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Adsorption / desorption

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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 Remarks
Remarks:
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.
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
Test temperature:
room temperature
Analytical monitoring:
yes
Details on test conditions:
For details on method and procedure, kindly refer to the attached background material section of the IUCLID.
Key result
Type:
other: Kaoc
Remarks:
adsorption coefficient (soil 1; loam)
Value:
18 251 L/kg
Remarks on result:
other: immobile
Key result
Type:
other: Kaoc
Remarks:
adsorption coefficient (soil 2; loamy sand)
Value:
16 679 L/kg
Remarks on result:
other: immobile
Key result
Type:
other: Kaoc
Remarks:
adsorption coefficient (soil 3; silt loam)
Value:
812 943 L/kg
Remarks on result:
other: immobile
Key result
Type:
other: Kdoc
Remarks:
desorption coefficient (soil 1; loam)
Value:
ca. 81 971 L/kg
Remarks on result:
other: immobile
Key result
Type:
other: Kdoc
Remarks:
desorption coefficient (soil 2; loamy sand)
Value:
ca. 73 459 L/kg
Remarks on result:
other: immobile
Key result
Type:
other: Kdoc
Remarks:
desorption coefficient (soil 3: silt loam)
Value:
ca. 1 111 200 L/kg
Remarks on result:
other: immobile
Key result
Type:
Koc
Remarks:
(mean)
Value:
ca. 282 624.3 L/kg
Remarks on result:
other: immobile
Adsorption and desorption constants:
-soil 1 (loam): Kfads = 630 ; soil 2 (loamy sand): Kfads = 1543; soil 3 (silt loam): Kfads = 2032
-soil 1 (loam): Kfdes = 2828 ; soil 2 (loamy sand): Kfdes = 6795; soil 3 (silt loam): Kfdes = 2778;
-soil 1 (loam): Kadsoc = 18251; soil 2 (loamy sand): Kadsoc = 16679; soil 3 (silt loam): Kadsoc = 812943
-soil 1 (loam): Kdesoc = 81971; soil 2 (loamy sand): Kdesoc = 73459; soil 3 (silt loam): Kdesoc = 1111200
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

Table 1. Results of screening test - adsorption

Soil 1

Soil 2

Soil 3

Concentration of test material [mg/L]

50

100

100

After contact of....h with soil

6

24

6

Correction for blank with soil

 -

 -

 -

Correction for blank without soil

-

-

-

Final corrected concentration [mg/L]

-

-

-

Initial concentration of test solution [mg/L]

50

100

100

Decrease in concentration [mg/L]

-

-

-

Quantity adsorbed [mg]

521.5

312.5

266.5

Quantity of soil [g of oven-dried equivalent]

0.486

0.482

0.489

Quantity adsorbed [mg] per gram of soil

4070.99

9725.10

9679.96

Test material adsorbed [%]

79

94

95

Temperature [°C]

room temp

room temp

room temp

Volume of solution recovered after centrifugation [mL]

-

-

-

Volume of solution not recovered [mL]

-

-

-

Corresponding quantity of test substance [mg]

Table 2. Results of screening test - desorption

Soil 1

Soil 2

Soil 3

Temperature [°C]

room temp

room temp

room temp

Concentration in combined washings [mg/L]

5.37

2.33

4.74

Corresponding quantity of test material [mg]

Quantity desorbed [mg]

