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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
Study period:
2010
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study
Reason / purpose for cross-reference:
reference to same study
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))
Deviations:
no
Principles of method if other than guideline:
n/a
GLP compliance:
yes
Type of method:
HPLC estimation method
Media:
soil/sewage sludge
Specific details on test material used for the study:
The Dow Chemical Company, Freeport, Texas (Lot# XA2355T643)
non-GLP certificate of analysis indicates purity of > 99% DIBK and DIBK isomers

Details on properties of test surrogate or analogue material (migrated information):
Reference substances applied as recommended in OECD 121. An additional reference subsance, acetophenone, was used to evaluate accuracy of the estimation method for a similar ketone substance.
Radiolabelling:
no
Test temperature:
25
Details on study design: HPLC method:
a calibration solution was prepared which contained the recommended reference substances, and this was analyzed in duplicate, followed by duplicate analyses of a standard solution of the test substance. Finally, the calibration solution was again analyzed in duplicate.
Retention times (tR) for each of the reference substances were determined based on for the HPLC assay was determined from duplicate analyses of a solution containing urea, a substance that is not retained on the HPLC column under the test conditions. Standard solutions of the test substance, prepared in methanol/water compositions similar to that of the HPLC eluents, were analyzed immediately following their preparation to avoid any possible degradation of the test substance. The concentrations of the test and reference substances were minimized to avoid the potential for overloading the HPLC column, yet allowing adequate sensitivity for detection in the HPLC assay. The DIBK concentrations in the analyzed standard solutions were approximately 118 and 189 mg/L in the Pow and Koc assays, respectively. Reference substance concentrations in the calibration solutions ranged from approximately 50 to 94.5 mg/L for both assays. To ensure the reproducibility of substance retention times in the HPLC assay, the HPLC columns were covered with foam insulation to minimize temperature changes. The air temperature next to the column was recorded during the analyses using a Lascar data logger.
Details on sampling:
not applicable
Details on matrix:
not applicable
Details on test conditions:
The HPLC column was jacketed with insulating foam to minimize fluctuation in its temperature during the separation of the reference and test substances. The average air temperatures near the HPLC column during the Koc assay was 24.4 ± 0.5°C. Therefore, temperature fluctuations were not expected to have influenced the precision of the HPLC-estimated values for Koc.
Computational methods:
The HPLC capacity factors (k’) for the reference and test substances in the HPLC assay was determined from the retention times for the compounds (tR) and the dead time (to) for the HPLC column using the following formula:
k’ = (tR-to)/to (Note: tR and to were recorded in minutes)
The dead time (to) for the HPLC assay is the average time for a non-retained solvent molecule to pass through the HPLC system. The log k’ data for the reference substances were plotted against their measured log Koc values, and the least-squares linear regression line for this relationship was determined. The estimated log Koc value for the test substance was determined from its measured capacity factor using the equation for the fitted regression line.
Type:
log Koc
Value:
2.07 dimensionless
Temp.:
25 °C
Remarks on result:
other: % org. carbon not applicable to HPLC method
Details on results (HPLC method):
The Log Koc value for DIBK was estimated based on its chromatographic retention time in a standard HPLC assay following the OECD 121 guideline. The test substance eluted as a single chromatographic peak, having a retention time of 3.03 minutes, which correlates to an estimated log Koc of 2.07.
Adsorption and desorption constants:
not applicable
Recovery of test material:
not applicable
Concentration of test substance at end of adsorption equilibration period:
not applicable
Concentration of test substance at end of desorption equilibration period:
not applicable
Details on results (Batch equilibrium method):
not applicable
Statistics:
not applicable

The OECD Guideline 121 states that, by using this method, the adsorption coefficient of a test substance can be estimated to within ± 0.5 log units of the value determined by the batch equilibrium method. Higher accuracy may be achieved if the reference substances used are structurally related to the test substance. The accuracy of this HPLC assay in estimating log Koc of DIBK and related substances was demonstrated through analysis of an additional reference substance (acetophenone). The analysis of acetophenone

provided a chromatographic peak with a retention time of 2.85 minutes and an associated log Koc of 1.81. The measured Koc for acetophenone is 1.80 (Meylan et al., 1992). These results indicate that the standard HPLC assay provides accurate estimations of Koc for this family of compounds (ketones), which is within the predictive accuracy reported by OECD (± 0.5 log Koc units).

Validity criteria fulfilled:
yes
Conclusions:
The Log Koc value for DIBK was estimated based on its chromatographic retention time in a standard HPLC assay following the OECD 121 guideline. The test substance eluted as a single chromatographic peak, having a retention time of 3.03 minutes, which correlates to an estimated log Koc of 2.07. The substance does not have a high affinity for adsorption to organic matter of sewage sludge, soil, or sediments.
Executive summary:

The Log Koc value for DIBK was estimated based on its chromatographic retention time in a standard HPLC assay following the OECD 121 guideline. The test substance eluted as a single chromatographic peak, having a retention time of 3.03 minutes, which correlates to an estimated log Koc of 2.07. The substance does not have a high affinity for adsorption to organic matter of sewage sludge, soil, or sediments.

Description of key information

The estimated organic carbon-normalized adsorption coefficient (log Koc) is 2.07, which indicates a low potential for adsorption to and accumulation in sewage sludge, soil, and aquatic sediments.

Key value for chemical safety assessment

Koc at 20 °C:
117

Additional information

The Log Koc value for DIBK was estimated based on its chromatographic retention time in a standard HPLC assay following the OECD 121 guideline. The test substance eluted as a single chromatographic peak, having a retention time of 3.03 minutes, which correlates to an estimated log Koc of 2.07. The predicted log Koc of 2.07 indicates a low potential for adsorption to, and accumulation in, sewage sludge, soil, and aquatic sediments. This potential for adsorption and accumulation is further reduced by the potential for rapid and complete biodegradation of the readily biodegradable substance.