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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:
other: This study was conducted under GLPs. There were no deviations.
Qualifier:
according to
Guideline:
OECD Guideline 121 (Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC))
Deviations:
no
GLP compliance:
yes
Type of method:
HPLC estimation method
Media:
soil/sewage sludge
Radiolabelling:
no
Details on study design: HPLC method:
A standard solution for calibration was prepared which contained the reference compounds. The calibration standard was analyzed in duplicate, followed by duplicate analyses of the test material. Finally, the calibration standard was again analyzed in duplicate. Retention times (tR) for each of the reference compounds were determined based on detection of chromatographic peaks in the refractive index detector (RID). Assignments of chromatographic peaks to the reference compounds were confirmed by analysis of single component standards and detection of chromatographic peaks in the RID. The dead time (to) for the HPLC assay was determined from duplicate analyses of a solution containing urea, a substance recommended in the test guideline as one which is not retained on the HPLC column under the test conditions. Stock solutions of the test substance, BADGE, and IPD were prepared in methanol and diluted in methanol/water (55%/45%; v/v) for analysis, which was performed using duplicate samples. The concentrations of the test and reference compounds were minimized to avoid the potential for overloading the HPLC column, yet allowing adequate sensitivity for detection in the HPLC assay. The concentration of BADGE-MXDA (#42) in the test solution was 200 milligrams per liter (mg/L). Reference compound concentrations in the standard solution were 50 mg/L per compound. The concentrations of urea, BADGE, and IPD in the analyzed solutions were each 200 mg/L. To ensure the reproducibility of compound retention times in the HPLC assay, a constant temperature of 30°C was maintained by the HPLC column heater.
Computational methods:
The HPLC capacity factor (k’) for reference materials and the test materials in the HPLC assay was determined from the retention time for the compounds (tR) and the dead time (to) for the column using the following formula: k’ = (tR-to)/to (Note: tR and to are measured in minutes). The log k’ data for the reference materials was plotted against their log Koc values and a linear regression line determined. Estimated log Koc values for the test materials were determined from their measured capacity factor using the equation for the fitted regression line, and a weighted average was taken.
Type:
log Koc
Value:
10.51 dimensionless
Temp.:
30 °C
Details on results (HPLC method):
The Log Koc values for components of BADGE-MXDA were estimated based on chromatographic retention times in a standard HPLC assay, following the OECD 121 guidelines. The HPLC assay was performed under both buffered and non-buffered mobile phase conditions. Log Koc estimations provided under buffered mobile phase conditions are preferred in this case due to (a) improved chromatographic peak resolution, (b) better conformance with estimated Koc values for MXDA amine, and (c) conformance with the OECD-recommended procedure for such estimations of ionizable substances.
BADGE: Under buffered mobile phase conditions, the potential test substance component (reactant) BADGE eluted as one major peak with an average retention time of 4.02 minutes. This retention time corresponds to an average estimated Koc value of 3.91, which is similar to that predicted for BADGE by KOCWIN (predicted log Koc of 3.81).
MXDA amine: Under buffered mobile phase conditions, MXDA amine eluted as one major and one minor peak. The major peak had an average retention time of 2.68 minutes, corresponding to an average estimated log Koc value of 3.30. This value is similar to the log Koc value predicted for MXDA amine by the KOCWIN program (predicted log Koc value = 2.71). The minor peak detected for MXDA amine had an average retention time of 1.72 minutes, corresponding to an average estimated log Koc value of 2.48. This peak may represent the presence of an impurity in the MXDA amine substance.
BADGE-MXDA (#42): Under buffered mobile phase conditions, the test substance eluted as three chromatographic peaks (one major, two minor). The average retention time for the major peak was 2.71 minutes, which corresponds to an estimated average log Koc value of 3.32. Retention time characteristics for this peak were similar to major chromatographic peak observed for MXDA amine, which is present in the test substance at 35.3% wt (Harfmann, 2012). Therefore, the major detected peak in BADGE-MXDA (#42) was attributed to the presence of unreacted MXDA amine. The two minor chromatographic peaks detected for BADGE-MXDA had average retention times of 1.70 and 9.03 minutes. The peak at 1.70 minutes had a retention time similar to the minor peak detected in the MXDA amine sample. This peak may therefore represent an impurity present in both MXDA amine and BADGE-MXDA (#42). The peak with an average retention time of 9.03 minutes corresponds to an average estimated log Koc value of 4.98, which is significantly lower than log Koc values predicted for products of the BADGE-MXDA adduct (see below). This peak was also not present in chromatograms for BADGE or MXDA amine. These factors, combined with the detection of this peak at a low percentage of the total detected peak area after integration, suggest this peak may correspond to another impurity present in BADGE-MXDA. Peaks with similar retention time characteristics to the major BADGE peak were not detected in BADGE-MXDA, and unreacted BADGE is not expected to be present in the test substance (Harfmann, 2012). The absence of BADGE in the test substance sample is consistent with the excess MXDA in the sample, which would readily react with BADGE if it were present.
BADGE MXDA adduct: BADGE-MXDA (#42) components representing products of the BADGE-MXDA adduct were not detected in this study. BADGE-MXDA is expected to retain structural features of BADGE and MXDA amine, and should be similarly detectable at the reference wavelength of 210 nm. Furthermore, chromatograms for BADGE-MXDA do not indicate elution of the test substance in the void volume. These observations suggest that the retention time of adduct products present in BADGE-MXDA was longer than could be observed under study conditions. Therefore, the BADGE-MXDA adducts present in BADGE-MXDA are estimated to have a log Koc higher than 5.63, the value attributed to DDT, which is the latest-eluting of the reference substances used.
Validity criteria fulfilled:
yes
Conclusions:
Three chromatographic peaks (one major, two minor) were observed for the HPLC-based estimation of log Koc values for the components of BADGE-MXDA. The major peak had an average estimated log Koc value of 3.32, and corresponded to the presence of unreacted MXDA amine in the test substance. The two minor peaks were associated with impurities present in the test material. BADGE-MXDA adduct products were not observed to elute in the HPLC assay, which suggests that these components have retention times longer than that of DDT under assay conditions and a log Koc of >6.59 which would correspond to the 35 minute run time of the HPLC assay.
As a surrogate, log Koc values for BADGE-MXDA adducts were calculated using the estimated log Koc values determined in the HPLC assay for BADGE and MXDA. This analysis calculates a log Koc of 10.51 for the smallest adduct product. This calculation is generally supported by quantitative structural activity relationship (QSAR) analyses of the BADGE-MXDA adduct structures, which have predicted log Koc values ≥ 6.67 (USEPA, 2010).
Executive summary:

