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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:
key study
Study period:
2021
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: accepted calculation method of a component
Justification for type of information:
QSAR prediction
Qualifier:
no guideline followed
Principles of method if other than guideline:
(Q)SAR calculation with calculation program US EPA EPI-Suite v4.11, component KOCWIN (v2.00) using first-order molecular connectivity index (1-MCI) corrected by fragment contribution factors
Type of method:
other: calculation
Key result
Type:
log Koc
Value:
3.591 L/kg
Remarks on result:
other: calculated value, log Kow method
Key result
Type:
log Koc
Value:
3.52 L/kg
Remarks on result:
other: calculated value, MCI method
Key result
Type:
Koc
Value:
3 896 L/kg
Remarks on result:
other: calculated value, log Kow method
Key result
Type:
Koc
Value:
3 311 L/kg
Remarks on result:
other: calculated value, MCI method

CALCULATION


 


KOCWIN Program (v2.00) Results:


==============================


SMILES: O=C(O)C(CCCCCCCC)CCCCCC


CHEM:


MOL FOR: C16 H32 O2


 


                 Koc may be sensitive to pH!


 


---------------------------  KOCWIN v2.00 Results  ---------------------------


 


  Koc Estimate from MCI:


  ---------------------


         First Order Molecular Connectivity Index  ................ :  8.719


         Non-Corrected Log Koc (0.5213 MCI + 0.60)  .......... :  5.1449


         Fragment Correction(s):


                  *   Organic Acid (-CO-OH)  ............................  :  -1.6249


         Corrected Log Koc  .................................................. :  3.5200


 


                         Estimated Koc:  3311 L/kg   <===========


 


  Koc Estimate from Log Kow:


  -------------------------


         Log Kow (User entered)  ............................................... :  6.21


         Non-Corrected Log Koc (0.55313 logKow + 0.9251)  .... :  4.3600


         Fragment Correction(s):


                  *   Organic Acid (-CO-OH)  ...................................  : -0.7694


         Corrected Log Koc  ........................................................ :  3.5907


 


                         Estimated Koc:  3896 L/kg   <===========


 


JUSTIFICATION


 


A reliable QSAR model was used to calculate the bioaccumulation potential of 2-hexyldecanoic acid. The Koc values were calculated using the KOCWIN v2.00 module embedded within the EPISuite v4.11) computer model. The calculated Koc (estimated on the Molecular Connectivity Index (MCI)) was 3311 L/kg, while the calculated Koc (estimated based on the Log Kow) was 3896 L/kg. The SMILES notation used for the predictions was:


 


O=C(O)C(CCCCCCCC)CCCCCC


 


The KOCWIN predicted Koc values are considered valid and fit for purpose. A calculated value from a QSAR model is considered valid and fit for purpose if the following conditions are met: 1) Results are derived from a (Q)SAR model whose scientific validity has been established; 2) The substance falls within the applicability domain of the (Q)SAR model; 3) Results are adequate for the purpose of classification and labelling and/or risk assessment and 4) Adequate and reliable documentation of the applied method is provided.


 


1) Results are derived from a (Q)SAR model whose scientific validity has been established


 


EPISuite and its modules (including KOCWIN) has been utilized by the scientific community for prediction of phys/chem properties and environmental fate and effect properties since the 1990’s. The program underwent a comprehensive review by a panel of the US EPA’s independent Science Advisory Board (SAB) in 2007. The SAB summarized that the EPA used sound science to develop and refine EPISuite. The SAB also stated that the property estimation routines (PERs) satisfy the Organization for Economic Cooperation and Development (OECD) principles established for quantitative structure-activity relationship ((Q)SAR) validation.


 


The EPISuite modules (including KOCWIN) have been incorporated into the OECD Toolbox. Inclusion in the OECD toolbox requires specific documentation, validation and acceptability criteria and subjects EPISuite to international use, review, providing a means for receiving additional and on-going input for improvements.


 


For QSAR determination of Koc values, Guidance on information requirements and chemical safety assessment Chapter R.7a: Endpoint specific guidance refers to several review articles. One of the articles Doucette, 2003) provides an in-depth review of the approaches used for QSAR determination of Koc values. In the review, the Molecular Connectivity Index method by Meylan et al., 1992 is considered the most well defined and recommended method. This is the method utilized by KOCWIN model.


