, 2.5, or 4.0 g soil (dry weight basis) for each of the five soils used in preliminary and definitive experiments.
- The soils were kept in sealed plastic bags at room temperature after the soil moisture content was determined.
- For the equilibration and definitive adsorption/desorption experiments, radiation sterilised soils were used. All five soils were sterilised using gamma radiation. The soils were aseptically transferred from the sealed plastic bags to sterile screw capped bottles prior to use.

PROPERTIES
- Soil properties can be seen in Table 1.

Details on test conditions:

SCREENING TEST

- Test Material Identity and Purity: The radiolabelled test material had a listed specific activity of 6.1 mCi/mmole which calculated to 95 460 dpm/μg. The test material was then analysed by HPLC with radiochemical and UV-detection to verify test material identity and purity against the appropriate reference standard. The identity of the test material was also confirmed using mass spectrometry.

- Preparation of the Treatment Solution for the Soil-to-Solution Test: A treatment solution of test material was prepared in 0.01 M CaCl2 solution with water. The solution contained 2 994 dpm/ μL (0.03136 μg/μL). A dose of approximately 19 μL of treatment solution per 6 mL of 0.01 M CaCl2 solution resulted in a concentration of ~0.1 μg/mL.

- Screening Test for the Determination of Soil-to-Solution Ratio: For the adsorption/desorption experiments, a soil-to-solution ratio resulting in 20 to 80 % adsorption was targeted. Three (1:1.25, 1:3, and 1:7) ratios were selected for the initial test in determining the soil-to-solution ratio for the test material. Two soils (California soil with a low clay content and Ohio soil with a high clay content) were used to determine the soil-to-solution ratio. For each soil, a total of three test vessels were prepared containing I, 2, and 4 grams (dry weight equivalent) of non-sterilised test soil. To each of the six tubes, 7, 6 or 5 mL of 0.01 M CaCl2 was added to achieve soil-to-solution ratios of 1:7, 1:3, and 1:1.25, respectively. The soils were pre-equilibrated overnight with the 0.01 M CaCl2 solution via mechanical agitation using a reciprocating shaker at 20 °C the day before the experiment. The soils were shaken at a speed sufficient to facilitate thorough mixing. Following pre-equilibration, one test vessel for each soil received 16 μL of the 2,994 dpm/μL treatment solution for the 1:1.25 ratio tubes, 19 μL of the treatment solution for the 1:3 ratio tubes, and 22 μL of the treatment solution for the 1:7 ratio tubes. After treatment, the test vessels were shaken horizontally for approximately 24 hours at 20 °C at a speed sufficient to facilitate thorough mixing. The samples were centrifuged at room temperature and the supernatants were quantitatively decanted. Triplicate 100-μL aliquots of the supernatant were analysed by LSC. The test vessels containing the soil pellets and the supernatants were retained and stored refrigerated. The percent adsorption of the test material to each soil at each soil-to-solution ratio was then calculated to determine the optimal soil-to-solution ratio.

- Determination of Test Material Stability During the Screening Test: The test material stability was determined for each soil tested using the test tube from the 1:3 soil-to-solution ratio. The supernatant was removed from the soil pellet and a 1 mL aliquot was analysed by HPLC to determine the test material stability in the respective soil-CaCl2 supernatant solution.
-Adsorption of the Test Material to Glass In the Screening Test: The potential for the adsorption of the test material to the test vessels (glass screw cap centrifuge tubes) was assessed. Two test vessels containing 8 mL of 0.01 M CaCl2 (no soil) received 25 μL of treatment solution at 2 994 dpm/μL to prepare a test solution -0.1 μg/mL. The test vessels were shaken for approximately 24 hours at 20 °C and aliquots of the solution were analysed by LSC. The LSC results were compared to initial values to determine radiocarbon recovery and adsorption to glass.


ADSORPTION/DESORPTION KINETICS

- Preparation of the Test Solution for the First Kinetics Experiment: A test solution was prepared by diluting a subsample of the stock solution. The test solution was prepared in 0.01M CaCL2 in water. The solution contained 3 079 dpm/μL (0.0323 μg/μL). A dose of approximately 19 μL of test solution per 6 mL of 0.0 IM CaCL2 solution resulted in a concentration of -0.1 μg/mL.

