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Reference
Endpoint:
adsorption / desorption: screening
Type of information:
(Q)SAR
Adequacy of study:
supporting study
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
Remarks:
Whether or not it falls into its applicability domain depends on logPow determination.
Justification for type of information:
1. SOFTWARE
EPIWIN software by US-EPA

2. MODEL (incl. version number)
KOCWIN v2.00

3. SMILES
OC(C[n+]1ccccc1)CS(=O)(=O)[O-]

4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
- Defined endpoint: log Koc – soil adsorption coefficient of organic compounds
- Unambiguous algorithm: log Koc  =  0.5213 MCI  +  0.60 + ΣPfN  
MCI – molecular connectivity index, ΣPfN - summation of the products of all applicable correction factor coefficients available in the data set multiplied by the number of times (N) that factor is counted for the structure.
- Defined domain of applicability: Currently, there is no universally accepted definition of model domain. The training set of the model contains diverse molecules, so that the fragment library is abundant. It is however possible that a compound has functional groups or other structural features that are not represented in the training set and for which no fragment coefficients were developed. Additionally, there can be more instances of a given fragment than the maximum for all training set compounds. These points should be taken into consideration while interpreting test results.
Molecular weight limits of the training set: 32 - 665 g/mol
Log Kow limits: -2.11-9.10
- Appropriate measures of goodness-of-fit and robustness and predictivity: for the statistics, training data set has been split up into two subsets: the one containing non-polar substances with no fragments subjected to corrections (i.e. those with ΣPfN = 0) and the one containing the remaining ones. For the non-polar set: N = 69 compounds, correlation coefficient R2 = 0.967, standard deviation sd = 0.247 and average deviation ad = 0.199. For the second set: N = 447 compounds, correlation coefficient R2 = 0.9, standard deviation sd = 0.34 and average deviation ad = 0.273. For the external validation data set: N = 158 compounds, correlation coefficient R2 = 0.85, standard deviation sd = 0.583 and average deviation ad = 0.459. For the 516 compounds in the training set, 93% are within 0.6 log units and 100% within 1 log unit.
- Mechanistic interpretation: The methodology and relationship between the first order molecular connectivity index (MCI) and adsorption coefficient is outlined in the reference paper: 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). MCI was initially successfully used to predict soil sorption coefficients for non-polar organics, and the developed new estimation method based on MCI and series of statistically derived fragment contribution factors made it useful also for the polar ones.

5. APPLICABILITY DOMAIN
Molecular weight of ca. 217.24 in molecular weight limits of the training set: 32 - 665 g/mol; log Kow of <-2 possibly below log Kow limits: -2.11-9.10; (possibly not completely) falling into its applicability domain

6. ADEQUACY OF THE RESULT
The organic substance PPSOH lies not completely within the applicability domain with a molecular weight of 217.24 and a log Kow of <-2; anyway, this QSAR has been entered as supporting study in addition to a data waiver as due to the very low logPow the result seems reasonable and no adsorption potential has to be expected.
Guideline:
other: REACH guidance on QSARs Chapter R.6
Version / remarks:
May 2008
Principles of method if other than guideline:
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).
GLP compliance:
no
Type of method:
other: QSAR estimation
Media:
soil
Computational methods:
Using the computer tool KOCWIN v2.00 by US-EPA (EPIWIN) the organic-normalized sorption coefficient for soil (soil adsorption, Koc) can be estimated. The following two different models are used: Salbjic molecular connectivity method (MCI) and the traditional method, which is based on the logPow value of the substance. In general, the MCI method is taken more seriously into account, due to the fact that it includes improved correction factors.
Key result
Type:
Koc
Value:
10 L/kg
Temp.:
25 °C
Remarks on result:
other: MCI method, includes improved correction factors - most relevant
Key result
Type:
log Koc
Value:
1 dimensionless
Temp.:
25 °C
Remarks on result:
other: MCI method, includes improved correction factors - most relevant
Type:
Koc
Value:
0.009 L/kg
Temp.:
25 °C
Remarks on result:
other: estimated LogPow-based estimate (traditional method)
Type:
log Koc
Value:
-2.042 dimensionless
Temp.:
25 °C
Remarks on result:
other: estimated LogPow-based estimate (traditional method)
Validity criteria fulfilled:
not applicable
Conclusions:
The study report describes a scientifically accepted calculation method for the soil absorption characteristics using the US-EPA software KOCWIN v2.00. No GLP criteria are applicable for the usage of this tool and the QSAR estimation is easily repeatable. The result (Koc = 10 L/kg; log Koc = 1) is adequate for the regulatory purpose. This QSAR has been entered as supporting study in addition to a data waiver as due to the very low logPow the result seems reasonable and no adsorption potential has to be expected.
Koc = 10 L/kg
Executive summary:

The prediction for soil adsorption property of the test substance was determined by the computer program KOCWIN v2.00 (EPIWIN software) by US-EPA .The program estimates the organic-normalized sorption coefficient for soil, which is designated as Koc. The following two models are used: the Salbjic molecular connectivity (MCI) method as well as the traditional method which is based on the logPow value of the substance.

The MCI method is taken more seriously into account, due to the fact that is includes improved correction factors, resulting in a Koc value of 10 L/kg.

Description of key information

Koc = 10 L/kg; log Koc = 1 (estimation by US-EPA software KOCWIN v2.00)

Key value for chemical safety assessment

Koc at 20 °C:
10

Additional information

[LogKoc: 1.0]