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Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
key study
Study period:
From March 10, 1987 to September 25, 1987
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
other: U.S. EPA Guideline subdivision N 163-1
Deviations:
no
GLP compliance:
yes
Type of method:
batch equilibrium method
Media:
soil
Specific details on test material used for the study:
- Physical state: Viscous light yellow/amber liquid
- Analytical purity: 30% active (no alcohol)
- Lot/batch: 05-6K
- Radiochemical purity (if radiolabelling): 98.4% by TLC
- Specific activity (if radiolabelling): Primary stock: 3.84 x 10E7 dpm/mL
- Locations of the label (if radiolabelling): Ring-UL-14C
- Storage condition of test material: Under refrigeration
Radiolabelling:
yes
Test temperature:
25±1°C
Analytical monitoring:
yes
Details on sampling:
- Isotopic dilutions: to ensure availability of enough test substance, 20 mL of the purified primary stock solution of the radiolabelled test substance (46 µg/mL in methanol) were placed into a 50 mL volumetric flask. The solvent was evaporated under nitrogen. 30 mL of non-radiolabelled test substance (1000 µg/mL in H2O) were added and brought to 50 mL total volume with water. The concentration of the isotopically diluted purified stock solution was 698 µg/mL (purity: 99.1% as per TLC-radiochemical determination). Five 50 µL replicates of this solution were assayed by LSC to calculate the specific activity. The specific activity was calculated to be 2.03E04 dpm/µg.
Details on matrix:
Test soil:
- Source: The #32 sand, #45 silt loam, #59 sandy loam and #58 clay loam were supplied by ABC laboratories. Representative subsamples of these soils were collected and shipped to A and L Mid west agricultural laboratories Inc, Omaha, Nebraska for characterisation.
- The soils were sieved through a 10 mesh screen and autoclaved at 20 degF (121 degC) and 15 psi for 1 h.
Properties:
- Soil texture:
- % sand: 93, 38, 64 and 28 for # 32 sand, #45 silt loam, #59 sandy loam and #58 clay loam respectively
- % silt: 3, 52, 20 and 38 for # 32 sand, #45 silt loam, #59 sandy loam and #58 clay loam respectively
- % clay: 4, 10, 16 and 34 for # 32 sand, #45 silt loam, #59 sandy loam and #58 clay loam respectively
- Organic carbon (%): 0.2, 1, 1.6 and 3.9 for # 32 sand, #45 silt loam, #59 sandy loam and #58 clay loam respectively
- CEC (meq/100 g): 3.8, 7.6, 9.5 and 20.9 meq/100 g for # 32 sand, #45 silt loam, #59 sandy loam and #58 clay loam respectively
- pH: 6.5, 7.7, 6.2 and 7.5 for # 32 sand, #45 silt loam, #59 sandy loam and #58 clay loam respectively
- Bulk density (g/cm3): 1.56, 1.45, 1.18 and 1.03 for # 32 sand, #45 silt loam, #59 sandy loam and #58 clay loam respectively
- Field capacity at 1/3 Bar: 7.77, 17.36, 15.12 for # 32 sand, #45 silt loam, #59 sandy loam and #58 clay loam respectively
Details on test conditions:
Preliminary study:
The objectives of the preliminary study were to select appropriate soil to water ratios and equilibrium times for the test compound and four soil types at a nominal test concentration of 1 µg/mL. The test containers were Pyrex culture tubes.
- At the 1:20 soil to water ratio, greater than 95% of the test substance was adsorbed to the soil (#32 sand, #45 silt loam, #59 sandy loam and #58 clay loam). Significant 14C-losses were attributed to adsorption of the test substance to the Pyrex test containers and to filters which were employed for filtration of supernatants.
- Additionally the preliminary study identified 4 experimental limitations. They were: (a) elimination of any filtration steps due to loss of the 14C-test substance onto filter media (b) use of direct addition of 14C-test substance onto the test systems to reduce 14C-losses incurred by manipulation of 0.01 M CaCl2 14C-test substance stock solutions (c) use of nalgene test containers rather than silanized glass to reduce adsorption of 14C- test substance to the test system surfaces (D) use of an increased water to soil ratio to decrease the percent 14C-test substance adsorbed to soil.
- The highest practical water to soil ratio that could be used was 200:1 since the size of the test container could not exceed a capacity which could be successfully centrifuged (1.e., 250 mL capacity).

