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Reference
Endpoint:
adsorption / desorption: screening
Type of information:
(Q)SAR
Adequacy of study:
key study
Study period:
2021
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:
The adsorption / desorption potential of Benzenesulfonic acid, mono-C11-13-branched alkyl derivs. (BAB acid), CAS number 68608-88-8, EC Number 271-807-5, was estimated using KOCWIN v2.00, [EPI Suite version 4.11]
Qualifier:
according to guideline
Guideline:
other: QSAR
Version / remarks:
The adsorption / desorption potential of BAB acid, CAS number 68608-88-8, EC Number 271-807-5, was estimated using KOCWIN v2.00, [EPI Suite version 4.11]
Principles of method if other than guideline:
Results Using Molecular Connectivity Index

PCKOCWIN (version 1) estimated Koc solely with a QSAR utilizing Molecular Connectivity Index (MCI).  This QSAR estimation methodology is described completely in a journal article (Meylan et al, 1992) and in a report prepared for the US EPA (SRC, 1991).  PCKOCWIN (version 2) utilizes the same methodology, but the QSAR has been re-regressed using a larger database of experimental Koc values that includes many new chemicals and structure types.

QSAR Derivation

 The same methodology as described in (Meylan et al, 1992) was used to develop the QSAR equations utilizing Molecular Connectivity Index (MCI).  Two separate regressions were performed.  The first regression related log Koc of non-polar compounds to the first-order MCI.  As noted above, non-polar compounds are now designated as "compounds having no correction factors" which simply means the MCI descriptor alone can adequately predict the Koc.  Measured log Koc values were fit to a simple linear equation of the form:

 log Koc  = a MCI  + b

where a and b are the coefficients fit by least-square analysis.  The 69 compounds used for this regression are listed in Appendix E.

The second regression included the 447 compounds having correction factors; these compounds are listed in Appendix F.  The correction factors descriptors are listed in Appendix D.  Correction factors are specific chemical classes or structural fragments.  The regression coefficients were derived via multiple linear regression of the correction descriptors to the residual error of the prediction from the non-polar equation.

The equation derived by the non-polar (no correction factor) regression is:

 log Koc  =  0.5213 MCI  +  0.60

(n = 69, r2 = 0.967, std dev = 0.247, avg dev = 0.199)

for comparison, the previous version of PCKOCWIN used a very similar equation:

 log Koc  =  0.53 MCI  +  0.62

Adding in the correction factor regression yields the final MCI equation:

log Koc  =  0.5213 MCI  +  0.60 + ΣPfN  

where ΣPfN is the summation of the products of all applicable correction factor coefficients from Appendix D multiplied by the number of times (N) that factor is counted for the structure.

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Estimation Using Log Kow

A traditional method of estimating soil adsorption Koc involves correlations developed with log octanol-water partition coefficient (log Kow) (Doucette, 2000).  Since an expanded experimental Koc database was available from the new MCI regression, it was decided to develop a log Kow estimation methodology that was potentially more accurate than existing log Kow QSARs for diverse structure datasets.

Effectively, the new log Kow methodology simply replaces the MCI descriptor with log Kow and derives similar equations.  The derivation uses the same training and validation data sets.  The training set is divided into the same non-polar (no correction factors) and correction factor sets.  The same correction factors are also used.

Separate equations correlating log Koc with log Kow were derived for nonpolar and polar compounds because it was statistically more accurate to do so than to use the approach taken with the MCI-based method.  The equation derived by the non-polar (no correction factor) regression is:

 log Koc  =  0.8679 Log Kow  -  0.0004

    (n = 68, r2 = 0.877, std dev = 0.478, avg dev = 0.371)

One non-polar compound was removed from the regression (hexabromobiphenyl) because it was the only compound without a recommended experimental log Kow and the accuracy of its estimated log Kow (9.10) is suspect.  This equation is used for any compound having no correction factors.

For the multiple-linear regression using correction factors, log Kow was included as an individual descriptor.  For compounds having correction factors, the equation is:

 log Koc  =  0.55313 Log Kow  +  0.9251 + ΣPfN  
GLP compliance:
no
Type of method:
other: QSAR
Specific details on test material used for the study:
The following SMILES string for Benzenesulfonic acid, mono-C11-13-branched alkyl derivs. was used as input to the model:
OS(=O)(=O)c1ccc(cc1)CC(C)CC(C)CC(C)CCC

Experimental Log Kow of 1.27 was used for calculation.
Radiolabelling:
no
Analytical monitoring:
not required
Key result
Sample No.:
#1
Type:
Koc
Value:
8 448 L/kg
Remarks on result:
other: QSAR
Remarks:
MCI Method
Key result
Sample No.:
#1
Type:
log Koc
Value:
3.93 L/kg
Remarks on result:
other: QSAR
Remarks:
MCI Method
Key result
Sample No.:
#2
Type:
Koc
Value:
42.42 L/kg
Remarks on result:
other: QSAR
Remarks:
Kow Method (using a log Kow value of 1.27; See IUCLID section 4.7 for details)
Key result
Sample No.:
#2
Type:
log Koc
Value:
1.63 L/kg
Remarks on result:
other: QSAR
Remarks:
Kow method (using a log Kow value of 1.27; see IUCLID section 4.7 for details)
Validity criteria fulfilled:
yes
Conclusions:
The adsorption / desporttion coefficients for Benzenesulfonic acid, mono-C11-13-branched alkyl derivs.were estimated using KOCWIN QSAR to be :-

Koc: 8448 L/kg (MCI method)
Log Koc: 3.93 (MCI method)
Koc: 42.42 L/kg (Kow method)
Log Koc: 1.63 (Kow method)
Executive summary:

The adsorption / desorption potential of BAB Acid, CAS number 68608 -88 -8, EC Number 271 -807 -5, was estimated using KOCWIN v2.00, [EPI Suite version 4.11]

The following SMILES string for Benzenesulfonic acid, mono-C11-13-branched alkyl derivs. was used as input to the model:

OS(=O)(=O)c1ccc(cc1)CC(C)CC(C)CC(C)CCC

The adsorption / desporttion coefficients for Benzenesulfonic acid, mono-C11-13-branched alkyl derivs.were estimated using KOCWIN QSAR to be :-

Koc: 8448 L/kg (MCI method)

Log Koc: 3.93 (MCI method)

Koc: 42.42 L/kg (Kow method)

Log Koc: 1.63 (Kow method)

The study has been assigned a reliability score of 2 in accordance with the criteria for assessing data quality set forth by Klimisch et al. (1997).

Description of key information

The adsorption / desorption potential of BAB Acid, CAS number 68608 -88 -8, EC Number 271 -807 -5, was estimated using KOCWIN v2.00, [EPI Suite version 4.11]

The following SMILES string for Benzenesulfonic acid, mono-C11-13-branched alkyl derivs. was used as input to the model:

OS(=O)(=O)c1ccc(cc1)CC(C)CC(C)CC(C)CCC

The adsorption / desporttion coefficients for Benzenesulfonic acid, mono-C11-13-branched alkyl derivs.were estimated using KOCWIN QSAR to be :-

Koc: 8448 L/kg (MCI method)

Log Koc: 3.93 (MCI method)

Koc: 42.42 L/kg (Kow method)

Log Koc: 1.63 (Kow method)

The study has been assigned a reliability score of 2 in accordance with the criteria for assessing data quality set forth by Klimisch et al. (1997).

Key value for chemical safety assessment

Koc at 20 °C:
42.42

Additional information

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