2-hexyldecanoic acid

Bioaccumulation: aquatic / sediment

Link to relevant study record(s)

Reference

Endpoint:

bioaccumulation in aquatic species, other

Remarks:

all trophic levels

Type of information:

(Q)SAR

Adequacy of study:

key study

Study period:

2021

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Validated QSAR model. Calculation for 2-hexyldecanoic acid

Justification for type of information:

QSAR prediction

Qualifier:

no guideline followed

Principles of method if other than guideline:

Calculation based on BCFBAF v3.01, Estimation Programs Interface Suite™ for Microsoft® Windows v 4.10. US EPA, United States Environmental Protection Agency, Washington, DC, USA.

GLP compliance:

no

Test type:

other: calculation

Details on estimation of bioconcentration:

BASIS INFORMATION
- Measured/calculated logPow: calculated log Pow (US EPA EPI Suite, program KOAWIN v1.10)

BASIS FOR CALCULATION OF BCF
- Estimation software: US EPA EPI Suite v4.00, program BCFBAF v3.01
- Result based on experimental log Pow of: 6.21

Key result

Type:

BCF

Value:

56.23 L/kg

Basis:

whole body w.w.

Remarks on result:

other: regression-based method

Key result

Type:

BCF

Value:

1 651 L/kg

Basis:

whole body w.w.

Remarks on result:

other: Arnot Gobas (including biotransformation rate estimates, upper trophic)

CALCULATION

 

BCFBAF Program (v3.01) Results:

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

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

CHEM   : Decanoic acid, 2-hexyl-

MOL FOR: C16 H32 O2

MOL WT : 256.43

 

--------------------------------- BCFBAF v3.01 --------------------------------

Summary Results:

  Log BCF (regression-based estimate):  1.75  (BCF = 56.2 L/kg wet-wt)

  Biotransformation Half-Life (days) :  5.65  (normalized to 10 g fish)

  Log BAF (Arnot-Gobas upper trophic):  3.73  (BAF = 5.31e+003 L/kg wet-wt)

 

Log Kow (experimental):  not available from database

Log Kow used by BCF estimates:  6.21 (user entered)

 

Equation Used to Make BCF estimate:

   Log BCF = 1.75 (Ionic; Log Kow dependent)

   Estimated Log BCF =  1.750  (BCF = 56.23 L/kg wet-wt)

 

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

Whole Body Primary Biotransformation Rate Estimate for Fish:

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

------+-----+--------------------------------------------+---------+---------

 TYPE | NUM | LOG BIOTRANSFORMATION FRAGMENT DESCRIPTION |  COEFF  |  VALUE 

------+-----+--------------------------------------------+---------+---------

 Frag |  2  |  Linear C4 terminal chain  [CCC-CH3]       |  0.0341 |  0.0682

 Frag |  1  |  Aliphatic acid   [-C(=O)-OH]              |  0.3803 |  0.3803

 Frag |  2  |  Methyl  [-CH3]                            |  0.2451 |  0.4902

 Frag | 12  |  -CH2-  [linear]                           |  0.0242 |  0.2902

 Frag |  1  |  -CH-   [linear]                           | -0.1912 | -0.1912

 L Kow|  *  |  Log Kow =   6.21 (user-entered   )        |  0.3073 |  1.9086

 MolWt|  *  |  Molecular Weight Parameter                |         | -0.6576

 Const|  *  |  Equation Constant                         |         | -1.5371

============+============================================+=========+=========

   RESULT   |        LOG Bio Half-Life (days)            |         |  0.7517

   RESULT   |            Bio Half-Life (days)            |         |   5.646

   NOTE     |  Bio Half-Life Normalized to 10 g fish at 15 deg C   |

============+============================================+=========+=========

 

Biotransformation Rate Constant:

 kM (Rate Constant):  0.1228 /day (10 gram fish)

 kM (Rate Constant):  0.06904 /day (100 gram fish)

 kM (Rate Constant):  0.03882 /day (1 kg fish)

 kM (Rate Constant):  0.02183 /day (10 kg fish)

 

Arnot-Gobas BCF & BAF Methods (including biotransformation rate estimates):

   Estimated Log BCF (upper trophic) =  3.218  (BCF = 1651 L/kg wet-wt)

   Estimated Log BAF (upper trophic) =  3.725  (BAF = 5312 L/kg wet-wt)

   Estimated Log BCF (mid trophic)   =  3.354  (BCF = 2261 L/kg wet-wt)

   Estimated Log BAF (mid trophic)   =  4.162  (BAF = 1.451e+004 L/kg wet-wt)

   Estimated Log BCF (lower trophic) =  3.395  (BCF = 2482 L/kg wet-wt)

   Estimated Log BAF (lower trophic) =  4.437  (BAF = 2.733e+004 L/kg wet-wt)

 

JUSTIFICATION

 

A reliable QSAR model was used to calculate the bioaccumulation potential of 2-hexyldecanoic acid. BCF values were calculated using the BCFBAF v3.01 module embedded within the EPISuite v4.11) computer model. The calculated BCF (regression-based model) was 56.23 L/kg wet-wt., while the BAF (Arnot-Gobas upper trophic) was 1651 L/kg wet-wt. The SMILES notation used for the predictions was:

 

O=C(O)C(CCCCCCCC)CCCCCC

 

The BCFBAF predicted bioaccumulation 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 BCFBAF) 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 BCFBAF) 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.