- Adsorption Kinetics: The first adsorption kinetics experiment was performed for method development using the California and Ohio test soils to estimate the equilibration times. To reduce the adsorption of the test material to glass, the test tubes were silanised using Supelco Sylon CT (dirnethyldichlorosilane). For each soil, fourteen test vessels were prepared containing 2 grams (dry weight equivalent) of non-sterilised test soil. To each tube, 6 mL of 0.01 M CaCl2 was added to achieve a 1:3 soil-to-solution ratio . The soils were pre-equilibrated overnight with the 0.01M CaCl2 solution via mechanical agitation using a reciprocating shaker at 20 °C the day before the experiment. The soils were shaken at a speed sufficient to facilitate thorough mixing. Following pre-equilibration, all the test vessels for each soil received 19 μL of test solution prepared at 0.0323 μg/μL in 0.01 M CaCl2. After treatment, the test vessels were mixed and shaken at 20 °C at a speed sufficient to facilitate thorough mixing. Duplicate samples were prepared for analysis at 2, 4, 6, 12, 24, 48 and 72 hours after treatment. The samples were centrifuged at room temperature and triplicate 0.1 mL aliquots of the supernatant were analysed by LSC. The test vessels containing the supernatants and soil pellets were retained and stored refrigerated. The percent adsorption of the test material to each soil was then calculated to determine the adsorption equilibration time. The 24-hour Ohio Rep 1 and California Rep 2 supernatants were removed from the soil pellet and a 1-mL aliquot was analysed by HPLC to determine the test material stability in the respective soil-CaCl2 supernatant solution. To check for material balance of the test material, the Rep 1 soil pellets of the 24 and 48 hour soil samples were combusted. The bottom of the tubes were frozen in a dry ice bath and cracked. The soil pellets and the broken glass were removed and placed into three oxidiser boats for three minute combustions

- Adsorption Kinetics- Test 2: The adsorption kinetics experiment was repeated using only the California soil for further method development. Due to the level of metabolism seen in previous experiments, sterile and non-sterile soils were compared by adding 2 grams dry weight of soil with 7.5 mL of 0.01M CaCl2 (1:3.75 ratio) per tube. Non-silanised glass test tubes were used for all the samples. 0.1 and 3 μg/mL concentrations with the California soil were tested. Each set of samples contained three individual replicate tubes which were sampled at 1, 4, and 24 hours after dosing. The first set contained 0.1 μg/mL with non-sterilised test soil. The second set contained 0.1 μg/mL with sterilised test soil, while the third set contained 3 μg/mL with non-sterilised test soil. The soil was sterilised by autoclaving the prepared soil tubes at nominal settings of 30 minutes at 121 °C. The soils were pre-equilibrated overnight with the 0.01M CaCl2 solution via mechanical agitation using a reciprocating shaker the day before the experiment. The soil tubes were shaken in a horizontal position at a speed sufficient to facilitate thorough mixing. Following pre-equilibration, the ~0.1 μg/mL test vessels for each soil received 21 μL of test material solution prepared at 3403 dpm/μL (0.0356 μg/μL) in 0.01 M CaCl2. The ~3 μg/mL test vessels for each soil received 96 μL of test solution prepared at 22 468 dpm/μL (0.2354 μg/μL) in 0.01 M CaCl2. After treatment, the test vessels were mixed and shaken at 20 °C at a speed sufficient to facilitate thorough mixing. Samples were prepared for analysis at 1, 4, and 24 hours after treatment for each set. The samples were centrifuged at room temperature and triplicate 0.1 mL aliquots of the supernatant were analysed by LSC. The test vessels containing the supernatants and soil pellets were retained and stored refrigerated. The percent adsorption of the test material to each soil was then calculated to determine the adsorption equilibration time. The supernatants were removed from the soil pellet and a 1 or 0.25 mL aliquot was analysed by HPLC to determine the test material stability in the respective soil-CaCl2 supernatant solution for each 1, 4, and 24 hour sampling time.

- Adsorption of the Test Material to Glass in the Kinetics Experiment: The potential for the adsorption of the test material to the test vessels (glass screw cap centrifuge tubes) was assessed. A method development test was performed to compare non-silanised to silanised glass tubes at low and high concentrations of test material. Test vessels (silanised and nonsilanised) were tested at ~0.1 μg/mL containing 8.5 mL of 0.01 M CaCl2 (no soil) and 38 μL of treatment solution prepared at 2 112 dpm/μL (0.022 μg/μL) in 0.01 M CaCl2. For the higher test concentration, the silanised glass tube was dosed with 517 μL of treatment solution prepared at 2,112 dpm/μL (0.022 μg/μL) in a total volume of 8.5 mL of 0.01 M CaCl2 for -1.35 μg/mL test concentration. The non-silanised glass tube was dosed with 1017 μL of treatment solution prepared at 2,112 dpm/μL (0.022 μg/μL) in a total volume of 8.5 mL of 0.01 M CaCl2 for -2.65 μg/mL test concentration. Each tube was mixed and triplicate 25 μL aliquots were LSC analysed to check the starting concentration. The test vessels were shaken for approximately 18 hours at 20 °C and aliquots of the solutions were analysed by LSC as before.