Main study:
A: Adsorption procedure:
- Ten one-gram portions of each soil were weighed and transferred into appropriately labelled Nalgene bottles. To each bottle, 200 mL aliquots of 0.01 M CaCl2 solution were added.
- Nominal test concentrations of 0, 0.1, 0.5, 1 and 2 µg/mL (i.e., equivalent to a measured concentration of 0.689, 0.441, 0.887 and 1.85 µg/mL) were prepared by pipetting appropriate aliquots of isotopically diluted purified primary stock solution of 14C-test substance at 698 µg/mL directly into nalgene test bottles containing 0.01 M CaCl2 solution and test soils. The 0.1, 0.5, 1 and 2 µg/mL nominal test concentrations received approximately 28 µL, 243 µL, 287 µL and 573 µL respectively.
- Equal volumes of test substance isotopically diluted purified primary stock solution were added directly into nalgene test bottles containing only 0.01M CaCl2 solution.
- Duplicate LSC samples were taken of each resulting 14C-test substance concentration (less soil) to measure the levels of the 14C-test substance present at initiation.
- The soil suspensions were shaken in darkness for 20 h on a mechanical shaker in an environmentally controlled chamber at 25±1°C. The suspensions were then centrifuged for 15 mins at approximately. 2000 rpm in centrifuge. Duplicate 5 mL aliquots of the supernatant were taken for liquid scintillation counting analysis directly from each nalgene test bottle. The remaining supernatant (approximately 186 mL) was removed from each bottle by decanting.
B. DEesorption procedure:
- 196 mL aliquots of sterile test water at a 0.01 M CaCl2 concentration were added to each sample. All soil suspensions were shaken in darkness on a mechanical shaker for 14 h and 45 min in an environmentally controlled chamber at 25±1°C.
- All soil suspensions were shaken in darkness on a mechanical shaken for 14 h and 45 min in an environmentally controlled chamber at 25±1°C.
- After shaking, the suspensions were centrifuged for 15 mins at approximately 2000 rpm in a centrifuge. Duplicate 10 mL aliquots of the supernatant were taken for liquid scintillation counting analysis directly from the nalgene sample bottles. The remaining supernatant was removed by pipetting. The soil was air dried, combusted in triplicate, and was then analyzed by liquid scintillation counting to determine the 14C-mass balance.
- Following the initial liquid scintillation counting analysis of these combusted soil samples, triplicate re-combustions were done on those samples that were determined to be "questionable".
- Questionable results included: 14C-residue levels at 14C-accountability <80% or >120% and at 14C-residue replicate levels having a high variability.
Duration:
20 h
Initial conc. measured:
0.689 other: µg/mL
Duration:
20 h
Initial conc. measured:
0.441 other: µg/mL
Duration:
20 h
Initial conc. measured:
0.887 other: µg/mL
Duration:
20 h
Initial conc. measured:
1.85 other: µg/mL
Computational methods:
Measurements of radioactivity were made using a Beckman liquid scintillation system, model 3801 for 5 minutes or to a 2 sigma value of 2.0. The beckman LSC system determines total counts and the results are reported in disintegrations per minute (DPM or ppm).

for
the definitive test samples were counted where the LSC system was interfaced with a Beckman data transporter. Data calculations were performed using an IBMR PC-XTR system.

Liquid sample aliquots were pipetted into scintillation vials where they received appropriate aliquots of beckman ready-SolvTM MP for LSC analysis.
Soilsamples for LSc analysis were combusted in a Packard 306D tri-carb sample oxidizer to determine 14C-mass balance.

Calculations:
The adsorption and desorption properties of the test substance were characterized by Freundlich isotherm:
x/m = Kd.Ce(1/n) 1n x/m = 1n Kd + 1/n 1n Ce
where,
X= the amount of chemical adsorbed in µg
M= mass of adsorbent in g.
When in equilibrium with an aqueous solution solution, where
Ce= concentration of chemical in aqueous solution
Kd= adsorption coefficient and
N= a constant

The Freundlich isotherm given as 1n x/m = 1n Kd + 1/n 1n Ce is the form of a line equation. When 1n Ce is plotted vs 1n x/m, the constants Kd and n are determined from the slope (1/n) and intercept (1n Kd) of the resultant straight line.

