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Adsorption / desorption

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Reference
Endpoint:
adsorption / desorption: screening
Type of information:
(Q)SAR
Adequacy of study:
supporting study
Study period:
2018-04-05
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:
1. SOFTWARE
EPIWIN software by US-EPA

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

3. SMILES
N(NC(=S)S1)C1=S

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 150.23 in molecular weight limits of the training set: 32 - 665 g/mol; log Kow of 1.8519 in log Kow limits: -2.11-9.10; applicability domain fulfilled

6. ADEQUACY OF THE RESULT
The organic substance 2,5-Dimercapto-1,3,4-thiadiazole (DMTD) lies within the applicability domain with a molecular weight of 150.23 and a log Kow of 1.8519; the result seems reasonable and considering the low logKow (1.85) and the quite low log koc as calculated in this QSAR, it is considered as adequate and acceptable to use this result for risk assessment purposes.
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: calculation method
Media:
soil
Key result
Type:
Koc
Value:
71.1 L/kg
Temp.:
25 °C
Remarks on result:
other: MCI based estimate
Type:
log Koc
Value:
1.852 dimensionless
Temp.:
25 °C
Remarks on result:
other: MCI based estimate
Validity criteria fulfilled:
not applicable
Conclusions:
The study report describes a scientifically accepted calculation method for the soil adsorption coefficient 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 = 71.1 L/kg; log Koc = 1.8519) is adequate for the regulatory purpose.
Executive summary:

Absorption coefficient was estimated via US-EPA software KOCWIN v2.00 to Koc = 71.1 L/kg; log Koc = 1.8519.

Description of key information

Absorption coefficient was estimated via US-EPA software KOCWIN v2.00 to Koc = 71.1 L/kg; log Koc = 1.8519.

Key value for chemical safety assessment

Koc at 20 °C:
71.1

Additional information

[LogKoc: 1.85]