263.06

112.69

233.48

[%] of adsorbed test material, which is desorbed

13

2

5

[%] of adsorbed test material, which is not desorbed

87

98

95

Validity criteria fulfilled:
yes
Conclusions:
Based on the results of the read across study, the test substance can be considered to be highly adsorbed onto soil, which does 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 (51.7% active in water) using the batch equilibrium, according to OECD Guideline 106, in compliance with GLP. No vehicles were used to dissolve the read across substance. Parallel method was used with separate test vessels for each concentration and time point of measurement. The soil/solution ratio used was 1:100 (0.5 g soil and 50 mL solution). The determination limit of the analytical method was 1.66 mg/L. Based on the high adsorption tendency of the test substance, the minimum test concentration was 20 mg/L for loamy soil and 50 mg/L for loamy sand and silt loam. The concentrations of the active ingredient were determined via spectrophotometry. Two centrifugation tubes with 50 mL of 20 mg/L of test substance in 0.01 M CaCl2 solution were shaken for 20 h at 175 rpm. The mean value of measurements showed a recovery rate of >90% Therefore, the stability of the test substance under the test conditions were assumed. There was no major adsorption on the surface of the centrifugation tube. The amount of substance adsorbed on the soils was calculated from the depletion of the test substance in the solution (indirect method). The read across substance adsorbed onto soil but did not desorb easily for the three soil types used. The correlations coefficients (r2) of the Freundlich isotherms ranged from 0.9592 to 0.9898 for adsorption and 0.988 to 0.9984 for desorption. In addition, the 14C-mass balance for the four soils types ranged from 65-85%. The low recovery rates in loamy sand and silt loam with higher organic carbon content, could be caused by irreversible adsorption of the test substance. The distribution coefficient (Kd), mobility coefficients (Koc), Freundlich isotherms and regression constants (1/n) were determined as summarized below: 

Soil types 

% OC

CEC (meq/100g)

Adsorption

Desorption

Adsorption distribution coefficient (Kdads)

Adsorption coefficient (Kaoc

Freundlich adsorption isotherm (Kfads)

1/n

(ads)

Desorption coefficient (Kddes)

Desorption coefficient (Kdoc

Freundlich desorption isotherm (Kfdes)

1/n

(des)

Loam 

3.45

18.3

390

18251

630

0.733

671

81971

2828

0.535

Loamy sand

9.25

32.7

1556

16679

1543

0.723

4211

73459

6795

0.576

Silt Loam

0.25

11.4

1816

812943

2032

0.771

1971

1111200

2778

0.729

 OC = organic carbon; ads = adsorption; des = desorption; CEC = Cation exchange capacity

The mean Kfads and Koc values for adsorption were calculated to be 1402 and 282,624.3 L/kg respectively. The high concentrations of read across substance used in the study (0.5 g read across 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. Under the study conditions, the read across substance adsorbed onto soil and did not desorb easily for the three soil types used, therefore it could be classified as immobile (Geffke, 1999).

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.
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
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. Soil samples 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:
other: Kaoc
Remarks:
adsorption coefficient (Sand)
Value:
6 171 657 L/kg
Temp.:
25 °C
Matrix:
#32 sand
% Org. carbon:
0.1
Remarks on result:
other: immobile
Key result
Type:
other: Kaoc
Remarks:
adsorption coefficient (Silt loam)
Value:
2 159 346 L/kg
Temp.:
25 °C
Matrix:
#45 silt loam
% Org. carbon:
0.5
Remarks on result:
other: immobile
Key result
Type:
other: Kaoc
Remarks:
adsorption coefficient (Clay loam)
Value:
1 663 039 L/kg
Temp.:
25 °C
Matrix:
#58 clay loam
% Org. carbon:
2
Remarks on result:
other: immobile
Key result
Type:
other: Kaoc
Remarks:
adsorption coefficient (Sandy loam)
Value:
640 389 L/kg
Temp.:
25 °C
Matrix:
#59 sandy loam
% Org. carbon:
0.8
Remarks on result:
other: immobile
Key result
Type:
other: Kdoc
Remarks:
desorption coefficient (Sand)
Value:
7 137 310 L/kg
Temp.:
25 °C
Matrix:
#32 sand
% Org. carbon:
0.1
Remarks on result:
other: immobile
Key result
Type:
other: Kdoc
Remarks:
desorption coefficient (Silt loam)
Value:
2 816 590 L/kg
Temp.:
25 °C
Matrix:
#45 silt loam
% Org. carbon:
0.5
Remarks on result:
other: immobile
Key result
Type:
other: Kdoc
Remarks:
desorption coefficient (Clay loam)
Value:
8 490 062 L/kg
Temp.:
25 °C
Matrix:
#58 clay loam
% Org. carbon:
2
Remarks on result:
other: immobile
Key result
Type:
other: Kdoc
Remarks:
desorption coefficient (Sandy loam)
Value:
12 067 457 L/kg
Temp.:
25 °C
Matrix:
#59 sandy loam
% Org. carbon:
0.8
Remarks on result:
other: 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. Adsorption (Kd) and mobility coefficients.(Koc)