The equilibrium concentration of the test compound (Ce) in the aqueous phase of the samples was determined by LSC analysis.
The amount of test compound in µg adsorbed, X, in each of the samples was calculated in the following manner,
Xad= [(µg/mL of test compound in solution at initiation (In) x (volume added at initiation)] – [(µg/mL of test compound in equilibrium after adsorption phase (ad) x (volume added at initiation)]

Desorption phase:
Xde= [(µg/mL of test compound in solution at initiation (In) x (volume added at initiation)] – [(µg/mL of test compound in equilibrium at adsorption phase (ad) x (volume of filterate removed at adsorption phase)]- [(µg/mL in solution at desorption phase (de)) x (volume added at initiation)]

The mass of soil, m, for each sample was the dry soil weight (1.000 g).

Calculations were made of x/m, 1n x/m and 1n Ce. From this data, 1n Ce was plotted vs 1n x/m and line equations for the adsorption isotherm and desorption isotherm for each of the four soil types were determined.

The constants Kd and n were determined for each soil type from the slope (1/n) and y intercept (1n Kd) of the corresponding line equation. The adsorption coefficient Koc for each soil sample was determined by using the equation Koc = (Kd x 100% O.C.) where % O.C. is the organic carbon content of the soil. Percent organic values received from agricultural labs were converted to % organic carbon by the equation % O.C. = (% O.M.)/2.0.)

The 14C-mass balance of test substance in each soil system was determined. The µg in soil after desorption was determined by combustion radioanalysis using the following formula:
µg in soil=
DPM/ S.A. (sample size g) x 1.0. g x % recovery from soil

Key result
Type:
Koc
Value:
6 171 657 L/kg
Temp.:
25 °C
% Org. carbon:
0.1
Remarks on result:
other: #32 sand -immobile
Key result
Type:
Kd
Value:
6 172 L/kg
Temp.:
25 °C
% Org. carbon:
0.1
Remarks on result:
other: #32 sand -immobile
Key result
Type:
Koc
Value:
2 159 346 L/kg
Temp.:
25 °C
% Org. carbon:
0.5
Remarks on result:
other: #45 silt loam -immobile
Key result
Type:
Kd
Value:
10 797 L/kg
Temp.:
25 °C
% Org. carbon:
0.5
Remarks on result:
other: #45 silt loam -immobile
Key result
Type:
Koc
Value:
640 389 L/kg
Temp.:
25 °C
% Org. carbon:
0.8
Remarks on result:
other: #59 sandy loam -immobile
Key result
Type:
Kd
Value:
5 123 L/kg
Temp.:
25 °C
% Org. carbon:
0.8
Remarks on result:
other: #59 sandy loam -immobile
Key result
Type:
Koc
Value:
1 663 039 L/kg
Temp.:
25 °C
% Org. carbon:
2
Remarks on result:
other: #58 clay loam -immobile
Key result
Type:
Kd
Value:
32 429 L/kg
Temp.:
25 °C
% Org. carbon:
2
Remarks on result:
other: #58 clay loam -immobile
Details on results (HPLC method):
The #32 sand at 0.1% organic carbon had an adsorption Kd and Koc as: 6172 and 6171657 respectively and a desorption Kd and Koc as: 7137 and 7137310 respectively.
The #45 silt loam at 0.5% organic carbon had an adsorption Kd and Koc as: 10797 and 2159346 respectively and a desorption Kd and Koc as: 14083 and 2816590 respectively.
The #59 sandy loam at 0.8% organic carbon had an adsorption Kd and Koc as: 5123 and 640389 respectively and a desorption Kd and Koc as: 96540 and 12067457 respectively.
The #58 clay loam at 2% organic carbon had an adsorption Kd and Koc as: 32429 and 1663039 respectively and a desorption Kd and Koc as: 165556 and 8490062 respectively.
Adsorption and desorption constants:
See 'Results and discussion: Adsorption coefficient'
Remarks on result:
other: See 'Any other information on results incl. tables'
Remarks on result:
other: See 'Any other information on results incl. tables'
Transformation products:
no
Details on results (Batch equilibrium method):
See 'Any other information on results incl. tables'

Table. Mean percentage of adsorption, desorption and total mass balance

Soil type

Mean percent adsorption

Mean percent desorption

Mean percent total mass balance

# 32 sand

97.91±0.72%

1.19±0.48%

100.04±15.20%

# 45 silt loam

98.67±0.16%

0.45±0.17%

103.29±10.69%

# 59 sandy loam

98.51±0.77%

0.23±0.05%

95.29±4.94%

# 58 clay loam

99.13±0.10%

0.09±0.02%

100.04±10.97%

 No apparent degradation occurred to the test substance in any of the four soils under the conditions of the study.