- Adsorption Kinetics- Test 3: An additional adsorption kinetics experiment was repeated using all five soils for further method development. To check the level of microbial degradation, all five non-sterile soils were tested by adding 2 grams dry weight of soil with 7.4 mL of 0.01 M CaCl2 (1:3.75 ratio) per tube. Non-silanised glass test tubes were used for all the samples. The concentration of ~3 μg/mL was tested in duplicate. An additional set of duplicate tubes was prepared at the 0.1 μg/mL concentration using only the sterilised California soil by adding 2 grams dry weight of soil with 7.5 mL of 0.01M CaCl2 (1:3.75 ratio) per tube. The soil was sterilised as before by autoclaving the prepared soil tubes at nominal settings of 30 minutes at 121 °C. The soils were pre-equilibrated overnight with the 0.01 M CaCl2 solution via mechanical agitation using a reciprocating shaker the day before the experiment. The soil tubes were shaken in a horizontal position at a speed sufficient to facilitate thorough mixing. Following pre-equilibration, the ~0.1 μg/mL test vessels for the sterilised California soil received 17 μL of test solution prepared at 4407 dpm/μL (0.0462 μg/μL) in 0.01M CaCl2. The ~3 μg/mL test vessels for each of the five soils received 84 μL of test solution prepared at 25,759 dpm/μL (0.2698 μg/μL) in 0.01 M CaCl2. After treatment, the test vessels were mixed and shaken at 20 °C at a speed sufficient to facilitate thorough mixing. Samples were prepared for analysis at 24 hours after treatment for each set. The samples were centrifuged at room temperature and triplicate 0.1 mL aliquots of the supernatant were analysed by LSC. The percent adsorption of the test material to each soil was then calculated to determine the adsorption equilibration time. The supernatants were removed from the soil pellet. A 0.25 mL aliquot, for the 3 μg/mL samples or a 1 mL aliquot for the 0.1 μg/mL sample was analysed by HPLC to determine the test material stability in the respective adsorption soil-CaCl2 supernatant solution for each 24-hour sampling time. After the adsorption phase, the desorption kinetics experiment was performed using all five soils plus the 0.1 μg/mL set. For each soil, the 24-hour adsorption kinetics samples were used to determine the desorption kinetics. After the supernatant from the 24-hour adsorption kinetics samples was decanted and refrigerated, it was replaced with an equal volume of fresh 0.01M CaCl2. After addition of the fresh 0.01 M CaCl2, the test vessels were mixed and shaken as before at 20 °C to keep the soil suspended in solution. Triplicate samples were analysed at 24 hours after starting the desorption cycle. The samples were centrifuged at room temperature and triplicate 0.1 mL aliquots of the supernatant were analysed by LSC for the 3 μg/mL test samples while 0.5 mL aliquots were analysed by LSC for the 0.1 μg/mL test samples. The test vessels containing the desorption supernatants and soil pellets were retained and stored refrigerated. The percent desorption of the test material to each soil was then calculated to determine the desorption parameters. The supernatants were removed from the soil pellet. A 1 mL aliquot, for the 3 μg/mL German and Swiss samples was analysed by HPLC to determine the test material stability in the respective desorption soil-CaCl2 supernatant solution for the 24 hour sampling time. To check for material balance of the test material, the Rep 1 soil pellets of the soil samples were combusted. The bottom of the tubes were frozen in a dry ice bath and cracked. The soil pellets and the broken glass were removed and placed into three oxidiser boats for three minute combustions. As a comparison, the Rep 2 soil pellets of the soil samples were extracted with 0.1 N sodium hydroxide to find the bound residue humic fraction. The tubes were mixed and shaken over the weekend at 20 °C. The samples were centrifuged at room temperature and triplicate 0.2-mL aliquots of the supernatant were analysed to calculate the amount of bound residue released from the humic fraction.