 


In summary, the EPISuite modules (including KOCWIN) have had their scientific validity established repeatedly.


 


2) The substance falls within the applicability domain of the (Q)SAR model


 


According to the KOCWIN documentation, there is currently no universally accepted definition of model domain.  However, the documentation does provide information for reliability of the calculations. Estimates will possibly be less accurate for compounds that 1) have a MW outside the ranges of the training set compounds and 2) have a functional group(s) or other structural features not represented in the training set, and for which no fragment coefficient was developed; and that a compound has none of the fragments in the model’s fragment library. The molecular weight of 2-hexyldecanoic acid is 256 which falls within the range of the training set (32 to 665) and the validation set (73 to 504).


 


In addition, the calculations clearly show that the organic acid functional group was considered in predicted value.


 


As a result, 2-hexyldecanoic acid would not be considered outside the estimation domain.


 


3) Results are adequate for the purpose of classification and labelling and/or risk assessment


 


Calculated Koc values from KOCWIN based on the Molecular Connectivity Index methodology utilize the following equation:


log Koc  =  0.5213 MCI + 0.60 + ΣPfN  


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


 


The KOCWIN-MCI model had the following statistics:


 


Training Set – No Corrections


  number = 69


  correlation coef (r2) = 0.967


 


Training Set – With Corrections


  number = 447


  correlation coef (r2) = 0.900


 


Validation Set


  number = 158


  correlation coef (r2) = 0.850


 


Calculated Koc values from KOCWIN based on the log Kow methodology utilize the following equation:


 log Koc  =  0.55313 Log Kow + 0.9251 + ΣPfN  


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


 


The KOCWIN-log Kow model had the following statistics:


 


Training Set – No Corrections


  number = 68


  correlation coef (r2) = 0.877


 


Training Set – With Corrections


  number = 447


  correlation coef (r2) = 0.855


 


Validation Set


  number = 150


  correlation coef (r2) = 0.778


 


These correlation coefficients indicate the KOCWIN model calculates results that are equivalent to those generated experimentally and are, hence, adequate for the purpose of classification and labelling and/or risk assessment.


 


4) Adequate and reliable documentation of the applied method is provided


 


Documentation of the KOCWIN model is provided in the following references:


 


References


Bahnick D.A.and W.J. Doucette (1988) Use of Molecular Connectivity Indices to Estimate Soil Sorption Coefficients for Organic Chemicals. Chemosphere 17, 1703-15.


Sabljic A. (1987) On the Prediction of Soil Sorption Coefficients of Organic Pollutants from Molecular Structure: Application of Molecular Topology Model. Environ. Sci. Technol. 21, 358-66


Meylan W. Howard, P.H. and R.S. Boethling (1992) Molecular topology/fragment contribution method for predicting soil sorption coefficients. Environ. Sci. Technol. 26, 1560-1567.


 


McFarland, M. et al. 2007. “Science Advisory Board (SAB) Review of the Estimation Programs Interface Suite (EPI SuiteTM)”.

Validity criteria fulfilled:
not applicable
Conclusions:
2-hexyldecanoic acid has a calculated Koc of 331 L/kg (KOCWIN-MCI) indicating a slight chance for soil mobility.
Executive summary:

The Koc of 2-hexyldecanoic acid was estimated with the program US EPA EPI Suite (v 4.11), program component KOCWIN. Based on the molecular connectivity index methodology, the log Koc was determined to be 3.52 (Koc = 3311 L/kg). Based on the log Kow methodology, the log Koc was 3.59 (Koc = 3896 L/kg). The Koc values indicate a slight of the substance to be mobile in soil based on the McCall classification scheme.


 


The KOC of this structure may be sensitive to pH. The estimated KOC represents a best-fit to the majority of experimental values. However, the KOC may vary significantly with pH.


 


McCall et al., 1981, Measurement of Sortpion coefficients of organic chemicals and their use in environmental fate analysis

Description of key information

A reliable Koc calculation of 3311 L/kg was obtained the the EPISuite (4.11) KOCWIN-MCI model.

Key value for chemical safety assessment

Koc at 20 °C:
3 311

Additional information