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Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2011-05-30 till 2011-06-28
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP guideline study
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
Principles of method if other than guideline:
The adsorption coefficient (K) is a partition coefficient and is defined as the ratio of the equilibrium concentrations of a dissolved substance in a two-phase system consisting of a sorbent (soil or sewage sludge) and an aqueous phase.
Koc = C soil (Suldge) / C water
HPLC is performed on analytical columns packed with a commercially available cyano soil phase chemically bound onto silica. Chemicals injected onto such a column move along it by partitioning between the mobile solvent phase and the stationary cyano-phase. The chemicals are retained in proportion to their solid phase/water partition coefficient, with water-soluble chemicals eluted first and soil (sludge)-soluble chemicals last. This enables the relationship between the retention time on a cyano phase column and the soil(suldge)/water adsorption coefficient to be established. The adsorption coefficient is deduced from the capacity factor (k), given by the expression where, tR is the retention time of the test item, and t0 is the dead-time, i.e. the average time a solvent molecule needs to pass the column. Quantitative analytical methods are not required; only the determition of retention times is necessary.
The HPLC method enables adsorption coefficient to be estimated in the log Koc range between 1.5 and 5. The pH value has a significant influeence on sorption behavior in particular for polar substances. For agricultural soils or tanks of sewage treatment olants pH normally varies between pH 5.5 and 7.5. For this reason the test is performed at pH 6 (e.g. by adding citrate buffer to the mobile phase).
In case than 10 % of the test item is dissociated at pH 6, a second test has to be performed at a pH where the test item is undissociated.
GLP compliance:
yes (incl. certificate)
Type of method:
HPLC estimation method
Media:
soil/sewage sludge
Radiolabelling:
no
Test temperature:
Remark:
In order to ensure a stable performance of the HPLC column, the column temperature was set to 40 °C. The reference Koc-values in the OECD guideline presumably refer to 25 °C. Even through the column temperature was 40 °C, this temperature has no influence on the result of the determination. Therefore the Koc-value of the test item determined within this study als refer to 25 °C.
Details on study design: HPLC method:
HPLC-method parameters
- Equipment: HPLC Agilent 1200
- Column: LiChrospher 100 CN, 250 nm lenght, 4 mm interal diameter, 5 µm particle size
- Eluent A: water (demineralized)
- Eluent B: acetonitrile (Fa. Merck, gradient grade, Art. no.: 1.00030
- Solvent program: Isocratic 45 % A and 55 % B
- Flow: 1 mL/min
- Column temperature: 40 °C
- Injection volume: 3 µL
- Detector: UV, 220 nm
Analytical monitoring:
no
Details on sampling:
The test concentration was 0.05 mg/mL.
Details on test conditions:
Determination of the pH-value of the aqueous part of the mobile phase
Procedure: The pH determination of the aqueous part of the mobile phase was done with a pH meter equipped with a calibrated single-rod glass electrode.
Result: pH 6.3

Determination of the adsorption coefficient
Preparation of the test solutions:
The calibration substances solutions were dissolved in a mixture of 10 % water and 90 % acetonitrile. The concentrations of the calibration substances after dilution with acetonitrile to the measuring concentration were between 0.05 mg/mL and 0.42 mg/mL.
The solution for the determination of the dead time was prepared by dissolving sodium nitrate in a mixture of 10 % water and 90 % acetonitrile. The
sodium nitrate solution was diluted to a final concentration of 0.12 mg/mL with acetonitrile.
The test item was dissolved in acetonitrile. The concentration of the test item after dilution with acetonitrile to the measuring concentration was 0.05 mg/mL.
Type:
log Koc
Value:
1.9
Temp.:
25 °C

Calibration and determination of the test item

 Calibration substance/ Test item

 Retention time tR in min Test 1

   Retention time tR in min Test 2

   Retention time tR in min Test 3

 Retention time tR in min Mean value

 Capacity factor K'

 log K'  log Koc
 Sodium nitrate (dead time t0)  2.501  2.502  2.503  2.503  -  -  -
 2-Nitrobenzamide  4.357   4.357   4.357   4.357  0.741  -0.130  1.45
 3-Nitrobenzamide 4.500    4.500    4.501    4.500   0.799  -0.097  1.95
3,5-Dinitrobenzamide   4.880   4.880  4.880    4.880  0.950  -0.022  2.31
 Fenthion 13.685    13.685   13.686   13.685  4.470  0.650  3.31
 Phenanthrene 15.312    15.312  15.312    15.312 5.120   0.790  4.09
 Diclofop-methyl 22.396   22.397   22.397   22.397 7.952   0.900  4.20
 1,3-dihydro-4(or 5)- methyl-2H-benzimida- zole-2-thione 4.633   4.633  4.634  4.633  0.852  -0.070  1.9
Validity criteria fulfilled:
not specified
Conclusions:
The adsorption coefficient of the test item is deteminined to be: log Koc = 1.9 or Koc = 79 L/kg.
Executive summary:

The adsorption coefficient of 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione was tested according to OECD Guideline 121 (Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC)). The adsorption coefficient of the test item is deteminined to be: log Koc = 1.9 or Koc = 79 L/kg.