- Equilibration Test: The stock test solution was diluted in 0.01 M CaCl2 to prepare the dosing solution. For the equilibration test, 0.4 mL of the 14C-stock was added and mixed with 13.6 mL 0.01 M CaCl2, then divided into five septum capped vials, each containing 1.6 mL. One vial was used to dose one of the five soils. The test was set up for ~ 3 μg/mL target concentration in 7.4 mL of 0.01M CaCl2. Each test tube was dosed with 80 μL of test solution. The calculated amount of material dosed varied due to the volatility of the test material. All five sterile soils were tested by adding 2.5 grams dry weight of soil with approximately 7.3 mL of 0.01 M CaCl2 (approximate 1:3 ratio) per tube. Nonsilanised glass test tubes were used for all the samples. A concentration of ~ 3 μg/mL was tested in duplicate, with sampling at 2, 6, 12, 24, 48, and 72 hours. The soils were sterilised by gamma radiation (minimum 26.1 kGy) and aseptically added to pre-sterilised tubes that were autoclaved for a minimum of 15 minutes at 121 °C. The soils were pre-equilibrated overnight with the sterile filtered 0.01 M CaCl2 solution via mechanical agitation using a reciprocating shaker the day before the experiment. The soil tubes were shaken in a horizontal position at a speed sufficient to facilitate thorough mixing. Following pre-equilibration, the ~3 μg/mL test vessels for each soil received 80 μL of test solution prepared at 27 630 dpm/μL (0.2894 μg/μL) in 0.01 M CaCl2. After treatment, the test vessels were mixed and shaken at 20 °C at a speed sufficient to facilitate thorough mixing. Samples were prepared for analysis at 2, 6, 12, 24, 48, and 72 hours after treatment for each soil set. The samples were centrifuged at room temperature and triplicate 0.1-mL aliquots of the supernatant were analysed by LSC. The test vessels containing the weighed supernatants and soil pellets were retained and stored refrigerated. The percent adsorption of the test substance to each soil was then calculated to determine the adsorption equilibration time. The supernatants were removed from the soil pellet and filtered prior to HPLC analysis. A 0.25 mL aliquot, for the 3 μg/mL Rep 1 samples was analysed by HPLC to determine the test material stability in the respective adsorption soil-CaCl2 supernatant solution at the 24-hour sampling time.


ADVANCED TEST FOR ADSORPTION AND DESORPTION

- Preparation of the Test Solution for the Advanced Test: The stock test solution was diluted in 0.01 M CaCL2 to prepare two final dosing solution concentrations for the advanced test adsorption and desorption experiment. For the high concentration of 3 μg/mL in 7.4 mL 0.01 M CaCL2 (30,782 dpm/μL = 0.3225 μg/μL), 0.4 mL of the 14C-stock was added and mixed with 13.6 mL 0.01 M CaCL2. For the low concentration of 0.3 μg/mL in 7.4 mL 0.01 M CaCl2 (3,000 dpm/μL = 0.0314 μg/μL), 0.04 mL of the 14C-stock was added and mixed with 13.6 mL 0.01 M CaCl2. The experiment was set up to test four target concentrations at ~3.0, 1.0, 0.3, and 0.1 μg/mL in approximately 7.4 mL of 0.01 M CaCI2. Following pre-equilibration, the test vessels for each soil received the following amount of test solution for the respective target concentrations: Nominal test solution concentrations (µg/µL): 0.3225, 0.3225, 0.0314 and 0.0314 had the following volume of test solution respectively (µL): 72, 24, 72 and 24 to give nominal concentrations of the test material per ~7.4 mL of 0.01 M CaCl2 (µg/mL) respectively: 3.1, 1.0, 0.3 and 0.1.

