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Adsorption / desorption

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Reference
Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
Study performed according to OECD and GLP guidelines.
Qualifier:
according to guideline
Guideline:
OECD Guideline 121 (Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC))
GLP compliance:
yes (incl. QA statement)
Type of method:
HPLC estimation method
Media:
soil
Specific details on test material used for the study:
Identity: TBzTD
Storate: at room temperature at about 20°C
Batch: 2041 0003
Purity: > 90%
Appearance: solid white to yellowish
Expiration date: October 31. 2006
Radiolabelling:
no
Details on study design: HPLC method:
- HPLC with UV/VIS detector
- reversed phase column
- aqueous mobile phase

The first test to determine the adsorption coefficient (Kod of TBzTD was performed with methanol as organic solvent. Methanol was not sufficient to elute the test item from the column. Referring to this, acetonitrile was used as organic solvent.

- Apparatus: Varian autosampler 9100, Varian pump ProStar 230, Varian UV/VIS detector ProStar 310, Jones column oven 7990
- Column: LiChrospher 100 CN, particle size 5 μm, 250 mm x 4 mm
- Pre-column: CN
- Mobile phase: Acetonitrile/water (55:45; v/v); pH 6.3
- Temperature: 25°C
- Injection volume: 10 μl
- Flow: 1.0 ml/min
- Run time: 10 minutes
Key result
Type:
log Koc
Value:
7.5
Temp.:
25 °C
Details on results (HPLC method):
The chromatography of the test item resulted in one main peak with a weIl-defined and reproducible retention time. The HPLC method was therefore considered to be suitable for the purpose of the study. Based on the chromatographic data, TBzTD was considered to be stable during the test procedure.

The mobility classification of TBzTD was obtained by comparing the calculated Koc value to the mobility classes according to P. J. McCall, D. A. Laskowski, R. L. Swann and H. J. Dishburger "Measurement of Sorption Coefficients of Organic Chemicals and Their Use in Environmental Fate Analysis"; 1981; Assoc. of Off. Anal. Chem., Arlington, VA; p 89 - 109.

ange of Koc  Mobility Class
 0 -50  very high
 50 -150  high
 150 -500  medium
 500 -2000  low
 2000 -5000  slightly
 > 5000  immobile

The test item solution was injected three times and the combined reference solution was injected six times. The log Koc of the test item was extrapolated from a regression curve (log k' vs. log Koc) to be 7.5, which is equal to a Koc value of 31 028 667. The retention time of the test item was higher than the retention time of the highest reference item used (2,4-DDT) with Koc 5.63, which is equal to a Koc value of 426 580. In the present study the reference items covered the range of log Koc 1.25 to log Koc 5.63.

The tabulated values represent rounded mean results, which were obtained by calculation using the exact raw data.

In conclusion, the log of the adsorption coefficient (Kod of TBzTD was estimated to be log Koc > 5.63 which is equal to a Koc value of > 426580 using the HPLC method. This value indicates that TBzTD is immobile and remains preferably in soil.

Table: results of the linear regression of Log k' vs Log Koc

No. of analysis   Mean retention time (min)  k'  log k'  log Koc
 Sodium nitrate (dead time) 2 1.12   -  -  -
 Reference items:          
 Acetanilide  6  2.80  1.50  0.17  1.25
 Isoproturon  6  3.22  1.86  0.27  1.86
 Linuron  6  3.55  2.16  0.34  2.59
 Pyrazophos  6  3.98  2.55  0.41  3.65
 Diclofop-methyl  6  5.54  3.04  0.48  4.20
 2.4 -DDT  6  5.57  3.96  0.60  5.63

Linear regression: slope (= 0.093), y-axis intercept (= 0.080), coefficient of regression (r = 0.994)

Table: Results of TBzTD analysis

 No. of analysis  retention time (min)  k'  log k'  log Koc  mean log Koc Koc   Mean Koc
 Test Item Peak              
 1  7.80  5.95  0.77417  7.45    28434088  
 2  7.99  6.11  0.78630  7.58    38382018  
 3  7.75  5.90  0.77097  7.42  7.5 26269895  31028667
Conclusions:
In conclusion, the log of the adsorption coefficient (Kod of TBzTD was estimated to be log Koc > 5.63 which is equal to a Koc value of > 426580 using the HPLC method. This value indicates that TBzTD is immobile and remains preferably in soil.

Description of key information

The log of the adsorption coefficient (Koc) of the test item was extrapolated from a regression curve (log k' vs. log Koc) to be 7.5, which is equal to a Koc value of 31028667. This value indicates that TBzTD is immobile and remains preferably in soil.

Key value for chemical safety assessment

Koc at 20 °C:
31 028 667

Additional information

In the present study using the High Performance Liquid Chromatography (HPLC) estimation method on Soil and Sewage Sludge the log of the adsorption coefficient (Koc) of the test item was extrapolated from a regression curve (log k' vs. log Koc) to be 7.5, which is equal to a Koc value of 31028667. The reference items covered the range of log Koc 1.25 to log Koc 5.63. Therefore, the retention time of the test item was higher than the retention time of the highest reference item used (2,4-DDT) with log Koc 5.63, which is equal to a Koc value of 426580. In conclusion the log Koc of TBzTD was judged to be log Koc > 5.63 which is equal to a Koc value of > 426580. This value indicates that TBzTD is immobile and remains preferably in soil.

[LogKoc: 7.5]

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