Conclusions:
Under the conditions of the study, the test substance was considered to have little or no potential for mobility in the soil and therefore should not pose a probable environmental risk for contamination of ground water.
Executive summary:

A study was conducted to determine the adsorption / desorption coefficients of the test substance according to US EPA Guideline Subdivision N 163 -1, in compliance with GLP. The coefficients determined by equilibrating with four soil types (sand, sandy loam, clay loam, silt loam). Based on the very high percent of 14C-test substance adsorption onto the test soil, i.e., 95.2 to 97.3% in a preliminary study conducted with a 1 : 20 soil : water ratio, the definitive study was carried out at 1 : 200 soil : water. Nominal test concentrations of 0, 0.1, 0.5, 1 and 2 µg/mL (equivalent to a measured concentration of 0.689, 0.441, 0.887 and 1.85 µg/mL) were prepared by pipetting appropriate aliquots of 14C-test substance at 698 µg/mL directly into test bottles containing 0.01 M CaCl2 solution and test soils. Liquid scintillation counting was employed to measure the test substance concentrations in the aqueous phase. The amount of the test substance remaining adsorbed on the soil was determined by combustion/radio analysis. Although the amount of 14C-test substance adsorbed onto the four test soils was well above the 20 to 80% recommended to ensure Freundlich isotherms, excellent correlations were obtained ranging from 0.9682 to 0.9983. In addition, the 14C-mass balance for the four soils types ranged from 95.3 to 103.2%. The #32 sand at 0.1% organic carbon had an adsorption Kd and Koc of 6172 and 6171657, respectively, and a desorption Kd and Koc of 7137 and 7137310, respectively. The #45 silt loam at 0.5% organic carbon had an adsorption Kd and Koc of 10797 and 2159346, respectively, and a desorption Kd and Koc of 14083 and 2816590, respectively. The #59 sandy loam at 0.8% organic carbon had an adsorption Kd and Koc of 5123 and 640389, respectively, and a desorption Kd and Koc of 96540 and 12067457, respectively. The #58 clay loam at 2% organic carbon had an adsorption Kd and Koc of 32429 and 1663039, respectively, and a desorption Kd and Koc of 165556 and 8490062, respectively. The mean Kd value was 13630 L/kg. No apparent degradation of the test substance occurred in any of the four soils. Under the conditions of the study, the test substance was considered to have little or no potential for mobility in the soil and therefore should not pose an environmental risk for contamination of ground water (Daly, 1988).

Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
key study
Study period:
From March 18, 1999 to April 30, 1999
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Justification for reliability incl. deficiencies'
Justification for type of information:
Study results have been assigned a validity of 2, due to the very high concentrations used of the test substance (0.5g test substance for 1g soil) causing extrapolations to lower concentrations to be less accurate. Adsorption is likely to be higher at lower concentrations than suggested by the outcome of this study.
Qualifier:
according to
Guideline:
OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Type of method:
batch equilibrium method
Media:
soil
Specific details on test material used for the study:
- Purity: 51.7% of test substance in water.
Test temperature:
room temperature
Analytical monitoring:
yes
Key result
Type:
other: Kadsoc (soil 1)
Value:
18 251 dimensionless
Key result
Type:
other: Kadsoc (soil 2)
Value:
16 679 dimensionless
Key result
Type:
other: Kadsoc (soil 3)
Value:
812 943 dimensionless
Adsorption and desorption constants:
-soil 1: Kfads = 630 ; soil 2: Kfads = 1543; soil 3: Kfads = 2032
-soil 1: Kfdes = 2828 ; soil 2: Kfdes = 6795; soil 3: Kfdes = 2778;
-soil 1: Kadsoc = 18251; soil 2: Kadsoc = 16679; soil 3: Kadsoc = 812943

Kfads / Kfdes: soil 1: 0.22; soil 2: 0.23; soil 3: 0.73

Testconcentrations:
- Euro soil 3: 20 mg/L,
- Euro soil 5: 50 mg/L,
- Euro soil 6: 50 mg/L.
Analysis of the active substance by means of spectrophotometry.