- Adsorption Isotherm Experiment: The adsorption isotherm experiment was conducted using all five soils. Ten test tubes (plus one extra) for each test soil were prepared by adding 2.5 grams dry weight of soil with approximately 7.3 mL of 0.01 M CaCl2 (approximate 1 :3 ratio) per tube. Two of the tubes were used as controls. Non-silanised glass test tubes were used for all the samples. ~3.0, 1.0, 0.3, and 0.1 μg/mL in ~7.3 mL of 0.01 M CaCl2 (approximate volume before addition of test solution) were tested in duplicate, with sampling at the 24 hour equilibration time. The soils were sterilised by gamma radiation (minimum 26.1 kGy) and aseptically added to pre-sterilised tubes that were autoclaved at nominal settings of 30 minutes at 121 °C. The soils were pre-equilibrated overnight with the sterile filtered 0.01 M CaCl2 solution via mechanical agitation using a reciprocating shaker the day before the experiment. The soil tubes were shaken in a horizontal position at a speed sufficient to facilitate thorough mixing. Following pre-equilibration, two test vessels for each soil at each concentration received 72 or 24 μL of the appropriate test solution to achieve final concentrations of about 3.0, 1.0, 0.3, and 0.1 μg/mL. After treatment, the test vessels were shaken for approximately 24 hours at 20 °C at a speed sufficient to facilitate thorough mixing. The samples were centrifuged at room temperature and triplicate 0.1 mL aliquots of the supernatant were analysed by LSC. The supernatant was decanted as completely as possible and the test vessels were weighed to determine the volume of adsorption supernatant removed from the test vessels. The scintillation vials containing the supernatants were stored refrigerated.

- Desorption Isotherm Experiment: Immediately after removing the supernatant following the adsorption phase, an equivalent volume of fresh 0.01 M CaCl2 solution to that removed was added to each of the soil samples. The soil in each sample was resuspended and was shaken for approximately 24 hours at 20 °C at a speed sufficient to facilitate thorough mixing. The desorption and control samples were then centrifuged at room temperature and triplicate 0.1 mL aliquots of the desorption supernatant were analysed by LSC. The desorption supernatant was decanted as completely as possible and the test vessels were weighed to determine the volume of desorption supernatant removed from the test vessels. The collected desorption supernatants and soil pellets were stored refrigerated.

- Determination of Test Material Stability During the Isotherm Experiments: Stability of the dose solution was tested at the start of the advanced adsorption and desorption test. The remaining dose solution from the TS#5 high concentration vial was placed in the test chamber at 20 °C. After the desorption was completed (48 hours), the dose solution was removed from the test chamber and HPLC analysed for radio purity to determine the test material stability in the CaCl2 solution.

- Determination of Mass Balance During the Isotherm Study: The mass balance was determined from both replicates at the highest concentration for each soil tested. The mass balance was determined by summing the radioactivity in the removed adsorption supernatant, in the removed desorption supernatant, and in the combusted final soil pellet.

Sample No.:

#1

Duration:

24 h

Initial conc. measured:

ca. 0.1 - ca. 3 other: ug/mL

pH:

7

Sample No.:

#2

Duration:

24 h

Initial conc. measured:

ca. 0.1 - ca. 3 other: ug/mL

pH:

6.33

Sample No.:

#3

Duration:

24 h

Initial conc. measured:

ca. 0.1 - ca. 3 other: ug/mL

pH:

6.91

Sample No.:

#4

Duration:

24 h

Initial conc. measured:

ca. 0.1 - ca. 3 other: ug/mL

pH:

7.2

Sample No.:

#5

Duration:

24 h

Initial conc. measured:

ca. 0.1 - ca. 3 other: ug/mL

pH:

5.42

Key result

Type:

Koc

Remarks:

Adsorption

Value:

28 L/kg

Temp.:

20 °C

Matrix:

Swiss

Key result

Type:

Koc

Remarks:

Adsorption

Value:

61 L/kg

Temp.:

20 °C

Matrix:

California

Key result

Type:

Koc

Remarks:

Adsorption

Value:

27 L/kg

Temp.:

20 °C

Matrix:

Ohio

Key result

Type:

Koc

Remarks:

Adsorption

Value:

14 L/kg

Temp.:

20 °C

Matrix:

German

Key result

Type:

Koc

Remarks:

Adsorption

Value:

43 L/kg

Temp.:

20 °C

Matrix:

Oregon

Key result

Type:

Koc

Remarks:

Desorption

Value:

144 L/kg

Matrix:

Swiss

Key result

Type:

Koc

Remarks:

Desorption

Value:

317 L/kg

Matrix:

California

Key result

Type:

Koc

Remarks:

Desorption

Value:

67 L/kg

Matrix:

Ohio

Key result

Type:

Koc

Remarks:

Desorption

Value:

74 L/kg

Matrix:

German

Key result

Type:

Koc

Remarks:

Desorption

Value:

134 L/kg

Matrix:

Oregon

Recovery of test material:

Mass balance ranges from 84.4 to 93.9 % and are close to the acceptable ranges of 90-110 %. Due to the extreme volatility of the test material some losses were unavoidable during sampling handling.

