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Environmental fate & pathways

Adsorption / desorption

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Administrative data

Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
key study
Study period:
16 May 2001 - 20 November 2001
Reliability:
1 (reliable without restriction)

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2002
Report Date:
2002

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)
Deviations:
no
GLP compliance:
yes
Type of method:
batch equilibrium method
Media:
soil

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
liquid
Radiolabelling:
yes
Remarks:
14C

Study design

Test temperature:
25°C

HPLC method

Details on study design: HPLC method:
UV: 254 or 255 nm
Solvent A: HPLC H20
Solvent B: Acetonitrile

Time % A % B
(min.)
0 90 10
3 90 10
25 0 100
30 90 10
35 90 10

The flow rate was 1 mL/min. The retention times (Rt) for NMC, AA-FNT, and fenitrothion were - 14.2 minutes, 15.5 minutes, and - 19.5 minutes, respectively. A representative HPLC UV trace of a mixed standard containing these reference substances

Batch equilibrium or other method

Analytical monitoring:
yes
Details on sampling:
At the end of the adsorption phase, the tubes containing the soil and test solution were centrifuged. The supernatant was decanted, volume measured and replaced with equal volume of 0.01 M CaCl2. Samples were vortexed to mix and stored frozen in 60 mL amber bottles. The equilibrated aqueous phases (adsorption supernatant) were radioassayed by LSC of triplicate aliquots.

For desorption, following addition of fresh 0.01 M CaCl2 solution, soils were resuspended by vortexing thoroughly. Samples were then placed back on the shaker for 24 hours. After centrifugation the supernatant was decanted and the volume measured. Triplicate aliquots of the equilibrated aqueous phases (desorption supernatant) were radioassayed by LSC



Matrix propertiesopen allclose all
Matrix no.:
#8
Matrix type:
other: light clay
% Clay:
26.4
% Silt:
31.9
% Sand:
41.7
% Org. carbon:
1.24
pH:
6.4
CEC:
9.8
Matrix no.:
#11
Matrix type:
loam
% Clay:
14.6
% Silt:
24.9
% Sand:
60.5
% Org. carbon:
2.45
pH:
6.4
CEC:
9.8
Matrix no.:
#16
Matrix type:
other: light clay
% Clay:
35.1
% Silt:
28.8
% Sand:
36.1
% Org. carbon:
2.17
pH:
6.1
CEC:
14.3
Matrix no.:
#20
Matrix type:
sand
% Clay:
4.7
% Silt:
5.2
% Sand:
90.1
% Org. carbon:
0.96
pH:
6.2
CEC:
6.4
Details on matrix:
Soil IDs: Japanese standard soil #8 (994W-006), Japanese standard soil #11 (994W-007), Japanese standard soil #16 (994W-008), and Japanese standard soil #20 (994W-009)
All soils were provided by Sumitomo Chemical Company. The soils were stored at room temperature. Prior to use in the study, the soils were passed through a 2 mm sieve and the sieved soils stored in plastic bags. The moisture content of the soils was determined by weighing aliquots before and after oven drying at 110°C for 30 hours.

Physicochemical characterization of the soils were provided by Sumitomo Chemical Company.
Details on test conditions:
The test system consisted of the soils described in "Matrix properties" section and 0.01 M CaCl2 solution.
For the definitive study, a total of ten Teflon® centrifuge tubes (50 mL) were prepared at each concentration. This allowed for duplicate samples for each soil at each concentration and duplicate soil-less samples at each concentration. Prior to dosing,
2g of the respective soils were weighed into pre-weighed centrifuge tubes. At dosing, 40 mL of the corresponding dose solutions were added to each of the tubes. Aliquots of the dosing solutions were taken for radioassay (LSC) before and after the dosing process to determine dose rate and the homogeneity of the dose solutions during the application process (Table III). All samples were then placed in a Wrist-Action™ Shaker and shaken continuously in the dark for 24 hours for the adsorption phase. The shaker was placed in a Hotpack Walk-in chamber incubator maintained at 25°C for the duration of the study.