The soil adsorption coefficients (Koc) for components of BADGE-MXDA were estimated using Organisation for Economic Co-operation and Development (OECD) Guideline 121: “Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC)”. This method compares the retention time of the test substance in a defined HPLC assay to the retention times of a series of reference substances with known Koc values. The reference substances utilized for this study included acetanilide, methyl benzoate, naphthalene, 1,2,3-trichlorobenzene, phenanthrene and DDT.

A linear regression line for reference substances was determined using the log k’ data plotted against the known log Koc values. The k’ value is the HPLC capacity factor that is derived from the retention time for a substance, corrected for the dead volume in the HPLC column. The Koc values of the test substance components are then determined from their measured HPLC capacity factors using the equation for the fitted regression line.

Three chromatographic peaks (one major, two minor) were observed for BADGE-MXDA. The major peak had an average estimated log Koc value of 3.32, and corresponded to unreacted MXDA amine in the test substance. The two minor peaks were concluded to be associated with impurities present in the test material. BADGE-MXDA adduct products were not observed the HPLC assay, which suggest that these components had a retention time longer than that of DDT under assay conditions and longer than the maximum elution time. BADGE-MXDA adducts are therefore estimated to have a log Koc value >5.63 (the log Koc value of DDT), and likely > 6.59 (the estimated log Koc value corresponding to the maximum elution time of the HPLC assay). As a surrogate, log Koc values for BADGE-MXDA adducts were estimated as the sum of the log Koc of the fragments BADGE and MXDA. Based on this calculation the log Koc for the BADGE-MXDA adduct (n = 0) calculates to 10.51.

Description of key information

A single study: ESTIMATION OF THE SOIL ADSORPTION COEFFICIENT (Koc) USING THE OECD GUIDELINE 121- HPLC METHOD
Log Koc is calculated from experimentally determined log Koc of moieties of BADGE MXDA adduct.

Key value for chemical safety assessment

Koc at 20 °C:
31 600 000 000

Other adsorption coefficients

Type:
log Kp (solids-water in soil)
Value in L/kg:
8.8
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in sediment)
Value in L/kg:
9.2
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in suspended matter)
Value in L/kg:
9.5
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in raw sewage sludge)
Value in L/kg:
9.98
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in settled sewage sludge)
Value in L/kg:
9.98
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in activated sewage sludge)
Value in L/kg:
10.07
at the temperature of:
20 °C

Other adsorption coefficients

Type:
log Kp (solids-water in effluent sewage sludge)
Value in L/kg:
10.07
at the temperature of:
20 °C

Additional information

The soil adsorption coefficients (Koc) for components of BADGE-MXDA were estimated using Organisation for Economic Co-operation and Development (OECD) Guideline 121: “Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC)”. This method compares the retention time of the test substance in a defined HPLC assay to the retention times of a series of reference substances with known Koc values. The reference substances utilized for this study included acetanilide, methyl benzoate, naphthalene, 1,2,3-trichlorobenzene, phenanthrene and DDT.

A linear regression line for reference substances was determined using the log k’ data plotted against the known log Koc values. The k’ value is the HPLC capacity factor that is derived from the retention time for a substance, corrected for the dead volume in the HPLC column. The Koc values of the test substance components are then determined from their measured HPLC capacity factors using the equation for the fitted regression line.

Three chromatographic peaks (one major, two minor) were observed for BADGE-MXDA. The major peak had an average estimated log Koc value of 3.32, and corresponded to unreacted MXDA amine in the test substance. The two minor peaks were concluded to be associated with impurities present in the test material. BADGE-MXDA adduct products were not observed the HPLC assay, which suggest that these components had a retention time longer than that of DDT under assay conditions and longer than the maximum elution time. BADGE-MXDA adducts are therefore estimated to have a log Koc value >5.63 (the log Koc value of DDT), and likely > 6.59 (the estimated log Koc value corresponding to the maximum elution time of the HPLC assay). As a surrogate, log Koc values for BADGE-MXDA adducts were estimated as the sum of the log Koc of the fragments BADGE and MXDA. Based on this calculation the log Koc for the BADGE-MXDA adduct (n = 0) calculates to 10.51.

[LogKoc: 10.5]