Transformation products:

yes

No.:

#1

Details on results (Batch equilibrium method):

TEST MATERIAL IDENTITY AND PURITY
- The radio purity was performed multiple times over the course of the study. The radiopurity of the [14C] test material was determined by HPLC to be greater than 96 % for all of the analyses. The identity of the test material was confirmed by HPLC co-injection of [14C]TEST MATERIAL with an authentic standard and by mass spectral analysis.

SCREENING TEST
- The California and Ohio soils averaged 41.7 % of the test material adsorbed to both soils at the 1:3 soil-to-solution ratio. The 1:1.25 soil-to-solution ratio was too dense and did not allow for good mixing on the shaker. Based on the results of the preliminary test, a 1:3 soil-to-solution ratio was chosen for the kinetics and isotherm studies to provide the appropriate adsorption for all five soils.
- A 1 mL aliquot of the supernatant from each soil at the 1:3 soil-to-solution ratio was analysed by HPLC. HPLC analysis of the supernatant showed only 43 and 24 % of the radioactivity as test material in the California and Ohio soils tested, respectively. Based on these results, soil sterilisation was required.

ADSORPTION/DESORPTION KINETICS
- Adsorption Kinetics: By plotting the percent adsorption against the time points, the adsorption equilibration time was approximated for all the soils. In the first adsorption kinetics experiment, the California and Ohio soils were tested using silanised glass tubes to improve the mass balance recovery. The duplicate samples were tested at 0.1 ppm up to 48 hours using a 1:3 soil to solution ratio with 2 grams dry weight of soil and 6 mL of the CaCl2. After 24 hours, the average percent adsorption was 60.9 and 62.1 % for the Ohio and California soils, respectively. HPLC analysis of the (Replicate 1) 24-hour supernatants determined the test material stability to be 44.3 and 0 % for the California and Ohio soils, respectively, showing a high level of possible microbial degradation. After combusting the soil pellets, the material balance at 24 hours was 57.5 and 82.2 % for the California and Ohio soil samples, respectively. In the second adsorption kinetics experiment, only the California soil was tested at 0.1 and 3 ppm using non-silanised glass tubes. Sterile and non-sterile soils were compared using a 1:3.75 soil to solution ratio by adding 2 grams dry weight of soil to 7.5 mL of CaCl2. After 24 hours, the average percent adsorption was 44.8 and 21.3 % for the 0.1 ppm sterile and non-sterile soils, respectively. HPLC analysis of the 24-hour supernatants determined the test material stability to be 100 % in the 0.1-ppm sterile soil, but only 58.84 and 96.82 % for the 0.1 and 3 ppm non-sterile soils respectively. This data shows that sterilisation of the soil was necessary to eliminate microbial degradation of the test material. In the third adsorption kinetics experiment, all five soils were tested at 3 ppm using non-silanised glass tubes in duplicate. Non-sterile soils were tested to evaluate the level of degradation in all five soils. A 1:3.75 soil to solution ratio was used by adding 2 grams dry weight of soil to 7.4 mL of CaCl2. The samples were analysed after 24 hours. The average percent adsorption was 18.18 % and ranged from 25 to 12.8 % for the five soils. HPLC analysis of the (Replicate 1) 24-hour supernatants determined that the test material stability ranged from 91.1 to 96.8 % for the five soils. After combusting the soil pellets, the material balance at 24 hours averaged 88.4 % and ranged from 91.9 to 83.8 % for all five soil samples. After the 24-hour adsorption phase with the sterile California soil tested at 0.1 ppm, the average percent adsorption was 14.1. The aqueous HPLC stability analysis was 100 %, while the material balance using the combusted soil pellet was 92.5 %.For comparison to combustion of the final soil pellets, the Rep 2 soil pellets were extracted with 0.1 N sodium hydroxide to release the bound humic fraction. This was not a superior method to recover the radiomaterial in the soil pellets as total recoveries averaged 85.6 % and ranged from 81.7 to 88.0 %.
- Desorption Kinetics: After the 24 hour desorption phase with the non-sterile soils, the average percent desorption was 14.9 %, and ranged from 0 to 32 % in all five soils. HPLC analysis of the 24-hour Swiss and German desorption supernatants determined the test material stability to be 82.3 and 92.3 %, respectively. After the 24 hour desorption phase with the sterile California soil, the average percent desorption was 33.0 %, and ranged from 30.8 to 35.1 %.