Method of preparation of application solutions
Five dose solutions were prepared to evaluate soil adsorption/desorption of [14C]fenitrothion (< 1% co-solvent was present in solution). For each
concentration the specified volume of [14C]fenitrothion was added to a volumetric flask and the toluene was evaporated. The unlabeled fenitrothion (0.97 mg/mL) was added to the volumetric flask and the volumetric flask was diluted to the mark with 0.01 M CaCl2 solution. Either a 500 mL volumetric flask or 2, 200 mL volumetric flasks were used for dose solution preparation.

For preparation of the 0.04 µg/mL dose solution, 10 µL of [14C]fenitrothion were added to a 4 mL amber vial. The toluene was evaporated and 1 mL of acetonitrile was added to the vial. The 0.04 µg/mL dose solution was prepared by adding 170 µL of the dilute [14C]fenitrothion to a 500 mL volumetric flask and diluting to the mark with 0.01 M CaCl2.

Duration of adsorption equilibrationopen allclose all
Sample No.:
#8
Duration:
24 h
Sample No.:
#11
Duration:
24 h
Sample No.:
#16
Duration:
24 h
Sample No.:
#20
Duration:
24 h
Duration of desorption equilibrationopen allclose all
Sample no.:
#8
Duration:
24 h
Sample no.:
#11
Duration:
24 h
Sample no.:
#16
Duration:
24 h
Sample no.:
#20
Duration:
24 h

Results and discussion

Adsorption coefficientopen allclose all
Sample No.:
#8
Type:
Koc
Value:
1 935
Sample No.:
#11
Type:
Koc
Value:
816
Sample No.:
#16
Type:
Koc
Value:
1 659
Sample No.:
#20
Type:
Koc
Value:
938

Results: HPLC method

Details on results (HPLC method):
- Details of fitted regression line (log k' vs. log Koc):
- Graph of regression line attached
- Average retention data for test substance:

The retention times (Rt) for NMC, AA-FNT, and fenitrothion were
- 14.2 minutes,15.5 minutes, and 19.5 minutes, respectively.
Stability:
Adsorption and desorption solutions of the highest dose rate (5 ppm) were analyzed by HPLC Fenitrothion represented 92.3-97.3% of the total radiocarbon in adsorption solutions and 88.3-93.8% in desorption solutions (Appendix P). The soil pellets for the highest dose rate samples (5 ppm) were extracted following desorption. HPLC analysis of the soil extracts showed that fenitrothion represented from 75.5-89.4% the extracted radiocarbon. These results demonstrate that fenitrothion was degraded during the adsorption and desorption processes in the four viable soils tested. In all cases, the only degradate formed was 3-methyl-4-nitrophenol (NMC).

Results: Batch equilibrium or other method

Adsorption and desorption constants:
The Freundlich adsorption coefficients (K values) for [14C]fenitrothion usmg concentrations in ppm were determined to be 24, 20, 36, and 9, for Japanese soil number 8 (994W-006), Japanese soil number 11 (994W-007), Japanese soil number 16 (994W- 008), and Japanese soil number 20 (994W-009) soils, respectively. The average K value for the four soils was 22.
The correlation coefficients (r2) for the adsorption isotherms averaged 0.9984 for ppm concentrations.

Koc values express adsorption on the basis of the percent organic carbon in soil. Koc values for [14C]fenitrothion were determined to be 1935 for Japanese soil number 8, 816 for Japanese soil number 11, 1659 for Japanese soil number 16, and 938 for Japanese soil number 20 soils, respectively
Based on the results fenitrothion is predicted to have low mobility in four soils.
Recovery of test material:
The material balance for the study is expressed as the sum of the radiocarbon recovered in the adsorption and desorption solutions, and the radiocarbon remaining in the soil after desorption. Radiocarbon recoveries ranged from 91.2 ± 5.0% to 98.7 ± 3.8% for the five concentrations used in the study.
Concentration of test substance at end of adsorption equilibration period:

Equilibrium Concentrations of [14C]Fenitrothion Concentrations in Solution and in Soil Following the Definitive Adsorption Phase.



