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Adsorption / desorption

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

adsorption / desorption: screening

Type of information:

read-across based on grouping of substances (category approach)

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 'Remark'

Remarks:

KL2 due to RA. 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.

Justification for type of information:

Refer to the Quaternary ammonium salts (QAS) category or section 13 of IUCLID for details on the category justification. The study with the read across substance is considered sufficient to fulfil the information requirements as further explained in the provided endpoint summary.

Qualifier:

according to guideline

Guideline:

OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

soil

Test temperature:

room temperature

Analytical monitoring:

yes

Key result

Type:

other: Kadsoc (soil 1)

Value:

18 251 L/kg

Key result

Type:

other: Kadsoc (soil 2)

Value:

16 679 L/kg

Key result

Type:

other: Kadsoc (soil 3)

Value:

812 943 L/kg

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

Test concentrations:
- 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:

Based on the results fo the read-across study, 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 read across substance, C12-16 ADBAC, according to OECD Guideline 106, in compliance with GLP. The soil adsorption / desorption properties were evaluated using the batch equilibrium method. The test substance adsorbed onto soil (soil 1: Kadsoc = 18,251; soil 2: Kadsoc = 16,679; soil 3: Kadsoc = 812,943) and did not desorb easily for the three soil types used. The high concentrations of test substance used in the study (0.5 g test substance for 1 g soil) led to a less accurate extrapolation to lower concentrations. Adsorption is likely to be higher at lower concentrations than suggested by the outcome of this study. Based on the results fo the read-across study, 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).

Reference 2

Endpoint:

adsorption / desorption: screening

Type of information:

read-across based on grouping of substances (category approach)

Adequacy of study:

key study

Study period:

From March 10, 1987 to September 25, 1987

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

KL2 due to RA

Justification for type of information:

Refer to the Quaternary ammonium salts (QAS) category or section 13 of IUCLID for details on the category justification. The study with the read across substance is considered sufficient to fulfil the information requirements as further explained in the provided endpoint summary.

Qualifier:

according to guideline

Guideline:

other: U.S. EPA Guideline subdivision N 163-1

Deviations:

no

GLP compliance:

yes

Type of method:

batch equilibrium method

Media:

soil

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 uL 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. DESORPTION 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: 6,172 and 6,171,657 respectively and a desorption Kd and Koc as: 7,137 and 7,137,310 respectively.
The #45 silt loam at 0.5% organic carbon had an adsorption Kd and Koc as: 10,797 and 2,159,346 respectively and a desorption Kd and Koc as: 14,083 and 2,816.590 respectively.
The #59 sandy loam at 0.8% organic carbon had an adsorption Kd and Koc as: 5,123 and 640,389 respectively and a desorption Kd and Koc as: 96,540 and 12,067,457 respectively.
The #58 clay loam at 2% organic carbon had an adsorption Kd and Koc as: 32,429 and 1,663,039 respectively and a desorption Kd and Koc as: 165,556 and 8,490,062 respectively.

Transformation products:

no

Details on results (Batch equilibrium method):

See the below table under 'any other information on results incl. tables' for percent adsorption and desorption and total mass balance.

Table 1. 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:

Based on the results of the read-across 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 of the read across substance, C12-16 ADBAC, according to U.S. EPA Guideline subdivision N 163-1, in compliance with GLP. The adsorption / desorption coefficients were determined by equilibrating with four soil types (sand, sandy loam, clay loam and silt loam). Based on the very high percent of 14C-test substance adsorption onto the test soil 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 measured concentrations 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 bottles containing 0.01 M CaCl2 solution and soils. Liquid scintillation counting was employed to measure the 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 6,172 and 6,171,657, respectively, and a desorption Kd and Koc of 7,137 and 7,137,310, respectively. The #45 silt loam at 0.5% organic carbon had an adsorption Kd and Koc of 10,797 and 2,159,346, respectively, and a desorption Kd and Koc of 14,083 and 2,816,590, respectively. The #59 sandy loam at 0.8% organic carbon had an adsorption Kd and Koc of 5,123 and 640,389, respectively, and a desorption Kd and Koc of 96,540 and 12,067,457, respectively. The #58 clay loam at 2% organic carbon had an adsorption Kd and Koc of 32,429 and 1,663,039, respectively, and a desorption Kd and Koc of 165,556 and 8,490,062, respectively. The mean Kd value was 13,630 L/kg. No apparent degradation of the test substance occurred in any of the four soils. Based on the results of the read-across study, the test substance was considered to have little or no potential for mobility in soil and therefore should not pose a probable environmental risk for contamination of ground water (Daly, 1988).