Freundlich (Kads(F) isotherm for adsorption:
Euro   log    1/n      r^2 soil  Kads(F)
____________________________
3    2.7991  0.773   0.9898
5    3.1883  0.7226  0.9619
6    3.308   0.7709  0.9592

Freundlich (Kdes(F) isotherm for desorption:
Euro   log    1/n      r^2 soil  Kdes(F)
_____________________________
3    3.4515  0.5353  0.988
5    3.8322  0.5762  0.9928
6    3.4437  0.7291  0.9984

Validity criteria fulfilled:
yes
Conclusions:
Under the study conditions, the test substance adsorbed onto soil and did not desorb easily for the three soil types used, therefore it could be classified as immobile.
Executive summary:

A study was conducted to determine the adsorption / desorption of the test substance according to OECD Guideline 106, in compliance with GLP. The batch equilibrium method was used in this experiment. The adsorption coefficients (Kadsoc) were determined to be 18251, 16679 and 812943 for soils 1, 2 and 3, respectively. Under the study conditions, the test substance adsorbed onto soil and did not desorb easily for the three soil types used, therefore it could be classified as immobile (Geffke, 1999).

Description of key information

Cationic surfactants adsorb to soil or sediment mainly via ionic interaction with negatively charged surfaces and there is poor correlation between adsorption and organic carbon content. Hence, sorption should not be normalized to organic matter and it is better to rely on Kd rather than Koc. As a worst case approach, the value for sediment was also used for soils and suspended particles. As a result, the following Kd values were used Kd soil = Kd sediment = Kd sup = 13,630 L/kg.

Key value for chemical safety assessment

Other adsorption coefficients

Type:
other: Kd values for soil, sediment and suspended matter
Value in L/kg:
13 630
at the temperature of:
25 °C

Other adsorption coefficients

Type:
log Kp (soil-water)
Value in L/kg:
2 040
at the temperature of:
25 °C

Other adsorption coefficients

Type:
log Kp (sediment-water)
Value in L/kg:
6 820
at the temperature of:
25 °C

Other adsorption coefficients

Type:
log Kp (suspended matter-water)
Value in L/kg:
3 410
at the temperature of:
25 °C

Additional information

Study 1. A study was conducted to determine the adsorption / desorption coefficients of the test substance according to US EPA Guideline Subdivision N 163 -1, in compliance with GLP. The coefficients determined by equilibrating with four soil types (sand, sandy loam, clay loam, silt loam). Based on the very high percent of 14C-test substance adsorption onto the test soil, i.e., 95.2 to 97.3% in a preliminary study conducted with a 1 : 20 soil : water ratio, the definitive study was carried out at 1 : 200 soil : water. Nominal test concentrations of 0, 0.1, 0.5, 1 and 2 µg/mL (equivalent to a measured concentration of 0.689, 0.441, 0.887 and 1.85 µg/mL) were prepared by pipetting appropriate aliquots of 14C-test substance at 698 µg/mL directly into test bottles containing 0.01 M CaCl2 solution and test soils. Liquid scintillation counting was employed to measure the test substance concentrations in the aqueous phase. The amount of the test substance remaining adsorbed on the soil was determined by combustion/radio analysis. Although the amount of 14C-test substance adsorbed onto the four test soils was well above the 20 to 80% recommended to ensure Freundlich isotherms, excellent correlations were obtained ranging from 0.9682 to 0.9983. In addition, the 14C-mass balance for the four soils types ranged from 95.3 to 103.2%. The #32 sand at 0.1% organic carbon had an adsorption Kd and Koc of 6172 and 6171657, respectively, and a desorption Kd and Koc of 7137 and 7137310, respectively. The #45 silt loam at 0.5% organic carbon had an adsorption Kd and Koc of 10797 and 2159346, respectively, and a desorption Kd and Koc of 14083 and 2816590, respectively. The #59 sandy loam at 0.8% organic carbon had an adsorption Kd and Koc of 5123 and 640389, respectively, and a desorption Kd and Koc of 96540 and 12067457, respectively. The #58 clay loam at 2% organic carbon had an adsorption Kd and Koc of 32429 and 1663039, respectively, and a desorption Kd and Koc of 165556 and 8490062, respectively. The mean Kd value was 13630 L/kg. No apparent degradation of the test substance occurred in any of the four soils. Under the conditions of the study, the test substance was considered to have little or no potential for mobility in the soil and therefore should not pose an environmental risk for contamination of ground water (Daly, 1988).

Study 2. A study was conducted to determine the adsorption / desorption of the test substance according to OECD Guideline 106, in compliance with GLP. The batch equilibrium method was used in this experiment. The adsorption coefficients (Kadsoc) were determined to be 18251, 16679 and 812943 for soils 1, 2 and 3, respectively. Under the study conditions, the test substance adsorbed onto soil and did not desorb easily for the three soil types used, therefore it could be classified as immobile (Geffke, 1999).