EQUILIBRATION
- All five soils were tested at -3 ppm using non-silanised glass tubes in duplicate. Radiation sterilised soils were tested to evaluate the level of degradation in all five soils. An approximate 1:3 soil to solution ratio was used by adding 2.5 grams dry weight of soil to 7 .3 mL of 0.01 M CaCl2. The additional soil (0.5 grams) was added to the tubes to increase the level of test material adsorbed, yet still allowed adequate mixing of the soil samples in test tubes that were almost completely filled. The aqueous samples were analysed by LSC after 2, 6, 12, 24, 48, and 72 hours. After 24 hours, the average adsorption was 13.6 % and ranged from 28.6 to 5.4 % for the five soils. HPLC analysis of the 24-hour supernatants determined the test material stability to range from 98.7 to 96.2 % for the five soils.
- Equilibration data (%Adsorbed vs. Time) was analysed for the five soils used in the AID experiment. In each case, the data was fit to a logarithmic growth curve of the form: Y =Yo + a* ln(x). Because of the difficulty of working with a volatile compound, the variance in all data sets was high, and correlation coefficients were generally low. However, the results were sufficient to determine the equilibration time of the test material as approximately 24 hours. The level of degradation required radiation sterilisation of all the test soils. To increase the mass balance recovery, it was necessary to minimise the air space in the test tube to reduce the amount of volatile [14C]test material lost. A small air space (about 100 μL) was needed to provide adequate mixing of the soil suspension.

ADSORPTION OF THE TEST MATERIAL IN CACL2 TO GLASS
- To determine if the test material adsorbed to the test vessels, control samples were prepared during the screening test and the kinetics experiment. Control samples were prepared at a nominal concentration of 0.1 ppm in 8 mL 0.01 M CaCl2 solution only (no soil). LSC analysis of the control samples showed recoveries of the (calculated) applied radioactivity of 91.1 %. An additional test was performed to compare silanised and non-silanised glass tubes at high (1.35 and 2.65 ppm) and low (0.1 ppm) concentrations of the test material in ~8.5 mL of 0.01 M CaCl2. LSC analysis of the samples showed recoveries of the applied radioactivity averaging 89.6 % for the silanised and 102.9 % for the non-silanised glass. A final adsorption to glass test was performed as control samples were prepared at a nominal concentration of 3 ppm in 8.5 mL 0.01M CaCl2 solution only (no soil). LSC analysis of the samples showed an average 96.4 % recovery of the applied radioactivity. These results show that the test material does not adsorb to the test vessel.

ADVANCED TEST FOR ADSORPTION AND DESORPTION
- Adsorption Results: The values for the adsorption coefficient, Kd, were calculated for all five soils at each of the four test solution concentrations. The average Kd values ranged from 0.4 mL/g in the German soil to 1.2 mL/g in the Ohio soil The adsorption coefficients were corrected for the organic matter and organic carbon content for each soil to calculate the soil adsorption coefficient, Kom and Koc. The average Kom values ranged from 8 mL/g in the German soil to 36 mL/g in the California soil. The average Koc values ranged from 14 mL/g in the German soil to 61 mL/g in the California soil
- Desorption Results: The values for the desorption coefficient, Kd. were calculated for all five soils at each of the four test solution concentrations. The average desorption Kd values ranged from 2.0 mL/g in the German soil to 3.2 mL/g in the California soil. The desorption coefficients were corrected for the organic matter and organic carbon content for each soil to calculate the soil adsorption coefficient, Kom and Koc. The average Kom values ranged from 39 mL/g in the Ohio soil to 184 mL/g in the California soil. The average Koc values ranged from 67 mL/g in the Ohio soil to 317 mL/g in the California soil.
- Isotherm Results: The values for the Freundlich adsorption isotherm parameters, Kf, ranged from 0.4 mL/g in the German soil to 1.1 mL/g in the Ohio soil. The values for 1/n ranged from 0.9126 in the Oregon soil to 1.0049 in the Swiss soil. The Freundlich adsorption isotherm parameters, Kf, were corrected for the organic matter and organic carbon content for each soil to calculate the soil sorption coefficients, KFom and KFoc. The KFom values ranged from 9 mL/g in the German soil to 34 mL/g in the California soil. The KFoc values ranged from 15 mL/g in the German soil to 59 mL/g in the California soil. The values for the Freundlich desorption isotherm parameters, Kf, ranged from 2.1 mL/g in the German soil to 2.9 mL/g in the Ohio soil. The values for 1/n ranged from 0.9417 in the California soil to 1.0131 in the German soil. The Freundlich adsorption isotherm parameters, Kf, were corrected for the organic matter and organic carbon content for each soil to calculate the soil adsorption coefficients, KFom and KFoc, The KFom values ranged from 39 mL/g in the Ohio soil to 153 mL/g in the California soil. The KFoc values ranged from 61 mL/g in the Ohio soil to 265 mL/g in the California soil.
- Test Material Stability and Identity: A 0.25-mL aliquot of the equilibration adsorption supernatant from one replicate from each soil at the ~3 ppm concentration was analysed by HPLC. HPLC analysis of the supernatants showed greater than 96 % of the radioactivity as test material in all of the soils. The identity of the test material in the supernatant was confirmed by HPLC chromatograph in the dosing solution.
- Mass Balance in the Advanced Test: Even with the extreme volatility of the test material, the material balances ranged from 84.4 to 93.9 % and are close to the acceptable guideline range of 90-110 % of the applied radioactivity. Due to the extreme volatility of the test material, some losses of test material were unavoidable during sample handling (for example, pouring the supernatant out of the test tube after the adsorption step allowed volatile losses from each sample). The average material balance of 88.6 % was considered adequate and is not considered to affect the results of the study, since adsorption is low.