Sample Concentration (µg/g) Ln Concentration
ppm Solution Soil Solution Soil
Japanese Standard Soil 8 (FNT-1, 994W-006):
5.0 2.559 48.669 0.940 3.885
2.5 1.106 28.573 0.101 3.352
1.0 0.435 11.151 -0.832 2.412
0.2 0.071 2.567 -2.645 0.943
0.04 0.010 0.496 -4.605 -0.701
Japanese Standard Soil 11 (FNT-2, 994W-007):

5.0 2.738 45.923 1.007 3.827
2.5 1.226 27.206 0.204 3.303
1.0 0.492 10.008 -0.709 2.303
0.2 0.092 2.264 -2.386 0.817
0.04 0.014 0.422 -4.269 -0.863
Japanese Standard Soil 16 (FNT-3, 994W-008):

5.0 1.976 60.873 0.681 4.109
2.5 0.809 33.860 -0.212 3.522
1.0 0.306 13.383 -1.184 2.594
0.2 0.061 2.820 -2.797 1.037
0.04 0.008 0.547 -4.828 -0.603
Japanese Standard Soil 20 (FNT-4, 994W-009):

5.0 3.556 27.683 1.269 3.321
2.5 1.786 15.943 0.580 2.769
1.0 0.700 5.949 -0.357 1.783
0.2 0.136 1.479 -1.995 0.391
0.04 0.020 0.296 -3.912 -1.217


Concentration of test substance at end of desorption equilibration period:
Soil Conc. in Solution (µg/mL) Conc. in Soil (µg/g)
Japanese Soil 8 Rep A 0.010 0.490
Japanese Soil 8 Rep B 0.010 0.502
Average 0.010 0.496

Japanese Soil 11 Rep A 0.014 0.418
Japanese Soil 11 Rep B 0.014 0.425
Average 0.014 0.422

Japanese Soil 16 Rep A 0.007 0.547
Japanese Soil 16 Rep B 0.008 0.546
Average 0.008 0.547

Japanese Soil 20 Rep A 0.019 0.299
Japanese Soil 20 Rep B 0.020 0.293
Average 0.020 0.296
Mass balance (%) at end of adsorption phaseopen allclose all
Sample no.:
#8
Duration:
24 h
% Adsorption:
48.6
Sample no.:
#11
Duration:
24 d
% Adsorption:
45.3
Sample no.:
#16
Duration:
24 h
% Adsorption:
58.2
Sample no.:
#20
Duration:
24 h
% Adsorption:
28.8
Mass balance (%) at end of desorption phaseopen allclose all
Sample no.:
#8
Duration:
24 h
% Desorption:
18
Sample no.:
#11
Duration:
24 h
% Desorption:
18.7
Sample no.:
#16
Duration:
24 h
% Desorption:
17.9
Sample no.:
#20
Duration:
24 h
% Desorption:
16.2
Transformation products:
yes
Remarks:
fenitrothion was degraded during the adsorption and desorption processes in the four viable soils tested. In all cases, the only degradate formed was 3-methyl-4-nitrophenol (NMC).
Details on results (Batch equilibrium method):
Adsorption and desorption solutions of the highest dose rate (5 ppm) were analyzed by HPLC. The recovery data showed that Fenitrothion represented 92.3-97.3% of the total radiocarbon in adsorption solutions and 88.3-93.8% in desorption solutions. The soil pellets for the highest dose rate samples (5 ppm) were extracted following desorption. HPLC analysis of the soil extracts showed that fenitrothion represented from 75.5-89.4% the extracted radiocarbon. These results demonstrate that fenitrothion was degraded during the adsorption and desorption processes in the four viable soils tested. In all cases, the only degradate formed was 3-methyl-4-nitrophenol (NMC).

