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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:
12 Nov 2018 to 17 Dec 2018
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
EU Method C.19 (Estimation of the Adsorption Coefficient (KOC) on Soil and Sewage Sludge Using High Performance Liquid Chromatography (HPLC))
Version / remarks:
March 04, 2016
Deviations:
no
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))
Version / remarks:
January 22, 2001
Deviations:
no
Qualifier:
according to guideline
Guideline:
other: EC Technical Guidance Document on Risk Assessment Part III Chapter 4.3: Use of (Quantitative) Structure Activity Relationships ((Q)SARs) - Soil and Sediment Sorption
Version / remarks:
2003
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Type of method:
HPLC estimation method
Media:
soil
Specific details on test material used for the study:
Appearance: Yellow powder
Purity/Composition: 98.25%
Test item storage: At room temperature protected from light desiccated
Radiolabelling:
no
Test temperature:
35°C ± 1°C
Details on study design: HPLC method:
Instrument: Acquity UPLC system (Waters, Milford, MA, USA)

Detector: Acquity UPLC TUV detector (Waters)

Column: Acquity UPLC HSS Cyano, 100 mm × 2.1 mm i.d., dp = 1.8 µm (Waters)

Column temperature: 35°C ± 1°C

Injection volume: 5 µL

Mobile phase: 55/45 (v/v) methanol/buffer pH 2 or 55/45 (v/v) methanol/buffer pH 7

Flow: 0.4 mL/min

UV detection: 210 nm
Analytical monitoring:
no
Type:
Koc
Value:
1 500 dimensionless
pH:
2
Temp.:
35 °C
Type:
log Koc
Value:
3.17 dimensionless
pH:
2
Temp.:
35 °C
Key result
Type:
Koc
Value:
< 18 dimensionless
pH:
7
Temp.:
35 °C
Key result
Type:
log Koc
Value:
< 1.26 dimensionless
pH:
7
Temp.:
35 °C

pKa Values

No pKa values for basic groups in the molecular structure of the test item in the logarithm range of 1 - 14 were calculated.

The pKa values in the logarithm range of 1 - 14 for acidic groups in the molecular structure of the test item were calculated using the Perrin calculation method.  The results are given in Table 12.

Table 12       

pKa Values of the Test Item

Acidic
RC6H4OCH2COOH pKa3.0

Koc HPLC Method – pH 2

UPLC-UV chromatograms of the test item solution and corresponding blank are shown in Figure 10 and Figure 11, respectively.  In the chromatogram of the test solution, one major peak was observed.

The results of the HPLC method are given in Table 13.  Figure 12 shows the calibration curve of the log k’ of the reference substances as function of log Koc.  The equation of the regression line was: log k’ = 0.327 ´ log Koc – 0.785 (r = 0.98, n = 14).

Table 13       

pH 2:  Koc of the Test Item

Substance Retention time (min) log Koc Koc
tr,1 tr,2 mean
Formamide (t0) 0.698 0.698 0.698    
Acetanilide 0.939 0.941   1.26  
Monuron 1.176 1.178   1.99  
Naphthalene 1.61 1.614   2.75  
Benzoic acid phenylester 1.895 1.903   2.87  
Fenthion 2.631 2.646   3.31  
Phenanthrene 2.93 2.946   4.09  
4,4’-DDT 7.57 7.654   5.63  
Test item 1.952 1.946 1.949 3.17 1.5× 103

Koc HPLC Method – pH 7

UPLC-UV chromatograms of the test item solution and the corresponding blank are shown in Figure 13 and Figure 14, respectively.  In the chromatogram of the test item solution, one peak with a mean retention time of 0.592 minutes was observed.  Under the same analytical conditions, the mean retention time of acetanilide (log Koc = 1.26) was 0.937 minutes.  It was concluded that the log Koc of test item was < 1.26 (Koc < 1.82 × 101).

Table 14       

pH 7:  Koc of the Test Item

Substance Retention time (min) log Koc Koc
tr,1 tr,2 mean
Acetanilide 0.937 0.937 0.937 1.26  
Test item 0.591 0.592 0.592 < 1.26 < 1.8× 101
Validity criteria fulfilled:
yes
Conclusions:
The HPLC method using soil-adsorption-reference data was applied for the determination of the adsorption coefficient (Koc) of CMTX 2-carboxymethyloxy-thioxanthone.
The Koc and log Koc values of the test item at pH 2 and pH 7 were:

pH 2: Koc = 1.5E3, log Koc = 3.17
pH 7: Koc < 18, log Koc < 1.26
Executive summary:

In this guideline (OECD 121) study conducted with GLP certification, the test material (EC 282-803-8) was determined to have the following adsorption coefficients:

  pH 2 pH 7
Koc log Koc Koc log Koc
Test item 1.5× 103 3.17 < 1.8× 101 <1.26

Description of key information

Study conducted to recognised testing guidelines with GLP certification.

Key value for chemical safety assessment

Koc at 20 °C:
18

Additional information

  pH 2 pH 7
Koc log Koc Koc log Koc
Test item 1.5´103 3.17 < 1.8´101 <1.26