Naphthalenesulfonic acid, di-C9-rich C8-10-branched alkyl derivs.

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption

Remarks:

adsorption

Type of information:

(Q)SAR

Adequacy of study:

weight of evidence

Study period:

May 13-17, 2013

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: QSAR procedures consistent with guidance document recommendations were employed.

Justification for type of information:

QSAR prediction

Qualifier:

no guideline available

Principles of method if other than guideline:

REACH guidance (Chapter R.7a, 2012) indicates that calculation and read-across should be the first step in estimating the Koc. No similar compounds were found which would provide read-across for DNNSA. The Guidance document (Chapter R.7a, 2012) recommends estimates be made using multiple models for a sensitivity check, therefore, a calculation of the Koc was conducted using the EPIWIN model KOCWIN and the models developed by Sabljic et al. (1995) which are described in TGD Part III (2003) and utilized by EUSES.

GLP compliance:

no

Type of method:

other: QSAR

Computational methods:

A calculation of the Koc was conducted using the EPIWIN model KOCWIN and the models developed by Sabljic et al. (1995) which are described in TGD Part III (2003) and utilized by EUSES.

Type:

log Koc

Value:

ca. 5.19

Validity criteria fulfilled:

not applicable

Conclusions:

The HPLC method (OECD 121) is not suitable for substances like DNNSA. The Log Koc for DNNSA that will be used for the environmental assessment will be 5.19, the average of the 3 values estimated by QSAR modeling

Executive summary:

There are experimental and QSAR approaches for the determination of the Soil Adsorption Coefficient (Koc). REACH guidance (Chapter R.7a, 2012) indicates that calculation and read-across should be the first step in estimating the Koc. No similar compounds were found which would provide read-across for DNNSA. The Guidance document (Chapter R.7a, 2012) recommends estimates be made using multiple models for a sensitivity check, therefore, a calculation of the Koc was conducted using the EPIWIN model KOCWIN (US EPA, 2012)and the models developed bySabljic et al. (1995) which are described in TGD Part III (2003) and utilized by EUSES.

 

1. KOCWIN Model Calculation of Koc

The Soil Adsorption Coefficient Program (KOCWIN) estimates the soil adsorption coeffiecient (Koc) of organic compounds.  Koc is defined as "the ratio of the amount of chemical adsorbed per unit weight of organic carbon (oc) in the soil or sediment to the concentration of the chemical in solution at equilibrium":

                   Koc =  (ug adsorbed/g organic carbon) / (ug/mL solution)

Traditional estimation methods rely upon the octanol/water partition coefficient or related parameters (Meylan et al. 1992). The EPA modeling manual reports that the KOCWIN methodology based on Log Kow has an r²of 0.86. 

 

The KOCWIN model estimates a Log Kow value to calculate the Koc. The KOCWIN Log Kow estimate for DNNSA is 8.52.  

 The results of the KOCWIN model for DNNSA are shown in Table 1.

 

Table 1. EPIWIN Model Output for DNNSA

MOL FOR: C28 H44 O3 S1

                

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

 

 Koc Estimate from Log Kow:

 -------------------------

        Log Kow (KOWWIN estimate):                                     8.52

        Non-Corrected Log Koc (0.55313 logKow + 0.9251):          5.6378

        Fragment Correction(s):

                 1  Sulfonic acid (-S(=O)-OH):                               0.0000

        Corrected Log Koc:                                                   5.6378

 

         Estimated Koc:                                                     4.343e+005 L/kg 

 

 

2.  Koc Estimates Based on Models of Sabljic et al. 2003

Sabljic and Güsten (1995) in an international project funded by the EC developed a series of models for different chemical classes. These models are utilized in EUSES and are recommended in TGD Part III. For estimates of the Koc for DNNSA, the organic acid and the alcohol and organic acid models were used.

 

Chemical Class	Equation	Statistics
Organic acids	Log Koc = 0.60 log Kow + 0.32	N = 23, r^2= 0.75
Alcohols and Organic acids	Log Koc = 0.47 log Kow + 0.50	N = 36, r^2= 0.72

These equations require a Log Kow estimate for the chemical being evaluated. The log Kow for DNNSA used is the calculated value of 8.52 estimated by KOWWIN in the previous section. 

