Chlorobenzene

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption, other

Remarks:

QSAR calculated endpoint

Type of information:

(Q)SAR

Adequacy of study:

key study

Study period:

12-Oct-2022 - 22-Nov-2022

Reliability:

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:

1. SOFTWARE
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

3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
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.

4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
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.

5. APPLICABILITY DOMAIN
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.

6. ADEQUACY OF THE RESULT
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.7.1.15.4) on waiving the adsorption/desorption endpoint. The substance exhibits a low partition coefficient value (< 3.0; https://echa.europa.eu/registration-dossier/-/registered-dossier/27583/4/8) but is not readily biodegradable (https://echa.europa.eu/registration-dossier/-/registered-dossier/27583/5/3/2), 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.

Guideline:

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:

no

Type of method:

other: QSAR

Specific details on test material used for the study:

- SMILES: C1=CC=C(C=C1)Cl
- 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

Type:

log Koc

Value:

2.369 dimensionless

Remarks on result:

other: MCI method

Key result

Type:

Koc

Value:

233.9 L/kg

Remarks on result:

other: MCI method

Type:

log Koc

Value:

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.

Type:

Koc

Value:

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 K_OC value of 2.15, obtained from the QSAR (KOCWIN v2.00) database

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

 

 

Validity criteria fulfilled:

yes

Conclusions:

The predicted values are suitable for purpose considering the approach for regulatory interpretation.

The QSAR determination revealed a logarithmic organic carbon-water partition coefficient of 2.369 of the test substance, and Koc value of 233.9 L/kg.

Executive summary:

The assessment indicates that the prediction is suitable for the regulatory conclusion to fulfil the REACH data requirement for the soil adsorption/desorption coefficient.

 

The QSAR determination revealed a logarithmic organic carbon-water partition coefficient of 2.369 of the test substance, and Koc value of 233.9 L/kg based on MCI method. 

The MCI method resulted in a value closer to the experimental, and therefore it is concluded that this value is the most appropriate for use (see details in QPRF).

Description of key information

Key, Rel 2, QSAR ((EPI) Suite v4.11); Blue Frog Scientific (2022): Koc=  233.9 L/kg/ log Koc=2.37 (MCI method) 

Key value for chemical safety assessment

Koc at 20 °C:

233.9

Additional information

The log Koc was calculated to be 2.37 corresponding to a Koc = 233.9 (EPISUITE v4.11 KOCWIN v2.00; 2022). In a publication from Dannenfelser (1991) log Koc values of 2.68 (Kow = 479) and 2.52 (Kow = 331) were reported for Chlorobenzene and the BUA report cited an experimental log Koc value of 2.18 (Kow = 151). In addition 4 calculated log Koc in the range 2.18 - 2.57 (Kow = 151 - 372) are reported in the BUA report. Therefore, the substance has only a low soil adsorption potential, a relevant adsorption to soil is not expected. Based on the available information the KOCWIN v2.00 calculated value of log Koc = 2.37 represents a reliable value which was used for the chemical safety assessment.

 

As the adsorption coefficient (Koc) of Chlorobenzene is 233.9 (Blue Frog Scientific, 2022), the result indicates that the substance is of medium mobility in soils according to McCall et al. (1981).

Range of Koc	Mobility class
0-50	Very high
50-150	High
150-500	Medium
500-2000	Low
2000-5000	Slightly
>5000	Immobile

McCall P.J., Laskowski D.A., Swann R.L., and Dishburger H.J., (1981), “Measurement of sorption coefficients of organic chemicals and their use, in environmental fate analysis”, in Test Protocols for Environmental Fate and Movement of Toxicants. Proceedings of AOAC Symposium, AOAC,Washington DC