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Environmental fate & pathways

Adsorption / desorption

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Reference
Endpoint:
adsorption / desorption, other
Remarks:
adsorption
Type of information:
experimental study
Adequacy of study:
key study
Study period:
Published 1985, subsurface samples used for the study collected in April 1982
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)
Version / remarks:
January 2000
Principles of method if other than guideline:
Sorption of organic contaminants to a low carbon subsurface core using a batch equilibrium method.
GLP compliance:
no
Type of method:
batch equilibrium method
Media:
soil
Specific details on test material used for the study:
radio-labelled C-14 2-Chlorotoluene was obtained from Pathfinders Laboratories, Inc.; St.Louis, Missouri. Purity not specified.
Specific activity of 2-chlorotoluene: 9.0 mci/mmol
Radiolabelling:
yes
Test temperature:
ambient temperature
Analytical monitoring:
yes
Details on matrix:
For Details on matrix, please see section "Any other information on materials and methods incl. tables".
Details on test conditions:
Please see section "Any other information on materials and methods incl. tables".
Duration:
23 h
Remarks:
Increasing mixing times up to 94 hr produced slight and inconsistent increases in distribution coefficients. Therefore, the duration was limited to 23 h.
Key result
Type:
log Koc
Value:
2.54
pH:
5.6
Temp.:
22 °C
Matrix:
Soil cores No 1 through 20; pH_min 4.4; pH_max 6.1; pH geometric mean: 5.6; ambient temperature
% Org. carbon:
>= 0.12 - <= 0.89
Remarks on result:
other: Direct method (solids extraction)
Key result
Type:
Koc
Remarks:
Geometric mean value over 20 values from 20 soil cores of depths between zero and 627 cm
Value:
344.4 L/kg
pH:
5.6
Temp.:
22 °C
Matrix:
Soil cores No 1 through 20; pH_min 4.4; pH_max 6.1; pH geometric mean: 5.6; ambient temperature
% Org. carbon:
>= 0.12 - <= 0.89
Remarks on result:
other: Direct method (solids extraction)
Type:
Koc
Value:
>= 170 - <= 880
pH:
5.6
Temp.:
22 °C
Matrix:
Soil cores No 1 through 20; pH_min 4.4; pH_max 6.1; pH geometric mean: 5.6; ambient temperature
% Org. carbon:
>= 0.12 - <= 0.89
Remarks on result:
other: Direct method (solids extraction)
Adsorption and desorption constants:
For details, please see section "Any other information on results incl. tables".
Recovery of test material:
Not reported
Concentration of test substance at end of adsorption equilibration period:
Not reported
Concentration of test substance at end of desorption equilibration period:
Desorption not assessed
Transformation products:
no
Remarks:
No specific analytical analysis but determination of 14C-labelled test item via scintillation counting. Transformation not expected due to stability of test item.
Details on results (Batch equilibrium method):
See section "Any other information on results including tables".

Due to the relatively low adsorption of the test item together with the low soil to solution ratio, adsorption results determined via the indirect method from the solution phase proved to be pronouncedly less reliable compared to results based on the direct method (extraction of solid phase). While the following results table gives results according to both methods, in line with the authors´conclusions only the values determined via the direct method will be used for hazard and risk assessment of 2-chlorotoluene.

Isotherm parameters determined fro 2-chlorotoluene - K and Koc values are given in L/kg:

  Solution phase   Extracted phase (direct method, preferred for the test item)
Soil K r2 Koc K r2 Koc      
1 1.8 0.77 380 1.4 0.99 290      
3 1.0 0.74 260 1.3 0.98 340      
4 2.7 0.74 1000 0.9 0.99 330      
5 2.3 0.75 820 0.9 0.99 320      
6 1.7 0.80 440 2.0 0.99 510      
7 3.7 0.92 420 2.6 0.99 290      
8 0.5 0.57 120 1.3 0.92 320      
9 1.1 0.49 280 1.6 0.99 410      
10 1.3 0.82 680 1.0 0.99 530      
11 0.7 0.57 470 0.4 0.98 270      
12 1.6 0.93 890 0.3 0.96 170      
13 1.0 0.88 590 0.3 0.87 180      
14 1.4 0.60 1750 0.7 0.98 880      
15 0.5 0.71 380 0.3 0.94 230      
16 1.8 0.66 1290 0.6 0.99 430      
17 1.5 0.86 1250 0.5 0.99 420      
18 2.0 0.67 1330 0.7 0.98 470      
19 1.5 0.59 650 0.8 0.90 350      
20 2.6 0.90 790 1.0 0.98 300      