Description of key information

Based on the experimentally determined mead Koc value of 1640329 L/kg for the read across substance (which is indicative of little or no potential for mobility in soil), C12 -14 TMAC is expected to have a similar behaviour in soil.

Key value for chemical safety assessment

Koc at 20 °C:

1 640 329

Additional information

Study 1.

A study was conducted to determine the adsorption / desorption of the read across substance, C12-16 ADBAC, according to U.S. EPA Guideline subdivision N 163-1, in compliance with GLP. The adsorption / desorption coefficients were determined by equilibrating with four soil types (sand, sandy loam, clay loam and silt loam). Based on the very high percent of 14C-test substance adsorption onto the test soil 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 measured concentrations 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 bottles containing 0.01 M CaCl2 solution and soils. Liquid scintillation counting was employed to measure the 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 6,172 and 6,171,657, respectively, and a desorption Kd and Koc of 7,137 and 7,137,310, respectively. The #45 silt loam at 0.5% organic carbon had an adsorption Kd and Koc of 10,797 and 2,159,346, respectively, and a desorption Kd and Koc of 14,083 and 2,816,590, respectively. The #59 sandy loam at 0.8% organic carbon had an adsorption Kd and Koc of 5,123 and 640,389, respectively, and a desorption Kd and Koc of 96,540 and 12,067,457, respectively. The #58 clay loam at 2% organic carbon had an adsorption Kd and Koc of 32,429 and 1,663,039, respectively, and a desorption Kd and Koc of 165,556 and 8,490,062, respectively. The mean Kd and Koc values were calculated to be 13,630 and 265,8608 L/kg. No apparent degradation of the test substance occurred in any of the four soils. Based on the results of the read-across study, the test substance was considered to have little or no potential for mobility in soiland therefore should not pose a probable environmental risk for contamination of ground water (Daly, 1988).

Study 2.

A study was conducted to determine the adsorption / desorption of the read across substance, C12-16 ADBAC, according to OECD Guideline 106, in compliance with GLP. The soil adsorption / desorption properties were evaluated using the batch equilibrium method. The test substance adsorbed onto soil (soil 1: Kadsoc = 18,251; soil 2: Kadsoc = 16,679; soil 3: Kadsoc = 812,943) and did not desorb easily for the three soil types used. The desoprtion coefficients (Kdoc) were determined to be 81971, 73459 and 1111200 for soils 1, 2 and 3 respectively. The mean Koc was calculated to be 282,624.3 L/kg. The high concentrations of test substance used in the study (0.5 g test substance for 1 g soil) led to a less accurate extrapolation to lower concentrations. Adsorption is likely to be higher at lower concentrations than suggested by the outcome of this study. Based on the results fo the read-across study, 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).

Based on the results of the read across studies, the test substance, C12 -14 TMAC, can be considered to be immobile in soil. It is well known that, because of the positive charge, cationic surfactants adsorb strongly to the negatively charged surfaces of sludge, soil and sediments. Therefore, it is not expected to pose an environmental risk for contamination of ground water. Further, following the same approach of risk assessment used in the Biocides dossier on the read across substance, C12-16 ADBAC, the mean Koc value of 1,640,329 L/kg from both the available studies has been used for hazard/risk assessment.

[LogKoc: 6.21]