 

BCFBAF is listed as one of the QSARs for use in predicting bioaccumulation values in the Guidance on information requirements and chemical safety assessment Chapter R.7c: Endpoint specific guidance. In summary, the EPISuite modules (including BCFBAF) have had their scientific validity established repeatedly.

 

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

 

According to the BCFBAF 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 and log Kow 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 256.43 which falls within the range of the training set (68.08 to 959.17) and its log Kow (6.21) also falls within the training set’s range (-1.37 to 11.26).

 

In addition, the BAF calculations clearly show that all fragments of the substance were analysed.

 

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

 

BCFBAF calculated the regression based BCF from the following equation:

 

  Log BCF = 0.6598 log Kow - 0.333 + Correction

 

      Correction(s):                    Value

      No Applicable Correction Factors

 

The BCFBAF model had the following statistics:

 

Training Set

  number = 527

  correlation coef (r2) = 0.833

 

Validation Set

  number = 158

  correlation coef (r2) = 0.82

 

These correlation coefficients indicate the BCFBAF 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 BCFBAF model is provided in the following references:

 

References

 

Arnot JA, Mackay D, Bonnell M. 2008b. Estimating metabolic biotransformation rates in fish from laboratory data. Environmental Toxicology and Chemistry 27: 341-351.

 

Arnot JA, Gobas FAPC. 2003. A generic QSAR for assessing the bioaccumulation potential of organic chemicals in aquatic food webs. QSAR and Combinatorial Science 22: 337-345.

 

Arnot, J.A. and F.A.P.C. Gobas. 2006. A review of bioconcentration factor (BCF) and bioaccumulation factor (BAF) assessments for organic chemicals in aquatic organisms. Environmental reviews 14(4): 257-297.

 

Arnot JA, Meylan W, Tunkel J, Howard PH, Mackay D, Bonnell M, Boethling RS. 2009. A QSAR for predicting metabolic biotransformation rates for organic chemicals in fish. Environmental Toxicology and Chemistry. 28: in press.

 

Meylan, W.M., Howard, P.H, Aronson, D., Printup, H. and S. Gouchie.  1997.  "Improved Method for Estimating Bioconcentration Factor (BCF) from Octanol-Water Partition Coefficient", SRC TR-97-006 (2nd Update), July 22, 1997; prepared for: Robert S. Boethling, EPA-OPPT, Washington, DC; Contract No. 68-D5-0012; prepared by: ; Syracuse Research Corp., Environmental Science Center, 6225 Running Ridge Road, North Syracuse, NY 13212.

 

Meylan,WM, Howard,PH, Boethling,RS et al. 1999.  Improved Method for Estimating Bioconcentration / Bioaccumulation Factor from Octanol/Water Partition Coefficient. Environ. Toxicol. Chem. 18(4): 664-672 (1999).ECHA (2012) “Guidance on information requirements and chemical safety assessment Chapter R.7b: Endpoint specific guidance”.

 

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

Validity criteria fulfilled:

not applicable

Conclusions:

Estimated BCF from regression-based method and BCF from Arnot-Gobas method values of 56.23 (log BCF = 1.75) and 1651 (log BCF 3.218 - upper trophic) respectively indicate a low bioaccumulation potential of the substance in aquatic organisms.

Executive summary:

The BCF of 2-hexyldecanoic acid (log Pow = 6.21) was estimated to be 56.23 L/kg ww (log BCF 1.75) regression-based method using the program BCFBAF v3.01 (Part of US EPA EPI Suite v4.1.1). In addition, a BCF (upper trophic) of 1651 (log BCF = 3.218) was calculated using the method of Arnot-Gobas.

 

The low BCF/BAF values indicate a low potential of the similar substance 2 -butyl octanoic acid for bioaccumulation in aquatic organisms.

Description of key information

Estimated BCF from regression-based method of 56.23 L/kg (log BCF = 1.75) indicates a low bioaccumulation potential of the substance in aquatic organisms.

Key value for chemical safety assessment

BCF (aquatic species):

56.23 L/kg ww

Additional information

These calculated BCF values likely overestimate the potential for the aliphatic acids to bioaccumulate because of the rapid and extensive metabolism of aliphatic acids in animals and plants.