Validity criteria fulfilled:

yes

Conclusions:

Under the conditions of this study, the test material did not readily adsorb to soil.

Executive summary:

The adsorption and desorption of the test material was investigated in accordance with the standardised guideline OECD 106, under GLP conditions.

The test material was tested with soils acquired from five different locations with the following textures: sandy loam, clay loam, loam and silt loam.

The test material was stable under the test conditions having adsorption equilibration times for all five radiation sterilised soils of less than 24 hours. The sorption coefficients, Kd, Koc and Kom were calculated for each soil at four concentrations of the test material. The average adsorption coefficients for each soil ranged from 0.4 to 1.2 mL/g for the Kd values, from 8 to 36 mL/g for the Kom values and from 14 to 61 mL/g for the Koc values. The average desorption coefficients for each soil ranged from 2.0 to 3.2 mL/g for the Kd values, from 39 to 184 mL/g for the Kom values and from 67 to 317 mL/g for the Koc values.

The values for the Freundlich isotherm parameters, Kf, KFom, and KFoc were derived from the linear form of the Freundlich equation. The Freundlich isotherm parameters for the adsorption phase ranged from 0.4 to 1.1 mL/g for the Kf values, from 9 to 34 mL/g for the KFom values and from 15 to 59 mL/g for the KFoc values. The Freundlich isotherm parameters for the desorption phase ranged from 2.1 to 2.9 mL/g for the Kf values, from 39 to 153 mL/g for the KFom values and from 67 to 265 mL/g for the KFoc values.

Under the conditions of this study, the test material did not readily adsorb to soil.

Description of key information

Under the conditions of this study, the test material did not readily adsorb to soil.

Key value for chemical safety assessment

Koc at 20 °C:

34.6

Additional information

The adsorption and desorption of the test material was investigated in accordance with the standardised guideline OECD 106, under GLP conditions.

The test material was tested with soils acquired from five different locations with the following textures: sandy loam, clay loam, loam and silt loam.

The test material was stable under the test conditions having adsorption equilibration times for all five radiation sterilised soils of less than 24 hours. The sorption coefficients, Kd, Koc and Kom were calculated for each soil at four concentrations of the test material. The average adsorption coefficients for each soil ranged from 0.4 to 1.2 mL/g for the Kd values, from 8 to 36 mL/g for the Kom values and from 14 to 61 mL/g for the Koc values. The average desorption coefficients for each soil ranged from 2.0 to 3.2 mL/g for the Kd values, from 39 to 184 mL/g for the Kom values and from 67 to 317 mL/g for the Koc values.

The values for the Freundlich isotherm parameters, Kf, KFom, and KFoc were derived from the linear form of the Freundlich equation. The Freundlich isotherm parameters for the adsorption phase ranged from 0.4 to 1.1 mL/g for the Kf values, from 9 to 34 mL/g for the KFom values and from 15 to 59 mL/g for the KFoc values. The Freundlich isotherm parameters for the desorption phase ranged from 2.1 to 2.9 mL/g for the Kf values, from 39 to 153 mL/g for the KFom values and from 67 to 265 mL/g for the KFoc values.

Under the conditions of this study, the test material did not readily adsorb to soil.