Soil Types

Adsorption coefficient (Kd)

Mobility coefficient (Koc)

Desorption coefficient (Kd)

Mobility coefficient (Koc)

# 32 Sand

6,172

6,171,657

7173

7137310

# 45 Silt loam

10,797

2,159,346

14083

2816590

# 58 Clay loam

32,429

1,663,039

165556

8490062

# 59 Sandyloam

5,123

640,389

96540

12067457

Table 2. 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.

Validity criteria fulfilled:
not specified
Conclusions:
Based on the results of the read across study, the test substance is 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.
Executive summary:

A study was conducted to determine the adsorption / desorption of the read across substance, C12-16 ADBAC (30% active and 98.4% radiolabeled purity) using batch equilibrium method, 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-read across 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-read across 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 read across substance remaining adsorbed on the soil was determined by combustion/radio analysis. Although the amount of 14C-read across 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 Freundlich isotherms, regression constants (1/n) and mobility coefficients (Koc), were determined as summarized below Freundlich constants were determined as summarized below:

Soil Types

% organic carbon

CEC (meq/100g)

Adsorption

Desorption

Freundlich adsorption isotherm (Kfads)

1/n

(ads)

Adsorption coefficient (Kaoc)

Freundlich desorption isotherm (Kfdes)

1/n

(des)

Desorption coefficient (Kdoc)

Sand

0.1

3.8

6,172

0.899

6,171,657

7173

0.83

7137310

Silt loam

0.5

7.6

10,797

0.94

2,159,346

14083

0.81

2816590

Clay loam

2.0

9.5

32,429

0.79

1,663,039

165556

1.01

8490062

Sandy loam

0.8

20.9

5,123

1.06

640,389

96540

0.95

12067457

OC = organic carbon; ads = adsorption; des = desorption; CEC = Cation exchange capacity

    

 The mean Kfads (referred as Kd in the study report) and Koc values for adsorption were calculated to be 13630 and 2,658,608 L/kg respectively. No apparent degradation of the read across substance occurred in any of the four soils. Under the conditions of the study, the read across substance was considered to have little or no potential for mobility in all the four soil/sediment types and therefore should not pose a probable environmental risk for contamination of ground water (Daly, 1988).  

Description of key information

Based on the results of the read across study, the test substanceis expected to have little or no potential for mobility 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 (30% active and 98.4% radiolabeled purity) using batch equilibrium method, 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-read across 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-read across 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 read across substance remaining adsorbed on the soil was determined by combustion/radio analysis. Although the amount of 14C-read across 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 Freundlich isotherms, regression constants (1/n) and mobility coefficients (Koc), were determined as summarized below Freundlich constants were determined as summarized below:    

Soil Types

% organic carbon

CEC (meq/100g)

Adsorption

Desorption

Freundlich adsorption isotherm (Kfads)

1/n

(ads)

Adsorption coefficient (Kaoc)

Freundlich desorption isotherm (Kfdes)

1/n

(des)

Desorption coefficient (Kdoc)

Sand

0.1

3.8

6,172

0.899

6,171,657

7173

0.83

7137310

Silt loam

0.5

7.6

10,797

0.94

2,159,346

14083

0.81

2816590

Clay loam

2.0

9.5

32,429

0.79

1,663,039

165556

1.01

8490062

Sandy loam

0.8

20.9

5,123

1.06

640,389

96540

0.95

12067457

OC = organic carbon; ads = adsorption; des = desorption; CEC = Cation exchange capacity