Applicant's summary and conclusion

Conclusions:
Adsorption/desorption isotherms of [14C]fenitrothion were determined using four soils (Japanese soil number 8 (Kochi Light Clay), Japanese soil number 11 ( Hokkaido Loam), Japanese soil number 16 (Wakayama Light Clay), and Japanese soil number 20 (Miyazaki Sand) soils). Adsorption Koc values ranged from 816 to 1935. These Koc values predict fenitrothion to exhibit low mobility in the four soils studied.The Koc values for desorption were higher than during the adsorption phase, indicating that once adsorbed to the soil fenitrothion is less likely to be removed with water or to leach in these soils (Koc values ranged from 1042 to 2177).
Results of HPLC analyses of adsorption and desorption solutions in addition to soil samples extracted after completion of the desorption phase, indicated that fenitrothion was partially degraded to 3-methyl-4-nitrophenol (NMC) under the study conditions.
Executive summary:

The adsorption/desorption characteristics of [14C]fenitrothion [0,0-dimethyl 0-4-nitro­m-tolyl phosphorothioate],

labeled in the phenyl ring were determined using four soils which varied in texture, percent organic matter,

pH and cation exchange capacity (CEC). A preliminary trial demonstrated that a soil to test solution ratio of 1 to 20

(2 g soil to 40 mL solution) was optimal for all of the four soils. An adsorption and desorption equilibrium period of

24 hours of shaking was selected for the definitive study.

For the definitive study, aqueous test solutions of [14C]fenitrothion in 0.01 M calcium chloride (CaCl2)

were prepared at five concentrations of approximately 0.04, 0.2, 1.0, 2.5 and 5 ppm.

The study was conducted at 25°C with 2.0 g of Japanese soil number 8 (light clay), Japanese soil number 11 (loam),

Japanese soil number 16 (light clay), or Japanese soil number 20 (sand), and 40 mL of test solution in Teflon centrifuge tubes.

Tubes were reciprocally shaken on a Wrist Action shaker for 24 hours for each phase. At the end of the adsorption phase,  

the tubes were centrifuged (5000 rpm, 25°C, 5 min) and the supernatants were decanted and radioassayed. For desorption,

fresh 0.01 M CaCl2 solution was added to the samples and the tubes were shaken and processed as above.

The overall mass balance for all soils and dose rates ranged from 91.2 ± 5.0% to 98.7 ± 3.8%.

High performance liquid chromatography (HPLC) analysis of the adsorption and

desorption solutions and soil extracts of the highest dose rate samples demonstrated that some degradation of

[14C]fenitrothion occurred during batch equilibrium. Soil-less control test solutions analyzed alongside the

samples during the definitive batch equilibrium study showed that no significant wall adsorption was observed

during the study period.

The Freundlich adsorption and desorption coefficients for [14C]fenitrothion were calculated using ppm (K values).

The adsorption K values averaged 22 with an average correlation coefficient (r2) of 0.9984. The desorption K values

averaged 27 with a correlation coefficient of 0.9978. The average adsorption and desorption Koc values were 1337 and 1589,

respectively. Based on the use of adsorption Koc values to predict leaching potential, [14C]fenitrothion is predicted to have low

mobility in the soils studied.

Adsorption/desorption isotherms of [14C]fenitrothion were determined using four soils: Japanese soil number 8 (Kochi Light Clay), Japanese soil number 11 ( Hokkaido Loam), Japanese soil number 16 (Wakayama Light Clay), and Japanese soil number 20 (Miyazaki Sand) soils).

Adsorption Koc values ranged from 816 to 1935. These Koc values predict fenitrothion to exhibit low mobility in the four soils studied.

The Koc values for desorption were higher than during the adsorption phase, indicating that once adsorbed to the soil fenitrothion is less likely to

be removed with water or to leach in these soils (Koc values ranged from 1042 to 2177).

Results of HPLC analyses of adsorption and desorption solutions in addition to soil samples extracted after completion of the desorption phase,

indicated that fenitrothion was partially degraded to 3-methyl-4-nitrophenol (NMC) under the study conditions.