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Environmental fate & pathways

Adsorption / desorption

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Reference
Endpoint:
adsorption / desorption: screening
Type of information:
(Q)SAR
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
results derived from a valid (Q)SAR model, but not (completely) falling into its applicability domain, with adequate and reliable documentation / justification
Justification for type of information:
QSAR prediction from a well-known and acknowledged tool. See below under ''attached background material section' for methodology and QPRF.
Qualifier:
according to guideline
Guideline:
other: REACH guidance on QSARs: Chapter R.6. QSARs and grouping of chemicals
Principles of method if other than guideline:
The Koc of the test substance was calculated using the MCI (Molecular Connectivity Index) and Kow based approaches of the KOCWIN v 2.01 program (EPISuite v 4.11). Since the test substance is an UVCB, the Koc values were estimated for individual constituents using SMILES codes as the input parameter.
Computational methods:
The Koc of the test substance was calculated using the MCI (Molecular Connectivity Index) and Kow based approaches of the KOCWIN v 2.01 program (EPISuite v 4.11). Since the test substance is an UVCB, the Koc values were estimated for individual constituents using SMILES codes as the input parameter.
Key result
Phase system:
other: Estimated
Value:
39.53 L/kg
Remarks on result:
other: MCI based method (Log KOC= 1.6)
Key result
Phase system:
other: Estimated
Value:
45.02 L/kg
Remarks on result:
other: Kow based method (Log KOC: 1.65)

Predicted value (model result):

The estimated Koc values for the different constituents using MCI and log Kow methods were as follows:

Table 1: Koc predictions: MCI method

Constituents/Carbon chain length*

Mean/adjusted conc

Mole fraction Xi = (mi/Mi)/∑ (mi/Mi)

Log Koc
MCI

Koc (L/kg)
MCI

Koc x Xi
(MCI)

MCI

C12

95

1

1.596926814

39.53

39.53

MW (ID),

Structural fragment (OD) - 1 out of 3 fragments (Aliphatic Alcohol (-C-OH))

 

 

 

 

Koc=

39.53

 

 

 

 

 

Log Koc=

1.60

 

* Glycerol or DEA residues have not been considered for QSAR predictions

Table 2: Koc predictions: Log Kow-based method

Constituents/Carbon chain length*

Mean/adjusted conc

Mole fraction Xi = (mi/Mi)/∑ (mi/Mi)

Log Koc
Log Kow

Koc (L/kg)
Log Kow

Koc x Xi
(Log Kow)

Log Kow

C12

95

1

1.653405491

45.02

45.02

MW (ID), log Kow (ID)

Structural fragment (OD) - 1 out of 3 fragments (Aliphatic Alcohol (-C-OH))

 

 

 

 

Koc=

45.02

 

 

 

 

 

Log Koc=

1.65

 

* Glycerol or DEA residues have not been considered for QSAR predictions

Koc prediction results:

SMILES : CCCCCCCCCCCC(=O)N(CCO)CCO

CHEM  : C12

MOL FOR: C16 H33 N1 O3

MOL WT : 287.45

--------------------------- KOCWIN v2.01 Results ---------------------------

 

 Koc Estimate from MCI:

 ---------------------

        First Order Molecular Connectivity Index ........... : 9.757

        Non-Corrected Log Koc (0.5213 MCI + 0.60) .......... : 5.6860

        Fragment Correction(s):

                 1  N-CO-C (aliphatic carbon) ............ : -1.0277

                 2  Nitrogen to Carbon (aliphatic) (-N-C).. : -0.4255

                 2  Aliphatic Alcohol (-C-OH) ........... : -2.6358

        Corrected Log Koc .................................. : 1.5970

 

                        Estimated Koc: 39.53 L/kg  <===========

 

 Koc Estimate from Log Kow:

 -------------------------

        Log Kow (Kowwin estimate) ......................... : 2.89

        Non-Corrected Log Koc (0.55313 logKow + 0.9251) .... : 2.5236

        Fragment Correction(s):

                 1  N-CO-C (aliphatic carbon) ............ : -0.0038

                 2  Nitrogen to Carbon (aliphatic) (-N-C).. : -0.0436

                 2  Aliphatic Alcohol (-C-OH) ........... : -0.8229

        Corrected Log Koc .................................. : 1.6534

 

                        Estimated Koc: 45.02 L/kg  <===========

Validity criteria fulfilled:
not applicable
Conclusions:
The Koc of the test substance was estimated using KOCWIN v 2.01 program (EPISuite v 4.11), to be 39.53 L/kg (log Koc = 1.6) with MCI method and 45.02 L/kg (log koc = 1.65) Log Kow method.
Executive summary:

The soil adsorption and desorption potential (Koc) of the test substance, C12 DEA, was earlier estimated using Molecular Connectivity Index (MCI) and Log Kow methods of the KOCWIN v 2.01 program (EPISuite v 4.11). Using the MCI and log Kow methods, the predicted Koc values for the constituent were estimated to be 39.53 and 45.02 L/kg, respectively. The corresponding log Koc values were 1.6 and 1.65 (US EPA, 2019). This indicates a low to moderate adsorption potential (US EPA, 2012). Overall, the Koc predictions for the test substance using the KOCWIN model of EPI Suite TM can be considered to be reliable with moderate confidence.