The mean Kfads (referred as Kd in the study report) and Koc values for adsorption were calculated to be 13630 and 2,658,608 L/kg respectively. No apparent degradation of the read across substance occurred in any of the four soils. Under the conditions of the study, the read across substance was considered to have little or no potential for mobility in all the four soil/sediment types and 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 (51.7% active in water) using the batch equilibrium, according to OECD Guideline 106, in compliance with GLP. No vehicles were used to dissolve the read across substance. Parallel method was used with separate test vessels for each concentration and time point of measurement. The soil/solution ratio used was 1:100 (0.5 g soil and 50 mL solution). The determination limit of the analytical method was 1.66 mg/L. Based on the high adsorption tendency of the test substance, the minimum test concentration was 20 mg/L for loamy soil and 50 mg/L for loamy sand and silt loam. The concentrations of the active ingredient were determined via spectrophotometry. Two centrifugation tubes with 50 mL of 20 mg/L of test substance in 0.01 M CaCl2 solution were shaken for 20 h at 175 rpm. The mean value of measurements showed a recovery rate of >90% Therefore, the stability of the test substance under the test conditions were assumed. There was no major adsorption on the surface of the centrifugation tube. The amount of substance adsorbed on the soils was calculated from the depletion of the test substance in the solution (indirect method). The read across substance adsorbed onto soil but did not desorb easily for the three soil types used. The correlations coefficients (r2) of the Freundlich isotherms ranged from 0.9592 to 0.9898 for adsorption and 0.988 to 0.9984 for desorption. In addition, the 14C-mass balance for the four soils types ranged from 65-85%. The low recovery rates in loamy sand and silt loam with higher organic carbon content, could be caused by irreversible adsorption of the test substance. The distribution coefficient (Kd), mobility coefficients (Koc), Freundlich isotherms and regression constants (1/n) were determined as summarized below: 

Soil types 

% OC

CEC (meq/100g)

Adsorption

Desorption

Adsorption distribution coefficient (Kdads)

Adsorption coefficient (Kaoc

Freundlich adsorption isotherm (Kfads)

1/n

(ads)

Desorption coefficient (Kddes)

Desorption coefficient (Kdoc

Freundlich desorption isotherm (Kfdes)

1/n

(des)

Loam 

3.45

18.3

390

18251

630

0.733

671

81971

2828

0.535

Loamy sand

9.25

32.7

1556

16679

1543

0.723

4211

73459

6795

0.576

Silt Loam

0.25

11.4

1816

812943

2032

0.771

1971

1111200

2778

0.729

 OC = organic carbon; ads = adsorption; des = desorption; CEC = Cation exchange capacity

The mean Kfads and Koc values for adsorption were calculated to be 1402 and 282,624.3 L/kg respectively. The high concentrations of read across substance used in the study (0.5 g read across 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. Under the study conditions, the read across substance adsorbed onto soil and did not desorb easily for the three soil types used, therefore it could be classified as immobile (Geffke, 1999).

Further, the biocides assessment reports on Coco TMAC and C12-16 ADBAC, which was published by the Italian authorities, concluded that the substances had “little or no potential for mobility in soil and should not pose an environmental risk for contamination of ground water”. And “it was well known that, because of their positive charge, cationic surfactants adsorb strongly to the negatively charged surfaces of sludge, soil and sediments”.For the purpose of risk assessment, a mean Koc value across all soil types and studies was considered in both the assessment reports. For C12-16 ADBAC, a mean value of 1,640,329 L/Kg and for Coco TMAC a mean value of 562,314 L/Kg (based on read across to DDAC) was considered ((ECHA biocides assessment report, 2015, 2016).Therefore, following the same approach as the biocides dossier, the mean Koc value of 1,640,329 L/kg based on Koc values from both the available studies for all soil types, has been used for hazard/risk assessment.