Endpoint:
adsorption / desorption: screening
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
REPORTING FORMAT FOR THE ANALOGUE APPROACH
Refer to Section 13.2 for read-across justification document.
Reason / purpose:
read-across source
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
Type:
log Koc
Value:
1.9
Temp.:
25 °C
Conclusions:
The adsorption coefficient of the test item is deteminined to be: log Koc = 1.9 or Koc = 79 L/kg.
Executive summary:

In a one-to-one read-across approach, the substance 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione (source substance) is considered appropriate for direct read-across (one-to-one) to zinc 4-methyl-2-thioxo-2,3-dihydrobenzimidazol-1-ide 7-methyl-2-thioxo-2,3-dihydrobenzimidazol-1-ide (target substance) for the endpoint adsorption / desorption.

The adsorption coefficient of 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione was tested according to OECD Guideline 121 (Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC)). The adsorption coefficient of the test item is deteminined to be: log Koc = 1.9 or Koc = 79 L/kg.

A full justification for the read-across approach is presented in IUCLID Section 13.2.

Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
February 2013
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Conducted according to OECD test guidelines and to GLP.
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 (incl. certificate)
Type of method:
HPLC estimation method
Media:
sewage sludge
Radiolabelling:
no
Test temperature:
20 deg C.
Type:
log Koc
Value:
1.19
Temp.:
20 °C
Type:
Koc
Value:
15.4
Temp.:
20 °C
Validity criteria fulfilled:
yes
Conclusions:
In an adsorption coefficient study with ZMB2, the Koc is 15.4 and log Koc is 1.19 at 20 deg C.

Description of key information

Key Study:

log Koc = 1.9 or Koc = 79 L/kg; OECD 121 (Currenta 2011), read-across from 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione (MB2)

 

Supporting Study:

log Koc = 1.19 or Koc = 15.4 L/kg; OECD 121 (Harlan 2013), study performed with zinc 4-methyl-2-thioxo-2,3-dihydrobenzimidazol-1-ide 7-methyl-2-thioxo-2,3-dihydrobenzimidazol-1-ide (ZMB2)

Key value for chemical safety assessment

Koc at 20 °C:
79.4

Additional information

The log Koc for zinc 4-methyl-2-thioxo-2,3-dihydrobenzimidazol-1-ide 7-methyl-2-thioxo-2,3-dihydrobenzimidazol-1-ide (ZMB2) was determined with 1.19 in this study (OECD 121). In the HPLC-UV analysis performed in this study, a mobile phase consisting of methanol:water (55:45 v/v) at a pH of 7.42 was applied. Under these aqueous conditions, it is expected that ZMB2 will instantly dissociate to/dissolve as MB2 and zinc ions (LANXESS, 2018). Thus, in this study it should not have been possible to detect ZMB2 in undissociated form.

 

However, in the discussion section of the report the authors assume ZMB2 to be present in the unionized form at approximately pH 7 and state “The testing for adsorption coefficient was therefore performed at approximately neutral pH on the molecular form” and “Based on the chromatographic data, the test item was considered to be stable during the test procedure” . Based on the weight of evidence presented in the read-across document (refer to Section 13.2), this statement must be considered to represent a misinterpretation.

This is further supported by the following considerations:

The following experimental log Koc results were obtained:

Log Koc(ZMB2) = 1.19 (OECD 121, Harlan 2013)

Log Koc(MB2) = 1.9 (OECD 121, Currenta 2011).

Based on the experimental log Kow values determined for both compounds,

Log Kow(ZMB2) = 3.07 (OECD 107, SafePharm 2004)

Log Kow(MB2) = 0.3-0.4 (OECD 117, Currenta 2011)

ZMB2 would be expected to be more adsorptive than 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione (MB2). This assumption is confirmed when applying the regressions developed by Franco and Trapp (2008) for predicting the Koc’s for electrolytes, i.e. acids, bases and amphoters (ECETOC Technical Report 123, p. 46 ff.) for estimating log Koc’s of MB2 and ZMB2 assuming both are present in their neutral, non-dissociated/non-deprotonated state:

Log Koc(ZMB2) = 2.68 (equation for organic bases used)

Log Koc(ZMB2) = 2.63 (equation for amphoters used)

Log Koc(MB2) = 2.17 (equation for organic acids used)

Estimations of log Koc’s using the regressions by Franco and Trapp (2008) confirm the trends as expected, i.e. ZMB2 is predicted to be more adsorptive than MB2 if both are present in neutral form.

Based on the weight of evidence as presented in the read-across document (refer to Section 13.2), in conclusion in the study report by Harlan (2013, Study Number 41206094), the adsorption coefficient for MB2, rather than intact ZMB2 was determined [LogKoc: 1.19; this value being lower than that that of the reference standard with the lowest log Koc used (acetanilide, log Koc = 1.25)]. However, this measured value appears to be quite low when comparing with the above respective regressions by Franco and Trapp for the log Koc’s. On the other hand, the adsorption coefficient of 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione (MB2) was tested according to OECD Guideline 121 (Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC)). The adsorption coefficient of the test item was determined to be log Koc = 1.9 or Koc = 79 L/kg, this value being higher than that of the reference standard with lowest log Koc used (2-Nitrobenzamide, log Koc = 1.45). As both log Koc studies (on MB2 and ZMB2) were performed according to OECD 121 under GLP, based on the read-across justification document (refer to Section 13.2) and the above discussion, the study on MB2 (log Koc = 1.9) is used as the key study for the adsorption / desorption endpoint.