Based on these equations and the Log Kow of 8.52, the Log Koc for DNNSA is 5.43 for the organic acids model and 4.50 for the alcohols and organic acids model.

 

3. Experimental Determination of Koc for DNNSA

To increase the accuracy of the Koc estimate, experimental methods are available. REACH guidance recommends that first consideration should be given to HPLC method described in OECD 121.  This guideline indicates that the HPLC procedure may not be suitable for moderate and strong acids, or surface active compounds. DNNSA is both a relatively strong acid and a surface active compound. Furthermore, the method states that it has been validated for a variety of organic compounds, however, no acids are shown in tables of validated compounds provided in the guideline. 

 

With a view to the stated cautions about the HPLC Koc estimation procedure, attempts to experimentally obtain a Koc were undertaken by King Industries and WIL Research. This testing gave unsatisfactory results with DNNSA retention times covering a range, both long and short, that was too broad to be useful for the assessment of the environmental behavior of DNNSA. It was concluded that these results were an artifact of the method for this type of chemistry and demonstrate the unsuitability of the method for determination of a Koc for DNNSA.

 

 

4.      Conclusions

 

In view of the results with HPLC testing, and of REACH guidance indicating that “Estimated values are essential for substances for which experimental measurement is not feasible i.e. for difficult substances”, the Koc for DNNSA that will be used for the environmental assessment will be 5.19, the average of the 3 values estimated by modeling.

 

Soil Adsorption Coefficient (Koc)for DNNSA

 

Model	Log Koc
KOCWIN	5.64
Organic acids*	5.43
Alcohols and Organic acids*	4.5
Average	5.19

*Sabljic et al. (1995)

 

 

5. References

Guidance on information requirements and chemical safety assessment.Chapter R.7a : Endpoint Specific Guidance Version 2.0 November 2012).

 

Sabljic, A., H. Güsten, H. Verhaar and J. Hermens (1995). QSAR modelling of soil sorption. Improvements and systematics of log Koc vs. log Kow correlations. Chemosphere 31, 4489-4514.

Meylan, W., P.H. Howard and R.S. Boethling, "Molecular Topology/Fragment Contribution Method for Predicting Soil Sorption Coefficients",Environ. Sci. Technol. 26: 1560-7 (1992).

Technical Guidance Document on Risk Assessment. Part III. 2003. European  Commission, Joint Research Centre.

 

USEPA. (2012). Estimation Programs Interface Suite™ for Microsoft® Windows, v 4.10.  Environmental,, DC,.

 

Description of key information

Results of HPLC testing (OECD 121) demonstrated the method was not suitable for DNNSA which is consistent with the guideline caution that the method may be inappropriate for strong acids and surface acting compounds.
The log Koc for DNNSA that will be used for the environmental assessment will be 5.19, the average of the 3 values estimated by QSAR modeling.

Key value for chemical safety assessment

Koc at 20 °C:

154 882

Additional information

There are experimental and QSAR approaches for the determination of the Soil Adsorption Coefficient (Koc). REACH guidance (Chapter R.7a, 2012) indicates that calculation and read-across should be the first step in estimating the Koc. No similar compounds were found which would provide read-across for DNNSA. The Guidance document (Chapter R.7a, 2012) recommends estimates be made using multiple models for a sensitivity check, therefore, a calculation of the Koc was conducted using the EPIWIN model KOCWIN and the models developed by Sabljic et al. (1995) which are described in TGD Part III (2003) and utilized by EUSES.

 

Results of HPLC testing (OECD 121) demonstrated the method was not suitable for DNNSA which is consistent with the guideline caution that the method may be inappropriate for strong acids and surface acting compounds. In accord with REACH guidance indicating that “Estimated values are essential for substances for which experimental measurement is not feasible i.e. for difficult substances”, the log Koc for DNNSA that will be used for the environmental assessment will be 5.19, the average of the 3 values estimated by modeling.

[LogKoc: 5.19]