Description of key information

Key value for chemical safety assessment

Koc at 20 °C:
884

Additional information

A study was conducted to determine the adsorption/desorption characteristics of the test substance N,N-bis(2-hydroxyethyl)-dodecanamide (abbreviated C12 DEA) according to OECD Guideline 106 (indirect method) and in compliance with GLP. The test substance was tested in five different soils at 20˚C. Test performance included the determination of: adsorption kinetics, adsorption isotherms (according to Freundlich), desorption kinetics and desorption isotherms (according to Freundlich). Pretests were performed in order to get an optimal soil to solution ratio and to check of the stability of the test substance under test conditions (mass balance). Chemical analysis was performed by LC-MS/MS. As initial experiments were performed using unsterile soil conditions and the results indicated a loss of the test substance during the incubation period, subsequent experiments were performed under sterile conditions and low amount of soil (soil:solution ratio 1:50). The mass balance subsequent to the performance of the adsorption and desorption kinetic experiments was in the range of 80 – 90% for four out of five soils. After an increase of the sample size by factor 2, mass balance >90% could be established for all 5 soils. Consequently, the isotherm experiments were performed with the scaled-up sample size. The incubation time of 24h was applied to reach equilibrium conditions. Four (IME-01A, IME-02A, IME-03G and IME-04A) of the five soils were provided. Sorption tests with different concentrations of the test substance were evaluated using the Freundlich equation. The tested concentration ranges were depending on the particular soil and were approx. 55 - 5500 µg/L (soils IME-03G, IME-04A and LUFA 6S) and approx. 8 - 600 µg/L (soil IME-01A and IME-02A). Recovery of N,N-bis(2-hydroxyethyl)dodecanamide from the test system was proved in a separate experiment considering an adsorption time of 23h. For four soils the recoveries were within the range of 90 – 110% and for soil IME-04A a recovery of 89% was determined. The adsorption coefficients (KF) in the adsorption tests varied up to a factor of 10 in a range between 3.7 and 36.8. Normalization to the organic carbon content of the soils results in KOCads values from 386 to 1127. This indicates that adsorption of N,N-bis(2-hydroxyethyl)-dodecanamide depends on the soil organic carbon content, while no dependence on the soil pH was observed. The 1/n values obtained from the adsorption test ranged between 0.73 and 0.79 for four of the five soils. Soil IME-01A showed s lower 1/n value of 0.53. This indicates that the sorption of N,N-bis(2-hydroxyethyl)dodecanamide is mostly linear. Adsorption equilibrium was achieved after 24h for all soils. The Freundlich adsorption isotherms showed good correlations with correlation coefficients of >0.96 for all soils. Desorption was proven to be almost independent from agitation time for all soils. The correlation coefficients of desorption isotherm are moderate in the range of 0.87 – 0.95. The reason for the moderate R2 values is the low amount of soil applied due to the limited stability of N,N-bis(2-hydroxyethyl)dodecanamide in the test system. 1/n varies in the range of 0.62 to 0.77. Desorption coefficients vary by a factor of 1.5 between 16.7 and 26.8. No correlation between organic carbon content of the soils and desorption could be observed since organic carbon normalized desorption coefficients differ up to a factor of about 4. Also, the soil pH value seemed not to influence the desorption behaviour. Under the conditions of the study, N,N-bis(2-hydroxyethyl)dodecanamide shows a fairly high adsorptive and low mobility in soils (Hüben, 2022).


 


The soil adsorption and desorption potential (Koc) of the test substance, C12 DEA, was earlier estimated using Molecular Connectivity Index (MCI) and Log Kow methods of the KOCWIN v 2.01 program (EPISuite v 4.11). Using the MCI and log Kow methods, the predicted Koc values for the constituent were estimated to be 39.53 and 45.02 L/kg, respectively. The corresponding log Koc values were 1.6 and 1.65 (US EPA, 2019). This indicates a low to moderate adsorption potential (US EPA, 2012). Overall, the Koc predictions for the test substance using the KOCWIN model of EPI Suite TM can be considered to be reliable with moderate confidence.