 

 

Validity criteria fulfilled:
not specified
Remarks:
No guideline study but a valid scientific publication; accordingly, validity criteria were not assessed.
Conclusions:
The adsorption of 2-chlorotoluen to soil was determined similar / equivalent to OECD TG 106 (batch equilibrium method) as the geometric mean Koc over 19 soil samples of differential depth (0-675 cm) at a geometric mean TOC concentration of 0.2 %. Adsorption was well correlated with the TOC of soil samples.
Koc = 344 L/kg
log Koc = 2.54
Executive summary:

Soil adsorption of 2-chlorotoluene was reliably assessed in a well-documented scientific study (peer reviewed publication; Banerjee et al., 1985) using 14C-radiolabelled test item. The method followed (batch equilibrium) was similar / equivalent to OECD TG 106.
20 subsurface soil samples were collected in a river alluvial plain, each core of 50 cm length, covering semi-continuously a depth of 0 to 675 cm.
Four to five replicates were prepared at each of five test item concentrations (prepared from 0.01M CaCl2 solution) at a soil:solution ratio of 1:25 (later modified to 2:25) without headspace. Tubes were mixed by tumbling for 23 hours at 360 inversions/hr. Adsorption was quantified both, via the indirect method (solution phase) and the direct method, while the latter was found pronouncedly more reliable (and used for reporting) considering the rather low adsorption at rather low soil:solution ratio. For the direct method the solids phase was extracted two times directly with scintillation cocktail and counted. This extraction procedure was verified to be quantitative. The data obtained (direct method) from equilibrium batch sorption isotherms were fit to a linear distribution equation to derive the distribution coefficient K (L/kg) and subsequently (based on the determined TOC content of soil core samples) the Koc.
Overall, Koc values could be determined for 19 soil samples of different depth with values ranging from 170 to 880 L/kg at TOC concentrations ranging from 0.08% to 0.89%. The distribution coefficient K was well correlated with the TOC of soil samples (correlation coefficient 0.82).
Conclusion:
The adsorption of 2-chlorotoluen to soil was determined as the geometric mean Koc over 19 soil samples of differential depth (0-675 cm) at a geometric mean TOC concentration of 0.2 %:
Koc = 344 L/kg
log Koc = 2.54

Description of key information

The adsorption of 2-chlorotoluen to soil was determined similar / equivalent to OECD TG 106 (batch equilibrium method) as the geometric mean Koc over 19 soil samples of differential depth (0-675 cm) at a geometric mean TOC concentration of 0.2 %. Adsorption was well correlated with the TOC of soil samples.
Koc = 344 L/kg
log Koc = 2.54

Key value for chemical safety assessment

Koc at 20 °C:
344.4

Additional information

Soil adsorption of 2-chlorotoluene was reliably assessed in a well-documented scientific study (peer reviewed publication; Banerjee et al., 1985) using 14C-radiolabelled test item. The method followed (batch equilibrium) was similar / equivalent to OECD TG 106.
20 subsurface soil samples were collected in a river alluvial plain, each core of 50 cm length, covering semi-continuously a depth of 0 to 675 cm.
Four to five replicates were prepared at each of five test item concentrations (prepared from 0.01M CaCl2 solution) at a soil:solution ratio of 1:25 (later modified to 2:25) without headspace. Tubes were mixed by tumbling for 23 hours at 360 inversions/hr. Adsorption was quantified both, via the indirect method (solution phase) and the direct method, while the latter was found pronouncedly more reliable (and used for reporting) considering the rather low adsorption at rather low soil:solution ratio. For the direct method the solids phase was extracted two times directly with scintillation cocktail and counted. This extraction procedure was verified to be quantitative. The data obtained (direct method) from equilibrium batch sorption isotherms were fit to a linear distribution equation to derive the distribution coefficient K (L/kg) and subsequently (based on the determined TOC content of soil core samples) the Koc.
Overall, Koc values could be determined for 19 soil samples of different depth with values ranging from 170 to 880 L/kg at TOC concentrations ranging from 0.08% to 0.89%. The distribution coefficient K was well correlated with the TOC of soil samples (correlation coefficient 0.82).
Conclusion:
The adsorption of 2-chlorotoluene to soil was determined as the geometric mean Koc over 19 soil samples of differential depth (0-675 cm) at a geometric mean TOC concentration of 0.2 %:
Koc = 344 L/kg
log Koc = 2.54