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Environmental fate & pathways

Adsorption / desorption

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adsorption / desorption, other
QSAR calculated endpoint
Type of information:
Adequacy of study:
key study
Study period:
12-Oct-2022 - 22-Nov-2022
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification
Justification for type of information:
Individual model KOCWIN included in the Estimation Programs Interface (EPI) Suite.

2. MODEL (incl. version number)
KOCWIN v2.00 included in EPISuite v 4.11, ©2000 - 2012

The SMILES notation for the substance was used in the model C1=CC=C(C=C1)Cl as well as the experimental value of log Koc of 2.15, obtained from the QSAR (KOCWIN v2.00) database.

Sorption coefficients are used to describe the equilibrium distribution of a substance between a soil or sediment and the aqueous phase that it is in contact with. Although sorption coefficients for a particular chemical vary significantly from soil to soil, it is widely accepted that it increases with an increase of the organic carbon content of the soil and with an increase in the hydrophobicity of the substance, leading to a general acceptance of organic carbon normalized sorption coefficients (Koc) as unique properties or constants for organic chemicals. Kocvalues have been estimated by quantitative structure-activity relationships (QSARs) through correlation with a variety of physical or chemical properties and structural descriptors related to the hydrophobicity of the chemical such as octanol-water partition coefficients, aqueous solubilities, molecular connectivity indices, molecular weight and molecular surface area. The selection and application of the most appropriate QSAR for predicting Koc depend on several factors, including the appropriateness of model to chemical of interest, and the methodology for calculating the necessary topological or structural information. A very high Koc value means it is strongly adsorbed onto soil and organic matter and does not move throughout the soil, while a very low value means it is highly mobile in soil. The QSAR analysis is determined by a close relationship of the mobility of the substance in soil and its maximum concentration that can be adsorbed onto the soil with physicochemical properties of the substance such as solubility in water and hydrophobicity.

KOCWIN estimates the soil adsorption coefficient of a substance using either the Molecular Connectivity Index (MCI) of a substance or the water-octanol partition coefficient of the substance. The molecular weight aids in assessing domain applicability. The molecular weight of the test substance is 112.56 g/mol. Therefore, the substance falls within the applicability domain of this model based on the molecular weight limits used in the training sets.

This prediction was performed to fulfil the adsorption/desorption coefficient endpoint (KOC or log KOC) for the substance being submitted under Annex VIII of Regulation (EC) No 1907/2006 (REACH) and for the purpose of chemical safety assessment inputs as a key value for the chemical safety assessment, should it be required.

The purpose of this estimation is to determine a predicted endpoint value for the soil adsorption coefficient of the test substance, in order to comply with the requirements of the REACH Regulation, as outlined in ECHA Chapter R.7a: Endpoint specific guidance (v6.0, June 2017; Section R. on waiving the adsorption/desorption endpoint. The substance exhibits a low partition coefficient value (< 3.0; but is not readily biodegradable (, so the REACH Annex VIII Section 9.3.1 Column 2 waiver “The study does not need to be conducted if: based on the physicochemical properties the substance can be expected to have a low potential for adsorption (e.g. the substance has a low octanol-water partition coefficient)” was used. However, to produce an acceptable waiver, Chapter R.7a guidance states that all organic substances manufactured or supplied in quantities of 10 tonnes per year or more, the Koc should be estimated using read-across or QSAR methods as a first step. This QSAR has been produced in order to support waiving the endpoint as a first step, by generating an estimated value.

The substance has a molecular weight of 112.56 g/mol, therefore it falls within the molecular weight range of the model’s training and validation sets. Structurally similar substances are also present in the training sets and the validation set, for which the predictions have been shown to be accurate, thereby supporting the applicability domain of the model for use with the test substance. Further, the best method appears to be that of the MCI methodology.

In light of the above, the prediction is considered to be accurate and suitable for purpose.
other: REACH guidance on QSARs R.6
Version / remarks:
May 2008
Principles of method if other than guideline:
- Software tool(s) used including version: The Estimation Program Interface (EPI) Suite v4.11. The Estimation Programs Interface was developed by the US Environmental Agency's Office of Pollution Prevention and Toxics and Syracuse Research Corporation (SRC). © 2000 - 2012 U.S. Environmental Protection Agency for EPI SuiteTM. Published online in November 2012.
- Model(s) used: KOCWIN v2.00 for estimating the soil adsorption coefficient (Koc)
- Model description: see field 'Attached justification'.
- Justification of QSAR prediction: see field 'Attached justification'.
GLP compliance:
Type of method:
other: QSAR
Specific details on test material used for the study:
- Molecular weight: 112.56 g/mol
Computational methods:
Software: Individual model KOCWIN included in the Estimation Programs Interface (EPI) Suite.

Model: KOCWIN v2.00 included in EPISuite v 4.11, ©2000 - 2012

The SMILES notation for the substance was entered into the model as well as the experimental value of log KOC of 2.15 for the substance from the KOCWIN v2.00 database and the model run.
Key result
log Koc
2.369 dimensionless
Remarks on result:
other: MCI method
Key result
233.9 L/kg
Remarks on result:
other: MCI method
log Koc
2.464 dimensionless
Remarks on result:
other: Log Kow method, using experimental log Koc value of 2.15 obtained from the QSAR (KOCWIN v2.00) database.
291.4 L/kg
Remarks on result:
other: Log Kow method, using experimental log Koc value of 2.15 obtained from the QSAR (KOCWIN v2.00) database.

Table: Estimated absorption coefficients of substance.

Estimated log10Koc

MCI method

log Kow method*

2.369 (233.9)

2.4644 (291.4)

*Using experimental log KOC value of 2.15, obtained from the QSAR (KOCWIN v2.00) database

(values in parenthesis are the KOC in L/kg)